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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]

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]

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]

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]

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]

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]

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]

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]