LC-ICP

Selenium is required, but levels must fall into a narrow window. Both deficiency and toxicity symptoms occur. The element is also used therapeutically in cancer treatment. It is the co-factor of the enzyme glutathione peroxidase which is thought to play an important role in oxygen toxicity. The determination of Se in blood or serum is not easy, as many incorrect, inaccurate and imprecise methods have been published (Magee and James 1994). A suggested procedure for Se in body fluids is based on GF-AAS (Thomassen et al. 1994)- For tissues SS-AAS may be used (Fler-ber 1994a). Recent developments by Turner et al. (1999) show that LC-ICP-MS is sensitive and reproducible at low levels. 

ICP is intolerant to the solvents commonly used in LC development. Consequently, most LC-ICP-AES systems have been employed with ion-exchange columns, as this separation process largely involves aqueous mobile phases that are amenable to the ICP-AES instrument. Use of acetonitrile or THF in the mobile phase has usually evoked a change in interface design to accommodate the different solvents. The advantages of LC-ICP-AES include multi-element detection and the ability to obtain real-time chromatograms. LC-ICP-AES... 

Table 7.75 summarises the main features of LC-ICP-MS. Various mass analysers (QMS, ITMS, ToF-MS,... 

Figure 7.36 Schematic of an LC-ICP-MS system. After DeNicola and Caruso [678]. Reproduced by permission of Reed Elsevier...

LC-ICP-MS Liquid chromatography - LVEI Low-voltage electron ionisation... 

LC-ICP Liquid chromatography None Inductively coupled plasma... 

LC-ICP-MS Liquid chromatography Inductively coupled plasma Mass spectrometry... 

In LC-ICP-MS, samples are separated on a chromatographic column, which may be a simple silica or alumina column with a relatively simple eluent. As the components elute from the column, they enter the ICP and the identity of the elements present and their concentration are determined based on the wavelengths of light (identity) and intensity of light (quantification) they emit. The exhaust from the ICP then enters the mass spectrometer, where the metals and their isotopic composition are determined based on their characteristic m/z ratios. The metals are thus identified and verified by two methods, ICP and MS [15]. 

On-line anion exchange LC/ICP-MS methods for selenium and chromium speciation have been published [30], In studies of selenium speciation in environmental samples LC/ICP-MS and LC/ ESI-MS methods have been used for the determination of both inorganic and organic selenium species [43]. For the determination of methyl selenide, strong anion exchange and RP chromatography have been employed [43], while for the determination of seleno-aminoacids, IP RP chromatography with on-line detection based on ICP-MS has been successfully employed [44],... 

Fig. 3. Schematic diagram of a LC-ICP-MS interface with hydride generation system. Reprinted from Story et al. [49] by permission of Preston Publications, a division of Preston Industries.

Fig. 1. LC—ICP-MS chromatogram of a standard mixture of organolead and inorganic lead compounds (Pb, trimethyllead and triethyllead) using reversed-phase HPLC. Mobile phase, 0.1 M ammonium acetate and 0.1 M acetic acid at pH 4.6, 30%...

Tellurium speciation has been described by Klin-kenberg et al. [40] using reversed-phase LC-ICP-MS for the analysis of tellurium in samples from a wastewater treatment plant. A method was developed for the separation of Te03 and HTe04 and, although at least 11 different organic Te compounds were detected, no attempt was made to identify them. This is essentially a problem with ICP detection since all structural information is lost by plasma sample decomposition. 

A heated pneumatic nebuliser is used to produce the aerosol in APCI and the ions are produced by ion-molecule reactions initiated by corona discharges in the ion source region. White et al. (1998) found atmospheric pressure ionisation MS and LC-ICP-MS to be complementary techniques. 

A detailed interlaboratory study of arsenic speciation in six different kinds of marine organisms was published (El Moll et al., 1996). Detection of arsenic species in the sample extracts was performed by means of LC-ICP-OES for AB and AC, and by HG-AAS for As111, Asv, MMA and DMA. Many precautions were taken to avoid contamination and losses of analytes, and to improve the accuracy of the results. Data for total As, extractable As, residual As and AB were reported. 

Most LC-ICP-MS hyphenation is performed by using isocratic elution. Gradient elution may be used to improve retention times and partition functions for a chromatographic separation with conventional LC detectors, but difficulties arise when gradients are introduced into the ICP. The changing load on the plasma due to the variations in mobile phase composition often causes plasma instability. In addition, optimal operating conditions evaluated for one mobile phase combination may not be valid when an organic constituent concentration is increased. 

Figure 10 Cation exchange liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS) of arsenic species spiked in (a) aqueous solution and (b) urine diluted (1 + 3). Amount of each species injected 0.44 ng. Peaks (1) DMA (2) As (III) (3) MM A (4) As (V) (5) AsB (6) TMAO (7) AsC (8) TMAs. (From Ref. 69.)...

Derivatization and Measurement by Liquid Chromatography Systems Apart from classical applications with liquid chromatography (LC)-ICP-MS (see above) two new applications have been reported. A vapor generation system and LC combined with ICP-MS were used to determine Hg species in extracts of biological tissues. The efficiency of the mobile phase, a mixture of L-cysteine and 2-mer-captoethanol, was evaluated for the LC separation of three Hg-species (Hg2+, Me-Hg, and ethyl-Hg). The LoDs (see Table 22.2) and repeatability of the... 

LC-ICP-MS system with a vapor generator were comparable to, or better than, that of an LC-ICP-MS system with conventional pneumatic nebulization [62]. 

After intravenous or oral administration of the drug, it undergoes several biotransformations that activate its toxicity (tumor cells as well as nephro- and neurotoxicity). A number of speciation studies that focused on characterization and quantification of parent drug and its possible metabohtes in vitro and in vivo have been reported. Element-specific ICP-MS detection has been applied after LC separation of platinum compounds. In Figure 6, the LC-ICP-MS chromatogram is presented, and this was obtained for the mixture of cancerostatic platinum compounds. ... 

Figure 6 LC-ICP-MS chromatogram obtained from a 24-h mixture of cisplatin (/Jf = 1.9 min), carboplatin (f t = 3.1 min), and oxaliplatin Rt = 5.1 min) in subboiled water using pentafluorophenylpropyl-functionalized sihca as stationary phase. In addition to the parent drugs, the chromatogram shows the major degradation products of cisplatin (monoaquacisplatin, Rt = 2.5 min diaquacisplatin Rt = 3.6 min)), the product of carboplatin (CP2, Rt = 2.7 min) and the product of oxaliplatin (OP 1, Rt = 4.5 min). (Reproduced with permission Hann, Stefanka, Lenz and Stingeder 2005, Springer Science Business Media)...

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