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In the present study a spectrophotometric method for Cr(VI) determination in organic fertilizers, especially those from tanning industry residues, is proposed. Conditions for chromium extraction, extract clean-up and analytical characteristics of the method were established. The method is based on the complexation of Cr(VI) with 1,5-diphenylcarbazide (DPC) in acid medium (pH 2.0). A mixture of NaOH and Na2CO3 solution at 0.125 and 0.07 mol L–1 (pH 12), respectively, and heating at 90 °C for 60 min were the best conditions for chromium extraction. Florisil and activated charcoal were tested for clean-up of the extract, with activated charcoal being effective. Under the established conditions, the calibration linear range is up to 2500 μg L–1 Cr(VI), the results obtained are in agreement with the value of a certified reference material (CRM041), precision is better than 5% for five consecutive determinations of a solution at 1000 μg L–1 of Cr(VI) and the limit of quantification is 1.62 μg g–1. In can be concluded that the method is robust, accurate and precise, and can be easily applied for the determination of Cr(VI) in routine analysis, since it complies with legislation of most countries regarding the maximum allowed concentration of 2 μg g–1 of Cr(VI).

A reliable, rapid, and low-cost procedure for determining very low concentrations of hexavalent chromium (Cr) in water is discussed. The procedure is based in the classical reaction of Cr6+ with diphenylcarbazide. Once this reaction has taken place, sodium dodecylsulfate is added to obtain an ion-pair, and Triton X-114 is incorporated. Next, the heating of the mixture allows two phases that can be separated by centrifugation to be obtained in a cloud point microextraction (CPE) process. The coacervate contains all the Cr6+ originally present in the water sample, so that the measurement by molecular absorption spectrophotometry allows the concentration of the metal to be calculated. No harmful organic solvents are required. The discrimination of hexavalent and trivalent forms is achieved by including an oxidation stage with Ce4+. To take full advantage of the pre-concentration effect inherent to the coacervation process, as well as to minimize reagent consumption and waste generation, a portable mini-spectrophotometer which is compatible with microvolumes of liquid samples is used. The preconcentration factor is 415 and a chromium concentration as low as 0.02 µg L−1 can be detected. The procedure shows a good reproducibility (relative standard deviation close to 3%). [ABSTRACT FROM AUTHOR]

In the present work, a comparative study of analytical methods for the simultaneous and quantitative determination of trivalent and hexavalent chromium is presented. For the analysis by ion chromatography-inductively coupled plasma-mass spectrometry, two different columns were tested, as well as different mobile phases and different pH of the samples. The optimized analytical method permitted the separation of Cr(III) and Cr(VI) using 75 mmol/L NH4NO3 pH 3 as chromatographic eluent. The method was validated and applied to real samples, allowing the determination of both species simultaneously, even when there is a huge difference of concentration between Cr(III) and Cr(VI). Limit of detection and limit of quantification for Cr(III) were found to be 0.016 and 0.054 g μ /L (0.3 and 1.1 g μ /kg), respectively, and for Cr(VI) 0.13 and 0.43 g μ /L (7 and 22 g μ /kg), respectively. Possible species interconversions were monitored through the use of chromium isotopic standards, which confirmed that the optimized methodology preserves chromium speciation during extraction and analysis. Fourier-transform ion cyclotron resonance-mass spectrometry permitted the structure elucidation of the complex formed during ethylenediaminetetraacetic acid extraction. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the practicability of exhaled breath condensate (EBC) as a biological matrix to detect and measure hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) in workers occupationally exposed to Cr(VI). EBC samples were collected from workers in France, Finland, Italy, The Netherlands and the United Kingdom from three different target activities: chrome platers, stainless steel welders and surface treatment workers. Pre and post working week EBC samples were collected from 177 exposed workers and 98 unexposed workers (control group). Hyphenated chromatography systems with inductively coupled plasma – mass spectrometry (ICP-MS) were for the analysis. The results showed that the occupationally exposed workers had significantly higher levels of Cr(VI) and Cr(III) than the control group. Chrome platers exhibited the highest Cr(VI) levels in their EBC samples, with a significant increase from their pre to post samples for both Cr(VI) and Cr(III). A significant difference was also found between pre and post EBC samples for Cr(III) in welders. This study has shown that EBC has the potential to be a valid, non-invasive biological matrix to assess occupational exposure to Cr(VI) and Cr(III) for biological monitoring assessment, with the ability to detect low level inhalation exposures. [Display omitted] • Exhaled breath condensate (EBC) reflects tri- and hexavalent chromium in the lungs. • Both chromium species were higher in EBC of workers compared to controls. • Both chromium species increased from pre to post workweek EBC in chrome platers. • EBC may provide lung-specific, non-invasive occupational exposure data for hexavalent chromium. [ABSTRACT FROM AUTHOR]

A reliable, rapid, and low-cost procedure for determining very low concentrations of hexavalent chromium (Cr) in water is discussed. The procedure is based in the classical reaction of Cr6+ with diphenylcarbazide. Once this reaction has taken place, sodium dodecylsulfate is added to obtain an ion-pair, and Triton X-114 is incorporated. Next, the heating of the mixture allows two phases that can be separated by centrifugation to be obtained in a cloud point microextraction (CPE) process. The coacervate contains all the Cr6+ originally present in the water sample, so that the measurement by molecular absorption spectrophotometry allows the concentration of the metal to be calculated. No harmful organic solvents are required. The discrimination of hexavalent and trivalent forms is achieved by including an oxidation stage with Ce4+. To take full advantage of the pre-concentration effect inherent to the coacervation process, as well as to minimize reagent consumption and waste generation, a portable mini-spectrophotometer which is compatible with microvolumes of liquid samples is used. The preconcentration factor is 415 and a chromium concentration as low as 0.02 µg L−1 can be detected. The procedure shows a good reproducibility (relative standard deviation close to 3%).

A paper-based analytical device (PAD) is presented with colorimetric/electrochemical dual readouts for the simultaneous sensing of total chromium (Cr) and hexavalent chromium (Cr(VI)). This device consists of a homemade three-electrode system and a patterned paper chip, integrating multiple functions including electrochemical detection, fluid driving, online oxidation, and colorimetric detection. The fiberglass filter paper with a hydrophilic microchannel was used to achieve self-driving fluidics without external equipment. One end of the microchannel was integrated with a homemade three-electrode system to achieve sample loading and electrochemical detection. The middle region on the microchannel was modified with oxidizing reagents to perform online pretreatment, and the yield of Cr(III) oxidation can reach 97.9%, ensuring reliable colorimetric detection of total Cr at another end of the microchannel modified with chromogenic agents. With this device, the signals of Cr(VI) (the signal peak at 0.29 V vs. Ag/AgCl) and total Cr can be obtained in one single injection. After optimization, the limit of detection (LOD) of Cr(VI) and total Cr were 0.01 mg L−1 and 0.06 mg L−1 and the linear ranges were 0.05–3.0 mg L−1 and 0.2–3.0 mg L−1, respectively. The relative standard deviations (RSD) of the electrochemical testing of Cr(VI) results were in a range 1.3%–8.7% (n = 3), and the RSD values of the colorimetric testing of total Cr were between 0.7–9.2% (n = 3). The device's reliability was demonstrated by performing the practical speciation of Cr in tap water, river water, and electroplating wastewater while the recoveries obtained using the present method were in the range 93.5–106%. Overall, the proposed device provides high application prospect in the on-site rapid Cr speciation. [ABSTRACT FROM AUTHOR]

This study examines the pollution of soil by chromium using statistical analysis and Empirical Bayesian Kriging (EBK) modeling around the leather tanning industries of Southern India. Sixty-four soil samples were collected from agricultural lands and analyzed for their major ions and trace elements using Atomic Absorption Spectrophotometer. It is observed that the concentration of trace elements, decreases in the following order: Cr > Fe > Ni > Pb > Mn > Cu > Zn. Also, the chromium present in the soil samples ranged between 0.1 and 2459 mg/kg. The higher concentration of Cr, Pb, Ni, and Zn observed in this study exceeds the permissible limit around tannery regions, indicating tannery effluents' impact. The positive correlation of Cr with Ca, Mg, Pb, and Mn specifies the discharge of tannery wastewater into the open land, thus contaminating the soil in the study area. The root mean square error (RMSE) values derived from the EBK model for Cr, Pb, Fe, and Ni are close to 1, indicating the model's validity. Moreover, the soil pollution index and Geo-accumulation index results around the tannery region show a profound impact of tannery effluent. The obtained results clearly emphasize the presence of toxic heavy metals in the study area that may cause extensive degradation of productive agricultural land. Hence, it is essential to make an appropriate strategy and implement a suitable remediation technique to solve the heavy metals pollution problem. [ABSTRACT FROM AUTHOR]

Chemical stabilization is one of the most widely used remediation strategies for chromium (Cr)-contaminated soils by reducing Cr(VI) to Cr(III), and its performance is affected by human and natural processes in a prolonged period, challenging long-term Cr stability. In this work, we established a method for evaluating the long-term effectiveness of remediation of Cr-contaminated soils, and developed an accelerated aging system to simultaneously simulate acid rain leaching and freeze-thaw cycles. The mechanisms and influencing factors of long-term (50-year) change in soil Cr speciation were unravelled after stabilization with Metafix®. Chemical stabilization remarkably decreased the contents of Cr(VI) soil , Cr total-leach and Cr(VI) leach , among which the removal rate of Cr(VI) in soil was up to 89.70 %, but it also aggravated soil Cr instability. During the accelerated aging process, Cr total-leach change rates in chemically stabilized soil samples were 0.0462–0.0587 mg/(L·a), and soil Cr became instable after 20-year accelerated aging. The proportion of Cr bound to organic matter and residual Cr increased in soil, and exchangeable Cr decreased. Linear combination fitting results of XANES also showed that Cr(VI) and Cr3+ were transformed into OM-Cr(III), Fh-Cr(III) and CrFeO 3 after restoration. During the accelerated aging process, acid rain leaching activated Cr(III) and dissolved Cr(VI), whereas freeze-thaw cycle mainly affected OM-Cr. Chemical stabilization, acid rain leaching and aging time were the major factors influencing the stability of soil Cr, and the freeze-thaw cycle promoted the influence of acid rain leaching. This study provided a new way to explore the long-term effectiveness and instability mechanisms at Cr-contaminated site after chemical stabilization. [Display omitted] • An accelerated aging system simulating acid rain and freeze-thaw cycle for Cr stability assessment. • Stabilization and acid rain leaching were key factors affecting soil Cr long-term stability. • Freeze-thaw cycle mainly affected OM-Cr to instabilize Cr. [ABSTRACT FROM AUTHOR]

A simple and environmentally friendly method for the speciation of chromium based on a spot test obtained from digital images has been developed. Due to rapidity and simplicity of the method and portability of the used devices, the proposed method is suitable for in situ determination of chromium. The method employed a smartphone to capture digital images of Cr(VI)-1,5-diphenylcarbazide colored complex in microplate wells which were accommodated in a wooden box. A color digitizer app was used to extract RGB values from captured images. To obtain total chromium content in the sample, Cr(III) was oxidized to Cr(VI) with Ce(IV) prior to analysis. Under the optimum conditions, the calibration curves were linear over the concentration ranges of 20 to 250 and 30 to 250 μg/L with the detection limits of 5 and 7 μg/L and RSD values of 5.8 and 6.3% for Cr(VI) and Cr(III), respectively. The proposed method was successfully applied to the speciation of chromium in spiked water samples. [ABSTRACT FROM AUTHOR]

Centrifuge less continuous sample drop flow-based microextraction is combined with graphite furnace atomic absorption spectrometry to develop a novel analytical procedure for the speciation and preconcentration of the trace amounts of chromium in the aqueous samples. The extraction procedure involves the sequential addition of the aqueous sample in form fine droplets through a switchable hydrophilic fatty acid as an extraction phase. In this study, the centrifugation step was eliminated by applying the salting-out phenomenon. The influence of the main variables on the efficiency of the procedure was evaluated by chemometric methods. Under optimised conditions, the linearity ranges of the proposed method are in the range of 1–20 µg L−1 with correlation coefficients exceeding 0.9993. The limit of detection and limit of quantification were 0.29 and 0.87 µg L−1, respectively. The recovery of analyte in tap, well, and river and wastewater ranged between 95.2% and 105.0% with relative standard deviations ranging from 1.30% to 5.78%. Hence, the method was successfully applied to the analysis of chromium in water samples. [ABSTRACT FROM AUTHOR]

For the first time, in-tube gel electro-membrane microextraction (IT-G-EME) system followed by microfluidic paper-based analytical devices (µPADs) as a low-cost reading platform was fabricated for the speciation of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) as model cationic and anionic compounds. In this new miniaturized extraction mode, a transparent narrow-bore polymeric tube was used as housing of the aqueous acceptor phase (AP, 30 µL), while an agarose gel membrane was placed as a micro plug (2.5 mm) at the beginning of the tube. A circular shape vial (1.5 mL, pH 5.5) containing chromium species as donor phase (DP) was connected between two tubes which previously filled with gel membrane and aqueous AP. By applying electric potential, the positively charged Cr(III) and negatively charged Cr(VI) in the DP migrated selectively toward cathodic and anodic tubes, respectively. After extraction, each AP was analyzed by µPAD, which had already been modified with diphenylcarbazide (DPC). Under the optimized extraction conditions, a good limit of detection (LOD) equal to 7.0 µg L–1 was achieved for both analytes, while the extraction recoveries for Cr(VI) and Cr(III) were 72% and 84%. In addition, the developed approach was used for the quantification of chromium species in water samples.

A new analytical procedure for the speciation of chromium (Cr) in plants by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was developed using a strong anion-exchange Mono Q column for the separation of the Cr species. To optimize the analytical procedure, Cr complexes were first synthesized from Cr-nitrate with the addition of an excess of ligand (90°C). Cr-oxalate, Cr-malate, Cr-citrate, Cr-aconitate and Cr-quinate complexes and Cr-nitrate (pH 6.5) were chromatographically separated from Cr(VI) by applying linear gradient elution from 100% water to 100% NH4Cl at a flow rate of 1.5 ml min−1 in 10 min. The column recoveries ranged from 100 to 104%. The exception was Cr-aconitate (column recovery 33%), where a quantitative synthesis was not possible. Good repeatability of the measurements (relative standard deviations better than ± 3%) and low limits of detection (below 0.37 ng ml−1 Cr) were achieved for the individual Cr species. The developed analytical procedure was applied to Cr speciation for dandelions (Taraxacum officinale) grown in soil with a high Cr content and a study of the uptake and metabolism of Cr species in dandelions grown in soil with a low Cr content treated with solutions of Cr(VI) or Cr-nitrate (5000 ng ml−1 Cr, pH 6.5) for 48 h. The separated Cr species were quantified by post-column isotope dilution ICP-MS, while the identification was based on retention times and was also supported by mass spectra obtained with high resolution mass spectrometry (HR-MS). The data indicate that for dandelions grown in Cr-rich soil and that treated with Cr-nitrate (pH 6.5), the Cr was mainly accumulated in the roots, while in plants treated with Cr(VI) (pH 6.5), the Cr was evenly distributed between the roots and the leaves. The Cr species found in dandelion roots and leaves were Cr-aconitate, Cr-malate, and Cr-quinate. The results revealed that Cr(VI) was completely reduced and metabolized to Cr(III) complexes. LA-ICP-MS data showed that the Cr in a leaf of dandelion grown in Cr-rich soil was localized mainly at the apex of the leaf.

Chromium accumulated from source water and pipeline lining materials in corrosion scales could potentially be released into bulk water in drinking water distribution systems (DWDS). This study examined the influence of pH (pH 4, pH 5.5, pH 7, pH 8.5, pH 10), temperature (5 °C, 15 °C, 25 °C), sulfate (50 mg/L, 150 mg/L, 250 mg/L), and chloride (50 mg/L, 150 mg/L, 250 mg/L) on chromium accumulation and release between iron corrosion scale phase and the surrounding water phase. For the first time, the accumulation and release behaviors of chromium were assessed and compared in two distinct layers of iron corrosion scales based on the speciation distributions of heavy metals. Results showed that in the outer and inner layers of corrosion scales, chromium exhibited an almost similar trend but significant differences in quantity, with the outer layer accumulating less and releasing more. In particular, the average difference of chromium released after Cr(VI) enrichment from the outer and inner layers was 50.53 μg/L under the same conditions. Further studies conclusively showed that in Cr(VI) accumulation process, a portion of Cr(VI) would be reduced to Cr(III) by Fe(II) in iron corrosion scales. The mechanisms of chromium retention based on different iron (oxyhydr)oxides were discussed. [ABSTRACT FROM AUTHOR]

The extraction of total Cr(VI) from commercially available cements, based on DTPA + 0.2 mol dm -3 (NH4)2SO4/NH4OH mixture solution and subsequent selective determination of Cr(VI) has been proposed. The determination was carried out using the adsorptive voltammetric stripping method. The study was conducted using three different commercially available cement samples. It has been checked that the proposed extraction procedure guaranteed no changes of chromium speciation during cement analysis. For comparison extraction was also carried out with the use of recommended by United States Environmental Protection Agency (EPA) Method 3060A, based on 0.28 mol dm -3 Na2CO3 + 0.5 mol dm -3 NaOH). Additionally, the extraction process was carried out using only distilled water as an extraction mixture which allows to evaluate concentration of only soluble Cr(VI) forms contained in cement. In all three cements, the content of soluble Cr(VI) was below 2 ppm, i.e. the limit value by European Union Directive 2003/53/EC. [ABSTRACT FROM AUTHOR]

Novel Cr(III)-imprinted poly(vinyl alcohol)/sodium alginate/AuNPs hydrogel membranes (Cr(III)-IIMs) were obtained and characterized and further applied as a sorbent for chromium speciation in waters. Cr(III)-IIMs were prepared via solution blending method using blends of poly(vinyl alcohol) and sodium alginate as film-forming materials, poly(ethylene glycol) as a porogen agent, sodium alginate stabilized gold nanoparticles (SA-AuNPs) as a crosslinking and mechanically stabilizing component, and Cr(III) ions as a template species. The physicochemical characteristics of pre-synthesized AuNPs and obtained hydrogel membranes Cr(III)-IIM were studied by UV-vis and FTIR spectroscopy, TEM and SEM observations, N2 adsorption–desorption measurements, and XRD analysis. The mechanism of the adsorption process toward Cr(III) was best described by pseudo-first-order kinetic and Langmuir models. Experiments performed showed that quantitative retention of Cr(III) is attained in 20 h at pH 6 and temperature 40 °C. Under the same conditions, the adsorption of Cr(VI) is below 5%. A simple and sensitive analytical procedure was developed for the speciation of Cr in an aquatic environment using dispersive solid phase extraction of Cr(III) by Cr(III)-IIM prior to selective Cr(VI) measurement by ETAAS in the supernatants. The detection limits and reproducibility achieved for the Cr speciation analysis fulfill the requirements for their monitoring in waters under the demand of the Water Framework Directive.

Chromium is widely recognized as a significant pollutant discharged into the environment by various industrial activities. The toxicity of this element is dependent on its oxidation state, making speciation analysis crucial for monitoring the quality of environmental water and assessing the potential risks associated with industrial waste. This study introduces a single-well fluorometric sensor that utilizes orange emissive thioglycolic acid stabilized CdTe quantum dots (TGA-QDs) and blue emissive carbon dots (CDs) to detect and differentiate between various chromium species, such as Cr (III) and Cr (VI) (i.e., CrO 4 2− and Cr 2 O 7 2−). The variations of fluorescence spectra of the proposed probe upon chromium species addition were analyzed using machine learning techniques such as linear discriminant analysis and partial least squares regression as a classification and multivariate calibration technique, respectively. Linear discriminant analysis (LDA) demonstrated exceptional accuracy in differentiating single-component and bicomponent samples. Additionally, the findings from the partial least squares regression (PLSR) showed that the sensor created has strong linearity within the 1.0–100.0, 1.0–100.0, and 0.1–15 μM range for Cr 2 O 7 2−, CrO 4 2−, and Cr3+, respectively. Furthermore, appropriate detection limits were successfully achieved, which were 2.6, 2.9, and 0.7 μM for Cr 2 O 7 2−, CrO 4 2−, and Cr3+, respectively. Ultimately, the successful capability of the sensing platform in the identification and quantification of chromium species in environmental water samples provides innovative insights into general speciation analytics. [Display omitted] • This study utilizes a single-well fluorometric sensor for chromium speciation. • The probe was developed by mixing TGA-QDs and CDs in an appropriate proportion. • The probe benefits from Machine Learning techniques for chromium speciation. • The probe monitors chromium pollution in environmental water samples in real-time. [ABSTRACT FROM AUTHOR]

This study aimed at the assessment of the impact of various culinary processes on the fate of chromium (Cr) species (Cr(III) and Cr(VI)) in infant formula milk, semi-skimmed milk and bovine meat samples. The cooking procedures were boiling at 70°C/100°C (milk samples) and frying without and with oil (95°C and 120°C) (bovine meat). The levels of Cr(III) and Cr(VI) in raw and cooked samples were determined by high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) using double spike species-specific-isotope dilution (SS-ID). The species were extracted by sequential complexation of Cr(III) with ethylenediaminetetraacetic acid and of Cr(VI) with 1,5-diphenylcarbazide in the same analytical run by heating at 70°C for 50 min. Anion exchange chromatography using a Dionex IonPac™ AG7 column and a mobile phase consisting of 10 mM HNO3, 2.5% MeOH and 30 mM EDTA at pH 2 was employed for species separation. The quantification limits were 0.013 and 0.049 µg kg−1 for Cr(III) and Cr(VI), respectively. ANOVA test used to compare the mean Cr species concentrations showed no significant differences between raw and cooked samples. The results obtained in the present study show that oxidation of Cr(III) to Cr(VI) does not occur during thermal cooking of milk and bovine meat samples. A selection of 10 samples of each type were analysed in terms of total Cr (Crtotal) as well as speciation (Cr(III) and Cr(VI)). Cr(VI) was not quantified in any of these samples, whereas Cr(III) levels ranged from 0.22 (infant formula milk) up to 80 µg kg−1 (chorizo sausage). Additionally, Cr(III) and Crtotal levels were comparable hence demonstrating that in the samples analysed in this study, Cr is found exclusively as Cr(III) species. [ABSTRACT FROM AUTHOR]

The mineralogical and chemical composition of chromite ore processing residue (COPR) from a site in the north of France (Lille) was investigated. The mineralogical composition was obtained by X-ray diffraction and Rietveld analysis. Geochemical characteristics were established based on elemental analysis, acid leaching, sequential extraction and a chemical equilibrium experiment. Remarkably, this COPR material is composed of 65% silica-rich amorphous phases. Another noticeable result is the presence of about 11% of quartz. Content in toxic Cr(VI) is about 4.9 g/kg, occurring in the solution phase or fixed in unstable crystalline cement phases. Literature data on most studied COPR materials allowed establishing a classification of the materials into (1) high calcium/low silica, (2) intermediate and (3) low calcium/high silica categories. This calcium–silica relation is indicative of the quality of the original ore and the geochemical changes having occurred in a COPR deposit over time, compared with fresh COPR produced from pure ore, and possibly the post-deposit admixture of other waste materials. The Lille material belongs to the third category. The high silica content has influenced the phase associations and their stabilities and favours Cr(VI) mobility. Extraction of leachable Cr(VI) from COPR induces formation of a new chemical equilibrium in the material with a recharge in mobile chromium due to dissolution of cement phases. However, the rate of equilibration is very slow. Four hundred days were needed for the high amorphous phase material in this study. Extraction of leachable Cr(VI) is not a suitable remediation method because it will not allow to withdraw the solid bound Cr(VI) from the material in a single treatment.

Amberlite XAD-4 resin (AXAD-4) was chemically modified to an aminated Amberlite XAD-4 (AAXAD-4) resin and characterized by infrared spectroscopy. AAXAD-4 resin was used as an efficient solid phase for the preconcentration and speciation of Cr(III) and Cr(VI) ions by column technique. The concentration of chromium species was determined by microsample injection system-flame atomic absorption spectrometer (MIS-FAAS). Selective retention of Cr(III) ions was achieved at pH 8.0 and eluted using 1.0 mL of 3.0 mol L–1 HCl and 1.0 mL of 2.0 mol L–1 NaOH, successively, at the flow rate of 5.0 mL min–1. The maximal sorption capacity of AAXAD-4 resin for Cr(III) ions was found to be 67.0 mg g–1. The limit of detection (LOD) and limit of quantitation (LOQ) for Cr(III) ions were found to be 0.041 and 0.131 µg L–1, respectively, with preconcentration factor (PF) of 375 and relative standard deviation (RSD) of 3.75% (n=11). The method was validated using certified reference materials (CRMs) and successfully applied to the real samples, spiked with Cr(III) and Cr(VI) ions.

A novel carboxyl-functionalized hybrid monolithic column was developed based on "thiol-ene" click reaction via "one-pot" by choosing mercaptosuccinic acid, γ-methyl methacrylate trimethoxysilane and tetramethoxysilane as reaction monomers. The design of the hybrid monolithic column was assisted by the comparison in computational simulation with existing carboxyl-functionalized materials. The characterization by scanning electron microscopy, energy dispersive X-ray spectroscopy, N 2 adsorption-desorption measurement, Fourier-transform infrared spectroscopy and elemental analysis showed that the carboxyl-functionalized material has the advantages of good permeability and high mechanical strength. Then, we used the prepared carboxyl-hybrid monolith column as solid phase microextraction adsorbent for separation of trace inorganic chromium species. Under pH 4.5, the hybrid monolith column can selectively enrich Cr(III) without adsorbing Cr(VI) and afterwards, Cr(III) can be eluted by 1.0 mol L−1 HCl. The chromium speciation separation method based on carboxyl-hybrid monolith column followed by inductively coupled plasma-mass spectrometry possessed the merits of facile preparation, low cost, simple and mild extraction condition, and sensitive detection, which has been successfully applied to the separation, enrichment and detection of inorganic chromium in environmental waters. Image 1 • A carboxyl hybrid monolithic column was one-pot prepared by thiol-ene click reaction. • Computational simulation was utilized as reference for selecting functional monomer. • All used reagents were simple, cheap and easy to obtain for the one-pot synthesis. • Speciation analysis of labile inorganic chromium was realized under mild conditions. [ABSTRACT FROM AUTHOR]

A combined approach based on multiple X-ray analytical techniques and conventional methods was adopted to investigate the distribution and speciation of Cr in a polluted agricultural soil, from the bulk-scale down to the (sub)micro-level. Soil samples were collected from two different points, together with a control sample taken from a nearby unpolluted site. The bulk characterization revealed that the polluted soils contained much higher concentrations of organic matter (OM) and potentially toxic elements (PTE) than the control. Chromium was the most abundant PTE (up to 5160 g kg−1), and was present only as Cr(III), as its oxidation to Cr(VI) was hindered by the high OM content. According to sequential extractions, Cr was mainly associated to the soil oxidisable fraction (74%) and to the residual fraction (25%). The amount of Cr potentially bioavailable for plant uptake (DTPA-extractable) was negligible. Characterization of soil thin sections by micro X-ray fluorescence (μXRF) and field emission scanning electron microscopy coupled with microanalysis (FEGSEM-EDX) showed that Cr was mainly distributed in aggregates ranging from tens micrometres to few millimetres in size. These aggregates were coated with an aluminosilicate layer and contained, in the inner part, Cr, Ca, Zn, P, S and Fe. Hyperspectral elaboration of μXRF data revealed that polluted soils were characterised by an exogenous organic-rich fraction containing Cr (not present in the control), and an endogenous aluminosilicate fraction (present also in the control), coating the Cr-containing aggregates. Analyses by high-resolution micro X-ray computed tomography (μCT) revealed a different morphology of the soil aggregates in polluted soils compared with the control. The finding of microscopic leather residues, combined with the results of bulk- and micro-characterizations, suggested that Cr pollution was likely ascribable to soil amendment with tannery waste-derived matrices. However, over the years, a natural process of Cr stabilization occurred in the soil thus reducing the environmental risks. [ABSTRACT FROM AUTHOR]

Persistent industrial activities have led to an increase in the chromium content in environmental water bodies. The accurate quantification of trace chromium species such as Cr(III) and Cr(VI) is crucial as Cr(VI) can exhibit toxicity even at sub‐ppb levels. We report herein a comparative chromium speciation study using two chemically functionalized nanoadsorbents and determination with hyphenated flow injection‐flame atomic absorption spectrometry (FI‐FAAS). The most efficient preconcentration performance was obtained by optimizing the chemical and hydrodynamic parameters. Cr(VI) concentration was ascertained by the reduction to Cr(III) as the nanoadsorbents were selective for Cr(III) adsorption only; thus, speciation was achieved. The method was selective for Cr(III) in the presence of interfering matrix components. Preconcentration factor >90 and detection limit <0.11 μg L−1 were obtained for both the nanoadsorbents (%RSD∼1.0 %). The adsorption capacity of CNT‐TYR and CNT‐ASA was found to be 42.0 and 43.2 mg g−1, respectively. The application of the proposed method to contaminated water samples gave recoveries >95 %. The accuracy of the method was verified using NIST SRM 1640a. [ABSTRACT FROM AUTHOR]

A major goal of green chemistry is to avoid the use of toxic organic solvents. In particular, there are few green methods allowing extraction and quantification of chromium species in environmental samples. Here, we developed home-made, dual-gel electromembrane extraction combined with a microfluidic paper-based analytical device for the simultaneous determination of Cr(III) and Cr(VI) in water, without using any organic solvent. The positively charged Cr(III) and negatively charged Cr(VI) migrated selectively into the cathodic (pH 2.0) and anodic (pH 3.0) aqueous acceptor phases, respectively. After extraction, the anodic acceptor phase containing Cr(VI) was analyzed directly by a microfluidic paper-based analytical device, after the addition of the diphenylcarbazide colorimetric reagent. The cathodic acceptor phase containing Cr(III) was mixed with Ce(IV) to oxidize Cr(III) to Cr(VI), and then, Cr(VI) ions were detected on the microfluidic paper-based analytical device after adding diphenylcarbazide. Under the optimized conditions, limits of detection of 2.0 and 3.0 ng/mL and extraction recoveries of 58.8% and 83.3% were achieved for Cr(VI) and Cr(III), respectively. [ABSTRACT FROM AUTHOR]

The determination of hexavalent chromium in textiles and clothes is challenging since during extraction, the original oxidation state should not be altered. Since, as a matter of fact, current analytical methods are focused only on total chromium determination, the purpose of this research is to develop a reliable analytical method for the determination of Cr(VI) in textiles and tissues of daily use for a reliable application of risk analysis models, which are usually based on total Cr data. After optimization, a 0.0025 M Na 3 PO 4 extraction solution was selected for the extraction of Cr(VI) from textiles. This solution minimizes possible interconversion redox reactions and interference, and provides good extraction recoveries (88.4 ± 2.5% - 105.5 ± 0.6 %, according to Cr(VI) concentration) and quantitation limits (0.017 mg/kg), fully complying the current limits set for Cr(VI) in textiles in contact with skin, and for leachable Cr(VI). The developed method was validated investigating intra-day repeatability (n = 10) and inter-day repeatability (n = 30) which were below 12%, and matrix effect which was below 6% confirming the precision of the method and the negligibility of a matrix interference during the whole analysis. The method, which was proved to be suited also for bioaccessibility studies in saliva and sweat, was applied to the analysis of tank top, coloured paper napkin, polyamide tights, panties, highlighting Cr(VI) content in the panties only at very low concentration (0.028 mg/kg). As verified by ECHA and US EPA approaches, this amount does not pose a non-carcinogenic risk for human health. As regards carcinogenic risk, considering both adult and child exposure, the dermal contact with the panties poses an acceptable risk (R ≤ 10−6). • Two different extraction approaches for Cr(VI) determination in clothes are compared. • The proposed analytical method is compliant with current standards. • The method has quantitative recoveries and does not suffer from matrix effect. • The method can also be applied to evaluate leachate Cr(VI) by biological fluids. • The importance of quantifying the risk of dermal contact with clothes was highlighted. [ABSTRACT FROM AUTHOR]

The stable chromium (Cr) isotope system is an emerging paleoredox proxy. Interpretation of sedimentary and seawater δ53Cr (53Cr/52Cr relative to SRM 979) hinges on our understanding of the isotopic fractionations during Cr sequestration from seawater to sediments. Seawater δ53Cr values reported thus far are for total dissolved Cr. This study reports the δ53Cr of both dissolved Cr (III) and dissolved Cr (VI) across the oxygen minimum zone in the eastern tropical North Pacific off Manzanillo, Mexico. Dissolved Cr (III) accounts for 48% to 54% total dissolved Cr in this region. There are no correlations between O2 and Cr concentrations, or O2 concentrations and δ53Cr throughout the water column. The δ53Cr of Cr (III) is lower than that of Cr (VI) by a relatively constant offset (0.42 ± 0.15‰, 1σ, n = 5) and is also uncorrelated with dissolved O2 concentration. These observations provide part of the foundation for using δ53Cr of the authigenic Cr in organic‐rich shales to reconstruct seawater δ53Cr. A survey of growing literature Cr concentration and δ53Cr data suggests that the Cr isotope fractionation factor in the global ocean is likely more complex than previously thought. More future species‐dependent Cr isotope studies could shed new light on the biogeochemical processes controlling the oceanic Cr isotope fractionation. Plain Language Summary: The chromium isotope system is widely used to reconstruct the Earth's oxygenation history. However, the behavior of the isotope system under low‐oxygen conditions in the modern ocean is still poorly understood. It is well known that both oxidized and reduced Cr species coexist in seawater, but all previous studies only measured total Cr isotope compositions. In this study, we sampled seawater from the oxygen minimum zone (OMZ) in the eastern tropical north Pacific region, separated different Cr species, and measured their isotopic compositions. We found that the offsets in isotope compositions between oxic and reduced Cr species are relatively small compared to intrinsic isotope fractionations determined in laboratory experiments, and the offsets are not correlated with dissolved oxygen concentrations. Our species‐specific Cr isotope data from the eastern Pacific OMZ, and some previous total Cr isotope data from eastern Atlantic OMZ, do not conform to a global isotope fractionation factor. Therefore, more species‐specific Cr isotope data are needed to better understand Cr isotope behavior in the ocean. Key Points: Dissolved Cr (III) accounts for 48–54% total dissolved Cr in the ETNP regionThe offset between dissolved δ53Cr(III) and δ53Cr(VI) is relatively constant and is uncorrelated with dissolved O2 concentrationMore species‐dependent Cr isotope data are needed to better constrain Cr isotope fractionation factors in the global ocean [ABSTRACT FROM AUTHOR]

Ferrous sulfate (FeSO4) is widely used to effectively stabilize hexavalent chromium (Cr(VI))‐contaminated soil. The leaching behavior, Cr(VI) content, and chromium speciation distribution in the stabilized soil are the most important indexes for determining the effectiveness of reduction treatment. Numerous factors, such as reductant dosage and soil particle size, affect the stabilization process; these factors are relatively important. This study investigated the influence of FeSO4 dosage and soil particle size on leachability and speciation distribution of chromium in contaminated soil. Results showed that the increase in FeSO4 significantly reduced the leachability and Cr(VI) content in the soil given the increased reducible species that stem from an acid soluble fraction of chromium. The small particle size of the soil that contains a large surface area facilitated the reaction between Cr(VI) and FeSO4, thereby resulting in low leachability and high reducible species of Cr(VI) in the stabilized soil. The leached Cr(VI) concentration was exponentially correlated to Cr(VI) content in the stabilized soil, and the leachability of Cr from the stabilized soil was linearly correlated to the exchangeable phase of Cr. In addition, the leached Cr(VI) concentration from the stabilized soil conform to the US Environmental Protection Agency and China regulatory limits; meanwhile, considerable Cr(VI) remained in a few stabilized soil and exceeded the environmental quality standards for soil in China. These results illustrated the importance of a comprehensive assessment of Cr(VI)‐contaminated soil, which is treated by reductants for enabling flexible future land use. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 500–507, 2019 [ABSTRACT FROM AUTHOR]

Abstract The tanning industry uses large quantities of Cr whose contribution to the contaminant burden of aquatic organisms is not yet fully understood. The present study investigated Cr bioaccumulation by indigenous chironomids in a freshwater ecosystem impacted by tannery effluents. Total Cr content in sediments and in chironomids was determined on several occasions. Chromium distribution among sediments and pore waters, and Cr speciation in overlying and pore waters were studied in detail to understand possible factors controlling Cr bioavailability to chironomids. Total chromium concentration ranged from 69 to over 3000 μg g−1 dry weight in sediments and from negligible to over 300 μg g−1 dry weight in chironomids (values corrected for sediment gut content). Filterable (<0.45 μm) Cr concentration in overlying waters and pore waters from the surface sediment layers (upper 2 cm) ranged from 3 to 120 μg L−1, with Cr(VI) representing 0.5–28% of the total filterable Cr. Chromium profiles in pore waters as determined by diffusive equilibration in thin films (DET) and diffusive gradient in thin films (DGT) were comparable. DGT-labile Cr accounted for <2% of the total Cr measured by DET. Although Cr concentrations in sedimentary and aqueous matrices were not directly proportional to Cr levels measured in chironomids, the available findings suggested that Cr inputs from tanneries were bioavailable to resident chironomids. These observations are of particular importance considering that Cr(III), putatively of limited bioavailability and ecotoxicological concern, is the predominant redox form of Cr in bed sediments impacted by tannery discharges. The companion paper provides further insight into Cr bioavailability and effects in tannery impacted ecosystems using a combination of in situ and laboratory approaches. Graphical abstract Unlabelled Image Highlights • Leather tanning uses large quantities of Cr(III) that mostly accumulates in sediments. • Bioavailability of chromium at tannery-contaminated sites is not fully understood. • Indigenous chironomids show Cr accumulation in zones impacted by tannery discharges. • Cr accumulation in chironomids is not proportional to Cr concentration in sediments. • Chironomid Cr burden exceeds reported tolerance levels for more sensitive organisms. [ABSTRACT FROM AUTHOR]

A green, sensitive and selective methods are described for the preconcentration and speciation of chromium species in natural waters. The developed methods are based on the environmentally friendly aqueous two-phase extraction with a system consisted of ammonium sulfate and polyethylene glycol, or, alternatively, alcohol (ethanol, isopropanol). The extraction of chromium species from aqueous solution into the upper organic phase was performed with 4-(2-pyridylazo)resorcinol and 1,5-diphenylcarbazide as chelating agents for Cr(III) and Cr(VI), respectively. Some predominant factors affecting the preconcentration and speciation of both Cr(III) and Cr(VI) species were evaluated and optimized. The concentration of chromium species in upper organic phase was determined by both spectrophotometric and electrothermal atomic-absorption spectrometry (ET AAS) methods. Under the optimum conditions, the calibration graphs obtained with spectrophotometric method were linear over the concentration ranges from 5 to 500 μg L-1 for Cr(III) and from 2.5 to 50 μg L-1 for Cr(VI). Corresponding concentration ranges determined by using ET AAS method were from 1 to 10 μg L-1 for both chromium species. The proposed methods were applied to the determination of chromium species in mine and waste waters with satisfactory results.

A reliable, rapid, and low-cost procedure for determining very low concentrations of hexavalent chromium (Cr) in water is discussed. The procedure is based in the classical reaction of Cr 6+ with diphenylcarbazide. Once this reaction has taken place, sodium dodecylsulfate is added to obtain an ion-pair, and Triton X-114 is incorporated. Next, the heating of the mixture allows two phases that can be separated by centrifugation to be obtained in a cloud point microextraction (CPE) process. The coacervate contains all the Cr 6+ originally present in the water sample, so that the measurement by molecular absorption spectrophotometry allows the concentration of the metal to be calculated. No harmful organic solvents are required. The discrimination of hexavalent and trivalent forms is achieved by including an oxidation stage with Ce 4+ . To take full advantage of the pre-concentration effect inherent to the coacervation process, as well as to minimize reagent consumption and waste generation, a portable mini-spectrophotometer which is compatible with microvolumes of liquid samples is used. The preconcentration factor is 415 and a chromium concentration as low as 0.02 µg L -1 can be detected. The procedure shows a good reproducibility (relative standard deviation close to 3%).

Amberlite XAD-4 resin (AXAD-4) was chemically modified to an aminated Amberlite XAD-4 (AAXAD-4) resin and characterized by infrared spectroscopy. AAXAD-4 resin was used as an efficient solid phase for the preconcentration and speciation of Cr(III) and Cr(VI) ions by column technique. The concentration of chromium species was determined by microsample injection system-flame atomic absorption spectrometer (MIS-FAAS). Selective retention of Cr(III) ions was achieved at pH 8.0 and eluted using 1.0 mL of 3.0 mol L-1 HCl and 1.0 mL of 2.0 mol L-1 NaOH, successively, at the flow rate of 5.0 mL min-1. The maximal sorption capacity of AAXAD-4 resin for Cr(III) ions was found to be 67.0 mg g-1. Th limit of detection (LOD) and limit of quantitation (LOQ) for Cr(III) ions were found to be 0.041 and 0.131 µg L-1, respectively, with preconcentration factor (PF) of 375 and relative standard deviation (RSD) of 3.75% (n = 11). The method was validated using certified reference materials (CRMs) and successfully applied to the real samples, spiked with Cr(III) and Cr(VI) ions. [ABSTRACT FROM AUTHOR]

Chromium(III) species is an essential micronutrient, whereas, its hexavalent form, Cr(VI) is considered to be a carcinogen. For the selective detection of Cr(III) in presence of Cr(VI), separation coupled spectroscopic techniques have been often used. For the first time in this work, we report a flow injection analysis coupled dual electrochemical detector (FIA-DECD) for separation-free detection of Chromium (III) and (VI) species. A gold nanoparticles decorated carbon nanofibres-chitosan modified electrode has been prepared by a quick and in-situ electrochemical deposition of Au 3+ ion in pH 7 phosphate buffer solution (PBS) and has been used as a dual electrochemical detector for Cr(VI)-reduction and Cr(III)-oxidation reactions in pH 2 PBS. Under an optimal hydrodynamic FIA-DECD condition, i.e., at applied potentials 0.1 V (for Cr(VI)-reduction) and 1 V vs Ag/AgCl (for Cr(III)-oxidation) and at a flow rate = 0.8 mL min −1 , calculated linear range and detection limit values are; 0.1–100 ppm and 0.69 ppb (0.72 ppt for 20 μL sample loop volume) for Cr(III) and 0.1–100 ppm with detection limit, 0.32 ppb (0.33 ppt for 20 μL) for Cr(VI). No marked interference from other cations and anions like Cu 2+ , Zn 2+ , Cd 2+ , Pb 2+ , Co 2+ , Ca 2+ , Fe 2+ , Mg 2+ , NO 3 − , NO 2 − , SO 3 2− and SO 4 2− were noticed. Selective detection of Cr species (Cr(III) and Cr(VI)) in industrial waste water samples with data comparable to ICP-OES was demonstrated. [ABSTRACT FROM AUTHOR]

A novel type of solvent named deep eutectic solvent (DES) has been considered as a green ionic liquid analogue. A novel method was developed for enrichment and speciation of chromium ion from water and food samples based on deep eutectic solvent and ultrasonic extraction. The procedure for this method was comprised of Cr(III) complex formation with a hydrophobic complexing agent (Z)‐N‐(3,5‐diphenyl‐1H‐pyrrol‐2‐yl)‐3,5‐diphenyl‐2H‐pyrrol‐2‐imine (azadipyrromethene dye). Metal complex was entrapped in a deep eutectic solvent as an extracting solvent. While Cr(III) recovery was quantitative, the recovery of Cr(VI) was found 5%. After reduction of Cr(VI) to Cr(III), the method was applied for determination of total chromium(III) ion. The amount of Cr(VI) was calculated as subtracting of Cr(III) from total chromium ion. Various analytical parameters were optimized. The certified reference materials were analyzed and standard addition method also carried out to real samples to check the accuracy of the developed method. Preconcentration factor was found to be 50. The limit of detection of chromium(III) was found to be 4.3 ng l‐1. The precision of developed method as the relative standard deviation (RSD) was found as 3.5 %. The developed method was applied successfully for the speciation of chromium ions in water and food samples. [ABSTRACT FROM AUTHOR]

A soft material formed by multiwall carbon nanotubes and 1-butyl-3-methyl imidazolium chloride was used as sorbent material to perform the chromium speciation in natural waters. This soft material was not yet used for the speciation of metals as chromium. Thus, a multicommutated flow system containing a minicolumn packed with the soft material was designed. The procedure was based on the capacity of the sorbent to retain Cr(VI) as Cr 2 O 7 = and allow to pass Cr(III) through the column. Then, a fully automated flow-batch analysis system was developed to quantify both species using chemiluminescence detection. Thus, Cr(III) was determined as catalyst of the luminol and hydrogen peroxide reaction and Cr(VI) as oxidant of luminol reaction. This represents a new approach because the oxidation of luminol using Cr 2 O 7 = has not been reported in literature. The variables of the two systems were optimized. The limits of detection were 1.4 μg L −1 for Cr(VI) and 4.0 μg L −1 for Cr(III). The precision of the method was 3.8% and 7.0% for Cr(VI) and Cr(III), respectively. The present method was applied to real water samples with recoveries between 95% and 107%. Besides, these results were in accordance with those obtained using inductive coupled plasma-optical emission spectrometry technique. [ABSTRACT FROM AUTHOR]

In the last decades, the extensive use of chromium in industrial activities has led to the discharge of different chromium species into the biosphere. The two stable chromium forms are Cr(III) and Cr(VI), which have dramatically different properties. While the first one is essential, the second is harmful and carcinogenic, even at very low concentration. Therefore, the appropriate analysis of chromium in environmental, biological, food and other kind of samples need a reliable separation and subsequent quantification of both Cr species. The present paper provides a critical review of chromium speciation methods in which solid phase extraction was employed as sample pretreatment using graphene and carbon nanotubes (and their diverse oxidized, functionalized and magnetic derivatives) as sorbents. The different published methods for the speciation of Cr(III), Cr(VI) or both species are described and classified on the basis of the separation strategy employed: (i) the selective retention of only one of the two species by the sorbent, (ii) the retention of a Cr-chelate formed by using a ligand selective for only one of the Cr-species, or (iii) the sorption of both Cr(III) and Cr(VI) species. In addition, the distinct applied SPE modes (on-column, dispersive or magnetic) and their automation possibilities, the analytical techniques utilized for measurement of the Cr-species after separation, as well as the analytical figures of merit of the methods developed up to date are evaluated. Finally, the expected future trends of solid phase extraction for Cr speciation based on carbon nanomaterials such as graphene, carbon nanotubes and their derivatives as sorbents are commented. [ABSTRACT FROM AUTHOR]

A new fluorimetric method with rhodamine-based fluorescent agent was developed for the rapid speciation of Cr(III)/Cr(VI) in tea, soil and water samples. The system, which utilizes a fluorescent reagent, was used for the first time after synthesis/characterization of 3′,6′-bis(diethylamino)-2-{[(1E)-(2,4-dimethoxyphenyl)methylene] amino}spiro[isoindole-1,9′-xanthen]-3(2H)-one (BDAS). The reagent responds instantaneously at room temperature in a 1:1 stoichiometric manner to the amount of Cr(III). The selectivity of this system for Cr(III) over other metal ions is remarkably high, and its sensitivity is below 0.01 mg L − 1 in aqueous solutions which enables a simplification without any pretreatment of the real sample. The method has a wide linear range of 0.1–10 mg L − 1 and a detection limit of 0.15 μg L − 1 for Cr(III) while the relative standard deviation was 0.1% for 0.1 mg L − 1 Cr(III) concentration. The results of detection and recovery experiments for Cr(III) in tea, soil and water were satisfactory, indicating that the method has better feasibility and application potential in the routine determination and speciation of Cr(III)/Cr(VI). The results of analysis of the certified reference material (INCT-TL-1 tea sample and CWW-TM-D waste water) are in good agreement with the certified value. [ABSTRACT FROM AUTHOR]

The application or disposal of char derived from tannery sludge is directly influenced by the mobility and bioavailability of Cr during pyrolysis process. This study focused on the changes of Cr speciation and organic matter in tannery sludge during low-temperature pyrolysis (100-400 °C) to evaluate the toxicity of char in terms of the leaching possibility of Cr. The results showed that (1) lower char yield and more porous structure were observed after pyrolysis. (2) Higher pyrolysis temperature increased Cr content in the char; however, Cr in this case was converted into the residual fraction which minimized its bioavailability therefore lowers its potential risk to the environment. (3) Organic matters in the acid and alkali leachates were mainly humic acid-like substance, and condensed organic matter might appear at 200 °C and then destruct. (4) Despite the comparatively high content of Cr in the char, the leaching toxicity of char was within the security range according to the national standard of China. The Cr content in the acid and alkali leachates decreased to the range of 16.5-35.3 and 0.2-6.8 mg/L, respectively. It was suggested that the potential toxicity of tannery sludge from Cr could be reduced before utilization or disposal by pyrolysis, especially under 400 °C. [ABSTRACT FROM AUTHOR]

A simple, rapid, highly accurate and sensitive kinetic method is proposed for determining chromium(VI). The method is based on its catalytic effect on the oxidation of Celestine blue (CB+) by H2O2 in the presence of 2,2′-bipyridyl (Bipyr) and cetylpyridinium chloride (CPC) at pH 6.50. The reaction was monitored spectrophotometrically by measuring the absorbance of indicator dye at 645 nm. The analytical variables, which have influences on the sensitivity, were investigated and the optimum conditions were established. The optimized conditions made it possible to determine and speciate chromium in a linear range of 5–200 μg L−1 with a detection limit of 0.65 μg L−1. The recoveries and relative standard deviations (RSDs) for the determination of 10, 25, 75 and 150 μg L−1 Cr(VI) (n: 5) were in the range of 99.0–99.8% and 0.2–3.5%, respectively. The selectivity was also studied and greatly enhanced by adding a suitable masking mixture. The method was successfully applied to the simultaneous analysis of Cr(III) and Cr(VI) in natural water and waste water samples with a recovery changing in the range of 95–103% for Cr(III) and 100–104% for Cr(VI). Its accuracy was validated by the analysis of certified reference materials with good agreement between certified and found values.

A novel nanosorbent is designed via crosslinking of nanolayer carboxymethyl cellulose (CMC) onto the surface of nano‑zirconium oxide (Nano-ZrO 2 ) using glutaraldehyde for the formation of Nano-ZrO 2 -glu-CMC. The nanosorbents were characterized using TGA, SEM, HR-TEM, FT-IR and surface area analysis. The particle size of Nano-ZrO 2 -glu-CMC was 22–39 nm. The potential implementation of Nano-ZrO 2 -glu-CMC sorbent for selective speciation and extraction of chromium ions from real water samples and aqueous solutions was explored and compared versus Nano-ZrO 2 sorbent using the batch technique in presence of various values of pH, time, mass of sorbent, concentration and competing ions. The maximum metal capacity values of chromium (VI) by Nano-ZrO 2 -glu-CMC and Nano-ZrO 2 were identified as 680 and 120 μmol g − 1 , respectively in pH 1.0–2.0, while the identified maximum values of chromium (III) were 1120 and 500 μmol g − 1 , respectively in pH 7.0. Nano-ZrO 2 -glu-CMC and Nano-ZrO 2 sorbents were further successfully applied for speciation of Cr(VI) and Cr(III) as well as adsorptive removal from tap water, sea water and industrial wastewater samples adjusted to pH 2.0 and pH 7.0, respectively. The identified percentage values of chromium species by the multistage microcolumn technique confirmed the superiority of ZrO 2 -glu-CMC versus Nano-ZrO 2 based on the determined recovery range 97.9–100.0% and 89.6–100.0%, respectively. [ABSTRACT FROM AUTHOR]

In this work, we developed dispersive solid-phase extraction method with the use of carbon nanotube based magnetic bucky gels. The hydrophilic carbon nanotube (CNT)-based magnetic bucky gels (M-BGs) were developed with the features of magnetic susceptibility to permit fast injection of sorbent, rapid retrieval of the sorbent and high dispersion of MWCNT in the aqueous sample. We combined magnetic multi-wall carbon nanotube nanocomposite (MMWCNTs) with hydrophilic ionic liquids in order to prepare highly stable carbon nanotube-based magnetic bucky gels. The hydrophilic ILs act simultaneously as modifier and disperser for MMWCNTs and reduce the agglomeration of sorbent in water .Consequently they enhance the extraction efficiency. We used the unique features of this responsive gel (fluidity, stability, magnetic properties, and strong sorbing ability) in developing a new, fast, sensitive, simple, and environmental-friendly magnetic bucky gel-based dispersive solid-phase extraction method (M-BG-dSPE) combined with fibre optic linear array detection spectrophotometer (FO-LADS) for preconcentration and speciation of Cr(VI) and Cr(III) in water samples. The properties of MMWCNT and magnetic bucky gels were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectrophotometer (FT-IR). Under the optimised conditions, the enrichment factor of the method was 318, the limit of detection was 0.1 ng mL−1and the repeatability of the method, expressed as the relative standard deviation (RSD,n = 5), varies between 3.2% and 2.5% in different concentrations. The proposed procedure has been applied for speciation of Cr(VI) and Cr(III) in water samples with good recoveries in the range from 90 to 105%. Validation of the method was carried out by comparison of the obtained results with results obtained by the ET-AAS and spiking-recovery method. [ABSTRACT FROM AUTHOR]

Hexavalent chromium species (Cr(VI)) are often carcinogenic, of high acute toxicity, highly mobile, and thus pose a severe risk to health and environment. Fertilizers usually contain significant amounts of chromium. Therefore, a reliable analysis of chromium and the fraction of Cr(VI) are crucial for safe use of fertilizers. This problem is expected to increase in the future, since more and more recycled fertilizers emerge due to increasing fertilizer demand and respective supply risks. However, existing analytical methods have been developed for conventional fertilizers and have to be tested whether they are suitable for the new materials. Thus, we performed a wet-chemical extraction for Cr(VI) on several matrices as well as respective quality control experiments including spiking with Cr(III) and Cr(VI) compounds. We found the Cr(VI) amounts to be below 2 mg/kg except for a thermally post-treated sewage sludge ash (SSA) that showed 12.3 mg/kg. The presence of organic matter e.g. in sludge or precipitated struvite caused a reduction of spiked Cr(VI) and thus no satisfying recovery for quality control. Cr(VI) reduction was also observed for SSA, presumably due to the presence of Fe(II) compounds. Even though the tested procedure can be hampered in some recycled fertilizer matrices, it might be adapted to be applicable also for these complex samples. [ABSTRACT FROM AUTHOR]

A simple, sensitive and reliable method has been developed for separation and preconcentration of chromium (VI) from aqueous samples before determination by electrothermal atomic absorption spectrometry. The method is based on the extraction of the hydrophobic complex of chromium (VI) with ammonium pyrrolidine dithiocarbamate in the coacervates made up of decanoic acid reverse micelles in the water-tetrahydrofuran mixture. Parameters affecting the extraction efficiency of the analyte were studied and optimised. Under the optimum conditions, the linear range, enhancement factor, the limit of detection and limit of quantification were found to be 0.008-0.4 μg L-1, 127, and 1.8 ng L-1 and 6.0 ng L-1, of Cr(VI), respectively. The relative standard deviation at the concentration level of 0.1 μg L-1 Cr(VI) (n = 6) was 4.2%. Total chromium was determined after the oxidation of Cr(III) to Cr(VI) with permanganate in acidic medium. The method was successfully applied to the determination of chromium species in water and human serum samples. [ABSTRACT FROM AUTHOR]

We have developed a chromium speciation and preconcentration method with the use of the graphite furnace atomic absorption spectrometry (GFAAS) technique. This method is based on single-drop microextraction (SDME) technique. Nowadays the microextractions have become popular, because low amount of organic solvent needs to be used for the separation. The sample was introduced into the extraction cell with a single chloroform droplet. For the separation and enrichment of chromium species, an ion-pair forming compound was used. After the extraction, the chromium content of the droplet was determined by GFAAS. The analytical sensitivity of the standard SDME technique was improved by increasing the volume of organic phase and by sample recirculation. Because of the increased contact area and the developed extraction device, the stability of droplet was markedly increased. As an application we have determined the Cr(VI) content of sea water by the GFAAS technique using these separation/enrichment methods. Under the optimized extraction conditions, the linear range, detection limit (S/N = 3) and precision (RSD, n = 3) for Cr(VI) were 0.14 - 5.00 μg/L, 0.042 μg/L, and ≤ 3.0%, respectively. The advantages of this method are the following: cost efficiency, the high enrichment of chromium species and easy usage with the GFAAS technique. Therefore the concentration of the chromium species can be determined at the ng/L level. [ABSTRACT FROM AUTHOR]

This work aims to investigate the nature and the specific mechanisms by which polycarboxylic compounds participate in the tolerance of Silene vulgaris to Cr with special attention given to the rhizosphere system. This knowledge is important to use this species in the implementation of phytoremediation technologies in Cr-polluted soils. According to the results, chromium is chelated and mobilized by the citric and malic acids in plant tissues, while oxalic acid might participate in the reduction and chelation of Cr in the rhizosphere. At the applied doses, the response of both exudation rate and root exudate composition (total polyphenols and quercitin) seems to involve a rearrangement in the lignification of the plant cell wall to immobilize Cr. Quercetin-3-dirhamnosyl-galactoside and apiin (apigenin-7-O-apiosyl-glucoside) have been identified as the major polyphenols in the root exudates of S. vulgaris. The increments found in the apiin concentration in root exudates seem to be related to the protection against Cr toxicity by chelation of Cr or by free radical scavenging. Though earlier response is detected in plant tissues, results from this work together with previous studies in S. vulgaris indicate that exudation might be a regulated mechanism of protection under Cr exposition in S. vulgaris that may involve mainly Cr reduction and chelation. [ABSTRACT FROM AUTHOR]

Selectivity of gold nanoparticles (AuNPs) depends upon surface functionality; small changes in structure or concentration bring significant changes in the behavior of AuNPs. In this study, citrate-capped AuNPs were functionalized with ortho- dicarboxylate substituted pyridine (2,3-PDCA) and detailed studies on experimental conditions were carried out to check the stability of AuNPs and response for Cr 3 + . Stability of PDCA-AuNPs was found sensitive to the pH, ionic strength of buffer and its type. Capping behavior of PDCA on C-AuNPs was examined by FTIR spectroscopy. Surface morphology and size of synthesized AuNPs were confirmed by AFM, XRD, and DLS techniques where particles were found 11 nm in size, monodisperse and spherical in shape. Interaction of stabilized AuNPs was tested with various metal ions; where Cr 3 + induced the changes in localized surface plasmon band (LSPR) of PDCA-AuNPs which leads to a color change from wine red to violet blue. The phenomenon is explained as cooperative effect of citrate and pyridine nitrogen on surface of AuNPs in contrary to meta -dicarboxylate substituted pyridine derivatives. Further, under optimized and controlled conditions Cr 3 + shows linear response with decrease in absorbance at LSPR intensity of AuNPs (518 nm). Moreover, to demonstrate the applicability of method, Cr 3 + was determined in the presence of Cr (VI) which shows 96% recovery. [ABSTRACT FROM AUTHOR]

A novel sorbent material employing magnetic nanoparticles (MNPs) coupled to graphene oxide (GO) functionalized with 4-aminobenzenesulfonic acid (M@GO-ABS) has been synthesized and applied to develop an inexpensive and automatic method for Cr(III) and Cr(VI) speciation in environmental samples; the developed method combines inductively coupled plasma optical emission spectrometry (ICP-OES) with on-line magnetic solid phase extraction (MSPE). Two magnetic-knotted reactors containing M@GO-ABS were installed in the eight-port injection valve of a flow injection (FI) manifold. Two different eluents were used, one for Cr(VI) (the most toxic chromium species) and one for total Cr concentration. Cr(III) concentration was calculated by the difference between Cr(VI) concentration and total Cr concentration. The optimized method presented detection limits (LOD, peak height) of 0.1 μg L−1 for chromium (VI) and 0.08 μg L−1 for total chromium, and enrichment factors of 15 and 23, respectively. Certified reference materials (TMDA 54.5 fortified lake water and SPS-SW2 surface water) and spiked aqueous samples were used to validate the developed method. The developed method was fruitfully applied to chromium speciation in environmental water samples such as seawater, well water and tap water collected in Málaga (Spain). The obtained values were in good agreement with the certified values, and the recoveries were found in the range of 91–108% for the spiked samples. [Display omitted] • A new magnetic chelating sorbent has been designed for chromium speciation and determination. • The M@GO-ABS system was optimized by two central composite designs (CCD). • The M@GO-ABS allows the preconcentration of Chromium(VI) and total Chromium in enviromental waters. • The method offers simplicity, accuracy, reproducibility and low cost. • The system can be applied in saline water, such as seawater samples. [ABSTRACT FROM AUTHOR]

In this study, a new sulfonamide based polymeric adsorbent (5ATT-CSPS) was prepared with reaction between 5-Amino-1,3,4-thiadiazole-2-thiol and chlorosulfonated polystyrene resin and characterized by FT-IR, FESEM-EDX, XPS, zeta potential. It was used for the first time as an adsorbent for speciation of chromium in various water samples and lettuce extracts in UBM saliva by dispersive solid phase micro extraction (d -SPµE). The total chromium concentration was determined by F AAS. The parameters affecting the recovery of Cr(III) such as pH, contact times, elution conditions, sample volume, co-existing ions and adsorption capacity were optimized. The adsorbent demonstrated a good performance for adsorption of Cr(III) (R%≥95). It was quantitatively adsorbed in the range of pH 2.0–4.0 whereas Cr(VI) was not adsorbed in the pH range of 2.0–8.0. Therefore Cr(VI) concentration was calculated indirectly. The elution was achieved by 5 mL of 2 mol L−1 HNO 3. Adsorption and elution contact times of the adsorbent were 3 min and 2 min, respectively. The preconcentration factor of the method was found to be 8. Considering optimal conditions, limit of detection was found to be 2.9 µg L−1, and precision of the method (as RSD%) was found to be ≤ 4.3%. The adsorption capacity of the 5ATT-CSPS for Cr(III) was 25 mg g−1. The accuracy of this method was verified by analyzing TMDA-70 certified reference material and by recovery studies in spiked water samples and lettuce extracts in the unified bioaccessibility method (UBM) saliva. [Display omitted] • A new sulfonamide based polymeric adsorbent was synthesized and characterized. • It was used for the first time as an adsorbent for speciation of chromium by d -SPµE. • Cr(III) was quantitatively adsorbed in the range of pH 2.0–4.0. • Adsorption and elution contact times of the adsorbent were ≤ 3 min • Chromium speciation was made in water samples and lettuce extracts in UBM saliva. [ABSTRACT FROM AUTHOR]

• Direct immersion dual-drop microextraction (DIDDME) was firstly developed for Cr species. • Cr(III) and Cr(VI) were separated and enriched into two drops at pH 3.5, respectively. • DIDDME did not require tedious oxidation/reduction or centrifugation/filtration steps. • This method avoided risk of sample contamination and analysis errors in redox speciation strategies. • Ingenious use of DIDDME made separation of Cr(III) and Cr(VI) convenient, efficient and time-saving. Non-chromatographic speciation methods generally involve speciation conversion, which may cause sample contamination, analysis errors and tedious operations. In this work, a direct immersion dual-drop microextraction (DIDDME) was firstly developed for separation and preconcentration of Cr(III) and Cr(VI). In DIDDME, two organic drops on needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent for reacting with a specific species. Thus, Cr(III) and Cr(VI) were selectively extracted into different drops. This method afforded detection limits of 3.0 and 4.1 ng/L, quantification limit of 10 ng/L and 14 ng/L, linear range of 0.01–30 ng mL−1 and enrichment factors of 354-fold and 326-fold for Cr(III) and Cr(VI), respectively. Precisions like repeatability and reproducibility were assessed by calculating relative standard deviations, which were lower than 5.4 % and 6.9 %, respectively. This procedure was used successfully for quantification of Cr(III) and Cr(VI) in food samples. [ABSTRACT FROM AUTHOR]