Fast mass programming and PWM controllers for super sonic GC-MS using DSP

In a Gas Chromatograph Mass Spectrometer (GC-MS) employing a quadrupole mass filter, molecules are ionized and transferred to a mass analyzer, where their mass to charge ratios (m/z) are measured. 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 (as the rest of the system is also optimized) to increase the amount of ions reaching the mass analyzer. In certain cases this dynamic mass-dependent optimization of the lenses can increase the signal by a factor of 2 or more. In addition, any GC-MS interface requires that the molecules vaporized and separated by the Gas Chromatograph (GC) will be transferred into the Mass Spectrometer (MS) at high temperature in order to avoid condensation. Any GC-MS and especially those with a supersonic molecular beams interface can benefit from the ability to change the temperature of this transfer-line between the GC and MS. To implement this dynamic optimization a digital circuit was developed, based on a digital signal controller and high voltage amplifiers that is able to optimize 8 independent high voltage channels ranging between ±150 V at a rate of 100 μs. In addition, 4 independent channels of high resolution PWM unit within the above mentioned controller was utilized in order to control the temperature.