Recently, hydrogen plasma arc melting (HPAM) has been expected to be a practical melting and refining technique for metals and alloys. The effect of $H_2$ addition to the Ar plasma gas on the purification of metals and alloys has been described by possible chemical reactions of impurities with activated hydrogen atoms on a molten metal as well as the increase in temperature of a metal surface. Trace impurity concentration of refined metals is determined using glow discharge mass spectrometry (GDMS). This method is used to determine trace elements quantitatively because GDMS is a direct solid-state analytical method that uses no chemical process and provides reliable quantitative concentrations for most elements below 0.01 ppm. We reviewed the refining effect of HPAM for several metals by trace impurity analysis using GDMS.