One of the important instruments in the field of analytical chemistry is the Mass Spectrometer (MS). In an MS, the analyte molecules are ionized and are then transferred to a mass analyzer, where their mass to charge (m/z) ratios are measured. One type of mass analyzer is the quadrupole mass filter, which has a scan-like operating procedure: The voltages on its rods (including an RF voltage), if kept constant, allow only a small range of m/z values to pass and reach the ion detector, while all the other ions collide with the rods and neutralize. By varying the rod voltages quickly and repeatedly, a scan over a range of the desired m/z values is performed.

Before the analyte molecules reach the quadrupole they must first be ionized. In most cases, when the MS is coupled with a Gas Chromatograph (GC) (and in some cases with a Liquid Chromatograph (LC)), the Electron Ionization (EI) ion source is used. After the ionization step, the ions pass through a series of ion-lenses that focus and guide them into the mass analyzer. The voltages on these lenses can be optimized for each specific m/z value to increase the amount of ions reaching the quadrupole. It can be beneficial, in terms of sensitivity, for the voltages on these ion-lenses to be synchronized with the quadrupole voltages scan, so that all the ion manipulating elements are perfectly tuned to the same specific m/z value at any given time. In certain cases this dynamic mass-dependent optimization of the lenses can increase the signal by a factor of 2 or more.

This work describes an implementation of such optimization and the synchronization between the ion-lenses and the quadrupole. To implement a dynamic mass-dependent optimization controller, a digital circuit based on a DSP and high voltage amplifiers was developed. A fast algorithm was used in order to calculate the optimized voltages in real time (using interpolation), utilizing only a small amount of memory. The controller can optimize up to 8 independent high voltage channels ranging between ±150 V at a rate of 100 ms, and can work in two operation modes: static and dynamic.