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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]

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]

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]

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]

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]