Precise Estimation of Emission Intensity of Alloyed Elements in Steel by Using Internal Standard Line in Glow Discharge Optical Emission Spectrometry

Precision in the emission intensity measurement of alloyed elements in steel is investigated when an emission line of iron is employed as an internal standard in d.c. glow discharge optical emission spectrometry. Long-term variations in their emission intensities can be well corrected using the internal standard of the iron emission line, probably because the fluctuation in the sputtering rate of samples is a major reason for their intensity variations. For instance, in an Fe-Cr alloy sample (Cr 0.50 mass%), the relative standard deviation (RSD) of the emission intensity of Cr I 425.433 nm is 0.678% with the internal standard method whereas the RSD is 2.14% without the internal standard. Also, daily variations in calibration curves are much suppressed by using the internal standard line. For instance, in Fe-V alloy samples, the RSDs of the calibration factor for vanadium analytical lines are 1.10-1.84%, which means that a re-calibration procedure is hardly needed for the analytical application. The internal standard method contributes to the precise determination of minor alloyed elements in steel samples.