Parts-Per-Billion Fourier Transform Ion Cyclotron Resonance Mass Measurement Accuracy with a “Walking” Calibration Equation

• Published in: Analytical chemistry (Washington) 2011-03, Vol.83 (5), p.1732-1736
• Main Authors: Savory, Joshua J, Kaiser, Nathan K, McKenna, Amy M, Xian, Feng, Blakney, Greg T, Rodgers, Ryan P, Hendrickson, Christopher L, Marshall, Alan G
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Calibration; Chemistry; Exact sciences and technology; Fourier transforms; Ions; Particle accelerators; Sorption; Spectrometric and optical methods
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac102943z

Ion cyclotron resonance frequency, f, is conventionally converted to ion mass-to-charge ratio, m/z (mass “calibration”) by fitting experimental data spanning the entire detected m/z range to the relation, m/z = A/f + B/f 2, to yield rms mass error as low as ∼200 ppb for ∼10 000 resolved components of a petroleum crude oil. Analysis of residual error versus m/z and peak abundance reveals that systematic errors limit mass accuracy and thus the confidence in elemental composition assignments. Here, we present a calibration procedure in which the spectrum is divided into dozens of adjoining segments, and a separate calibration is applied to each, thereby eliminating systematic error with respect to m/z. Further, incorporation of a third term in the calibration equation that is proportional to the magnitude of each detected peak minimizes systematic error with respect to ion abundance. Finally, absorption-mode data analysis increases mass measurement accuracy only after minimization of systematic errors. We are able to increase the number of assigned peaks by as much as 25%, while reducing the rms mass error by as much as 3-fold, for significantly improved confidence in elemental composition assignment.