Self-absorption effects in radially and axially viewed inductively coupled plasma-atomic emission spectrometry – the key role of the operating conditions

Abstract

Self-absorption effects leading to curvatures of the upper part of calibration graphs were investigated in multichannel detection ICP–AES. A dual view Optima 3000 ICP system was used to enable the simultaneous determination of 38 lines for both radial and axial viewing. Resonance and non-resonance lines were selected for both atomic and ionic lines. The concentrations of 22 standards were in the range 0.1–100 mg L^–1 and two sets of operating conditions, namely power and carrier gas flow rate, were used to evaluate their influence. It was found that these two conditions, and in particular the carrier gas flow rate, play a major role in self-absorption effects. Except for strongly absorbing lines, it was possible, under suitable conditions, to reduce or to suppress differences between self-absorption effects in radial and axial viewing, enabling extension of the range of linearity of axial viewing to higher concentrations. A diagnostic tool, based on emission line ratios, is proposed for detection of self-absorption. A calibration procedure is given for strongly absorbing lines affected by self-absorption even when operating conditions were optimized.