Direct analysis of tramp elements in steel by radio-frequency glow discharge optical emission spectrometry associated with bias-current introduction - The application to quantitative determination of tin

A radio-frequency glow discharge optical emission spectrometry is applied to perform rapid and quantitative analysis of tin, which is included in commercial steels as a typical tramp element. The measuring method to introduce a bias current into the glow discharge plasma is effective for enhancing the emission intensity and thus improving the detection sensitivity. Two atomic emission lines of tin: SnI 303.411 nm and SnI 317.504 nm, can be selected as the analytical line for the determination of tin in steels. By conducting the bias current of 52 mA at the r.f. power of 120 W, their emission intensities are 14 times larger than those obtained with the conventional plasma. In the case of Sal 303.411 nm, a calibration curve almost passing through the origin is obtained. leading to the limit of determination of less than 0.01 mass% Sn (several 10 ppm Sn). However, if the sample contains chromium, CrI 303.419 nm may interfere with the accurate estimation of the SnI intensity. On the other hand, major alloyed elements including chromium have no emission lines overlapping with SnI 317.504 nm, although a weak FeII line overlaps just with the tin line which gives a calibration curve not passing through the origin. When SnI 317.504 nm is employed as the analytical line, the limit of determination can be estimated to be about 0.01 mass% Sn.