Application of a multi-way method to study long-term stability in ICP-AES

Although major advantages have been made in developing robust, easy-to-use ICP-AES instruments offering sub mug g(-1) detection limits and relative in terference free operation, long-term drift of the analytical signal continu ous to be problematic and necessitates regular re-calibration. The work pre sented here focuses on the effect of two instrumental parameters, i.e. the rf power and the nebuliser gas flow rate, on the robustness of the signals. The effects on the long-term stability when varying these two factors was systematically studied using an experimental design protocol. A "drift diag nosis" on thirty emission lines was performed at 12 different sets of opera ting conditions by repeated determination of a multi-element solution over several hours. The results were studied using standard parameters, i.e., Mg ratio, sensitivity, drift error, drift patterns and multi-way analysis. Pa rallel factor analysis (PARAFAC) was employed to analyse the 3-way data arr ay generated: "emission lines x replicates x operating conditions". The phy sical interpretation of the new PARAFAC-factors is shown to enable a better understanding of the drift phenomenon by mathematically characterising the causes of long-term instability. Finally, the robustness of the technique using different operating conditions is evaluated and the appropriate use o f internal standards to correct for drift is discussed.