Preprints
https://doi.org/10.5194/amt-2021-149
https://doi.org/10.5194/amt-2021-149

  07 Jun 2021

07 Jun 2021

Review status: this preprint is currently under review for the journal AMT.

Correcting Bias in Log-Linear Instrument Calibrations in the Context of Chemical Ionization Mass Spectrometry

Chenyang Bi1, Jordan E. Krechmer2, Manjula R. Canagaratna2, and Gabriel Isaacman-VanWertz1 Chenyang Bi et al.
  • 1Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24060, USA
  • 2Aerodyne Research Inc., Billerica, Massachusetts 01821, USA

Abstract. Quantitative calibration of analytes using chemical ionization mass spectrometers (CIMS) has been hindered by the lack of commercially available standards of atmospheric oxidation products. To accurately calibrate analytes without standards, techniques have been recently developed to log-linearly correlate analyte sensitivity with instrument operating conditions. However, there is an inherent bias when applying log-linear calibration relationships that is typically ignored. In this study, we examine the bias in a log-linear based calibration curve based on prior mathematical work. We quantify the potential bias within the context of a CIMS-relevant relationship between analyte sensitivity and instrument voltage differentials. Uncertainty in three parameters has the potential to contribute to the bias, specifically the inherent extent to which the nominal relationship can capture true sensitivity, the slope of the relationship, and the voltage differential below which maximum sensitivity is achieved. Using a prior published case study, we estimate an average bias of 30%, with one order of magnitude for less sensitive compounds in some circumstances. A parameter-explicit solution is proposed in this work for completely removing the inherent bias generated in the log-linear calibration relationships. A simplified correction method is also suggested for cases where a comprehensive bias correction is not possible due to unknown uncertainties of calibration parameters, which is shown to eliminate the bias on average but not for each individual compound.

Chenyang Bi et al.

Status: open (until 02 Aug 2021)

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Chenyang Bi et al.

Chenyang Bi et al.

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Short summary
Calibration techniques have been recently developed to log-linearly correlate analyte sensitivity with CIMS operating conditions particularly for compounds without authentic standards. In this work, we examine the previously ignored bias in the log-linear based calibration method and estimate an average bias of 30 %, with one order of magnitude for less sensitive compounds in some circumstances. A step-by-step guidance was provided to reduce and even remove the bias.