A. G. Kuzmin, P. V. Mikhnovets
Institute for Analytical Instrumentation RAS, Saint-Petersburg
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 %.