Determination of analytical limits in solid sampling ETAAS: a new approachtowards the characterization of analytical quality in rapid methods

Ln the present study the lower analytical limits of solid sampling electrot hermal atomization atomic absorption spectrometry (SS-ETAAS) were character ized by means of blank measurements and - for the first time - by means of the calibration curve method, where a calibration near the range of these l imits (limit of decision, detection and quantification) was performed. The limit of decision as derived from blank measurements was calculated accordi ng to the 3 sigma-criterion to be 0.003 and 0.019 ng for Cd and Pb, respect ively. For Pb and Cd a roughly threefold increase of these limits was obser ved when the calibration method according to DIN 32 645 was applied. When s olid reference material was used, only a slight increase could be observed. The analytical limits were 2 to 20 times lower than reported for sample de composition methods. The blank measurement and conventional calibration cur ve method, however, do not account for factors relating to solid sampling s uch as sample mass and matrix. Therefore, the calibration curve model was a pplied to data derived from comparisons between direct solid sampling ETAAS and a compound reference method (ETAAS following sample homogenization and digestion). The observed analytical limits were not found to be substantia lly increased if enough samples with low element contents were available fo r calibration. Coupling of the calibration curve model with the comparison of methods included real test samples and thus the relevant maximum sample mass and analyte content in the range of the lower analytical limits. As va lidation procedures frequently include comparisons of methods, the present approach might prove to be of some general interest for the characterizatio n of analytical quality in rapid methods.