Direct determination of impurities in high purity chemicals by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

An ELCAD-AES method was reported for direct determination of metallic impurities in different high purity chemicals such as ammonium hydroxide, hydrogen peroxide and sulphuric acid. Direct analysis of these chemicals for their impurities was found to be feasible by ELCAD-AES without going for chemical processing/treatment like dilution or evaporation of matrix. 100% solutions of NH4OH and H2O2 chemicals produced stable ELCAD plasma, whereas 0.5% solution produced stable plasma for H2SO4. As standard addition calibration method to quantify impurities in these chemicals could not be useful, an alternative aqueous calibration method was examined and found to be suitable for their quantification by ELCAD-AES. As the certified reference materials for these chemicals were not available, the ELCAD-AES results were validated with the corresponding graphite furnace atomic absorption spectrometer (GF-AAS) results for NH4OH and H2O2 whereas for sulphuric acid they were validated with inductively coupled plasma optical emission spectrometer (ICP-OES) and supplier's results. ELCAD-AES method was free from matrix related problems and did not demand for the dilution of NH4OH and H2O2. The method was found to be useful for direct determination of trace and ultra trace metallic impurities in NH4OH and H2O2 pure chemicals and also for trace impurities in H2SO4 chemicals. Repeatability and accuracy of this method were found to be < 10% and between 10 and 20% respectively. Thus ELCAD-AES could be an alternative analytical, rapid and direct analysis technique to check levels of metallic impurities (i.e. metal salts) and quality of these high purity chemicals for various industries.