Sensitivity and Selectivity of Switchable Reagent Ion Soft Chemical Ionization Mass Spectrometry for the Detection of Picric Acid

Abstract

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.

Evaluation of NO<sup>+</sup> reagent ion chemistry for online measurements of atmospheric volatile organic compounds

“…Alcohols and aldehydes can lose H 2 O, lowering the sensitivity to the protonated parent mass; their product ion masses then coincide with those of hydrocarbons, making independent measurement difficult (Španěl et al, 1997;Buhr et al, 2002). Furthermore, H 3 O + CIMS is not sensitive to small (∼ C 8 and smaller) saturated alkanes, as their proton affinities are lower than or very close to that of water (Arnold et al, 1998;Gueneron et al, 2015). This is a serious limitation in studies of urban air or emissions from oil and natural gas extractions, where small alkanes can contribute a large fraction to the total gas phase carbon and chemical reactivity (Katzenstein et al, 2003;Gilman et al, 2013).…”

“…SIFT methods use a quadrupole mass filter between the ion source and ion-molecule reactor, which provides a very pure reagent ion source but limits the primary ion signal. SIFT studies have identified the major products of the reaction of NO + with VOCs representative of many different functional groups (Španěl and Smith, 1996(Španěl and Smith, , 1998a(Španěl and Smith, , b, 1999Španěl et al, 1997;Arnold et al, 1998;Francis et al, 2007a, b). Aldehydes and ketones are easily separable: ketones cluster with NO + , forming mass (m + 30) ions, whereas aldehydes react by hydride abstraction, forming mass (m − 1) ions (where m is the molecular mass of the species).…”

“…Jordan et al (2009a) have developed a hollowcathode ion source capable of switchable reagent ion chemistry, and they demonstrated laboratory measurement with NO + of several aromatics, chlorinated aromatics, and carbonyls, with sensitivities comparable to H 3 O + CIMS. The NO + capability of the Jordan et al instrument has been used in the laboratory by Inomata et al (2013) to investigate detection of n-tridecane, by Agarwal et al (2014) to measure picric acid, and by Liu et al (2013) to investigate the be-havior of methyl vinyl ketone (MVK) and methacrolein in a reaction chamber.…”

Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives

“…There are several analytical techniques that belong to the DI-SCIMS category [38,39], with proton transfer reactionmass spectrometry (PTR-MS) arguably the most widespread. PTR-MS was purposely designed for the monitoring of volatile organic compounds (VOCs) [40], but has developed further to analyse liquid and solid compounds [38], being successfully applied to the detection of explosives and explosive-related compounds in positive-ion mode [41][42][43][44][45][46][47][48][49][50]. Technically speaking, PTR-MS only refers to the use of hydronium as the reagent ion.…”

Hyphenation of proton transfer reaction mass spectrometry with thermal analysis for monitoring the thermal degradation of retinyl acetate

“…Instead of hard ionization techniques, mass detectors based on soft ionization result in mass spectra that are easier to interpret . Among soft ionization mass detectors, proton transfer reaction mass spectrometry (PTR‐MS) has become a benchmark method for the simultaneous real‐time monitoring of VOCs . The working principle behind PTR‐MS is based on the protonation of volatile molecules (VOCs) with hydronium ions (H 3 O + ).…”