Uncertainty Estimations for Collision Cross Section Determination via Uniform Field Drift Tube-Ion Mobility-Mass Spectrometry.

Abstract

Uniform field drift tube ion mobility-mass spectrometry (DTIM-MS) has emerged as a valuable tool for a range of analytical applications. In focus here are standardized collisional cross section values from DTIM-MS (DTCCS) as a candidate identification point for various analytical workflows. Of critical importance in establishing this parameter as a valid identification point is a rugged estimation of uncertainties according to the procedures used for their derivation. Relying on the assumption of the zero-field limit, the primary method of measurement for DTCCS values involves experimental determination of arrival times of an ion measured at several different field strengths transiting a drift tube filled with high purity drift gas, while a method using measurements of external calibrants at a single field strength is employed to allow for online measurements of transient signals (e.g., chromatographic peaks). Both approaches are here considered with respect to the uncertainty of input experimental variables (temperature, pressure, voltages, physical constants) and the steps of the calibration function employed. Estimations of uncertainty were performed according to EURACHEM with Monte Carlo simulations and reveal that existing consensus calibration standards from experimental stepped-field IM-MS determinations have estimated expanded uncertainties in the range of 2.7 to 4.6% (k = 2). Application of these standards for calibration considering these input uncertainties reveals uncertainty estimates of 4.7-9.1% (k = 2) for measured values using an established single-field calibration approach. Finally, directions for improving this situation via new experimental efforts toward standard reference and calibration materials are presented.