In an r.f. glow-discharge plasma, a d.c. bias current can be introduced by connecting an electric circuit comprising a low-pass filter and a variable resistor. The bias current promotes the emission excitations in the plasma, leading to an improvement of the detection power in the optical-emission spectrometry. By conducting a bias current of 27 mA, the emission intensities of the atomic resonance lines were several-times larger than those obtained with conventional r.f.-powered plasmas. The detection limits for the determination of alloyed elements in Fe-based low-alloyed standard samples were estimated to be 2 ppm Mn for Mn I 403.08 nm, 2 ppm Al for Al I 396.15 nm, 7 ppm Si for Si I 288.158 nm, and 8 ppm Cr for Cr I 425.43 nm.
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