Abstract-The relatively minor instrumental modifications necessary to allow the operation of a CEC-21-11OB mass spectrometer at pressures as high as 0.5 torr are discussed. The chemical ionization mass spectra of a series of substituted benzophenones have been investigated with several reactant gases: methane, ethane, propane and isobutane. The spectra and behavior of these gases are discussed in general and the specific fragmentation processes of these substituted benzophenones with propane are presented in some detail. Table 1 shows chemical ionization spectra obtained on our instrument at about I50 to 180°C and repeller = 0 V at a methane pressure of 0.30 torr. These data are compared with some previously reported at a methane pressure of 1.00 torr. The agreement is fair: there are appreciable differences in the relative concentrations of some of the major ions. The most reasonable explanation for this disagreement is an effect of pressure outside the source. Wojcik and Futrell report good agreement with the earlier data of Table 1 at pressures up to 1 torr.5bThe variation of spectra with pressure is shown in Fig. 1

The chemical ionization mass spectra of several hydroxy steroids were obtained using methane as the reactant gas. The spectra are much less complex than the electron ionization spectra and little fragmentation of the steroid nucleus is observed. The major fragment ions involve the loss of water from [M + HI+. A 3-keto group in the steroids was characterized by an abundant [M + C,H,]+ ion. 5a-and 5p-Dihydrotestosterone could be distinguished by their spectra, with H, as the reactant gas by marked differences in amounts of [M + HI+, [M + H -H,O]+ and [M + H -

CHs's on tertiary C's), 1.95 (s, 1, H on C with -NHC02Et). The two methyl groups on each of the four secondary insertion products should each appear as a doublet. The singlet listed at 0.87 is the envelope of these closely spaced, unresolved doublets. The primary insertion product was not present in sufficient quantity for analysis and assignment was based on retention time and selectivity data.The stereospecificty and selectivity were then calculated from the peak areas in the usual manner.The absolute yield was determined by using acetophenone as an external standard. Total moles of insertion product was then calculated from the area/mol for acetophenone using the calibration factor of 0.78 for the products relative to acetophenone. It was assumed that all the insertion products have the same detector sensitivity.

The CI mass spectra of aryl ketones, +COR, were studied and found to give primarily

No abstract