An optimization of transmission measurement of an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF MS)

Abstract

Evaluating an instrument's performance is just as important, if not more, than its intended purpose. Mass spectrometers, in particular, have been extensively studied and analyzed due to their key role in many applications across various fields. One type of mass spectrometer, the atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF MS), is widely used for measuring reactive trace gases and aerosol precursors. This study investigates the transmission efficiency of an APi-ToF MS coupled with two distinct ionization sources: an electrospray ionizer (ESI) and a nickel–chromium wire generator. Each ion source was integrated into a separate experimental setup, with the ESI paired with a planar differential mobility analyzer (P-DMA) and the wire generator combined with a Half-mini differential mobility analyzer (Half-mini DMA). The transmission efficiency was quantified by calculating the ratio of ions entering the mass analyzer to those detected at the end detector. The primary aim of this study is twofold: (1) to develop and validate a standardized procedure for quantifying transmission efficiency in APi-ToF MS systems, and (2) to critically evaluate an alternative measurement approach using a distinct ionization–mobility setup. We propose an optimized protocol for assessing transmission efficiency, providing a framework that future researchers can adapt to characterize their own instruments. Our results reveal different transmission trends between negative and positive samples, and compares the different methods explored in this study with each other and with previous studies. The ESI–P-DMA–APi-ToF MS setup was shown based on our results to be significantly more accurate, mainly since the errors on the mass/charge axis are remarkably lower, than the wire generator–Half-mini DMA–APi-ToF MS setup in determining the transmission efficiencies.