Identification of position isomers by energy‐resolved mass spectrometry

Abstract

This study reports an energy-resolved mass spectrometric (ERMS) strategy for the characterization of position isomers derived from the reaction of hydroxyl radicals ((●)OH) with diphenhydramine (DPH) that are usually hard to differentiate by other methods. The isomer analogues formed by (●)OH attack on the side chain of DPH are identified with the help of a specific fragment ion peak (m/z 88) in the collision-induced dissociation (CID) spectrum of the protonated molecule. In the negative ion mode, the breakdown curves of the deprotonated molecules show an order of stability (supported by density functional theory (DFT) calculations) ortho > meta > para of the positional isomers formed by the hydroxylation of the aromatic ring. The gas phase stability of the deprotonated molecules [M - H](-) towards the benzylic cleavage depends mainly on the formation of intramolecular hydrogen bonds and of the mesomeric effect of the phenol hydroxyl. The [M - H](-) molecules of ortho and meta isomers result a peak at m/z 183 with notably different intensities because of the presence/absence of an intramolecular hydrogen bonding between the OH group and C9 protons. The ERMS approach discussed in this report might be an effective replacement for the conventional methods that requires very costly and time-consuming separation/purification methods along with the use of multi-spectroscopic methods.

Transformation Reactions of Radicals from the Oxidation of Diphenhydramine: Pulse Radiolysis and Mass Spectrometric Studies

“…The absorption bands between 300–350 nm region (335 in the present case) with nearly diffusion controlled rate constants (k 2 =(1.08 ± 0.06) × 10 10 dm 3 mol −1 s −1 in the present case) are widely accepted as the characteristic bands of hydroxycyclohexadienyl – type radicals . Additionally, characterization of ortho, meta and para hydroxylated analogues of DPH during our end‐product studies as well as in our previous report further supports the involvement of a number of unresolved radicals on the transient spectra. Furthermore, minor contributions from a number of other radicals were also expected in this transient spectrum and are i) one more aromatic hydroxylated adduct radical at either one of the equivalent ipso positions ( 1 and 1’ ) of DPH ( b ) and ii) one or more radical species formed as a result of the abstraction of a hydrogen atom from DPH (discussed later).…”

“…for C 17 H 22 NO 2 272.1645). An energy‐resolved mass spectrometry (ERMS) based characterization of these compounds has been already developed and is discussed in our earlier report . Identification of position isomers of this kind, that are generated due to the non‐position selectivity of • OH during its reaction with aromatic compounds, otherwise requires multi‐stage separation/purification processes and the use of multi‐spectroscopic techniques.…”

Degradation of pharmaceuticals by ultrasound-based advanced oxidation process

“…We have mainly utilized time-offlight mass spectrometry for the identification of the intermediate products during various oxidation processes such as UV photolysis (Sunil Paul et al 2014), sonolysis (Nejumal et al 2014) and other oxidation processes (Thomas et al 2014). Recently, various positional isomers, formed during the oxidation reaction, have been differentiated by this technique (Menachery et al 2015;Sreekanth et al 2014). The influence of some micropollutants on the degradation of methylparaben has also been investigated by this high-resolution mass spectrometric technique (Sasi et al 2015).…”

“…There have been several techniques, especially mass spectrometric technique for the identification of the oxidation products. The most common method applied for the identification of degraded products is liquid chromatography-based techniques such as liquid chromatography mass spectrometry (Hisaindee et al 2013), time-of-flight mass spectrometry and hybrid quadrupole time of flight, in combination with ultrahigh-performance liquid chromatography (Menachery et al 2015;Sasi et al 2015). Since most of the species are in the aqueous phase and contains polar groups, therefore gas chromatography-based technique is applied very rarely (Hisaindee et al 2013).…”

“…It causes a more violent cavitational collapse of the bubbles to release the reactive species. The increased power also leads to the vibration of the pollutants in the liquid medium, which causes the faster movement of the pollutant toward the interface region (Mason et al 1990). However, when the number of bubbles in the medium is increased, it could scatter the sound wave and return back to the surface of the transducer.…”