Study on column SPE with synthesized graphene oxide and FAAS for determination of trace amount of Co(II) and Ni(II) ions in real samples.

A selective method for the preconcentration and separation of trace amounts of Co(II) and Ni(II) by column solid phase extraction has been developed. The method is based on the adsorption of metal ions as N-(5-methyl-2-hydroxyacetophenone)-N'-(2-hydroxyacetophenone) ethylene diamine (MHE) complex on synthesized graphene oxide. Computational modeling based on PM6 semi-empirical potential energy surface was utilized to investigate the interaction of metallic complexes with graphene oxide sheet. The adsorption was achieved quantitatively on graphene oxide at pH6.0 and then the retained analyte contents on the column were quantitatively eluted with 3.0 mol L(-1) HNO3. Experimental conditions for effective separation of trace levels of the analyte ions such as pH, flow rate, concentration of eluent, sample volume and interference ions were investigated. A preconcentration factor of 250 was achieved by passing 1250 mL of sample through the solid phase, while the limit of detection of Co(II) and Ni(II) ions were found to be 0.25 and 0.18 ng mL(-1), respectively. The method was applied to the determination of analyte ions in water, black tea and tomato samples.

Determination of organophosphorus pesticides by gas chromatography with mass spectrometry using a large-volume injection technique after magnetic extraction.

A fast and efficient method was developed for the extraction and determination of organophosphorus pesticides in water samples. Organophosphorus pesticides were extracted by solid-phase extraction using magnetic multi-walled carbon nanotubes and determined by gas chromatography with ion-trap mass spectrometry. Parameters affecting the extraction were investigated. Under optimum conditions of the method, 10 mg magnetic multi-walled carbon nanotubes were added into 10 mL sample. After 2 min, adsorbent particles settled at the bottom of test tube with a magnet. After removing aqueous supernatant, the analytes were desorbed with acetonitrile. Then, 70 µL of acetonitrile phase was injected into the gas chromatography and mass spectrometry system that had an ion-trap analyzer. To achieve high sensitivity, the large-volume-injection technique was used with a programmed temperature vaporization inlet, and the ion-trap mass spectrometer was operated in single ion storage mode. Under the best conditions, the enrichment factors and extraction recoveries were in the range of 113-124 and 74-103%, respectively. The limits of detection were between 3 and 15 ng/L, and the relative standard deviations were < 10%. This method was successfully used for the determination of organophosphorus pesticides in dam water, lagoon water, and river water samples with good reproducibility and recovery.

Column solid phase extraction and flame atomic absorption spectrometric determination of manganese(II) and iron(III) ions in water, food and biological samples using 3-(1-methyl-1H-pyrrol-2-yl)-1H-pyrazole-5-carboxylic acid on synthesized graphene oxide.

A modified, selective, highly sensitive and accurate procedure for the determination of trace amounts of manganese and iron ions is established in the presented work. 3-(1-Methyl-1H-pyrrol-2-yl)-1H-pyrazole-5-carboxylic acid (MPPC) and graphene oxide (GO) were used in a glass column as chelating reagent and as adsorbent respectively prior to their determination by flame atomic absorption spectrometry. The adsorption mechanism of titled metals complexes on GO was investigated by using computational chemistry approach based on PM6 semi-empirical potential energy surface (PES). The effect of some parameters including pH, flow rate and volume of sample and type, volume and concentration of eluent, as well as the adsorption capacity of matrix ions on the recovery of Mn(II) and Fe(III) was investigated. The limit of detection was 145 and 162 ng L(-1) for Mn(II) and Fe(III), respectively. Calibration was linear over the range of 0.31-355 µg L(-1) for Mn(II) and 0.34-380 µg L(-1) for Fe(III) ions. The method was successfully applied for the determination of understudied ions in water, food and biological samples.

Development of a robust ionic liquid-based dispersive liquid-liquid microextraction against high concentration of salt for preconcentration of trace metals in saline aqueous samples: application to the determination of Pb and Cd.

A new ionic liquid-based dispersive liquid-liquid microextraction method was developed for preconcentration and determination of compounds in aqueous samples containing very high salt concentrations. This method can solve the problems associated with the limited application of the conventional IL-based DLLME in these samples. This is believed to arise from dissolving of the ionic liquids in aqueous samples with high salt content. In this method, the robustness of microextraction system against high salt concentration (up to 40%, w/v) is increased by introducing a common ion of the ionic liquid into the sample solution. The proposed method was applied satisfactorily to the preconcentration of lead and cadmium in saline samples. After preconcentration, the settled IL-phase was dissolved in 100 microL ethanol and aspirated into the flame atomic absorption spectrometer (FAAS) using a home-made microsample introduction system. Several variables affecting the microextraction efficiency were investigated and optimized. Under the optimized conditions and preconcentration of only 10 mL of sample, the enhancement factors of 273 and 311 and the detection limits of 0.6 microg L(-1) and 0.03 microg L(-1) were obtained for lead and cadmium, respectively. Validation of the method was performed by both an analysis of a certified reference material (CRM) and comparison of results with those obtained by ISO standard method.

Simultaneous extraction and preconcentration of uranium and thorium in aqueous samples by new modified mesoporous silica prior to inductively coupled plasma optical emission spectrometry determination.

A new synthesized modified mesoporous silica (MCM-41) using 5-nitro-2-furaldehyde (fural) was applied as an effective sorbent for the solid phase extraction of uranium(VI) and thorium(IV) ions from aqueous solution for the measurement by inductively coupled plasma optical emission spectrometry (ICP OES). The influences of some analytical parameters on the quantitative recoveries of the analyte ions were investigated in batch method. Under optimal conditions, the analyte ions were sorbed by the sorbent at pH 5.5 and then eluted with 1.0 mL of 1.0 mol L(-1) HNO(3). The preconcentration factor was 100 for a 100mL sample volume. The limits of detection (LOD) obtained for uranium(VI) and thorium(IV) were 0.3 microg L(-1). The maximum sorption capacity of the modified MCM-41 was found to be 47 and 49 mg g(-1) for uranium(VI) and thorium(IV), respectively. The sorbent exhibited good stability, reusability, high adsorption capacity and fast rate of equilibrium for sorption/desorption of uranium and thorium ions. The applicability of the synthesized sorbent was examined using CRM and real water samples.