Researchers Detect and Research a Series of [M-H]⁺ during Electrospray

May 12, 2014     Email"> PrintText Size

The common peaks generated by electrospray mass spectrometry (ESI-MS) in positive-ion mode are [M + H]⁺ and [M + Na]⁺ and in negative-ion mode are [M - H]^- and [M + Cl]^-. The peak formed by loss of a hydride anion, [M – H]⁺, has been only rarely detected in ESI.  

Researchers in Prof. WU Zhijun lab at the Chengdu Institute of Biology, Chinese Academy of Sciences firstly investigated cyclopenta[b]indoles having antidepressants using ESI-MS. Unexpectedly, Prof. WU and his colleagues detected the rare ions formed by loss of a hydride anion, that is [M – H]⁺. The location from which the hydride anion was lost was confirmed by hydrogen–deuterium exchange labeling experiment and density functional theory (DFT) calculations. No detection of [M + H – H₂]⁺ ion in MS/MS spectrum of [M + H]⁺ indicates the direct loss of a hydride anion.  

However,when trace sour was added to the solvent, ESI revealed a significant peak attributable to the [M – H]⁺, which further supports the direct loss of a hydride anion. More interestingly, several high-abundance diradical cations resulting from [M – H]⁺ were detected in subsequent CID experiments. DFT calculations predict the diradical cation to be more stable than the diradical coupled cation.  

This finding of [M – H]⁺, along with the detected radical and diradical cations, is of great scientific interest. What's more vital is that this observation of active hydride anion release might aid advances in the development of hydrogen storage materials. This research entitled "Unexpected [M – H]+ ions in cyclopenta[b]indoles detection by electrospray ionization mass spectrometry" was published in J. Mass Spectrom.