Shona McSheehy

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.

The speciation of arsenic in biological tissues and the certification of reference materials for quality control

Arsenic is an ubiquitous element. Its toxicity, environmental mobility and accumulation in living organisms usually depend on the form in which the element is present. Information on the chemical forms is important for understanding the role of the element present as well as revealing its environmental cycle. This requirement stimulates the need for information on the speciation of arsenic and the development of suitable analytical methodology. It is well known that seafood can contain considerable quantities of naturally-acquired arsenic and developments in speciation have focused on seafood samples. It seems that the major arsenic species in fish, crustaceans and molluscs have the tetraalkylarsonium structure (R4As+) and the species in marine algae and bivalves have the trialkylarsine oxide structure (R3AsO). However, the concentrations are still low enough to require a sensitive analytical method based on the isolation, identification and quantification of the individual arsenic-containing species. This review will discuss the accepted techniques for the speciation of arsenic in biological tissues and the need for quality assurance of speciation analyses. Quality control will be discussed, focusing on the use of certified reference materials. As well as validation of methods, reference-material certification involves the participation of several laboratories, enabling the evaluation of state-of-the-art analytical techniques. The certification process of a candidate oyster-tissue reference material for different chemical species of elements (including arsenic species) is discussed.

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 of seleno compounds in yeast aqueous extracts by three-dimensional liquid chromatography with inductively coupled plasma mass spectrometric and electrospray mass spectrometric detection

A three-dimensional liquid chromatographic purification protocol based on sequential size-exclusion, anion-exchange and cation-exchange separation mechanisms was developed for the mapping of seleno compounds in aqueous yeast extracts. The method allowed the demonstration of the presence of more than 30 different seleno compounds. Semi-preparative size-exclusion and anion-exchange chromatography were optimized for maximum resolution using electrospray-compatible buffers in order to purify the compounds for mass spectrometric analysis. Molecular masses were attributed to many of the compounds on the basis of the selenium isotopic pattern in the electrospray mass spectra and of the collision-induced fragmentation patterns. Limitations preventing the ultimate identification of the selenium species detected are discussed.

Speciation of arsenic in edible algae by bi-dimensional size-exclusion anion exchange HPLC with dual ICP-MS and electrospray MS/MS detection

Anion-exchange (AE) high-performance liquid chromatography (HPLC) with ICP-MS detection was revisited for speciation of arsenic in biomaterials with particular attention given to arsenic-containing ribosides (arsenosugars) in seaweeds. Signal identification by retention time matching and spiking experiments was found to be difficult because of the co-elution of the ribosides with other arsenic species [As(III), monomethylarsonic acid], the medium- and long-term irreproducibility of retention times of arsenic species and an uncontrolled matrix effect on the retention times. Size-exclusion (SE) HPLC was proposed for the fractionation of organoarsenic species and matrix removal prior to detection of arsenosugars by AE-HPLC followed by signal identification by spiking experiments and retention time matching. The results were compared with those obtained by pneumatically-assisted electrospray tandem MS (ESI MS/MS) of the SE-HPLC fractions. A number of 10 commercially available edible algal food samples of different origins available on the French market were investigated. The approaches developed for the identification and determination of arsenosugars (SE-AE-HPLC-ICP-MS and SE-HPLC-ESI MS/MS) were discussed using the example of Hizikia fusiforme.

Identification of dimethylarsinoyl-riboside derivatives in seaweed by pneumatically assisted electrospray tandem mass spectrometry

Pneumatically-assisted electrospray tandem mass spectrometry (ES MS/MS) was proposed as a technique for the identification of dimethylarsinoyl-riboside derivatives (arsenosugars) in seaweed (Laminaria). Conditions for the acquisition of MS and MS/MS spectra were optimized. A size-exclusion HPLC (SE HPLC) step was developed for the purification of algal extracts prior to ES MS. The arsenosugar fraction was found to elute prior to the majority of other arsenic compounds. The identity of the compounds expected to be arsenosugar compounds was confirmed by the collision induced dissociation (CID) of the relevant protonated molecule ions. An independent confirmation of the identity of analytes was obtained by two-dimensional (size-exclusion–anion exchange) HPLC–ICP MS with signal identification by spiking with the appropriate arsenosugar standards.

Investigation of arsenic speciation in oyster test reference material by multidimensional HPLC-ICP-MS and electrospray tandem mass spectrometry (ES-MS-MS).

Multidimensional (size-exclusion-anion-exchange-cation-exchange) liquid chromatography with ICP-MS detection was developed to produce a map of water-soluble species in an oyster test reference material. The presence of arsenobetaine, trimethyl(2-carboxyethyl)arsonium inner salt, arsenocholine, dimethylarsonic acid, tetramethylammonium ion, As(v) and two arsenosugars was demonstrated by ES-MS-MS. A previously unreported compound was isolated and identified by ES-MS-MS as 5-dimethylarsinoyl-beta-ribofuranose. Anion-exchange chromatography was optimized to produce a chromatographically pure peak of arsenobetaine (accounting for ca. 64% of all water-soluble As present) that was used to quantify this compound.

Complementarity of multidimensional HPLC-ICP-MS and electrospray MS–MS for speciation analysis of arsenic in algae

Abstract HPLC-ICP-MS using different separation mechanisms: reversed-phase, anion-exchange, cation-exchange, and size-exclusion was revisited and comprehensively evaluated using a set of 14 standards of arsenic species. An analytical protocol based on three-dimensional (size-exclusion–anion-exchange–reversed-phase) chromatography, capable of isolating individual arsenocompounds from a biological sample, and electrospray tandem mass spectrometry (ES MS–MS), for their identification, was developed. Two minor arsinoylribosides could be detected in addition to As(V) and one major riboside in the algae ( Hizikia fusiforme ) sample investigated. The other minor species isolated showed different chromatographic behavior than the standards available while the ES MS–MS fragmentation patterns indicated the presence of an arsenoylriboside moiety.

Gas and liquid chromatography with inductively coupled plasma mass spectrometry detection for environmental speciation analysis — advances and limitations☆

Abstract Recent advances in the coupling of gas chromatography (GC) and high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP MS) and their role in trace element speciation analysis of environmental materials are presented. The discussion is illustrated with three research examples concerning the following topics: (i) development and coupling of multicapillary microcolumn GC with ICP MS for speciation of organotin in sediment and biological tissue samples; (ii) speciation of arsenic in marine algae by size-exclusion-anion-exchange HPLC-ICP MS; and (iii) speciation of cadmium in plant cell cultures by size-exclusion HPLC-ICP MS. Particular attention is paid to the problem of signal identification in ICP MS chromatograms; the potential of electrospray MS/MS for this purpose is highlighted.

Identification of selenocompounds in yeast by electrospray quadrupole-time of flight mass spectrometryElectronic supplementary information (ESI) available: electrospray TOFMS spectra of fractions III and I of the SEC?HPLC, Figs. A?C. See http://www.rsc.org/suppdata/ja/b2/b201015c/

The performance of a quadrupole-time of flight (Q-TOF) tandem mass spectrometer was evaluated for the identification of low-molecular weight selenocompounds in an aqueous yeast extract. The accuracy of mass measurements, evaluated with selenomethionine, selenoethionine and selenocystine standards was found to be between 0.005 and 0.01% (0.01–0.02 u). The low molecular weight fraction was obtained by collecting selenocompounds eluted in the total volume of a G-15 size-exclusion column. The fraction gave three peaks in anion-exchange HPLC of which the identity was investigated by ES-Q-TOFMS/MS. Altogether, eight clusters with the isotopic pattern corresponding to the presence of Se were observed. They were further investigated by collision induced dissociation TOFMS leading to the demonstration of the presence of a series of new selenocompounds, all characterized by the presence of an adenosyl functional group.