Abstract

The appearance time of an analyte relative to the timing of the sample probe insertion is an important factor that determines the integrated intensity and precision of direct sample insertion inductively coupled plasma atomic emission spectrometry. The ICP background drops significantly with the insertion of a sample probe. Matrix effects can be severe if the the analyte appearance times are shifted relative to the background drop. In this study, matrix effects of NaCl on the temporal emission profiles and integrated emission intensities of Zn I and Zn II were shown to relate to the appearance time of the analyte. The peak maxima of the temporal profiles of Zn I and Zn II emissions were displaced by about 0.2 s in an aqueous matrix, but the maxima coincided in NaCl matrices. In addition, integrated emission intensities of the more difficult to excite Zn II species increased with an earlier appearance time. The changes in peak profiles and relative intensities are due to redistribution in the proportion of Zn atoms and Zn ions in the vaporized Zn population. The effects of the appearance time of Zn were further demonstrated using different sample probe insertion speeds to change the appearance time of the analyte relative to the background drop.