Determination of serum iron by aas: Deproteinization versus direct analysis

Abstract

Atomic absorption spectroscopy (aas) offers sensitivity for the trace metal analysis of biological materials. Flame or electrothermal atomization (eaas) have been used depending on analyte concentration and the amount of sample required for the analysis. Most methods proposed for the routine determination of serum iron by aas involve either a deproteinization by acids [l-6] or dilution of the serum sample [7-111. Deproteiuization has the purpose of removing protein and haemoglobin iron which interfere in the determination of transferrin-bound iron. Higher iron concentrations were found [2,7] when serum was only diluted, than when it was deproteinized, possibly due to iron contamination due to non-visible haemolysis [12]. Enhancement of up to 50% can result from non-visible haemoglobin and over 100% from slight visible haemolysis. On other hand, it is desirable to avoid deproteinization, not to minimize contamination, to simplify the procedure, and to exclude co-precipitation of iron and proteins as well as the incomplete separation of iron from proteins [7]. The accuracy of serum iron assays has been checked by recovery tests [1,13], comparison with independent analytical methods [2,5-g] and validation with quality control serum or certified material [9]. According to the last recommendations of the International Committee for Standardization in Haematology (ICSH) [14], iron in reference materials should be assayed by independent methods such as aas, and serum for reference materials must be collected with stringent precautions against haemolysis. This latter recommendation is to prevent the liberation of iron from lyophilized haemoglobin in reconstituted serum.