Directly-coupled chromatography-analytical atomic spectroscopy for trace metal speciation
The form of trace metals, so called "speciation", is of vital importance in many fields, e.g., toxicology and environmental monitoring. A promising analytical approach to speciation studies is the coupling of chromatography, for species separation, to the selectivity and sensitivity of atomic spectroscopy for detection. The suitability of such couplings are discussed and the applications of both gas and liquid chromatography reviewed. The success of coupled gas chromatography (GC) - flame atomic absorption spectroscopy (FAAS) is demonstrated for the unequivocal identification of petrol residues in forensic applications. The advantages and disadvantages of this technique are discussed with reference to both sufficiently volatile and non-volatile compounds. The advantages of high performance liquid chromatography (HPLC) for many studies are discussed. As coupled HPLC-ETA-AAS (electrothermal atomisation - atomic absorption spectroscopy) suffers from non-continuous detection, coupling is difficult and chromatography constrained. In contrast, a simple HPLC-FAAS coupling utilising pulse nebulisation and a modified atom cell was developed which produced continuous chromatograms in real time. Application of this system to determining tributyltin (TBT+) compounds in seawater yielded a detection limit of 200 ng ml ˉ¹. A directly coupled system utilising continuous flow hydride generation is described, and for species with non-volatile hydrides, on-line UV photolysis was incorporated. The effects of various parameters on analytical performance are discussed, and applications to real samples given. Detection limits for TBT+ were improved 100 fold. A novel sample transport interface using rotating platinum wire spirals controlled by a microprocessor, utilised the attractive features of flame atomisers but sample introduction via the nebuliser was avoided. Applications are reported using both minibore HPLC for alkyllead speciation and fast protein liquid chromatography for speciating zinc in human serum. Applications of the above techniques for determining organometallic species of Pb, As, Sn, Cu, Zn and Cd are described and possible future work discussed.