Monika Shah

Identification and characterization of selenium species in enriched green onion (Allium fistulosum) by HPLC-ICP-MS and ESI-ITMS

In this study speciation of selenium in selenium-enriched green onions (Allium fistulosum) was done with reversed-phase ion-pairing high performance liquid chromatography (RP-IP-HPLC) and size-exclusion chromatography (SEC) coupled on-line to ICP-MS for selenium specific detection. The plant extract obtained using sodium hydroxide (0.1 mol l−1) analyzed by SEC (CAPS 10 mmol l−1, pH 10.0) with ICP-MS detection showed the incorporation of selenium in both high (∼12 kDa) and low molecular weight (0.36–2 kDa) fractions. Presumably protein bound selenoamino acids were released using enzymes (Proteinase K and Protease XIV) and selenoamino acids found in cytosol in their free form were extracted using 0.1 M HCl. The extracts were analyzed for speciation studies by RP-IP-HPLC [0.1% (v/v) heptafluorobutyric acid, 5% (v/v) methanol, pH 2.5]. Matching the chromatographic retention times with commercially available standards provided evidence for the presence of Se-cystine, methylselenocysteine, Se-methionine, and inorganic selenium. Electrospray ionization ion trap mass spectrometry (ESI-ITMS) confirmed the presence of γ-glutamyl-Se-methylselenocysteine in green onions as has been reported in other onion types.

Iodine speciation studies in commercially available seaweed by coupling different chromatographic techniques with UV and ICP-MS detection

Speciation of iodine in commercially available commonly consumed seaweed samples was performed using a multidimensional chromatographic approach coupled with inductively coupled plasma mass spectrometry (ICP-MS) for element specific detection. Analysis of alkaline extract (0.1 mol l−1 NaOH) by size-exclusion chromatography coupled to ICP-MS (0.03 mol l−1 Tris-HCl, pH 8.0) indicated the association of iodine with both high as well as low molecular weight fractions in Wakame, while in case of Kombu, only low molecular weight iodine species were found. Likely association of iodine with protein as well as polyphenolic species was indicated in the case of Wakame. Anion-exchange chromatography coupled to ICP-MS (0.005 mol l−1 NaOH) confirmed that the most predominant inorganic iodine species present in both type of seaweeds is iodide. Protein bound iodinated species were hydrolyzed by enzymatic digestion using Proteinase K. Analysis of the hydrolysate using reversed-phase HPLC-ICP-MS (0.01 mol l−1 Tris-HCl pH 7.3 ∶ 0.01 mol l−1 Tris-HCl pH 7.3 and 50% MeOH) revealed the presence of monoiodotyrosine and di-iodotyrosine in Wakame, which was later identified by matching the chromatographic retention time with the retention time of commercially available standards.

Localization and speciation of selenium and mercury in Brassica juncea—implications for Se–Hg antagonism

The occurrence and form of selenium and mercury were investigated in Indian Mustard, Brassica juncea, a selenium accumulating plant, which had been co-exposed to varying concentration levels of these two elements. Plants were grown and exposed in hydroponic solutions. Following exposure, root exudates were collected in fresh solutions and the head-space around the aerial portions of the plants was sampled. These samples and the harvested plant tissues were then processed for determination of Se and Hg-containing compounds. For the plant tissues, roots, stems and leaves were separated and extracted using a sequential procedure that removed water-soluble species, water-soluble proteins, and dodecyl sulfate-soluble proteins. Size exclusion chromatography allowed further fractionation. High molecular-weight selenium/mercury-containing compounds were found primarily in the plant root extract. Evidence suggests that a Se and Hg complex of high molecular weight may be protein associated. For the analysis of exudate solutions, ion-pairing reversed phase chromatography coupled to ICP-MS was used. Multiple selenium and mercury species were detected, with one mercury-containing compound observed eluting near selenocystine. Plant head-space was sampled with solid phase microextraction and analyzed with GC-ICP-MS and GC-TOFMS. Apart from the primary selenium volatiles and elemental mercury, no volatile species simultaneously containing Se and Hg could be detected.

Determination of organophosphorus fire retardants and plasticizers in wastewater samples using MAE-SPME with GC-ICPMS and GC-TOFMS detection

Determination of organophosphorus fire retardants and plasticizers at trace levels in wastewater is described. In this work, microwave assisted extraction (MAE) and solid-phase microextraction (SPME) are used for sample preparation to extract and preconcentrate the analytes, followed by analysis by gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS) for phosphorus-specific detection. Gas chromatography coupled to time of flight mass spectrometry (GC-TOF-MS) was used to confirm the organphosphorus fire retardants in wastewater. The detection limits of organophosphorus fire retardants (OPFRs) were 29 ng L(-1) for tri-n-butyl phosphate (TnBP), 45 ng for L(-1) for tris(2-butoxyethyl)phosphate (TBEP), and 50 ng L(-1) for tris(2-ethylhexyl)phosphate (TEHP). Optimized extraction conditions were performed at 65 degrees C for 30 min and with 10% NaCl. Application of MAE during the sample preparation prior to the SPME allowed the detection of tris(2-ethylhexyl) phosphate, which has been difficult to determine in previous work. Application of the method to wastewater samples resulted in detecting 3.1 microg L(-1) P from TnBP, 5.0 microg L(-1) P from TBEP, and 4.0 microg L(-1) P from TEHP. The presence of these compounds were also confirmed by SPME-GC-TOF-MS.