Averaging peak-to-peak voltage detector for absolute mass determination of single particles with quadrupole ion traps

A sine wave that controls a quadrupole ion trap is generated from a low voltage source, boosted to high voltage through a transformer. Since not even the best transformers can keep a flat amplitude response with respect to frequency, knowing the accurate peak-to-peak value of the sine wave is paramount when the frequency is varied. We have developed an averaging peak-to-peak voltage detector for such measurements and demonstrated that the device is an essential tool to make possible high-precision mass determination of single charged microparticles with masses greater than 1 × 10 11 u . Tests of the detector with sine waves from a FLUKE 5720A standard source in the neighborhood of 1400 V p p and frequencies ranging from 100 to 700 Hz showed a measurement accuracy better than 10 ppm . The detector settled within 5 s after each reset to 5 digits of DVM rock-steady reading, and the calibration against the same source after 3 weeks of continuous use of the circuit produced a mere overall 1 ppm difference.