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.

Inductively coupled plasma optical emission spectrometry with axially viewed configuration: an overview of applications

“…Similar self-absorption effects were observed when axially and radially viewed systems were compared, 20 with a better signal-to-noise ratio for the axially viewed equipment. However, self-absorption effects for resonant lines were more evident in the axially viewed system.…”

“…The authors concluded that the axial mode seemed to have definitive advantages over radial viewing. 20 Similar conclusions were presented when figures of merit of both systems were compared. 70 Axially viewed configuration presented better detection power, even when complex samples were analysed.…”

“…According to Chausseau et al, 20 the poor reputation of axial viewing with regard to self-absorption effects seems to be "unjustified" and this viewing mode "has definite advantages over radial viewing".…”

“…In addition, resonant lines are more sensitive to auto-absorption effects than non-resonant lines, even under robust conditions. 20 Analysis of these publications indicate the complexity of the matrix effects in ICP OES. However, accuracy was improved when Sb, Sc, Y, or Be were used as internal standards in axially viewed ICP OES.…”

Atomic emission spectroelectrochemistry applied to dealloying phenomena: I. The formation and dissolution of residual copper films on stainless steel

“…Concentrations higher than 10 mg/l were not used in this work so as to avoid contaminating the nebulization system, however linearity is normally maintained to concentrations above 100 mg/l. Deviations from linearity at high concentration are due to self-absorption [40] in which photons emitted in the center of the plasma are absorbed by unexcited atoms in the cooler outer part of the plasma. Table 2 gives the performance conditions typical of the experiments performed in this work.…”