A re-calibration procedure for interoperable lipid collision cross section values measured by traveling wave ion mobility spectrometry

Abstract

Collision cross sections (CCS) have been described as relevant molecular descriptors in metabolomics and lipidomics analyses for ascertaining compound identity. Ion mobility spectrometry (IMS) allows to determine CCS with different techniques, such as drift tube ion mobility spectrometry (DTIMS), traveling wave ion mobility spectrometry (TWIMS) or trapped ion mobility spectrometry (TIMS). In contrast with DTIMS where CCS can be obtained directly with measured drift times and mathematical relationship, TWIMS and TIMS techniques require an additional step of calibration to obtain CCS values. However, literature reports significantly disparate CCS values depending on the calibrant used (often more than 10%), as no consensus has been reached to define a universal CCS reference standard or harmonized calibration procedure. Therefore, publicly available CCS databases cannot be regarded as readily interoperable and exchangeable. Here, we performed a comprehensive evaluation of 11 distinct CCS calibrants in a traveling wave ion mobility spectrometry-mass spectrometry (TWIMS-MS) instrument. We showed that, using lipids from plasma as model compounds, CCS determination drastically fluctuates from one calibrant to the other with up to 25% differences, which precludes direct CCS comparison. Using the large panel of calibration curves generated, we showed that any CCS value can be efficiently re-calibrated relatively to the calibration curve made with the widely used Tune Mix solution whatever the calibration procedure originally used. The re-calibrated CCS values for each calibrant constitute a database which allows to correct any deviation on lipid CCS values whatever the calibrant originally used. Resulting corrected CCS values from plasma lipids were thus efficiently matched to those previously reported in the literature (with deviations<2%). Therefore, this work shows that unique and comparable CCS values can be obtained upon re-calibration relatively to Tune Mix CCS values, while also paving the way for the establishment of a universal CCS database of various metabolite or lipid classes.

Keywords: Collision cross section; Ion mobility calibration; Ion mobility-mass spectrometry; Lipidomics; Metabolomics; TWIMS.