Digitally synthesized high purity, high-voltage radio frequency drive electronics for mass spectrometry

Abstract

Reported herein is development of a quadrupole mass spectrometer controller (MSC) with integrated radio frequency (rf) power supply and mass spectrometer drive electronics. Advances have been made in terms of the physical size and power consumption of the MSC, while simultaneously making improvements in frequency stability, total harmonic distortion, and spectral purity. The rf power supply portion of the MSC is based on a series-resonant LC tank, where the capacitive load is the mass spectrometer itself, and the inductor is a solenoid or toroid, with various core materials. The MSC drive electronics is based on a field programmable gate array (FPGA), with serial peripheral interface for analog-to-digital and digital-to-analog converter support, and RS232/RS422 communications interfaces. The MSC offers spectral quality comparable to, or exceeding, that of conventional rf power supplies used in commercially available mass spectrometers; and as well an inherent flexibility, via the FPGA implementation, for a variety of tasks that includes proportional-integral derivative closed-loop feedback and control of rf, rf amplitude, and mass spectrometer sensitivity. Also provided are dc offsets and resonant dipole excitation for mass selective accumulation in applications involving quadrupole ion traps; rf phase locking and phase shifting for external loading of a quadrupole ion trap; and multichannel scaling of acquired mass spectra. The functionality of the MSC is task specific, and is easily modified by simply loading FPGA registers or reprogramming FPGA firmware.

Accurate Xe Isotope Measurement Using JPL Ion Trap

“…Errors in mass determination are mainly caused by voltage fluctuations, space charge effects, and long-term drifts caused by temperature variations. Voltage fluctuations are compensated for using custom electronics stabilization design described elsewhere [17]. Space charge reduces the trapping efficiency and limits the maximum ion density within the device.…”

“…In the latter case, JPL-QIT serves primarily as the high mass sensor (up to 1000 u) but with relatively low mass resolution [15]. General description of the quadrupole ion trap can be found elsewhere [16], whereas here we focus on the specifics of the JPL-QIT mechanical design as well as the electrical radio frequency (rf) drive [17] relevant for the Xe isotopic measurements.…”

“…The rf power supply is described in detail elsewhere [17], and here we report only recent modifications regarding the introduction of the feedback loop necessary to stabilize the rf drive, that is to say, the output of the rf board was capacitively divided by 1000 and fed to the envelope converter (gives RMS value of the rf signal) and further processed by an analog-to-digital converter (ADC) to a number that corresponds to the ramp height in peak-voltage mode control. Output of the voltage divider is also synchronized in the same manner.…”

Higher order parametric excitation modes for spaceborne quadrupole mass spectrometers

“…FPGA-based control of quadrupoles has been previously studied and successfully implemented in the laboratory. 23,24 FPGA technology has also been successfully flown on spacecraft, 25 making these devices a suitable medium for development. While not a tremendous problem for terrestrial applications, the stability of the quadrupole RF source is an issue for space sensors due to the mass and power limitations of the instrument, as well as the large variations in ambient temperature that the instrument is likely to encounter.…”