A computer program performs calculations to calibrate a quadrupole mass spectrometer in an instrumentation system for identifying trace amounts of organic chemicals in air. In the operation of the mass spectrometer, the mass-to-charge ratio (m/z) of ions being counted at a given instant of time is a function of the instantaneous value of a repeating ramp voltage waveform applied to electrodes. The count rate as a function of time can be converted to an m/z spectrum (equivalent to a mass spectrum for singly charged ions), provided that a calibration of m/z is available.
The present computer program can perform the calibration in either or both of two ways: (1) Following a databased approach, it can utilize the count-rate peaks and the times thereof measured when fed with air containing known organic compounds. (2) It can utilize a theoretical proportionality between the instantaneous m/z and the instantaneous value of an oscillating applied voltage. The program can also estimate the error of the calibration performed by the data-based approach. If calibrations are performed in both ways, then the results can be compared to obtain further estimates of errors.
This program was written by Seungwon Lee of Caltech for NASA's Jet Propulsion Laboratory.
This software is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (626) 395-2322. Refer to NPO-45181.
This Brief includes a Technical Support Package (TSP).
Calculations for Calibration of a Mass Spectrometer
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Overview
The document titled "Calculations for Calibration of a Mass Spectrometer" is a technical support package from NASA's Jet Propulsion Laboratory, focusing on the mass calibration process essential for the Vehicle Cabin Air Monitor (VCAM) Project. This calibration is critical for converting raw mass spectrum data into mass-to-charge ratios, which are necessary for identifying various compounds in gas chromatograms.
The mass calibration process is outlined in a series of steps. Initially, a total ion chromatogram is created by summing ion counts over channels for each scan time. The calibration involves identifying channel peaks from elution peaks, starting with the air elution peak. The two largest channel peaks from the air peak are assigned calibration masses of 28 and 32, forming channel-mass pairs. These pairs are then used to derive a linear equation that relates channel numbers to mass.
If additional elution peaks, such as those from acetone, are identified, further channel peaks are analyzed. The two largest channel peaks from the acetone elution are assigned calibration masses of 43 and 58, and these pairs are combined with the air peak pairs to refine the calibration. The document emphasizes the importance of estimating errors from the linear equations derived from these channel-mass pairs. The maximum error is determined for both scenarios: using only the air peak and using both air and acetone peaks.
The final calibration success is determined by comparing the maximum error against a threshold of ±0.2 amu. If the error is within this range, the calibration is deemed successful; otherwise, it fails. Additionally, an alternative method for mass calibration using Mathieu’s equation is mentioned, which provides a theoretical framework independent of the data-based method. This serves as a sanity check against the empirical results.
Overall, the document provides a comprehensive overview of the methodologies and calculations involved in mass spectrometer calibration, highlighting the significance of accurate mass-to-charge ratio determination for effective gas analysis in aerospace applications. It serves as a valuable resource for researchers and engineers involved in mass spectrometry and related fields.
