Liquid chromatography speciation analysis

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

C.B. Hymer and J.A. Caruso, Arsenic and its speciation analysis using high-performance liquid chromatography and inductively coupled plasma mass spectrometry. J. Chromatogr.A 1045 (2004) 1-14. 

The application of atomic spectroscopic instruments as element-specific detectors in chromatography has been reviewed by van Loon More recently, Krull has extensively reviewed their use in high pressure liquid chromatography (HPLC). Atomic spectrometry has found wide acceptance in the field of liquid chromatography because, in most cases, the fractions can be directly analysed after elution from the column. However, it is possible to use the technique for the analysis of solid samples without first dissolving the matrix. This is particularly useful after electrophoresis, where the fractions are fixed either in a gel or on paper. Kamel et al. have shown that it is possible to cut the appropriate sections and insert them into the carbon furnace for analysis. The disadvantage of this approach is that the precision is usually poorer (about 10%) and it is difficult to calibrate the instrument. Nevertheless, this approach is very useful if it is used for qualitative speciation. 

J. Gomez-Ariza, M.-A. Caro-de-la-Torre, I. Giraldez and E. Morales, Speciation analysis of selenium compounds in yeasts using pressurized liquid extraction and liquid chromatography-microwave-assisted digestion-hydride generation-atomic fluorescence spectrometry. Anal. Chim. Acta, 524(1-2), 2004, 305-314. 

Thompson, J. J. and Houk, R. S., Inductively coupled plasma mass spectrometric detection for multielement flow injection analysis and elemental speciation by reversed phase liquid chromatography, Anal. Chem., 58, 2541-2548, 1986. 

Basic techniques for speciation analysis are typically composed of a succession of analytical steps, e.g. extraction either with organic solvents (e.g. toluene, dichloromethane) or different acids (e.g. acetic or hydrochloric acid), derivatisa-tion procedures (e.g. hydride generation, Grignard reactions), separation (gas chromatography (GC) or high-performance liquid chromatography (HPLC)), and detection by a wide variety of methods, e.g. atomic absorption spectrometry (AAS), mass spectrometry (MS), flame photometric detection (FPD), electron capture detection (ECD), etc. Each of these steps includes specific sources of error which have to be evaluated. 

Gonzalez-Toledo, E., R. Compano, M. Granados, et al. 2003. Detection techniques in speciation analysis of organotin compounds by liquid chromatography. Trends Anal. Chem. 22 26-33. 

Rosenberg, E., V. Kmetov, and M. Grasserbauer. 2000. Investigating the potential of high-performance liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry as an alternative method for the speciation analysis of organotin compounds. Fresenius J. Anal. Chem. 366 400-407. 

High performance liquid chromatography coupled with hydride generation-direct current plasma emission spectrometry has been used for trace analysis and speciation studies of methylated organotin compounds in water [263],... 

Platinum-based compounds are commonly used as cancer treatment agents. Pharmacokinetic studies of these antitumor drugs require ultratrace analysis. Electrothermal vaporization ICP-MS provides low detection limits for small samples [256]. High-performance liquid chromatography with ICP-MS detection allows speciation of platinum compounds in tissues [256]. LA-ICP-MS can be used to study the distribution of platinum in tissues and tumors [256]. Natural levels of Pt are below typical quadrupole ICP-MS detection limits [257]. 

J. Szpunar, Trace element speciation analysis of biomaterials by high performance liquid chromatography with inductively coupled plasma mass spectrometric detection (HPLC-ICP MS), Trends Anal. Chem., 19 (2000), 127D137. 

C. F. Harrington, S. Elahi, S. A. Merson, P. Ponnampalavanar, A method for the quantitative analysis of iron speciation in meat by using a combination of spectrophoto-metric methods and high-performance liquid chromatography coupled to sector t>eld inductively coupled plasma mass spectrometry, Anal. Chem., 73 (2001), 4422D4427. 

J. Szpunar, P. Pellerin, A. Makarov, T. Doco, P. Williams, B. Medina, R. Lobinski, Speciation analysis for biomolecular complexes of lead in wine by size-exclusion high-performance liquid chromatography D inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 13 (1998), 749D754. 

E. H. Larsen, Method optimization and quality assurance in speciation analysis using high performance liquid chromatography with detection by inductively coupled plasma mass spectrometry, Spectrochim. Acta, 53B (1998), 253-265. 

S. McSheehy, P. Pohl, J. Szpunar, M. Potin-Gautier, R. Lobinski, Analysis for selenium speciation in selenized yeast extracts by two-dimensional liquid chromatography with ICP-MS and electrospray MS-MS detection. J. Anal. Atom. Spectrom., 16 (2001), 68-73. 

L. N. Liang, G. B. Jiang, J. G. Liu, J. T. Hu, Speciation analysis of mercury in seafood by using high-performance liquid chromatography on-line coupled with cold-vapor atomic fluorescence spectrometry via a post column microwave digestion, Anal. Chim. Acta, Ml (2003), 131-137. 

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