ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
1781
Electron Capture Negative Ion Chemical Ionization Mass Spectrometry Donald F. Hunt* and Frank W. Crow Department of Chemistry, University of Virginia, Charlottesville, Virginia 2290 7
I n this paper we discuss the analytical potential of electron capture negative ion chemical ionization mass spectrometry, provide data which define the lowest level of sample detection achieved with our present instrument configuration, and furnish experimental details on the operation of a negative ion chemical ionization quadrupole mass spectrometer. Detection of dopamine, amphetamine, and A9-tetrahydrocannabinol derivatives at the attomole ( level by conventional GCMS selected ion monitoring methodology is reported.
In an earlier paper we described new methodology, pulsed positive ion-negative ion CI (PPINICI) ( I ) , which facilitates simultaneous recording of positive and negative ion CI spectra on a quadrupole mass spectrometer. Also discussed were unique analytical applications of several negative ion chemical ionization (NICI) reagent gases and t h e capability of NICI to provide conformation of sample molecular weight, structural information complementary to t h a t obtained in the positive ion mode of operation, and sample ion currents 100 to 1000 times greater than that available from positive ion methodology. It was also suggested that electron capture NICI would facilitate detection and quantitation of many organics a t the 10-'*-10-13 g level and therefore would find widespread use as a technique for the quantitation of trace level mixture components by combined GC-MS. In this paper we discuss the analy+cal potential of electron capture NICI in greater detail, provide data which define the lowest level of sample detection achieved using electron capture NICI with our present instrument configuration, and furnish additional experimental details on t h e operation of a NICI quadrupole mass spectrometer. Papers describing unusual negative ion-molecule isotope exchange reactions ( 2 ) ,the utility of OH- as a CI reagent ion (31, electron capture NICI methodology for detecting metal chelates (41, and t h e first biological assay using t h e GC-MS electron capture NICI technique ( 5 ) have appeared recently. A review of negative ion CIMS (6) and a paper reporting negative ion studies under atmospheric pressure ionization conditions have also been published (7). EXPERIMENTAL General. All spectra were recorded on a Finnigan model 3300 quadrupole mass spectrometer (Finnigan Corp., Sunnyvale, Calif.), equipped with a standard CI source. Primary ionization of the CI reagent gas was accomplished using a 100-eV beam of electrons generated from a heated rhenium filament. Reagent gas and sample pressures were maintained at 0.6-0.8 Torr and
