Decomposition Kinetics of Nitroglycerine·Cl^–(g) in Air at Ambient Pressure with a Tandem Ion Mobility Spectrometer

Abstract

A dual-shutter ion mobility spectrometer operating at atmospheric pressure and interfaced to a gas chromatograph for sample introduction has been used to study the reaction of Cl(-) with explosives. Of particular interest was an investigation of the formation of NO3(-) from the reaction of the Cl(-) with nitroglycerin (NG). The adduct NG·Cl(-) together with NO3(-) and NG·NO3(-) compose the mobility spectrum. Over the temperature range 111 to 122 °C, NG·NO3(-) is stable, but NG·Cl(-) decomposes to NO3(-) and 1,2-dinitro-3-chloropropane (DNClP). The activation energy and pre-exponential factor for this first order decomposition are 80 ± 3 kJ mol(-1) and 1.3 × 10(12) s(-1), respectively. Ab initio calculation shows that the reaction is a substitution reaction occurring over a two well potential energy profile with stable ion-molecule complexes NG·Cl(-) and DNClP·NO3(-).

Lifetimes and stabilities of familiar explosive molecular adduct complexes during ion mobility measurements

“…This can be challenging with explosive molecular ions which may exhibit brief lifetimes and undergo reactions or decompositions in either the reaction region or in the drift region. 9, 10 While sufficient understanding existed on the ionization chemistry and stability of ions in air at ambient pressure to justify the development of ETDs based on IMS, precise knowledge of the kinetics of ion decompositions and even the means to measure ion lifetimes in air at ambient pressure were not developed until recently.…”

“…14 Reactions including loss of NO 3 − and Cl − from thermalized ions require energy which has been measured with the kinetic IMS method as 60 to 89 kJ/mol and match favorably with ab initio calculations. 9, 10 These reactions are dependent not only on temperature and moisture but also on the precursor ion. While commercial ETDs produce Cl − by dissociative electron capture in a beta emitter source, electrospray ionization (ESI) sources affords flexibility and convenience to form adducts from other anions by spiking the ESI starting solution with various salts.…”

Atmospheric pressure chemical ionization of explosives induced by soft X-radiation in ion mobility spectrometry: mass spectrometric investigation of the ionization reactions of drift gasses, dopants and alkyl nitrates

“…The most important product ion used to verify the presence of alkyl nitrates in IM spectrometry is the adduct ion [M + Cl] – . DFT calculations suggest that the binding energy of the adduct ion [NG + Cl] – (−117 kJ/mol) is higher than that of the adduct ion [NG + NO 3 ] – (−96 kJ/mol) . A consequence of this affinity of the alkyl nitrates to Cl – is its application as a dopant ion.…”

“…The latter can be the result of two reaction channels. In the temperature range of 111–122 °C, the complex ion [NG + Cl] – possesses a limited stability and decomposes into NO 3 – and 1,2‐dinitro‐3‐chloropropane . The NO 3 – thus released can subsequently react with neutral NG yielding the [NG + NO 3 ] – adduct ions.…”

Tandem differential mobility spectrometry with ion dissociation in air at ambient pressure and temperature

“…This produces a negative alpha function and negative ΔK where the ion peak is displaced from 0 CV, opposite in polarity to ions with the positive ΔK values. 27 These studies demonstrated that ion dissociations and fragmentations can be controlled by the effective temperature of ions, T eff , and reactions occur on timescales of mobility measurements at ambient pressure. Ions between 100 and 300 Da may exhibit a positive alpha function in early stages of E/N, which turns negative when the ion is declustered at large E/N, leaving only the increased resistance to motion by collisions.…”