Iterative Method for Mass Spectra Recalibration via Empirical Estimation of the Mass Calibration Function for Fourier Transform Mass Spectrometry-Based Petroleomics

We describe a mass spectra recalibration method, which enables analysis of petroleum samples with Orbitrap FTMS. In this method, the mass calibration function is estimated on the basis of mass-to-charge ratios and abundances of internal calibrants without a need for theoretical description of residual mass errors. Importantly, to maximize the estimation accuracy of the mass calibration function, an iterative approach is implemented to obtain sufficiently high number of internal calibrants covering the entire ranges of mass-to-charge ratios and abundances of interest. For petroleomic samples, the method routinely provides root-mean-square (RMS) mass accuracies at sub-ppm level and hence allows for reliable assignment of elemental compositions. Moreover, since the achieved mass accuracies are normally limited only by random errors of low-abundance analytes, the method maximizes the range of abundances of assignable species for a given signal-to-noise ratio of experimental data. Additionally, despite being initially developed for Orbitrap FTMS, the method is likewise applicable for ion cyclotron resonance FTMS.