Vertically resolved measurement of analyte emission was investigated as an on-line indicator for flagging matrix effects and system drift in inductively coupled plasma-atomic emission spectrometry. The method is based on the fact that plasma behavior and excitation conditions are heterogeneous along the ICP vertical axis. As a result, the relative magnitude and even the direction of the change in emission intensity caused by a matrix effect or system drift are not constant, but are functions of observation height in the plasma. Since the determined concentration of an analyte in a sample is proportional to the measured intensity, any change in matrix effects or system drift along the vertical profile will similarly shift the determined concentration, allowing the drift or interference to be detected. It was verified that the new method can successfully flag matrix interferences caused by a change in plasma conditions (so-called plasma-related matrix effects), a change in sample aerosol generation or transport (so-called sample-introduction-related matrix effects) or spectral interference from emission lines of the matrix. Similarly, the method responded effectively to system drift caused by a change in sample throughput, central-channel gas flow and plasma forward power.
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