Development of an Advanced Thermospray Interfaced HPLC-AAS System for Speciation Studies of Cadmium Species Excreted From Human Body Fluids: Interaction Between Metallothionein Cadmium and Zinc.

A new technique has been developed to reveal different metal species at very low concentrations (lower ppb level) in human body fluids. Using this technique it was determined that urine contained many different species of cadmium and that perspiration contained many other species of cadmium. This indicated that there were two avenues for the elimination of cadmium from the body. Quantitative data showed that much more cadmium was eliminated through perspiration than urine and that the biological half life of cadmium in the body was less than 1.5 years--not 20-30 years as currently believed. Further, in vitro experiments showed that zinc ions displaced cadmium from metallothionein complexes at mole ratio as low as 1:100:1,000, with actual concentrations of 0.015:1.0:40 ppm of zinc:cadimum:metallothionein, respectively. These results suggest that zinc ions may displace cadmium from metallothionein in vivo and caution should be exercised in taking zinc tablets. This new system interfaced high performance liquid chromatography (HPLC) with flame atomic absorption spectroscopy (FAAS) using an advanced thermospray (TSP) nebulizer. The procedure maintained high chromatographic resolution in the system. No sample pretreatment was necessary, eliminating many sources of analytical error. The TSP nebulizer, an electrothermally heated stainless steel capillary, has the ability to convert HPLC effluents into an aerosol/vapor jet with relatively small and uniform particles of dried solute. The jet can be directly delivered into the flame, therefore, interfacing HPLC with FAAS. The enhancement of sensitivity and the optimization of the TSP interface led to a study of TSP desolvation mechanism. A new concept of the mechanism was proposed in which a TSP induced solute-enrichment, by way of forming a solute plug , achieved the desolvation. Quantitative studies showed that 4.5 ppb of analytical sensitivity and 0.45 ng of absolute sensitivity for cadmium were achieved. The optimum standard deviation obtained at the 200 ppb level of cadmium was 7.0 $\times$ 10$\sp{-4}$ absorbance. The relative standard deviation at that level was 0.3%. The technique should be applicable to the speciation and accurate determination of many metals at low concentration level in body fluids, and other aqueous and non-aqueous solutions