FUNDAMENTAL-STUDIES ON PNEUMATIC GENERATION AND AEROSOL TRANSPORT IN ATOMIC SPECTROMETRY - EFFECT OF MINERAL ACIDS ON EMISSION INTENSITY ININDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

The mechanism of the mineral acid interference has been studied in ICP -AES. For this study five mineral acids have been evaluated (HCl, HNO3 , HClO4, H2SO4 and H3PO4) in four concentrations (0, 0.5, 5 and 30%). In order to investigate this interference emission signal, sample upta ke rate, primary and tertiary drop size distributions, total analyte t ransport rate and excitation temperature have been measured. From the results obtained, it seems that this interference is contributed by a reduction of the analyte transport rate and, also, by a decrease in th e plasma temperature. The degree of the contribution to the interferen ce of each one of these causes depends on the type of acid and sample uptake mode. The physical properties of the acid solutions are in the origin of the interference. These physical properties modify the sampl e uptake rate and/or the primary drop size distribution of the aerosol s. The acids evaluated can be classified in two groups. The first grou p would consist of HCl, HNO3 and HClO4, and the second one of H2SO4 an d H3PO4. In natural uptake mode the interference is mainly due to chan ges in sample uptake rate, and in controlled uptake mode to changes in primary drop size distribution of the aerosols. In both sample uptake modes a density-effect may appear on increasing acid concentration. A h these factors tend to decrease the analyte transport rate and, hence , the emission signal. Finally, a cooling effect of the plasma due to a higher load of acids ii superimposed to these causes. We think that from this study the mineral acid interference in ICP-AES, with pneumat ic nebulization, should be better understood.