An automated gas chromatography time-of-flight mass spectrometry instrumentfor the quantitative analysis of halocarbons in air

[摘要] We present the characterization and application of a new gaschromatography time-of-flight mass spectrometry instrument (GC-TOFMS) forthe quantitative analysis of halocarbons in air samples. The setup comprisesthree fundamental enhancements compared to our earlier work (Hokeret al., 2015): (1) full automation, (2) a mass resolving power R = m/Δm of the TOFMS (Tofwerk AG, Switzerland) increased up to 4000 and (3) a fully accessible data format of the mass spectrometric data.Automation in combination with the accessible data allowed an in-depthcharacterization of the instrument. Mass accuracy was found to beapproximately 5 ppm in mean after automatic recalibration of the mass axisin each measurement. A TOFMS configuration giving R = 3500 was chosen toprovide an R-to-sensitivity ratio suitable for our purpose. Calculateddetection limits are as low as a few femtograms by means of the accuratemass information. The precision for substance quantification was 0.15 %at the best for an individual measurement and in general mainly determinedby the signal-to-noise ratio of the chromatographic peak. Detectornon-linearity was found to be insignificant up to a mixing ratio of roughly150 ppt at 0.5 L sampled volume. At higher concentrations, non-linearitiesof a few percent were observed (precision level: 0.2 %) but could beattributed to a potential source within the detection system. Astraightforward correction for those non-linearities was applied in dataprocessing, again by exploiting the accurate mass information. Based on theoverall characterization results, the GC-TOFMS instrument was found to bevery well suited for the task of quantitative halocarbon trace gasobservation and a big step forward compared to scanning, quadrupole MS withlow mass resolving power and a TOFMS technique reported to be non-linear andrestricted by a small dynamical range.

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