On the use of line intensity ratios and power adjustments to control matrix effects in inductively coupled plasma optical emission spectrometry

In inductively coupled plasma optical emission spectrometry, matrix effects can be substantially reduced by applying robust operating conditions, i.e. a high rf power level and a low nebulizer gas flow. However, dissimilar line intensity changes are still observed, in particular with varying salt matrices. Calcium and, to a lesser extent, Mg induce stronger effects than Na and K. In 0.1, 0.3 and 1.0% Ca matrices, signal changes for 29 atomic as well as ionic lines have been determined with respect to the Ca-free solution. The changes range from –5 to –30% for the 1.0% Ca matrix. Starting from robust conditions in radial viewing, the rf power has been adjusted until the Cr ion-to-atom line ratio measured for the calcium solutions equalled the ratio determined during the calibration (0% Ca). By this power adjustment, the changes are within ±4%. No matrix effects originating from the sample introduction system are observed, probably due to the high acid concentrations used. The practical application of power adjustments is illustrated with results for certified sediment samples and with multiple line analysis for qualitative and semiquantitative analysis. The approach is an attractive alternative to matrix matching or standard additions. Internal standardization based on one atomic and one ionic line of the same element is indicated as another possibility.