AAS-Untersuchungen über Verdampfungs- und plasmaprozesse in der Graphitrohrküvette Zur Optimierung der Bestimmungen von Cd-, Zn- und Mn-Spuren in AIIIBV-Halbleiter-Matrices

As a basis for optimizing the analysis conditions for the determination of traces of Cd, Zn and Mn in A^III B^V semiconductor samples by graphite furnace atomic absorption spectrometry (AAS), the authors made a systematic investigation of the matrix effects. The evaporation behaviour of the matrices was studied to assess the possibility of thermal separation of trace element and matrix. Absorption spectra of Ga³⁺ and In³⁺ matrices in 1 N HCl and 1 N HNO₃ between 190 and 330 nm were measured to explain unspecific absorption effects. Intense absorption bands were identified as originating from the diatomic molecules GACl, InCl, GaO and InO. Absorbance vs time curves were determined to study the effects of the matrices on the AA signals. It was established that the formation of diatomic molecules in the gaseous state is a major cause of signal depressions. This effect occurs when the analytes and the matrices or their anionic components evaporate concomitantly. Strong signals depressions were found when the matrices were present in hydrochloric acid (formation of CdCl, ZnCl and MnCl), but not when nitric acid was used. The eventually adopted analytical conditions were chosen so as to make an optimum use of the thermal hydrolysis of the matrices. A detailed discussion of the results is presented and it is shown that direct trace determinations with nitric acid solutions are feasible below the ppm (μg/g) level with a sample size of 0.01 to 0.2 mg.