An Ultra-Sensitive Mass Spectrometer System for Quantitative Biological Studies

A dedicated minicomputerized high pressure ionization mass spectrometer with pulse-counting electronics was developed for quantitative biological studies using the molecular isotope dilution method. The two-chamber differentially pumped vacuum system maintained by two 800 1/s turbomolecular pumps contains a 3/8" quadrupole analyzer, ion detector, and low pressure ion collection optics. Ions that are produced in the ion-molecule reaction chamber and initiated by the 63 Ni source are carried through a 40 μm aperture by the N 2 gas jet. The low pressure optics focus the ions into the quadrupole mass spectrometer while the bulk of the gas is pumped away. The signal from the pulse-counting detector is transmitted directly to a PDP 8/e minicomputer via an optically isolated, specially designed interface unit. Sensitivity in the single-ion monitoring mode for 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (5fg) has been determined.