Computer-Controlled Peak-Top Search Procedure
Computerized acquisition of mass spectral data in the pulse-counting mode requires that the mass position be represented by a voltage that can be controlled by the computer. In a magnetic instrument operating at a fixed accelerating voltage, this is most easily accomplished by using a Hall probe to sense the magnetic field. A calibration function can then be established between analyzed mass and Hall voltage. However, this function may change slightly with time as a result of thermal effects or magnetic hysteresis. It is therefore advantageous to have an automatic procedure controlled by the computer that efficiently seeks the top of a mass peak from a starting point determined by the calibration function. A three-stage procedure has been developed for use on an ARL IMMA, and will be explained in detail in this paper.