Estimation of the homogeneity of reference materials by SS-ETAAS and use of the "tape-sandwich" sample-introduction...

The so called "tape sandwich", a novel sample-introduction technique developed for SS-ETAAS, has been employed in a study of the microheterogeneity of some biological CRM. Pb, Cd, and Cr were measured by use of a laboratory-assembled instrument with graphite-cup atomizer. Aqueous standards were found satisfactory for calibration. The average mass of sub-samples atomised was in the range 0.250-0.660 mg+/-30%. The relative sampling error found for the CRM investigated varied from 15-34%. Calculated relative homogeneity constants of the order of 4-21 mg(1/2) were obtained, and were reduced considerably by reduction of the particle size. The minimum sample sizes representative of the CRM were, with one exception, much lower (11-75 mg) than those recommended in the documentation accompanying the standards (100-200 mg). In a Chinese hair reference sample Cr data were normally distributed but the presence of nuggets was observed for Cd and Pb; this was associated with severe radial and longitudinal gradients of these elements in hair.