NH4+ Association and Proton Transfer Reactions With a Series of Organic Molecules

Abstract

In this study, we present reactions of with a series of analytes (A): acetone (C 3 H 6 O), methyl vinyl ketone (C 4 H 6 O), methyl ethyl ketone (C 4 H 8 O), and eight monoterpene isomers (C 10 H 16 ) using a Selective Reagent Ionization Time-of-Flight Mass Spectrometer (SRI-ToF-MS). We studied the ion-molecule reactions at collision energies of 55 and 80 meV. The ketones, having a substantially lower proton affinity than NH 3 , produce only cluster ions (A) in detectable amounts at 55 meV. At 80 meV, no cluster ions were detected meaning that these adduct ions are formed by strongly temperature dependent association reactions. Bond energies of cluster ions and proton affinities for most monoterpenes are not known and were estimated by high level quantum chemical calculations. The calculations reveal monoterpene proton affinities, which range from slightly smaller to substantially higher than the proton affinity of NH 3 . Proton affinities and cluster bond energies allow to group the monoterpenes as a function of the enthalpy for the dissociation reaction . We find that this enthalpy can be used to predict the (A) cluster ion yield. The present study explains product ion formation involving ion chemistry. This is of importance for chemical ionization mass spectrometry (CIMS) utilizing as well as (H 2 O) as reagent ions to quantitatively detect atmospherically important organic compounds in real-time.

Detection of Triacetone Triperoxide (TATP) and Hexamethylene Triperoxide Diamine (HMTD) from the Gas Phase with Differential Ion Mobility Spectrometry (DMS)

“…The acetone residues reduced the detection capability of the DMS detector. The PA for acetone is 812 kJ/mol [ 38 ], which is lower than the PA of the added ammonia (853.6 kJ/mol [ 39 ]); therefore, the use of ammonium as an admixture in the carrier gas will help to reduce the appearance of acetone peaks. When detecting improvised explosives using differential ion mobility spectrometry, the carrier gas should be doped with a minimum of 200 ppb NH 3 to reduce the effect of acetone (TATP contamination).…”

Investigation of corona discharge ionization of barbituric acid using ion mobility spectrometry along with quantum chemical calculations

“…1 Proton transfer reactions (PTRs) are among the basic ion-molecule reactions that are frequently observed for positively charged ions. 2 Recently, PTRs have drawn considerable attention owing to their being fundamental in biomolecular interactions that influence the composition of the interstellar medium. 3 Moreover, PTRs play a crucial role in a variety of photochemical and biological systems.…”

Styrene radical cations for chemical ionization mass spectrometry analyses of monoterpene hydrocarbons

“…This allows real‐time quantification of atmospheric monoterpenes at concentration levels down to 1 part per billion per volume, ppbv, and lower. Recently, NH 4 + reagent ions were introduced in the SRI‐TOF‐MS, Selective Reagent Ionization Time‐of‐Flight, instrumentation, where their reaction with limonene results in formation mostly of the NH 4 + C 10 H 16 adduct ions while protonated molecules are the main products with other studied monoterpenes . Another sensitive CIMS approach has been implemented using benzene and benzene dimer cations reacting with monoterpenes in a reactor operating at 100 mbar .…”

“…4 SOAs have a great impact on the climate 5 and health 6 where their reaction with limonene results in formation mostly of the NH 4 + C 10 H 16 adduct ions while protonated molecules are the main products with other studied monoterpenes. 12 Another sensitive CIMS approach has been implemented using benzene and benzene dimer cations reacting with monoterpenes in a reactor operating at 100 mbar. 13,14 An advantage of this technique is not only its higher sensitivity, but also the good match of the relatively low 8.6 eV benzene dimer ionization energy (IE) 15 to the range of monoterpene IEs (e.g.…”