Sensitivity and selectivity of switchable reagent ion soft chemical ionization mass spectrometry for the detection of picric acid

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  • Bishu Agarwal
  • Matteo Lanza
  • Philipp Sulzer
  • Tilmann D. Märk
  • Chris A. Mayhew


We have investigated the reactions of NO+, H3O+, O2+, and Kr+ with picric acid (2,4,6 trinitrophenol, C6H3N3O7, PiA) using a time-of-flight mass spectrometer with a switchable reagent ion source. NO+ forms a simple adduct ion PiA·NO+, while H3O+ reacts with PiA via nondissociative proton transfer to form PiAH+. In contrast, both O2+ and Kr+ react with PiA by nondissociative charge transfer to produce PiA+. For Kr+, we also observe dissociation of PiA, producing NO2+ with a branching percentage of approximately 40%. For the reagent ions H3O+ and O2+ (and operating the drift tube with normal laboratory air), we find that the intensities of the PiAH+ and PiA+ ions both exhibit a peak at a given drift-tube voltage (which is humidity dependent). This unusual behavior implies a peak in the detection sensitivity of PiA as a function of the drift-tube voltage (and hence E/N). Aided by electronic-structure calculations and our previous studies of trinitrotoluene and trinitrobenzene, we provide a possible explanation for the observed peak in the detection sensitivity of PiA.


Original languageEnglish
Pages (from-to)8229-8236
Number of pages8
JournalThe Journal of Physical Chemistry A
Issue number37
Early online date17 Mar 2014
Publication statusPublished - 18 Sep 2014