Development of Negative ion proton transfer reaction time-of-flight mass spectrometry (NI-PTR TOF MS) for the measurement of gas phase acids in the troposphere

We report on progress in coupling of a flow reactor with a time of flight mass spectrometer (MS) for investigating trace organic acids in the troposphere via negative ion proton transfer reactions (PTR). Compared to other spectrometric methods, time-of-flight (TOF) has the advantage of superior mass resolution, higher sensitivity, wider mass range, and multiplexed spectral acquisition. The PTR is highly selective and yields unique ionic products reducing interference from other reactants. We focus on organic acids which play a key role in the acidity of atmospheric condensed water and acid precipitation. Much of the thermochemical and kinetic data for these reactions and their hydrates is not well quantified therefore several carboxylic acids and the hydration effects will be investigated to better understand the reaction rates, equilibrium constants, and free energies of these reactions. The fast time response and high sensitivity of the NI-PTR TOF MS method make it a promising technique for online measurement of trace organic acids. We report specifically on commissioning progress and some initial performance and characterization measurements. This work is supported in part by both NOAA (Award NA06OAR4810187) and NSF (award 0803016).