HPLC-ICP

HPLC (in both NP and RP modes) is quite suitable for speciation by coupling to FAAS, ETAAS, ICP-MS and MIP-MS [571,572]. Coupling of plasma source mass spectrometry with chromatographic techniques offers selective detection with excellent sensitivity. For HPLC-ICP-MS detection limits are in the sub-ng to pg range [36]. Metal ion determination and speciation by LC have been reviewed [573,574] with particular regard to ion chromatography [575]. 

Table 7.33 reports the main characteristics of GC-ICP-MS. Since both GC and ICP-MS can operate independently and can be coupled within a few minutes by means of a transfer line, hyphenation of these instruments is even more attractive than GC-MIP-AES. GC-ICP-MS is gaining popularity, probably due to the fact that speciation information is now often required when analysing samples. Advantages of GC-ICP-MS over HPLC-ICP-MS are its superior resolution, resulting in sharper peak shapes and thus lower detection limits. GC-ICP-MS produces a dry plasma when the separated species reach the ICP they are not accompanied by solvent or liquid eluents. This reduces spectral interferences. Variations on the GC-ICP-MS... 

Principles and Characteristics Plasma source techniques are more widely used in connection with liquid chromatography than atomic absorption spectrometry (see Section 7.3.3). ICP is a natural complement to liquid chromatography, and HPLC-ICP procedures... 

LA-ICP-MS allows quick simultaneous oligo-element homogeneity determinations in mg samples of polymeric material. Coupling of ICP-MS to chromatographic techniques provides element speciation capabilities, especially as a detector for LC. Kingston et al. [417] have described a speciated technique for the determination of Cr(III) and Cr (VI) by HPLC-ICP-MS. 

Other techniques used for organotin speciation comprise GC-FAAS, GC-GFAAS, GC-ICP-MS, HPLC-FAAS, HPLC-GFAAS, HPLC-DCP (after continuous on-line hydride generation), HPLC-ICP-AES, HPLC-ICP-MS, etc. [555], Whereas ICP-AES does not provide an adequate response for ng levels of tin, ICP-MS can detect sub-ng to pg levels. GC-ICP-ToFMS... 

Kolasa et al. [562] have reported changes in the degree of oxidation of chromium (from Cr6+ to Cr3+) in the course of probe mineralisation of PE for AAS analysis. HPLC-ICP-MS has been used as a selenium-specific detector [563]. Other selenium speciation work by ICP-MS has been reported [564]. Numerous other examples of speciation analysis have been described for the most appropriate techniques (Chapter 7). 

Vonderheide, A.P., Mounicou, S., Meija, J., Henry, H.F., Caruso, J.A., and Shann, J.R., Investigation of selenium-containing root exudates of Brassica juncea using HPLC-ICP-MS and ESI-qTOF-MS, Analyst, 131, 33-40, 2006. 

A1-Rashdan A, Heitkemper D, Caruso JA. 1991. Lead speciation by HPLC-ICP-AES and HPLC-ICP-MS. J Chromatogr Sci 29(3) 98-102. 

Polatajko, A., Encinar, J. R., Schaumloffel, D., and Szpunar, J., Quantification of a selenium-containing protein in yeast extract via an accurate determination of a tryptic peptide by species-specific isotope dilution capillary HPLC-ICP MS, Chemia Analityczna 50(1), 265-278, 2005. 

Ballihaut, G., Tastet, L., Pecheyran, C., Bouyssiere, B., Donard, O., Grimaud, R., and Lobinski, R., Biosynthesis, purification and analysis of selenomethionyl calmodulin by gel electrophoresis-laser ablation-ICP-MS and capillary HPLC-ICP-MS peptide mapping following in-gel tryptic digestion. Journal of Analytical Atomic Spectrometry 20(6), 493 99, 2005. 

If the method is more complex such as HPLC, ICP, AA etc. then it is more likely to require three levels of testing. 

Importantly, neither arsenobetaine nor arsenocholine forms an arsine on treatment with borohydride solutions. Consequently, arsenobetaine and arsenocholine may remain undetected in samples, seawater for example, when arsines are generated and determined in an arsenic speciation analysis. The technique HPLC/ICP-MS is most suitable for the analysis of these (non-arsine-forming) compounds (49). Use of the highly sensitive ICP-MS detector allows application of small quantities of material to the chromatography column, thereby obviating possible sample matrix effects previously observed for arsenobetaine (50). 

Fig. 3. Typical separation of four arsenosugars and DMA by HPLC/ICP-MS using an ODS reversed-phase column at pH 3.2 under conditions described in Ref. 60. The sensitivity and specificity of the detector allows the determination of arsenosugars and other arsenic compounds to be conducted on dilute aqueous extracts of the marine samples.

Clearly there is much to be learned from further examination of arsenic levels in seawater and porewaters. However, low concentrations and analytical difficulties presented by the salt matrix continue to complicate these analyses (33, 85). Techniques such as HPLC/ICP-MS suffer from interference by the molecular ion 40Ar35Cl +, formed by combination of the plasma gas and chloride ion, with the monoisotopic 75As+. Techniques to separate the arsenic compounds from the salt matrix before HPLC/ICP-MS have not been fully investigated because they may result in fractionation of the compounds and loss of speciation information. Nevertheless, methods to establish the presence or otherwise in seawater of some of the arsenic-containing compounds important in other marine compartments is worth pursuing. 

The application of high-sensitivity ICP-MS detectors coupled to HPLC has enabled the detection of trace arsenic compounds present in marine animals. Thus, arsenocholine has been reported as a trace constituent (<0.1% of the total arsenic) in fish, molluscs, and crustaceans (37) and was found to be present in appreciable quantities (up to 15%) in some tissues of a marine turtle (110). Earlier reports (46,47) of appreciable concentrations of arsenocholine in some marine animals appear to have been in error (32). Phosphatidylarsenocholine 45 was identified as a trace constituent of lobster digestive gland following hydrolysis of the lipids and detection of GPAC in the hydrolysate by HPLC/ICP-MS analysis (70). It might result from the substitution of choline with arsenocholine in enzyme systems for the biogenesis of phosphatidylcholine (111). 

Preliminary experiments in which HPLC/ICP-MS techniques have been used to monitor arsenic transformations within planktonic crustaceans feeding on a cultured unicellular alga containing arsenosugars at high concentrations have also been unable to demonstrate the production of arsenobetaine (98). Clearly there is much scope for work in this area. 

Figure 5.21 Schematic of hyphenated ICP mass spectrometric techniques HPLC-ICP-MS for the application of isotope dilution techniques. (K. G. Heumann, L. Rottmann, j. Vogl, ]. Anal. At. Spectrom., 12, 1381 (1994). Reproduced by permission of The Royal Society of Chemistry.)...

A further application of the isotope dilution technique is the determination of selenomethionine in human blood serum by capillary HPLC-ICP(ORC) MS. 

Dill HPLC-ICP-QMS (Agilent with collision cell) chromatographic separation Se (total) and Se species MeSeCys, MeSeMet <0.1 p.gg- /O.Wp.gg-1 (control)-31.8 (jLgg 1 (supplemented) Cankur et al.32... 

Miniaturization of HPLC-ICP-MS is an important issue in bioanalytical chemistry when small amounts of sample (e.g., single cells) need to be investigated.33 ICP-MS (with an octopole collision cell) in combination with nano-HPLC (75 pun column) was optimized for the detection of selenopeptides in a selenium-yeast protein digest after 100-fold preconcentration on a C18 capillary precolumn (300 (im column for salt removal and cleanup).34 Under identical separation and preconcentration conditions, electrospray MS/MS (using Nanospray qQqToF-MS - QSTAR from Applied... 

Figure 9.20 Different selenium species determined by HPLC-ICP-MS in leaves, stems and roots of dill (1) Se (VI) (2) Se (IV) (3) SeCys2 (4) MeSeMet (5) MeSeCys (6) SeMet. (O. Cankur, S.K.V. Yathavakilla, J.A. Caruso, Talanta, 70, 784 (2006). Reproduced by permission of Elsevier.)...

Szpunar, Lobinski el al. have reported on several hyphenated techniques (especially CE-ICP-MS and HPLC-ICP-MS) for elemental speciation in biological systems,51-54 describing e.g. the quasi-simultaneous determination of more than 30 selenopeptides using HPLC-ICP-MS. 

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