Investigation of ionization processes in a pulsed glow-discharge mass spectrometric ion source

The pulsed glow-discharge ion source is installed in a MC7303 commercial mass spectrometer. The effect of the voltage pulse width and rate on the output ion current of the sample was studied. It has been shown that the discharge conditions differently affect the output intensities of ions of different nature. Under the discharge conditions optimal for the sample ion formation, the intensity of argon and organic fragment ions decreases. This allows one to reduce the influence of spectral overlapping and make easier mass spectrum treatment, especially for low-resolution instruments. The obtained mass spectra demonstrate that the MC7303 mass spectrometer with the pulsed glow-discharge ion source can provide 10 ppm impurity detection limits at a resolution of 1-1.5 M at 50 % peak height level, which is enough for routine elemental analyses of solid samples as is the mass spectrometer mass range from 1 to 500. It is shown that pressure stability of argon in a discharge chamber is critical for the stability of discharge conditions and reproducibility of results. To maintain the output current stability at a 3 % level, the pressure stability should be as high as 0.1 %.