Optimisation of analytical methodology through proficiency testing schemes : trace metal analysis

Abstract

Accurate and precise methods for the determination of trace metals in biological fluids were devised using graphite furnace atomic absorption spectrometry with Zeeman background correction. The five different trace metals investigated were aluminium in plasma and dialysis water, lead in whole blood, and copper, selenium and zinc in bovine serum. For zinc, flame atomic absorption spectrometry was also performed to compare the two methods. For all metals, the methods were based on an appropriate dilution with a mixture of 0.2% Triton X-100 with 0.2% antifoam B. The technique of standard addition was employed to eliminate matrix effects which were present. A palladium (II) chloride modifier was found to be the best modifier in comparison to others as it gave optimum results for lead, copper and selenium. The precision of the results obtained was quite high with %RSD values of<5%. To validate the methods used for the determination of trace metals in biological fluids by GF AAS our laboratory took part in three separate interlaboratory comparison schemes. One scheme was for aluminium, another for lead and the other covering copper, selenium and zinc together. The aim of these interlaboratory testing schemes was to demonstrate the validity of the analytical methods which were devised. The numbers of participants were always greater than 20 in each of these schemes. These numbers were large enough to ensure that the results of the statistical analysis were reliable. The overall results obtained were sufficient for all the metals.