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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]

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]

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]

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]

[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]

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] • 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]

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]

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]

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]