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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]

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]

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]