Ryszard Łobiński

Sample preparation and HPLC separation approaches to speciation analysis of selenium in yeast by ICP-MS

Eight solid-liquid extraction procedures were evaluated for the recovery of selenium species from yeast. Speciation of Se in the extracts was characterized by different types of HPLC, including size-exclusion, anion-exchange and reversed-phase chromatography with ICP-MS detection. The results obtained depended critically on the sample preparation procedure used. Leaching with water and with methanol led only to 10-20% recoveries of Se, split into eight compounds, among which Se(IV) and selenomethionine could be identified. Leaching with pectinolytic enzymes released an additional 20% of selenomethionine. Leaching with sodium dodecyl sulfate solution allowed the solubilization of a selenoprotein that accounted for ca. 30% of the total Se present. Leaching with proteolytic enzymes led to recoveries of Se above 85%, the majority as selenomethionine. Hydrolysis of the yeast with tetramethylammonium hydroxide solubilized the sample completely but the Se species present were entirely degraded to selenomethionine and inorganic selenium. A sequential leaching procedure is proposed for the evaluation of selenium speciation in yeast without the need for a coupled technique.

Speciation analysis of selenium in garlic by two-dimensional high-performance liquid chromatography with parallel inductively coupled plasma mass spectrometric and electrospray tandem mass spectrometric detection.

Speciation of selenium in garlic harvested in naturally seleniferous soil was investigated. The sample was leached with water and the aqueous extract was fractionated by preparative size-exclusion chromatography. Selenium was found in only one (low-molecular mass) fraction. The chromatographic purity of the fraction was verified by reversed-phase chromatography with inductively coupled mass spectrometric detection. Again, one major signal accounting for more than 95% of the total selenium was observed. The heartcut fraction containing this compound produced an intense peak in an electrospray mass spectrum with the selenium pattern centered at m/z 313 (80Se). Protonated molecular ions corresponding to the four Se isotopes gave rich fragmentation patterns by collision induced dissociation that allowed the identification of the selenium species to be γ-glutamyl-Se-methylselenocysteine without the need for an authentic standard.

An approach to the identification of selenium species in yeast extracts using pneumatically-assisted electrospray tandem mass spectrometry

An approach to the identification of unknown signals in selenium speciation analysis of yeast by reversed-phase chromatography with ICP-MS detection is described. The analytical strategy was based on: (i), heart-cutting of a Se-containing fraction in the reversed-phase chromatographic eluate followed by its lyophilization; (ii), pneumatically-assisted electrospray (ESI) MS and ESI tandem MS of the lyophilizate; and (iii) confirmation of the fragmentation pattern obtained using the sulfur analogue of the seleno compound that was expected to have been identified. The approach developed allowed the identification of Se–adenosylhomocysteine as the major selenium species in an extract of a selenized yeast sample.

Investigation of metallodrug–protein interactions by size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry (ICP-MS)

The coupling of size-exclusion HPLC with ICP-MS was developed for the studies of the kinetics of metallodrug binding to human serum proteins. Two platinum- and three ruthenium-based drugs were investigated. Various SEC columns (of different lengths and with different packings) were compared for the separation of the protein-bound and unbound fractions of a metallodrug prior to on-line detection of the metal (Ru or Pt). The approach developed offers considerable advantages over the methods based on ultrafiltration followed by the off-line metal determination in terms of speed, simplicity, precision and selectivity regarding the molecular weight of the complexes involved.

Rapid speciation of butyltin compounds in sediments and biomaterials by capillary gas chromatography-microwave-induced plasma atomic emission spectrometry after microwave-assisted leaching/digestion

A rapid procedure for the simultaneous determination of mono-, di- and tributyltin in sediments and biological materials is described. The target compounds in sediments were subject to quantitative microwave-assisted leaching with acetic acid. Biomaterials were dissolved in a tetramethylammonium hydroxide solution under the action of a low-power microwave field in such a way that the organotin moiety remained intact. The leaching of the analytes from a sediment as well as the dissolution of a biomaterial in a focused microwave field took only 1–5 min, which is much faster than previously reported methods. It was also demonstrated that the leaching efficiency of monobutyltin from certified reference sediments was superior to that of most literature procedures. The butyltins were derivatized with sodium tetraethylborate (NaBEt4) in the aqueous phase, and simultaneously extracted into isooctane (5 min). The analysis was carried out by capillary gas chromatography (GC) with microwave-induced plasma atomic emission detection. The sample throughput was limited by the duration of the GC run (10 min). The detection limit was 2 ng g–1 for 0.2 g of sample (dry) without preconcentration; it could be improved by a factor 10 if preconcentration was applied. The developed method was applied to a variety of real samples and was validated by analysing three certified reference materials: PACS-1, CRM 462 and NIES 11.

Ultratrace determination of uranium and plutonium by nano-volume flow injection double-focusing sector field inductively coupled plasma mass spectrometry (nFI–ICP-SFMS)

A sensitive analytical procedure based on nano-volume flow injection (FI) and inductively coupled plasma double-focusing sector field mass spectrometry (ICP-SFMS) was developed for the ultratrace determination of uranium and plutonium. A 54-nl sample was injected by means of a nanovolume injector into a continuous flow of carrier liquid at 7 μl min−1 prior to ICP-SFMS. The absolute detection limits were 9.1 × 10−17 g (3.8 × 10−19 mol, ∼230000 238U atoms) and 1.5 × 10−17 g (6 × 10−20 mol, ∼38000 242Pu atoms) for uranium and plutonium, respectively. The method was validated for the determination of the uranium isotope ratios by the analysis of a certified isotope reference material (NIST U350). The analysis of a contaminated urine sample showed the enriched uranium to be the origin of contamination. Another application concerned the determination of plutonium at the subfemtomolar level in water with a detection limit down to the ag ml−1 range (6 × 10−18 g ml−1).

Speciation analysis of nickel in the latex of a hyperaccumulating tree Sebertia acuminata by HPLC and CZE with ICP MS and electrospray MS-MS detection

Speciation of nickel was investigated in a hyperaccumulator tree, Sebertia acuminata, by liquid chromatography (LC) with parallel ICP MS and electrospray MS-MS detection. The latex of the tree was leached with water. Two separation mechanisms, size-exclusion (SEC) and capillary zone electrophoresis (CZE), were investigated for the separation of Ni-complexes. A preparative scale SEC allowed the isolation of six stable nickel species. A nickel complex with Mr 360 was identified by ES MS. The collision induced fragmentation (CID) of the m/z 360 ion suggested the presence of three carboxylic and one amino groups, and allowed the identification of a Ni-complex with nicotianamine. A modification of the SEC column with Ni2+ ions allowed the isolation of a fraction containing nickel citrate. Quantification of the species showed that in the water extract of the latex 99.4% of the nickel is complexed by citrate and 0.3% by nicotianamine.

Analysis for selenium speciation in selenized yeast extracts by two-dimensional liquid chromatography with ICP-MS and electrospray MS-MS detection

An analytical approach allowing the detection of previously unreported glutathione S-conjugates with selenocompounds in water extracts of nutritional yeast supplements was developed. The procedure was based on the use of two-dimensional size-exclusion and reversed-phase HPLC for the separation of selenospecies, ICP-MS for the monitoring of the eluting selenium, and electrospray MS-MS for the identification of the eluted species. The presence of six compounds with molecular masses of 197, 603, 562, 584, 372 and 432 (in the elution order from reversed-phase HPLC) was identified on the basis of the selenium isotopic pattern. The identity of the Mr 197 and 432 species was confirmed, by collision induced dissociation MS, to be selenomethionine and Se-adenosylhomocysteine, respectively. The compounds with larger Mr (562, 584, 604) were demonstrated, by reaction with dithiothreitol followed by HPLC-ICP-MS and ES-MS-MS, to contain a Se–S bridge between glutathione (γGlu–Cys–Gly) and a selenocompound that did not respond in the positive ES-MS mode. The MS-MS analysis of the original compound confirmed the presence of a selenium-containing fragment that could be fragmented only at high fragmentation energies. A similar Se-containing moiety (m/z 227), resistant to collision induced dissociation, was found in the 372 compound attached to a glutamine (Gln) residue as demonstrated by MS-MS.

Speciation analysis by gas chromatography with plasma source spectrometric detection

Abstract State-of-the-art species-selective analysis by gas chromatography (GC) with plasma source spectrometric detection is discussed for organometal and organometalloid compounds. Various plasmas, inductively coupled plasma, microwave induced plasma, capacitatively coupled plasma, direct current plasma and alternating current plasma, are characterized and critically compared as sources of radiation for atomic emission spectrometry and sources of ions for mass spectrometry. Interfaces between gas chromatography (packed, wide-bore, capillary and multicapillary) and plasma source spectrometry are characterized. Particular emphasis is given to applications of GC with plasma source detection to real-world analytical problems, which are comprehensively reviewed. The use of plasmas for the acquisition of auxiliary molecular information such as empirical formulae and structural information is discussed. Recent developments relating to sample preparation and presentation to the hyphenated system are addressed. The most significant trends in speciation analysis are highlighted.

Speciation Analysis for Organotin Compounds in Biomaterials after Integrated Dissolution, Extraction, and Derivatization in a Focused Microwave Field

Hydrolysis with acetic acid carried out in a low-power focused microwave field in the presence of sodium tetraethylborate and nonane is shown to shorten the sample preparation time for gas chromatographic determination of organotin compounds in biological materials. After a 3-min reaction time, ethyl derivatives of mono-, di-, and tributyltin, and triphenyltin are quantitatively (>95%) found in the supernatant organic phase that is injected onto a capillary GC column. Two rapid one-step analytical procedures, using flame photometric and atomic emission detection, respectively, were developed on this basis and validated by analyzing the NIES11 certified reference fish tissue.