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A preconcentration procedure is presented for the dispersive micro solid-phase extraction (DMSPE) of trace amounts of Pb(II), Cd(II), Zn(II), Cr(III), Mn(II), and Fe(III) as their batophenanthroline chelate complexes on the graphene oxide (GO) nanosheets prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The influence of analytical parameters including pH, type and concentration of eluent, amount of complexing reagent, sorption time and sample volume on the quantitative recoveries of analytes were investigated in order to obtain the optimum conditions. The experiment shows that metal ions can be simultaneously preconcentrated at pH of 8 with high recoveries (in the range of 90–97%) and excellent precision (RSDs within 1.6–3.0%). The detection limits are 0.25, 0.06, 0.16, 0.06, 0.12 and 0.21 ng mL−1 for Pb(II), Cd(II), Zn(II), Cr(III), Mn(II), and Fe(III), respectively. The method was successfully applied for the determination trace amounts of analytes in food and water samples. Unlabelled Image • Sorption of batophenanthroline - metal chelates on graphene oxide • Graphene oxide using as adsorbent in DMSPE • Using ICP-OES for the detection of Pb, Cd, Zn, Cr, Mn and Fe • Detection limit suitable for food and environmental analysis • Simple, fast, sensitive and environmental friendly method [ABSTRACT FROM AUTHOR]

Obtaining new nanocomposites with sorption properties towards chromium is highly important not only from the environmental point of view but also for developing eco-friendly methods of chromium determination. The potential use of aluminum oxide-coated nano-graphite (Al2O3/nano-G) as a new nanosorbent in ultrasound-assisted dispersive micro-solid-phase extraction (DMSPE) for rapid speciation of trace chromium(III) and chromium(VI) ions in natural water was evaluated. In the developed method, the crucial issue is the new nanocomposite synthesized by coating alumina on a nano-graphite surface with sorption properties. Structural researches of the nanocomposite were carried out by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Raman spectroscopy. Maximum adsorption capacity of Al2O3/nano-G towards Cr(III) was 32.8 mg g−1. The influence of the method’s factors like pH, sample volumes, contact time, coexisting ions, and humic acid on the recovery of chromium was examined. The nanocomposites have been found to be stable and effective as a sorbent in water with high concentrations of selected cations and anions present in water as well as in water of various pH. Al2O3/nano-G is selective for Cr(III) in presence of Cr(VI). Cr(III) was determined by the developed method, total Cr after reduction of Cr(VI) to Cr(III), and Cr(VI) was calculated as the difference between total Cr and Cr(III). After sorption, the nanocomposite with chromium was collected on 5-mm diameter filters and analyzed by energy-dispersive X-ray fluorescence spectrometry (EDXRF) to determine the chromium concentration. The method was characterized by correlation coefficient 0.999, limit of detection (LOD) 0.04 ng mL−1, and relative standard deviation (RSD) 3.5%. Al2O3/nano-G combined with proposed DMSPE/EDXRF was verified by analysis of certificate reference material of natural water (NIST 1640a).ᅟ [ABSTRACT FROM AUTHOR]

Among cereals, rice is the second most cultivated staple crop in the world. It may be contaminated by toxic heavy metals present in water or soil. Therefore, monitoring the presence of heavy metals in rice and its products is a matter of a great importance from the nutritional and toxicological view. In this paper, a simple and effective analytical procedure based on dispersive micro solid-phase extraction with the use of oxidized multiwalled carbon nanotubes and batophenanthroline was developed for the determination of lead, cadmium, zinc, manganese and iron in white and wild rice samples. Due to the high preconcentration factor of 200, the optimized procedure allows obtaining detection limits between 0.13 and 0.35 ng mL −1 using flame atomic absorption spectrometry (FAAS). Novel preconcentration method can successfully be applied in food analysis with accuracy better than 7% rel. and repeatability lower than 3%. [ABSTRACT FROM AUTHOR]

Graphene oxide decorated with cerium(IV) oxide (GO/ CeO2) was synthesized and applied in adsorption of several metal ions such as As(III), As(V), Se(IV), Cu(II), and Pb(II) from aqueous samples. The important feature of GO/CeO2 nanocomposite is also its selectivity toward selenite in the presence of selenate. The structure of GO/CeO2 has been proven by microscopic and spectroscopic techniques. The maximum adsorption capacities of GO/CeO2 calculated by Langmuir model toward arsenic, selenium, copper, and lead ions are between 6 and 30 mg g-1. An interesting feature of this adsorbent is its excellent dispersibility in water. Thus, GO/CeO2 nanocomposite is ideal for fast and simple determination of heavy metal ions using dispersive microsolid phase extraction (DMSPE). Moreover, coupling DMSPE with energy-dispersive X-ray fluorescence spectrometry (EDXRF) is extremely beneficial because it allows direct analysis of adsorbent. Thus, the analyte elution step, as needed in many analytical techniques, was obviated. The influence of sample volume and the sorption time as well as the influence of foreign ions and humic acid on the recovery of determined elements are discussed in the paper. The results showed that developed methodology provided low limits of detection (0.07- 0.17 μg/L) and good precision (RSD < 4%). The GO/CeO2 nanocomposite was applied to analysis of real water samples and certified reference materials (CRM) groundwater (BCR-610) and pig kidney (ERM-BB186). [ABSTRACT FROM AUTHOR]

A new solid-phase microextraction method for preconcentration and determination of ultra-trace Au(III) and AuNPs was developed. For this purpose, a nanosized aluminum-magnesium layered double hydroxide (AlMg-LDH)/graphene oxide (GO) nanocomposite was synthesized. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy confirmed the successful synthesis of the nanocomposite AlMg-LDH/GO with a well-crystallized hexagonal structure. The synthesized nanomaterial allows sorption with 100% recovery of AuNPs at pH 1–5 or AuNPs and Au(III) ions at pH 1–2. Therefore, gold ions and corresponding gold nanoparticles can be together or separately determined. The maximum sorption capacity of the nanocomposite is 12 mg g−1 for Au(III). After adsorption, gold was directly determined on the AlMg-LDH/GO by energy-dispersive X-ray fluorescence spectrometry with a detection limit of 0.06 ng mL−1, precision ca. 4%, and recovery >90%. According to the Green Chemistry rule, the method has significant advantages, such as reducing the amount of sorbent required and eliminating solvent. The elution of analytes from the nanosorbent is completely eliminated in the developed method. The developed method was successfully used to extract and determine ultra-trace gold in cosmetics products. [Display omitted] • Discrimination of AuNPs and Au(III) using MgAL-LDH/GO. • Direct determination of Au onto MgAL-LDH/GO without elution. • Method based on SPME-LDH/GO beneficial in terms of time, energy and money consumption. • Cosmetics analysis towards Au content. [ABSTRACT FROM AUTHOR]

A solid phase extraction method is presented for the preconcentration of trace lead ions on oxidized multiwalled carbon nanotubes (ox-MWCNTs). In the first step, the cationic Pb(II) complex of 2,2-bipyridyl is formed which, in a second step, is adsorbed on ox-MWCNTs mainly due to electrostatic and van der Waals interactions. The Pb(II) ions were then eluted with dilute nitric acid and quantified by FAAS. The effects of pH value, mass of sorbent, concentration of 2,2-bipyridyl, stirring time, of type, concentration and volume of eluent, of eluent flow rate and sample volume were examined. Most other ions do not affect the recovery of Pb(II). The limits of detection are 240 and 60 ng L for sample volumes of 100 and 400 mL, respectively. The recovery and relative standard deviation are >95 % and 2.4 %, respectively. Other figures of merit include a preconcentration factor of 160 and a maximum adsorption capacity of 165 mg g. The method was successfully applied to the determination of Pb(II) in spiked tap water samples. The accuracy of the method was verified by correctly analyzing a certified reference material (NCS ZC85006; lead in tomatoes). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] Graphene oxide (GO) covalently bonded to the spherical silica. [•] Very stable sorbent for SPE of metal ions. [•] Excellent contact with solution due to the softness and flexibility of GO nanosheets. [•] Several adsorption–elution cycles without any loss of adsorptive properties. [•] High adsorption capacity due to the wrinkled structure of GO nanosheets. [Copyright &y& Elsevier]

Abstract: In this paper, the adsorptive properties of graphene nanosheets were used for simultaneous preconcentration of cobalt, nickel, copper and lead ions from water samples. The developed methodology is based on dispersive micro-solid phase extraction (DMSPE) which is miniaturized and a simplified version of classical solid phase extraction technique. In proposed procedure only 200μL of suspension containing graphene (0.2mg), ammonium pyrrolidine dithiocarbamate (APDC) (0.8mg) and Triton-X-100 (0.1mg) is rapidly injected to 50mL of water sample. Then, graphene nanosheets with adsorbed metal-APDC chelates are collected on membrane filter and measured using energy-dispersive X-ray fluorescence (EDXRF) spectrometry. The various parameters including pH, amount of APDC, sample volume, amount of Triton-X-100 and sorption time were optimized in order to obtain the best recoveries. The experiment shows that Co, Ni, Cu and Pb can be simultaneously preconcentrated at pH of 5 with high recoveries (97%, 96%, 99% and 96% for Co, Ni, Cu and Pb, respectively) and very good precision (RSDs within 2.6–3.4%). Due to the excellent enrichment factors ranging from 400 to 2500 the proposed DMSPE–EDXRF procedure offers low detection limits. For optimized measurement conditions (voltage and current of X-ray tube, primary beam filter) the detection limits are even 0.08, 0.07, 0.08 and 0.20ngmL−1 for Co, Ni, Cu and Pb, respectively. [Copyright &y& Elsevier]

Highlights: [•] Application of graphene (G) and graphene oxide (GO) in analytical chemistry. [•] Adsorption capacity of G and GO towards organic compounds and metal ions. [•] Application of G and GO in SPE, magnetic-SPE and SPME. [ABSTRACT FROM AUTHOR]

[Display omitted] • Superior nanoadsorbent for highly effective adsorption of Pb(II) ions. • Impressive adsorption capacity and selectivity of the adsorbent toward Pb(II). • Extremely small adsorbent dosage and very short adsorption time. • Very low detection limit of 2.3 pg mL−1 using a benchtop TXRF instrument. • Simple and accurate analysis of complex matrix samples. In this paper, the graphene oxide (GO) decorated with fullerenol nanoparticles C 60 (OH) 22 has been designed for the highly selective separation and ultrasensitive determination of lead ions. The grafting fullerenol nanoparticles to the surface of GO solves the problem of their high solubility in aqueous solutions and simultaneously uses their high hydrophilicity and deprotonation ability. The research has revealed unique adsorption properties of GO-C 60 (OH) 22 toward Pb(II) ions at pH 5.5, i.e., minimal adsorbent dose (5 mg L−1), impressive resistance to ionic strength (up to 1 mol L−1), and enormous adsorption capacity (1307 mg g−1), much higher than those of any of the currently reported sorbents. The adsorption isotherms, kinetics, and effect of ionic strength indicate that an inner-sphere model based on surface complexation is the main mechanism of Pb(II) adsorption on GO-C 60 (OH) 22. The high-resolution O1s and Pb4f X-ray photoelectron spectra confirm the strong chelation of Pb(II) ions and suggest the various coordination of Pb(II) ions to the oxygen functional groups. The exceptional properties of GO-C 60 (OH) 22 , including the possibility of application in micro-quantities, were the basis for the development of the method for ultra-sensitive detection of Pb(II) ions using such micro-analytical technique as total-reflection X-ray fluorescence spectrometry (TXRF). The method allows obtaining an extremely low detection limit of 2.3 pg mL−1 using a low-power TXRF instrument. Due to the impressive selectivity of the method, the ultra-trace Pb(II) ions can be highly accurately determined in complex matrix samples, including high salinity waters challenging to analyze using other analytical techniques. [ABSTRACT FROM AUTHOR]

An environmentally friendly analytical procedure of pre-concentration of cobalt, nickel, and copper according to the rules of green chemistry has been developed. The proposed method is based on using chitosan for sorption of trace elements from water samples. The novel modification of the sorption process is the combination of an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6]) with chitosan. Ionic liquid partly decreases the crystallinity of the chitosan. The crystalline regions of the polymer are not accessible to metal ions. Although the ionic liquid cannot completely disrupt the crystalline domains of chitosan, it may gain in the reactive groups of the chitosan, even at the center of the particle. Consequently, the sorption of metal ions by chitosan is significantly improved. In this paper, adsorption characteristics of cobalt, nickel, and copper using newly developed sorption are studied. The effect of pH and time of chitosan activation, as well as sorption, salt concentration, some metals ion concentrations, and the amount of adsorbent on the extent of adsorption, are investigated. Chitosan with adsorbed metal ions was dissolved in acetic acid. After evaporation a solvent film formed and was then analyzed using X-ray fluorescence spectrometry (XRF). As it meets the criterion of thin samples for XRF analysis, the matrix effects can be neglected. With the proposed procedure we obtained detection limits of 7 ng mL−1for cobalt, 5 ng mL−1for nickel, and 4 ng mL−1for copper. [ABSTRACT FROM AUTHOR]

The rapid development in nanomaterials and nanotechnologies has provided many new opportunities in the area related to analytical chemistry. In this paper the unique properties of these materials were used in order to preconcentrate heavy metals prior to detection by spectroscopic techniques. A novel, simple and highly reliable method for the preconcentration of trace amounts of chromium, manganese, cobalt, nickel, copper and zinc using electrochemically assisted sorption on oxidized multiwalled carbon nanotubes (MWCNTs) is developed. The proposed method is based on the application of an electric field to support the sorption process on oxidized MWCNTs. The proposed method was used to preconcentrate trace elements from water of pH = 4. After the preconcentration process, oxidized MWCNTs were directly measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer that reduces the number of chemicals required and minimizes sample handling. Besides EDXRF, any spectroscopy technique allowing the measurement of solid samples can be applied. The various parameters including pH of the solution, amounts of oxidized MWCNTs, sample volume and the influence of voltage as well as the time of assisted electric field on the sorption process were investigated for the optimization of the analytical procedure. Under optimized conditions the proposed preconcentration method offers a high recovery of 99% (Cr), 97% (Mn), 94% (Co), 96% (Ni), 92% (Cu) and 93% (Zn) and good precision of sample preparation (RSD) within 3.5–7%. If measurements are performed using the EDXRF spectrometer, the detection limits are 1 ng mL−1, 5 ng mL−1, 5 ng mL−1, 7 ng mL−1, 1 ng mL−1, 8 ng mL−1 for Cr(iii), Mn(ii), Co(ii), Ni(ii), Cu(ii) and Zn(ii), respectively. [ABSTRACT FROM AUTHOR]

Ultrasound-assisted solid-phase extraction (SPE) with multiwalled carbon nanotubes (MWCNTs) as a solid sorbent and 1-(2-pyridylazo)-2-naphthol (PAN) as a chelating agent was developed for the determination of trace and ultratrace amounts of Cd(ii) ions in aqueous samples. The solution containing Cd(ii) complexed with PAN was passed through the syringe filter with a PVDF membrane loaded with 25 mg of MWCNTs. The elution process was performed with 2.0 mL of 2.0 mol L−1 HNO3 with assistance of sonication. In order to obtain the high recovery of the Cd(ii) ions, the proposed procedure was optimized for various analytical parameters such as pH, amounts of PAN, sample volume, and elution conditions such as volume and concentration of eluent and influence of sonication and temperature. The investigation shows that sonication considerably improves the recovery, whereas temperature does not influence the elution process. Under optimized conditions Cd(ii) ions can be determined with very good recovery (99 ± 3%), precision (RSD = 3.2%) and detection limit (0.3 ng mL−1) for an enrichment factor of 50. The effect of common coexisting ions was also investigated. Cd(ii) can be determined in the presence of heavy metal ions and alkali metals. The proposed ultrasound-assisted SPE was applied for the determination of Cd(ii) in water samples and biological samples (Lobster Hepatopancreas). [ABSTRACT FROM AUTHOR]

Directly suspended droplet microextraction (DSDME) for determination of phosphate by energy-dispersive X-ray fluorescence spectrometry (EDXRF) is proposed. The method is based on the determination of phosphate, through molybdenum in the phosphomolybdenum blue complex. Because phosphorus is determined indirectly via molybdenum fluorescent radiation the difficulties of low fluorescent yield and low energy of phosphorus radiation are successfully overcome. A good ratio of phosphorus to molybdenum (1 to 37) and a sensitive Kα line of molybdenum give the possibility to determine a low concentration of phosphorus. Under the optimized conditions, good linearity, up to 20 μg of phosphorus (r = 0.9995), and the detection limit (2.8 ng mL−1) for the sample of 1.5 mL were achieved. The total RSD for the EDXRF determination of phosphorus followed by DSDME was 2.6% and taking into account all steps preceding the determination and the uncertainty of EDXRF measurements, the proposed method can be recognized as highly precise. The enrichment factor was equal to 56.8. The developed method was used to determine the total phosphorus content in surface waters. The accuracy and repeatability of the proposed procedure were checked by the standard addition method. The recovery in the range 93.5–97% was satisfactory and indicated the usefulness of the developed procedure. [ABSTRACT FROM AUTHOR]

Abstract: The determination of fatty acid methyl esters (FAME) in diesel fuel blends is an important aspect of production and blending process as well as quality control of distribution operations. In this study, energy-dispersive X-ray fluorescence spectrometer (EDXRF) is used for the first time for determination of FAME in biodiesel blends. The principle of the method is based on intensity difference of X-ray radiation scattered from hydrocarbons and from FAME. The experiment shows that coherent and incoherent radiation, commonly applied for evaluation of the average atomic number of the sample with light matrix, cannot be applied for FAME determination. However, the application of scattered continuous radiation gives excellent correlation between FAME concentration and intensity of scattered radiation. The best results are obtained if continuum is collected in the range of energy between 10.5 and 15.0keV for rhodium X-ray tube, operated at 35kV. Linear relationship between the FAME concentration and the inverse of scattered continuous radiation is obtained with the correlation coefficients of 0.999. Standard deviation of measurement is ca. 0.46% (v/v) of FAME and detection limit is 1.2% (v/v) for 600s counting time and 50% dead-time loss using Si-PIN detector. The investigation shows that crucial issue in determination of FAME in biodiesel blends using EDXRF spectrometer is the precision of measurements resulting from the counting statistics. Therefore, much better results (0.20% (v/v) standard deviation and 0.52% (v/v) detection limit) can be expected if higher intensity of primary radiation is applied and X-ray spectrum is collected by silicon drift detector of high input count rate. For concentration of FAME from 10 to 100% (v/v), the differences between reference method (Fourier transform infrared spectrometry) and the proposed method usually do not exceed 1% (v/v) of FAME. The proposed method is fast, simple and enables FAME determination in wide range of concentration up to 100% of FAME without any sample treatment. [Copyright &y& Elsevier]

Analysis of small samples of lanthanum-doped lead zirconate titanate (PLZT) by wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) is presented. The powdered material in ca. 30 mg was suspended in water and collected on the membrane filter. The pure oxide standards (PbO, La2O3, ZrO2 and TiO2) were used for calibration. The matrix effects were corrected using a theoretical influence coefficients algorithm for intermediate-thickness specimens. The results from XRF method were compared with the results from the inductively coupled plasma optical emission spectrometry (ICP-OES). Agreement between XRF and ICP-OES analysis was satisfactory and indicates the usefulness of XRF method for stoichiometry determination of PLZT. [ABSTRACT FROM AUTHOR]

A method to determine zinc, yttrium and europium in luminophore type materials: ZnS:Cu+, ZnS:Ag+, Y2O2S:Eu3+ in solution is presented in this paper. Scattered radiation was used to correct for the influence of the acid matrix. The results obtained using the W Lα1 Compton scatter peak were compared with these obtained using the coherent scattered Lα1 and Lβ1 as well as the continuum measured near the lines of the analyte. To correct the matrix influence, equations with total mass attenuation coefficients were also applied. The best results were achieved with Compton scattered radiation and the continuum measured near the lines of the analyte. Preparation of the luminophore samples for X-ray fluorescence analysis involves digesting of 25 mg of sample in acid mixtures depending on the analyzed material. The analysis is conducted by the standard addition method. The results achieved are comparable to the results obtained by inductively coupled plasma atomic emission spectrometry. Relative standard deviations (R.S.D.) for zinc, yttrium and europium with contents of 65% Zn, 68% Y and 5% Eu amount to approximately 1%. [Copyright &y& Elsevier]

[Display omitted] • Ultrasensitive and selective determination/speciation of Se. • Reliable and highly precise analysis of the samples with complex matrix. • Wide range of applicability for various samples, i.e., water, beverages or foods. • Low detection limits of pg/mL using TXRF spectrometry. • Reduction of wastes and toxic reagents with the exclusion of organic solvent usage. The paper presents a new analytical procedure for the determination and speciation of trace and ultratrace selenium in water, beverages, seafood, milk, and vegetables. The developed method is based on the dispersive micro-solid phase extraction with the use of new thiosemicarbazide-incorporated graphene as a solid sorbent, in combination of the total-reflection X-ray fluorescence spectrometry (TXRF). As a result, we have created an auspicious analytical tool for fast and sensitive analysis of samples with a complex matrix. Regardless of the specimen type, the method is characterized by a very low detection limit of 1.7 pg mL−1 and high precision. The developed strategy allowed us to solve common problems associated with selenium loss during the sample preparation for the TXRF measurement and also improve its performance toward the analysis of beverages and high saline/solid samples, which may even be impossible to perform using standard sample preparation procedures for a TXRF measurement. [ABSTRACT FROM AUTHOR]

• Superior nanoadsorbent (GO-TSC) for highly effective adsorption of Hg(II) ions. • Very high adsorption capacity even in acidic solution. • Extremely small adsorbent dosage and very short adsorption time. • Impressive selectivity of the GO-TSC toward Hg(II). • Chemisorption confirmed by X-ray photoelectron spectroscopy. In this work, the superior nanoadsorbent (GO-TSC) for highly effective adsorption of mercury ions from water solutions was developed, by grafting the thiosemicarbazide molecules (TSC) to the graphene oxide (GO) nanosheets. GO-TSC combines the extraordinary properties of GO, such as high specific surface area and an excellent dispersibility in aqueous solutions with strong affinity of TSC molecules to Hg(II) ions. The experiments show that the adsorption of Hg(II) on the GO-TSC is significant in a broad pH range, and reaches maximum value (close to 100%) at pH 3–4, with the maximum adsorption capacity of 231 mg g−1 at pH 3.5. Due to the excellent dispersibility of GO-TSC nanosheets, an extremely small GO-TSC dosage of 5 mg L-1 is required to remove Hg(II) ions from aqueous solution in a short contact time (from 10 to 30 min for adsorption of 90–95% Hg(II)). X-ray photoelectron spectroscopy indicate that the adsorption of Hg(II) is based on the chemisorption, and Hg(II) ions can be complexed by a single TSC molecule as bidentate chelating agent (S–Hg–N), or two neighboring TSC molecules (S–Hg–S). Due to the formation of strong S–Hg–N and S–Hg–S interactions, the selectivity of the GO-TSC toward Hg(II) is impressive. Hg(II) ions can be removed from aqueous solutions with very high ionic strength and high concentration of potentially coexisting ions. [ABSTRACT FROM AUTHOR]

Sorptive and selective mini-membranes based on TiO2 directly synthesized onto cellulose filters (TiO2@cellulose) have been developed. The in situ synthesis of TiO2@cellulose applied is simple and economically advantageous. The obtained membranes can be useful for (1) separating arsenic(V) and selenium(IV) from other ions and organic matter, (2) speciation of arsenic and selenium, and (3) determining ulratraces of these ions in water samples. The membranes exhibit good stability and high maximum adsorption capacities for Se(IV) (71 mg g−1) and As(V) (41 mg g−1). A monolayer chemical adsorption of analytes on the membranes was confirmed. The structure of membranes was examined with scanning electron microscopy, x-ray diffractometry, and micro energy-dispersive x-ray fluorescence spectrometry (μ-EDXRF). The membranes were characterized by homogenous distribution of TiO2 onto cellulose. The TiO2@cellulose was used as a new sorbent in micro-solid phase extraction for determination of Se(IV) and As(V) by EDXRF. Using direct analysis of mini-membranes after sorption of analytes avoids the elution step. Thus, the proposed procedure is an attractive and solvent-free option for quantitative monitoring of Se(IV) and As(V) in different materials. Both analytes were quantitatively and simultaneously separated/determined from samples at pH 2 with very good recovery (close to 100%), precision (4.5%), and detection limits (0.4 ng mL−1 Se and 0.25 ng mL−1 As). TiO2@cellulose membranes were applied to water analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly selective and ultrasensitive determination of mercury ions. • Very low detection limits using benchtop EDXRF and TXRF instruments. • Simple and robust analysis of waters, beverages, seafood, plants, etc. • Green approach based on reducing the reagent usage and sample preparation time. The paper presents novel analytical methods for sensitive mercury determination in various samples, i.e., waters, beverages, seafood, plants, and biological samples. The procedure is based on selective preconcentration/separation of Hg(II) ions using graphene oxide/thiosemicarbazide in dispersive micro-solid phase extraction (DMSPE) and detection by energy-dispersive (EDXRF) and total-reflection X-ray fluorescence spectrometry (TXRF). The DMSPE/EDXRF and DMSPE/TXRF procedures are characterized by very high enrichment factors and low detection limits (LODs). DMSPE/TXRF allows obtaining LODs of 2.1 pg mL−1 for liquids and 1.8 ng g−1 for solid samples. In the case of DMSPE/EDXRF, the LODs are higher, 60 pg mL−1 for liquid and 73 ng g−1 for solid samples, due to the worse sensitivity of EDXRF measurement. The method was validated using spiked samples (water, apple juice, beer, wine) and certified reference materials (seawater, groundwater, wastewater, herring, cormorant and cod tissues, pig kidney, lobster, tobacco, scallion, celery, and spinach). [ABSTRACT FROM AUTHOR]

In this study, we investigated different metal pairings of Au nanoparticles (NPs) as potential catalysts for glycerol dehydration for the first time. All of the systems preferred the formation of hydroxyacetone (HYNE). Although the bimetallics that were tested, i.e., Au NPs supported on Ni, Fe and Cu appeared to be more active than the Au/SiO2 system, only Cu supported Au NPs gave high conversion (ca. 63%) and selectivity (ca. 70%) to HYNE. [ABSTRACT FROM AUTHOR]

An ultrasound-assisted methodology for the determination of dissolved silicate in water has been developed by combining the miniaturized ion-associated based preconcentration method with energy dispersive X-ray fluorescence spectrometry (EDXRF). The method has been devised for the determination of silicate through molybdenum in the ion-associated complex between 12-molybdosilicate and crystal violet. Because silicate is determined indirectly via molybdenum fluorescent radiation the difficulties resulting from low fluorescence yield and low energy of silicon radiation were successfully overcome. A good ratio of silicon to molybdenum (1 to 41) and a sensitive Kα line of molybdenum make possible the determination of low concentration of silicon in the form of dissolved silicate. Under optimized conditions, good linearity, up to 5 μg of silicon in the form of silicate (r = 0.9990) and a detection limit of 9 ng mL−1 were achieved. The total RSD for the EDXRF determination of silicate, followed by precipitation of the ion-associated complex and its dissolution in a microdrop of isoamyl alcohol, was 6.5%. The enrichment factor was equal to 142. The developed method was used to determine the dissolved silica content in surface waters. The accuracy and repeatability of the proposed procedure were checked by the standard addition method and compared to the results obtained using the ICP-OES technique. The recovery (in the 93–97% range) was satisfactory and indicated the usefulness of the developed procedure. [ABSTRACT FROM AUTHOR]

Hexavalent chromium is much more toxic than trivalent chromium and is severe environmental pollution caused by human activity. The presence of Cr(VI) ions in waters comes from anthropogenic sources, mainly from industries, and poses an enormous danger. Because of the health effects of Cr(VI) ions on humans, even at very low concentrations, it is necessary to control its levels in the water. However, the determination and speciation of Cr(VI) in water samples remains a sophisticated subject, and according to the WHO recommendation, further studies on reliable and validated methods should be continued. In this study, graphene oxide (GO) was modified with tetraethylenepentamine (TEPA) for the highly effective adsorption and determination of Cr(VI) ions by energy-dispersive X-ray fluorescence (EDXRF) and total-reflection X-ray fluorescence spectrometry (TXRF). The experiment shows that Cr(VI) ions can be adsorbed from aqueous solutions at pH 3.5 with a maximum adsorption capacity of 102 mg g−1 using minimal adsorbent doses, 10–50 μg mL−1, much lower than those of the currently reported adsorbents. These adsorptive properties of GO-TEPA and selectivity toward Cr(VI) in the presence of Cr(III) indicate its potential use as a micro-adsorbent in the determination and speciation of chromium. Due to the high preconcentration factors of 865 and 100, for EDXRF and TXRF, respectively, and high recovery of 98.5–100%, the method based on dispersive micro-solid phase extraction allows obtaining extremely low detection limits of 53 and 3.5 pg mL−1 for EDXRF and TXRF. The exceptional adsorptive properties of GO-TEPA, including the possibility of application in micro-quantities, allow for the development of the ultra-trace method according to the fundamental principles of green analytical chemistry. It significantly expands the possibilities of using the EDXRF, as well as the TXRF technique in water analysis. [Display omitted] • Very low detection limit of 3.5 and 53 pg mL−1 Cr(VI) using TXRF and EDXRF instruments. • Simple and accurate speciation of chromium. • Superior nanoadsorbent for highly effective separation of hexavalent chromium. • Extremely small adsorbent dosage (0.5 mg). • High adsorption capacity (102 mg g−1) and selectivity of the adsorbent toward Cr(VI). [ABSTRACT FROM AUTHOR]

Abstract: Dispersive liquid–liquid microextraction (DLLME) using sodium diethyldithiocarbamate (DDTC) as a chelating agent was investigated for the simultaneous determination of iron, cobalt, nickel, copper, zinc, selenium and lead ions in water samples. The procedure was performed using 5mL of the sample, 100μL of a 0.5% solution of DDTC, 30μL of carbon tetrachloride (extraction phase) and 500μL of methanol (disperser solvent). The experiments showed that Fe, Co, Ni, Cu, Zn and Pb can be simultaneously extracted at a pH of 5 and that Se can be extracted at a pH of 2–3. The results were compared with those obtained using ammonium pyrrolidine dithiocarbamate as a chelating agent. For all analytes, a linear range was observed up to 0.4μgmL−1. If Fe and Zn are present in concentrations 10 times higher than those of the other analytes, then the linearity is observed up to 0.2μgmL−1. In the present study, the organic phase that contained preconcentrated elements was deposited onto a Millipore filter and measured using energy-dispersive X-ray fluorescence spectrometry. The obtained detection limits were 2.9, 1.5, 2.0, 2.3, 2.5, 2.0 and 3.9ngmL−1 for Fe, Co, Ni, Cu, Zn, Se and Pb, respectively. This combination of DLLME and the dried-spot technique is promising for multielement analyses using other spectroscopy techniques, such as laser ablation‐inductively coupled plasma‐mass spectrometry, laser-induced breakdown spectroscopy or total-reflection X-ray fluorescence spectrometry. [Copyright &y& Elsevier]

Controlling carbon and nitrogen chemistry is essential for human life and civilization. In particular, high-temperature combustion of carbon fuels in the air results in the formation of ecotoxic carbon and nitrogen oxides (NOx). Specifically, NOx needs to be removed from the flue gases of electric power stations. The selective catalyst reduction (SCR) systems support the deNOx (NOx removal) process; however, surface deposits deactivate the SCR system while operating. Moreover, the surface texture is damaged during the exploitation. We show here how this damage reveals itself in the pore landscape of the commercial SCR catalysts. In particular, for the first time, we showed how this could be assessed by a combination of thermoporometry (TPM) and gas physisorption. Accordingly, a correlation between the assessed quality of the pore landscape and the catalyst activity was determined and discussed. We designed a broad collection of new innovative regeneration procedures, which appear to be robust and selective methods for removing surface poisons. The optimal regeneration scheme fully restored the catalyst activity. [Display omitted] • New regeneration procedures for commercial SCR catalysts were designed and tested. • Selective method for removing catalyst poisons was developed. • Thermoporometry (TPM) is a new method for assessment of catalyst pore landscape. • Catalyst activity correlates with and TPM pore landscape. • A method for reconstruction of catalyst pore landscape was developed. [ABSTRACT FROM AUTHOR]

In this work, a fast and low-cost method for the highly selective determination of ultratrace Hg(II) ions by total-reflection X-ray fluorescence spectrometry (TXRF) is presented. The procedure is based on dispersive micro-solid phase extraction (DMSPE) using thiosemicarbazide-functionalized carbon nanotubes (CNT-TSC). The experiment shows that Hg(II) ions are affectively adsorbed on CNT-TSC at pH 2 within 10 min using an extremely low adsorbent dosage of 1 μg mL−1. Moreover, CNT-TSC is characterized by excellent selectivity toward Hg(II) ions, which can be quantitatively adsorbed from the solution of very high ionic strength (5 mol L−1) and in the presence of the coexisting ions at extremely high concentrations (100 000-fold excess). After the preconcentration/separation step, the suspension of CNT-TSC with adsorbed Hg(II) ions is pipetted onto a quartz reflector and dried. This article shows that the procedure allows overcoming the problems with the volatilization losses of mercury and eliminating the matrix effects in high salinity water. The quantitative DMSPE/TXRF analysis can be performed using the classical calibration curve and simplified approach using only an internal standard. The method is characterized by a very low detection limit of 2.6 pg mL−1 and uses minimal amounts of chemical reagents and a low-power TXRF instrument. The method was applied to analyze water samples, including seawater, and biological samples: lobster hepatopancreas, herring, cormorant, and cod tissues. The excellent selectivity and high adsorption capacity of CNT-TSC toward Hg(II) ions (188 mg g−1) also open the path for the effective removal of Hg(II) ions from aqueous solutions. [ABSTRACT FROM AUTHOR]

Alumina supported on graphene oxide (Al 2 O 3 /GO) nanocomposite as new nanosorbent in dispersive micro-solid phase extraction (DMSPE) for As(V) and Cr(III) preconcentration is described. The crucial issue of the study is synthesis of novel nanocomposite suitable for sorption of selected species of arsenic and chromium. Al 2 O 3 /GO demonstrates selectivity toward arsenates in the presence of arsenites at pH 5 and chromium(III) ions in the presence of chromate anions at pH 6. The Al 2 O 3 /GO nanocomposite was characterized by scanning electron microscopy (SEM) transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and the Raman spectroscopy. The maximum adsorption capacity calculated based on the Langmuir adsorption model were 43.9 mg g −1 and 53.9 mg g −1 for As(V) and Cr(III), respectively. The nanocomposite was used as solid sorbent in preconcentration of As(V) and Cr(III)_ions from water samples and their determination using energy dispersive X-ray fluorescence spectrometry (EDXRF). The As(V) and Cr(III) ions can be quantitatively preconcentrated from 25 to 100 mL aqueous samples within 5 min using DMSPE procedure and 1 mg of Al 2 O 3 /GO. The nanocomposite was also used for preparation of Al 2 O 3 /GO membrane. Then, As(V) and Cr(III)_ions can be retained under flow condition by passing analyzed solution through Al 2 O 3 /GO membrane. Under the optimized conditions, As(V) and Cr(III) ions can be determined with very good recovery (92–108%), precision (RSD 2.7–4.0%) and excellent limit of detection (0.02 ng mL −1 As and 0.11 ng mL −1 Cr). The accuracy of the method was studied by analyzing certified reference materials (NIST 1640a) and spiked real water samples. [ABSTRACT FROM AUTHOR]

A simple method for highly selective determination of trace and ultratrace arsenic ions, i.e. arsenite and arsenate, was developed. The method is based on new miniaturized membranes, 5 mm diameter and 4.4 mg weight, which are prepared by synthesis of amorphous silica coating on cellulose fibers followed by the modification with (3-mercaptopropyl)-trimethoxysilane. The batch adsorption experiments show that membranes have high selectivity toward arsenite in the presence of heavy metals and anions that usually exist in natural water. Arsenite can be quantitatively adsorbed at pH 1 from 50 mL sample within 60 min using the miniaturized membrane with maximum adsorption capacity of 60 mg g −1 . The excellent adsorptive properties of membranes open the path to simple and selective determination of trace and ultratrace arsenite in water. Moreover, the membranes can be applied in the arsenic speciation due to their selectivity toward arsenite in the presence of arsenate. After adsorption, the arsenite retained onto the membrane is directly measured by energy-dispersive X-ray fluorescence spectrometry, avoiding elution step usually required in other spectroscopy techniques. The method is characterized by excellent enrichment factor of 972, detection limit of 0.045 ng mL −1 and can be successfully applied in analysis of high salinity water, which is difficult to analyze by other spectroscopy techniques. The proposed method is a solvent-free approach based on the use of miniaturized membranes as sorbent followed by the direct measurement using a low-power X-ray spectrometer without either elution step or gas consumption during measurement. It can be considered as environmentally friendly and meets the standards of green analytical chemistry principles. [ABSTRACT FROM AUTHOR]

We described the preparation of a series of new catalysts, i.e., nano-silica supported Re, Ru, Ir, Rh NPs as well as various combinations of the above-mentioned metals as potential catalysts of glycerol acetalization with acetone or butanone for the first time. In fact, it was discovered that nano-SiO 2 supported Re in particular is a highly efficient selective catalyst of glycerol acetalization for five-membered cyclic acetals. While Re supported on nano-SiO 2 prefers five-membered cycles its replacement to Mo destroys this selectivity and both five- and six-membered products can be observed. Under optimal conditions, the TON that was observed significantly outperforms those that have been reported in the literature for other catalytic systems. [ABSTRACT FROM AUTHOR]

Microextraction techniques, both liquid-liquid and solid-phase microextraction, are becoming increasingly popular as a sample pre-treatment step mainly due to their simplicity and environmental-friendliness. Nevertheless, the small amount of the sample obtained after preconcentration step requires application of special measurement techniques and/or development of different strategies used for introduction of micro-samples into spectroscopic instruments and chromatographs. In this review the most recent approaches that have been applied for introduction of micro-amounts of samples into different measurement systems are presented. Advantages and disadvantages of developed sample introduction systems as well as new achievements in these approaches are discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper we report a new nanometallic, self-activating catalyst, namely, Ni-supported Pd nanoparticles (PdNPs/Ni) for low temperature ammonia cracking, which was prepared using a novel approach involving the transfer of nanoparticles from the intermediate carrier, i.e. nano-spherical SiO2, to the target carrier technical grade Ni (t-Ni) or high purity Ni (p-Ni) grains. The method that was developed allows a uniform nanoparticle size distribution (4,4±0.8 nm) to be obtained. Unexpectedly, the t-Ni-supported Pd NPs, which seemed to have a surface Ca impurity, appeared to be more active than the Ca-free (p-Ni) system. A comparison of the novel PdNPs/Ni catalyst with these reported in the literature clearly indicates the much better hydrogen productivity of the new system, which seems to be a highly efficient, flexible and durable catalyst for gas-phase heterogeneous ammonia cracking in which the TOF reaches a value of 2615 mmolH2/gPd min (10,570 molNH3/molPd(NP) h) at 600°C under a flow of 12 dm3/h (t-Ni). [ABSTRACT FROM AUTHOR]

A dispersive micro-solid phase extraction (DMSPE) with graphene as a solid adsorbent and ammonium pyrrolidinedithiocarbamate (APDC) as a chelating agent was proposed for speciation and detemination of inorganic selenium by the energy-dispersive X-ray fluorescence spectrometry (EDXRF). In developed DMSPE, graphene particles are dispersed throughout the analyzed solution, therefore reaction between Se(IV)–APDC complexes and graphene nanoparticles occurs immediately. The concentration of Se(VI) is calculated as the difference between the concentration of selenite after and before prereduction of selenate. A central composite face-centered design with 3 center points was performed in order to optimize conditions and to study the effect of four variables (pH of the sample, concentration of APDC, concentration of Triton-X-100, and sample volume). The best results were obtained when suspension consisting of 200 µg of graphene nanosheets, 1.2 mg of APDC and 0.06 mg of Triton-X-100 was rapidly injected to the 50 mL of the analyzed solution. Under optimized conditions Se ions can be determined with a very good recovery (97.7±5.0% and 99.2±6.6% for Se(IV) and Se(VI), respectively) and precision (RSD=5.1–6.6%). Proposed DMSPE/EDXRF procedure allowed to obtain low detection limits (0.032 ng mL −1 ) and high enrichment factor (1013±15). The proposed methodology was successfully applied for the determination of Se in mineral, tap, lake and sea water samples as well as in biological materials (Lobster Hepatopancreas and Pig Kidney). [ABSTRACT FROM AUTHOR]

We tested for the first time the efficiency of SiO 2 -, Cu-, and Ni-supported Au in deep glycerol oxidation in a diluted and viscous H 2 O 2 /H 2 O liquid phase. Acetic acid (AA), the C 2 oxidate, was preferentially formed in such a system. High conversion (100%) and AA yields (90%) were observed for the sol–gel SiO 2 -supported Au in diluted solutions. Although with the increase of glycerol concentration in the viscous liquid phase these values decreased to ca. 40% (conversion) and 20% (AA yield), the addition of acetonitrile improved the AA yield to ca. 40%, while the surfactants were found to be capable of a many-fold enhancement of the catalyst activity at the room temperature highly viscous liquid phase. High performances were also observed for the bimetallic Au/Cu and Au/Ni catalysts obtained by nano-Au transfer; however, these catalysts were destroyed during the reaction by the Cu or Ni leaching effect. [ABSTRACT FROM AUTHOR]

Energy consumption steadily increases and energy production is associated with many environmental risks, e.g., generating the largest share of greenhouse gas emissions. The primary gas pollution concern is CO2, CH4, and nitrogen oxides (NOx). Environmental catalysis plays a pivotal role in NOx mitigation (DeNOx). This study investigated, for the first time, a collection of ceramic foams as potential catalyst support for selective catalytic NOx reduction (SCR). Ceramic foams could be an attractive support option for NOx removal. However, we should functionalize the surface of raw foams for such applications. A library of ceramic SiC, Al2O3, and ZrO2 foams ornamented with nanorod ZnO and TiO2 as W and V oxide support was obtained for the first time. We characterized the surface layer coating structure using the XPS, XRF and SEM, and TEM microscopy to optimize the W to V molar ratio and examine NO2 mitigation as the SCR model, which was tested only very rarely. Comparing TiO2 and ZnO systems reveals that the SCR conversion on ZnO appeared superior vs. the conversion on TiO2, while the SiC-supported catalysts were less efficient than Al2O3 and ZrO2-supported catalysts. The energy bands in optical spectra correlate with the observed activity rank. [ABSTRACT FROM AUTHOR]

In this paper the combination of dispersive micro solid-phase extraction (DMSPE), using multiwalled carbon nanotubes (MWCNTs) as solid sorbents, with total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for preconcentration and determination of lead and cadmium ions in water samples. The proposed sample preparation is quite simple and economic. After the sorption processes of the metals on the MWCNTs, the aqueous sample is separated by centrifugation and the metal loaded MWCNTs are suspended using a small volume of an internal standard solution and analyzed directly by TXRF. Parameters affecting the extraction process (complexing agent, pH of the aqueous sample, amount of MWCNTs) and TXRF analysis (volume of the deposited suspension on the reflector, drying mode, and instrumental parameters) have been carefully evaluated to test the real capability of the developed methodology for the determination of Cd and Pb at trace levels. For both elements the linear range is observed up to 50 ng mL−1. Under optimized conditions detection limits are 1.0 ng mL−1 and 2.1 ng mL−1 for Cd(ii) and Pb(ii) ions, respectively. Both of the examined elements can be determined with quantitative recoveries (ca. 100%) and with an adequate precision (RSD = 6.0% and 10.5% for Cd(ii) and Pb(ii), respectively). Our results give insight into the possibilities of the combination of DMSPE and TXRF for trace metal determination in different types of environmental waters (sea, river and waste water). [ABSTRACT FROM AUTHOR]

A methodology based on dispersive micro solid-phase extraction (DMSPE) using multiwalled carbon nanotubes (MWCNTs) as solid sorbent prior to measurement with energy-dispersive X-ray fluorescence (EDXRF) spectrometry is proposed. The procedure consists of chelating of nickel, cobalt, copper, and lead ions with ammonium pyrrolidinedithiocarbamate (APDC) and posterior adsorption of metal chelates on MWCNTs (1 mg) dispersed in the aqueous samples (100 mL). DMSPE promotes immediate interaction between the metal chelates and MWCNTs and shortens time of sample preparation in comparison with classical solid-phase extraction. After microextraction process, MWCNTs are collected onto filter and directly measured by EDXRF. With this technique, the direct quantification of metal species held in solid materials is possible and, therefore, the elution step can be avoided. The effects of various experimental parameters such as pH of the solution, amounts of MWCNTs and APDC, sample volume, and time of stirring were investigated. With the best analytical conditions (1 mg of MWCNTs, 2 mg of APDC, 100 mL sample volume, pH = 7, and 5 min time of stirring), Co(II), Ni(II), Cu(II), and Pb(II) can be simultaneously determined with very good recoveries (101%, 98%, 96%, 99%, respectively) and detection limits (0.43, 0.11, 0.46, 0.15 ng mL−1, respectively). The method was applied in determination of trace metal ions in tap water and wastewater samples. [ABSTRACT FROM AUTHOR]

A dispersive solid-phase microextraction (DSPME) with multiwalled carbon nanotubes (MWCNTs) as solid sorbent and ammonium pyrrolidinedithiocarbamate (APDC) as chelating agent was developed for determination of selenium. In the proposed procedure, the Se(iv)–APDC complex is adsorbed on MWCNTs dispersed in aqueous samples. After the adsorption process, the aqueous samples are filtered and MWCNTs with selenium chelate are collected onto a filter. The loaded filters are directly measured using X-ray fluorescence (XRF) spectrometry. In order to obtain high recovery of the Se ions on MWCNTs, the proposed procedure was optimized for various analytical parameters such as pH, amounts of MWCNTs and APDC, sample volume and time of the sorption process. Under optimized conditions Se ions can be determined with very good recovery (97 ± 3%), precision (RSD = 3.2%) and detection limits (from 0.06 to 0.2 ng mL−1, depending on counting time and XRF equipment). The effect of common coexisting ions was also investigated. Se(iv) can be determined in the presence of heavy metal ions and alkali metals. The chemical interferences observed for high concentrations of Cu(ii), Fe(iii), and Zn(ii) can be completely eliminated using precipitation with NaOH. The proposed method was applied for the determination of Se in mineral water and biological samples (Lobster Hepatopancreas). The proposed method can also be applied for selenium speciation. The concentration of selenate can be obtained as the difference between the concentration of selenite after and before prereduction of selenate to selenite. [ABSTRACT FROM AUTHOR]

Abstract: The preconcentration of trace elements on multiwalled carbon nanotubes (MWCNTs) followed by a wavelength-dispersive X-ray fluorescence analysis (WDXRF) has been investigated. The proposed preconcentration procedure is based on the sorption of trace elements on MWCNTs dispersed in analyzed solution. After sorption, the MWCNTs with the metal ions were collected onto the filter, and then the preconcentrated elements were determined directly by WDXRF. The preconcentration method was optimized, and in consequence, in order to obtain satisfactory recoveries using 100mL of samples, the sorption process was performed with 1mg of MWCNTs within 5min. Some conditions of the preconcentration process such as the pH of analyte solution, amounts of MWCNTs, the volume of the sample, the contact time between analytes and MWCNTs (stirring time), and the effects of foreign metals are discussed in detail in the paper. Adsorption onto raw and oxidized MWCNTs was also studied. The proposed procedure allows obtaining the detection limits of 0.6, 0.6, 1.0, 0.7, 0.6, 0.5, 0.9 and 1.9ngmL−1 for Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II), respectively. The recoveries of determined elements were about 100%. Because the analytes are not eluted from the sorbent before WDXRF analysis, the risk of contamination and loss of analytes is reduced to minimum. Moreover, because the samples are analyzed as a thin layer, the matrix effects can be neglected. The proposed preconcentration method using MWCNTs coupled with WDXRF spectrometry was successfully applied to determine trace elements in natural water samples. [Copyright &y& Elsevier]

Abstract: A method of separation and preconcentration of cadmium, cobalt, copper, nickel, lead and zinc at trace level from plant matrix using 2,2′-bipyridyl and rose Bengal is proposed. The above heavy metals were determined after preconcentration by inductively coupled plasma optical emission spectrometry (ICP-OES). The results were compared with those obtained using flame atomic absorption spectrometry (F-AAS). The influence of several parameters such as pH, molar ratio of 2,2′-bipyridyl to rose Bengal, duration of co-precipitation was examined. Moreover, effects of inorganic matrix on recovery of the determined elements were studied. The detection limits (DL) for ICP-OES were 0.36, 0.66, 3.3, 1.4, 3.5 and 3.2μgL−1 for Cd, Co, Cu, Ni, Pb and Zn, respectively, whereas for F-AAS DL were 0.77, 5.8, 1.1, 3.2, 3.0 and 0.71μgL−1. The recovery of the method for the determined elements was better than 94% with relative standard deviation between 0.68% and 1.7%. The preconcentration factor was 40. The proposed method was applied for determination of Cd, Co, Cu, Ni, Pb, and Zn in plant materials. Accuracy of the proposed method was verified using certified reference material (NCS ZC85006 Tomato). [Copyright &y& Elsevier]

In this paper, the determination of ultratrace heavy metal ions was developed by combining a preconcentration method using graphene oxide/carbon nanotubes membranes (GO/CNTs) and total-reflection X-ray fluorescence spectrometry (TXRF). Due to the excellent adsorptive properties of the GO, the foregoing membranes are suitable for effective simultaneous sorption of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) from aqueous solutions. In this method, the aqueous solution is passed through the GO/CNTs membrane. The analytes are eluted from the GO and afterward transferred onto a siliconized quartz reflector for further TXRF analysis using W and Mo target X-ray tubes. The maximum recoveries for all the elements were obtained at pH 5; thus it was chosen for all further experiments. The face centered central composite design was performed to study the influence of the flow-rate and volume of the solution on the recovery of the determined metal ions. Recovery values higher than 96% for all studied metals allow performing efficient preconcentration with an enrichment factor of 133, achieving the limits of detection (LODs) in the range of 0.08–0.21 ng mL−1 for W target X-ray tube with a measurement time of 2000 s, and much lower LODs for Mo target X-ray tube: 0.001–0.002 ng mL−1 with the exception for Cd (0.11 ng mL−1) with a very short measurement time of 600 s. Certified reference materials of spring water and seawater were examined to verify the reliability of the method. The evaluated procedure does not require toxic reagents or organic solvents, thus minimizes the portion of the sample for TXRF measurement, and stands in good accordance with green analytical chemistry basic principles. Unlabelled Image • New procedure for TXRF ultratrace analysis based on membrane preconcentration. • Extremely low detection limits at ppt level suitable for environmental analysis. • Analysis of the aqueous samples with complex matrix and/or high salinity. • Simple, fast, inexpensive method compliant with the GAC basic principles. [ABSTRACT FROM AUTHOR]

A new method based on the application of amino-silanized cellulose membranes for selective adsorption of hexavalent chromium ions was developed. The membranes were prepared by coating the cellulose fibers with amorphous silica modified with three amino-silanes containing different numbers of amino groups. The structure and morphology of the membranes denoted as cellulose-1N, cellulose-2N and cellulose-3N were characterized by microscopic and spectroscopic techniques. The batch adsorption experiments show that Cr(VI) can be selectively separated from Cr(III) at pH 4. The maximum adsorption capacities toward Cr(VI) differ from each other significantly and are proportional to the number of protonated amino groups present on the membrane surface: 10.2, 18.1, 34.7 mg g−1 for cellulose-1N < cellulose-2N < cellulose-3N, respectively. The membranes can be applied in the removal of Cr(VI) from aqueous solutions as well as in determination or speciation of chromium due to their selectivity toward Cr(VI) in the presence of Cr(III). In the developed method, Cr(VI) ions were adsorbed at pH 4 from 20 mL sample within 300 min. The presented approach is advantageous since the preconcentration procedures combined with other spectroscopic techniques the elution step is not required and Cr(VI) retained onto the membrane can be directly measured by EDXRF. Due to the very high enrichment factor of 650 the method is characterized by good detection limit of 0.16 ng mL−1. In addition, it is based on the use of miniaturized membranes and their direct measurement using a low-power X-ray spectrometer without gas consumption during the measurements. Therefore, the method can be treated as environmentally favorable and lies in the green analytical chemistry principles. Unlabelled Image • A new preconcentration procedure for Cr(VI) determination • Novel amino-silanized cellulose membranes for selective adsorption of Cr(VI) • Low detection limit suitable for environmental analysis • Simple, fast, inexpensive and environmental friendly method [ABSTRACT FROM AUTHOR]

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO2, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H2O2 as a clean oxidant. We tested different levels of Au loading (0.1–1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au–Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation—the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO2 at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO2 might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones. [ABSTRACT FROM AUTHOR]

A nanocomposite prepared from graphene nanosheets and cerium nanoparticles (G/CeO2) was applied to the extraction of Se(IV), As(V), As(III), Cu(II) and Pb(II). The structure of G/CeO2 was investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The optimal pH values for extraction are 4.0 for As(V), 3.0 for Se(IV), and 6.0 for both Cu(II) and Pb(II). The maximum adsorption capacity of G/CeO2 (expressed as mg·g−1) were calculated by the Langmuir model and are found to be 8.4 for As(V), 14.1 for Se(IV), 50.0 for Cu(II) and 75.6 for Pb(II). The sorbent was applied to dispersive solid phase microextraction prior to direct quantitation by energy-dispersive X-ray fluorescence spectrometry without the need for prior elution. The limits of detection (in ng·mL−1 units) are 0.10 for As(V), 0.11 for Se(IV), 0.19 for Cu(II) and 0.21 for Pb(II). The precisions (RSDs) are <4.5%. The accuracy of the method (1 - 4%) was verified by analysis of the certified reference material (CRM 1640a - natural water). The method was successfully applied in ultratrace element determination and to the speciation of selenium in environmental waters.The method gives possibility of simultaneous preconcentration and determination in environmental waters of both anionic (As(V) and Se(IV)) and cationic (Cu(II) and Pb(II)) forms of selected metals using graphene nanosheets and cerium nanoparticles. Se(IV) can be selective determined in the presence of Se(VI). [ABSTRACT FROM AUTHOR]