Sa. Pergantis et al., ACCURATE MASS MEASUREMENTS OF POSITIVE-IONS IN THE DESORPTION CHEMICAL-IONIZATION MODE, Organic mass spectrometry, 29(8), 1994, pp. 439-444
Desorption chemical ionization mass spectrometry employing ammonia as
the reagent gas has been extensively used to obtain molecular mass and
structural information on a wide variety of compounds. Mass-deficient
reference standards normally used for calibration purposes in mass sp
ectrometry do not provide adequate mass spectra under ammonia chemical
ionization conditions. In order to overcome this problem a mixture of
ammonia and methane as reagent gases was employed. In high-resolution
accurate mass measurement experiments, this gas mixture allows the si
multaneous detection of mass spectra of perfluorokerosene adequate for
calibration purposes and spectra containing molecular mass informatio
n of the analyte. A needle valve system was used to control the compos
ition of the gas mixture introduced into the ion source. For positive-
ion accurate mass measurements of higher masses (up to m/z = 2300), Fo
mblin 18/8 oil was successfully used as a reference standard under amm
onia, methane and isobutane desorption chemical ionization conditions.