DISCRIMINATION OF THE CAUSES OF IMPRECISION IN THE DIRECT DETERMINATION OF METALS IN ORGANIC-SOLID SAMPLES BY ELECTROTHERMAL ATOMIZATION ATOMIC-ABSORPTION SPECTROMETRY

The contribution of various factors (instrumental, working conditions, the use of subsamples of 1-2 mg and the direct atomization of solids) to the total variance on the determination of metals in organic solid samples by ETAAS has been studied using four different samples. The l ack of homogeneity of the small subsamples used, which is not always i mproved by reducing particle size, appears to be the main cause of the high RSD values obtained, to such an extent that the influence of the other factors studied appears irrelevant. The technique, which pro,id es results in accordance with the amount of analyte introduced into th e atomizer, is perfectly suitable for controlling the homogeneity of c ertified reference samples or any other material, although its use as a conventional method of determining metals makes it necessary to carr y out several measurements in order to obtain sufficiently reliable re sults.