Identification of position isomers by energy-resolved mass spectrometry.
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.
School of Environmental Sciences, Mahatma Gandhi University, Priyadarsini Hills, Kottayam, Kerala, India.
Sunil Paul M
SP
Menachery
Laboratory of Analytical Chemistry and Experimental Toxicology, University Paris Descartes, Paris, France.
Olivier
O
Laprévote
Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Republic of Korea.
Thao P
TP
Nguyen
Advanced Centre of Environmental Studies and Sustainable Development (ACESSD), Mahatma Gandhi University, Priyadarsini Hills, Kottayam, Kerala, India.
Usha K
UK
Aravind
Department of Chemistry, N.S.S. Hindu College, Changanachery, Kerala, India.
Pramod
P
Gopinathan
School of Environmental Sciences, Mahatma Gandhi University, Priyadarsini Hills, Kottayam, Kerala, India.|Inter University Instrumentation Centre (IUIC), Mahatma Gandhi University, Priyadarsini Hills, Kottayam, Kerala, India.
Charuvila T
CT
Aravindakumar
D004155:Diphenhydramine / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry*; D007536:Isomerism; D013058:Mass Spectrometry / Q000379:methods*
D017665:Hydroxyl Radical; D004155:Diphenhydramine
collision-induced dissociation; energy-resolved mass spectrometry; hydroxyl radicals; mesomeric effect; position isomerism