Metallothionein isoforms separation and cadmium speciation by capillary electrophoresis with ultraviolet and quadrupole-inductively coupled plasma mass spectrometric detection

A complete characterisation of metallothioneins (MTs) in biological systems requires first an optimal separation of the different isoforms and sub-isoforms present. A method for the adequate separation of rabbit liver MT1 and MT2 mixtures by capillary zone electrophoresis (CZE) with UV detection is developed here. Different experimental conditions affecting both, peak shape and resolution achieved, are investigated in detail. Thus, the influence of the composition, ionic strength and pH of the buffer solution, and the separation voltage, have been studied. In order to improve the resolution between sub-isoforms, the electroosmotic flow has been also changed and its effect investigated by adding organic modifiers. Analytical performance characteristics are evaluated: calibration graphs were linear between 70 and 205 mug ml(-1) for MT1 and between 83 and 242 mug ml(-1) for MT2, while the detection limits were 4 and 3 mug ml(-1), respectively. Speciation of the metal-MTs compounds has been accomplished by the coupling CZE-ICP-MS by means of different nebulisers: a conventional concentric Meinhard nebuliser, a Babington type one and a high efficiency nebuliser (HEN). Finally, real sample MTs analyses have been carried out in mussel hepatopancreas cytosols, previously exposed to a metal enriched environment. (C) 2001 Elsevier Science B.V. All rights reserved.