Quantification of discharge gas to optimize discharge parameters for relative sensitivity factors (RSFs) determination by slow-flow glow discharge mass spectrometry (GDMS)†
Accurate determination of impurities present in a matrix by glow discharge mass spectrometry (GDMS) requires use of relative sensitivity factors (RSFs). In general, RSFs are obtained from reference materials with a comparable matrix composition as that of the sample being measured. Further, RSFs are sensitive to variation in discharge conditions. Thus, in the present study, various combinations of glow discharge parameters, namely current, voltage and argon flow are studied on a powder certified reference material, NIST silicon 57b, using indium sheets. Likewise, quantification of discharge gas, argon is carried out to facilitate the optimization of GDMS parameters. Furthermore, discharge parameters leading to optimum crater in a flat silicon sample is also considered before selecting optimum discharge condition for RSFs determination. As a result, two sets of RSFs are built – one based on calibrated values reported by NIST and the other based on values obtained after analysis of the same powder by inductively coupled plasma mass spectrometry (ICP-MS). Both sets of RSFs are tested further using another powder certified reference material, NIST 195, using both certified and ICP-MS values. The results of this study indicate that there is no considerable variation in concentration for most of the elements/isotopes including argon when discharge current and voltage are in range of 2–3 mA and 1.2–1.4 kV, respectively. It is found that for most of the elements, RSFs built based on both ICP-MS analysis and certified NIST values give comparable result with error below 20%. However, calcium showed ∼80% discrepancy based on certified values as compared to ∼10% based on ICP-MS values.