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Chemical ionization tandem mass spectrometer for the in situ measurement of...
A new approach for measuring gas-phase methyl hydrogen peroxide ͓͑MHP͒ CH3OOH͔ utilizing chemical ionization mass spectrometry is presented. Tandem mass spectrometry is used to avoid mass interferences that hindered previous attempts to measure atmospheric CH3OOH with CF3O− clustering chemistry. CH3OOH has been successfully measured in situ using this technique during both airborne and ground-based campaigns. The accuracy and precision for the MHP measurement are a function of water vapor mixing ratio. Typical precision at 500 pptv MHP and 100 ppmv H2O is Ϯ80 pptv ͑2 sigma͒ for a 1 s integration period. The accuracy at 100 ppmv H2O is estimated to be better than Ϯ40%. Chemical ionization tandem mass spectrometry shows considerable promise for the determination of in situ atmospheric trace gas mixing ratios where isobaric compounds or mass interferences impede accurate measurements.