Dispersive liquid liquid microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic selenium in environmental water samples.

A novel method based on dispersive liquid liquid microextraction (DLLME) followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) determination was proposed for the speciation of inorganic selenium by using 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (Bismuthiol II) as both chelating reagent and chemical modifier. In this method, 500 µL ethanol (as disperser solvent) containing 70 µL chloroform (as extraction solvent) and 0.2 g L(-1) Bismuthiol II (as chelating reagent) was rapidly injected into a sample solution to form cloudy solution. The complex of Se(IV) with Bismuthiol II was rapidly extracted into the extraction solvent at pH 2.0, while Se(VI) was remained in the aqueous solutions. Thus, the separation of Se(IV) and Se(VI) could be realized. After centrifugation, the complex of Se(IV) and Bismuthiol II concentrated in the extraction solvent was introduced into the ETV-ICP-MS for determination of Se(IV). Se(VI) was reduced to Se(IV) prior to determination of total selenium, and its assay was based on subtracting Se(IV) from total selenium. The main factors influencing the DLLME and the vaporization behavior of selenium in ETV were investigated systematically. Under the optimal conditions, the limit of detection (LOD) for Se(IV) was 0.047 ng mL(-1). The relative standard deviation (RSD) was 7.2% (CSe(IV)=1.0 ng mL(-1), n=8) with an enhancement factor of 64.8-fold from only 5 mL of water sample. The proposed method was successfully applied to the speciation of inorganic selenium in different environmental water samples with recoveries ranging from 94.8 to 108% for the spiking samples. In order to validate the proposed method, a Certified Reference Material of Environment Water (GBW(E)080395) was analyzed, and the determined value obtained was in good agreement with the certified value.

Chiral speciation and determination of selenomethionine enantiomers in selenized yeast by ligand-exchange micellar electrokinetic capillary chromatography after solid phase extraction.

A new phenylalanine derivative (L-N-(2-hydroxy-propyl)-phenylalanine, L-HP-Phe) was synthesized and its chelate with Cu(II) (Cu(II)-(L-HP-Phe)(2)) was used as the chiral selector for the ligand-exchange (LE) chiral separation of D,L-selenomethionine (SeMet) in selenized yeast samples by micelle electrokinetic capillary chromatography (MEKC). In order to improve the sensitivity of MEKC-UV, two-step preconcentration strategy was employed, off-line solid phase extraction (SPE) and on-line large volume sample stacking (LVSS). D,L-SeMet was first retained on the Cu(II) loaded mesoporous TiO(2), then eluted by 0.1 mL of 5 mol L(-1) ammonia, and finally introduced for MEKC-UV analysis by LVSS injection after evaporation of NH(3). With the enrichment factors of 1400 and 1378, the LODs of 0.44 and 0.60 ng mL(-1) for L-SeMet and D-SeMet was obtained, respectively. The developed method was applied to the analysis of D,L-SeMet in a certified reference material of SELM-1 and a commercial nutrition yeast, and the results showed that most of SeMet in the SELM-1 selenized yeast was l isomer and the recovery for L and D isomers in the spiked commercial nutrition yeast was 96.3% and 103%, respectively. This method is featured with low running cost, high sensitivity and selectivity, and exhibits application potential in chiral analysis of seleno amino acids in real world samples.

Speciation of selenomethionine and selenocystine using online micro-column containing Cu(II) loaded nanometer-sized Al2O3 coupled with ICP-MS detection.

A flow injection online speciation procedure by using micro-column packed with Cu(II) loaded nanometer-sized Al(2)O(3) coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the separation and determination of selenomethionine (SeMet) and selenocystine (SeCys(2)) has been developed. The main factors affecting the separation and preconcentration of SeMet and SeCys(2) including pH value, sample flow rate, eluent concentration, eluent volume and flow rate, and interfering ions have been investigated. It was found that SeCys(2) could be selectively retained by micro-column packed with Cu(II) loaded nanometer-sized Al(2)O(3) at pH 4.0, and the retained SeCys(2) could be eluted by 1.0 mol L(-1) HNO(3), while SeMet was not retained and passed through the micro-column directly at this pH. Both SeMet and SeCys(2) could be quantitatively adsorbed by the micro-column at pH 9.0, and the retained SeMet and SeCys(2) could be easily eluted with 1.0 mol L(-1) HNO(3). The content of SeMet was obtained by subtracting the SeCys(2) from the total content of seleno amino acids. With the enrichment factor of 7.8 and 7.7, the limits of detection (LODs) for SeMet and SeCys(2) were found to be 24 pg Se mL(-1) and 21 pg Se mL(-1), respectively. The relative standard deviations (RSDs) for SeCys(2) and SeMet with seven replicate determinations of 1.0 ng mL(-1) SeMet and SeCys(2), were 2.1% and 1.6%, respectively, the sampling frequency of 8h(-1) was obtained. The proposed method was applied to the speciation of SeMet and SeCys(2) in selenized yeast, human urine and serum with satisfactory results.

Separation and determination of seleno amino acids using gas chromatography hyphenated with inductively coupled plasma mass spectrometry after hollow fiber liquid phase microextraction.

A new derivatization-extraction method for preconcentration of seleno amino acids using hollow fiber liquid phase microextraction (HF-LPME) was developed for the separation and determination of seleno amino acids in biological samples by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS). Derivatization was performed with ethyl chloroformate (ECF) to improve the volatility of seleno amino acids. Parameters influencing microextraction, including extraction solvent, pH of sample solution, extraction time, stirring speed, and inorganic salt concentration have been investigated. Under the optimal conditions, the limits of detection (LODs) obtained for Se-methyl-selenocysteine (SeMeCys), selenomethionine (SeMet), and selenoethionine (SeEth) were 23, 15, and 11 ng Se l(-1), respectively. The relative standard deviations (RSDs) were 14.6%, 16.4%, and 19.4% for SeMeCys, SeMet, and SeEth (c = 1.0 ng ml(-1), n = 7), respectively, and the RSDs for SeMeCys, SeMet could be improved obviously if SeEth was utilized as the internal standard. The proposed method was applied for the determination of seleno amino acids in extracts of garlic, cabbage, and mushroom samples, and the recoveries for the spiked samples were in the range of 96.8-108% and 93.4-115% with and without the use of SeEth as internal standard. The developed method was also applied to the analysis of SeMet in a certified reference material of SELM-1 yeast and the determined value is in good agreement with the certified value.

High-sensitivity capillary electrophoresis for speciation of organomercury in biological samples using hollow fiber-based liquid-liquid-liquid microextraction combined with on-line preconcentration by large-volume sample stacking.

A hollow fiber-based liquid-liquid-liquid microextraction (HF-LLLME) combined with on-line large-volume sample stacking (LVSS) has been developed for the speciation of organomercury in biological samples by CE with UV detection. Separation was achieved in less than 11 min with an electrolyte consisting of 35 mM sodium tetraborate at pH 9.1. In LVSS, a reverse electrode polarity-stacking mode (REPSM) was applied as on-line preconcentration strategy. In HF-LLLME, the analytes were extracted from 12 mL volume of sample solution (pH adjusted to 3.0) into bromobenzene impregnated in the pores of the hollow fiber, and into an acceptor solution of L-cysteine (15 microL, 0.02% w/v) inside the hollow fiber. Under the optimized conditions, concentration factors of 2610-4580 were achieved and LODs in the range of 0.03-0.14 microg/L were feasible. The linearity was found to be over two orders of magnitude with correlation coefficient of 0.9991-0.9996. The developed method has been validated using a certified reference material (DORM-2, dogfish muscle), and the determined values coincided very well with the certified values. The method was also applied to the speciation of organomercury in three kinds of fish samples and human hair samples.

Organic and inorganic selenium speciation in environmental and biological samples by nanometer-sized materials packed dual-column separation/preconcentration on-line coupled with ICP-MS.

A novel, fast, and cheap nonchromatographic method for direct speciation of dissolved inorganic and organic selenium species in environmental and biological samples was developed by flow injection (FI) dual-column preconcentration/separation on-line coupled with ICP-MS determination. In the developed technique, the first column packed with nanometer-sized Al(2)O(3) could selectively adsorb the inorganic selenium [Se(IV), Se(VI)], and the retained inorganic selenium could be eluted by 0.2 mol l(-1) NaOH, while the organic Se [selenocystine (SeCys(2)) and selenomethionine (Se-Met)] was not retained. On the other hand, the second column packed with mesoporous TiO(2) chemically modified by dimercaptosuccinic acid (DMSA) could selectively adsorb Se(IV) and SeCys(2) and barely adsorb Se(VI) and Se-Met. When the sample solution was passed through the column 1, separation of inorganic selenium and organic selenium could be achieved first. Then, the effluent from column 1 was successively introduced into the column 2 and the speciation of organic selenium could be attained due to the different adsorption behaviors of Se-Met and SeCys(2) on DMSA modified TiO(2). After that, the eluent from column 1 contained Se(IV), and Se(VI) was adjusted to desired pH and injected into column 2, and the speciation of Se(IV) and Se(VI) could also be realized thanks to their different retention on column 2. The parameters affecting the separation were investigated systematically and the optimal separation conditions were established. The detection limits obtained for Se(IV), Se(VI), Se-Met and SeCys(2) were 45-210 ng l(-1) with precisions of 3.6-9.7%. The proposed method has been successfully applied for the speciation of dissolved inorganic and organic selenium in environmental and biological samples. In order to validate the methodology, the developed method was also applied to the speciation of selenium in certified reference material of SELM-1 yeast, and the determined values were in good agreement with the certified values.

Analysis of PBDEs in soil, dust, spiked lake water, and human serum samples by hollow fiber-liquid phase microextraction combined with GC-ICP-MS.

A novel method for the analysis of four polybrominated diphenyl ethers (PBDEs) in environmental and human serum samples based on hollow fiber-liquid phase microextraction (HF-LPME) followed by gas chromatography-inductively coupled plasma mass spectrometric (GC-ICP-MS) detection has been developed. The organic solvent in the porous hollow fiber was first dipped into the sample for extraction at a given time, and the retracted organic phase was introduced into the GC-ICP-MS for analysis. The addition of methanol has a strong effect on the HF-LPME extraction efficiency. Other significant parameters affecting the extraction efficiency of HF-LPME were also studied. HF-LPME was effective to isolate the analytes from the complex matrix. Under the optimized conditions, the detection limits of the proposed method varied from 15.2 to 40.5 ng/L. In general, the relative standard deviations (RSDs) were less than 10%. Good linearity was obtained with the correlation coefficients all better than 0.999. The proposed method is simple, quick, few microliters of organic solvent required, and is especially suitable for the analysis of the real sample with small amount available. The overall process of HF-LPME with GC-ICP-MS was applied successfully for the determination of polybrominated diphenyl ethers (PBDEs) in environmental and spiked human serum samples, and the results were satisfactory.

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry determination of gold, palladium, and platinum using chelating resin YPA(4) as both extractant and chemical modifier.

A new method for determination of trace gold (Au), palladium (Pd), and platinum (Pt) in environmental and geological samples by electrothermal vaporization (ETV)-inductively coupled plasma atomic emission spectrometry (ICP-AES) with the use of chelating resin YPA(4) as both solid phase extractant and chemical modifier has been developed. The resin loaded with analytes was prepared to slurry and directly introduced into the graphite furnace without any pretreatment. The factors affecting the vaporization behaviors of Au, Pd, and Pt were investigated in detail. It was found that, in the presence of YPA(4), Au and Pd could be quantitatively vaporized at lower vaporization temperature of 1900 degrees C. Compared with the conventional electrothermal vaporization, the vaporization temperature was decreased by 700 degrees C, and the detection limits for Au and Pd was decreased by a three-fold. However, a little effect of YPA(4) on the ETV-ICP-AES determination of Pt was found. Under the optimized conditions, the detection limits (3sigma) of Au, Pd, and Pt for this method are 75, 60, and 217pg, respectively; and their relative standard deviations (R.S.D.) are 4.4, 5.6, and 3.7%, respectively (n=9, C=0.2mugml(-1)). The proposed method has been applied to the determination of trace Pd and Pt in sewage sludge, and the results well agreed with the recommended values. In order to further verify the accuracy of the developed method, a GBW07293 certified geological reference material and an auto catalyst NIST SRM 2557 reference material were analyzed, and the determined values coincided with the certified values very well.