Fragmentation pathways of negative ions produced by electrospray ionization of acyclic dicarboxylic acids and derivatives

Abstract

Fragmentation pathways have been studied on the monoanions formed during electrospray ionization of a wide range of aliphatic dicarboxylic acids and their monoesters. All negative ion spectra were obtained from alcoholic or aqueous methanolic solutions without buffers or adjustment of pH, using either a Finnigan LCQ ion trap or a VG-Micromass Quattro triple quadrupole mass spectrometer. Fragmentation pathways were studied using collision-induced dissociation and isotopic-labelling techniques. Two primary fragmentation pathways of the dicarboxylic acid monoanions were observed, namely decarboxylation of the non-ionized carboxyl group and loss of water from this group. The fragmentations were strongly dependent on the chain lengths of the diacids. In the case of a monoester anion, loss of a molecule of alcohol paralleled the loss of water from the diacid monoanion. Losses of water or alcohol were shown to lead to formation of reactive ynolate anions (HOOC(CH2)xC≡CO–, x = 3–9), which in the ion trap spectrometer engaged in complex ion – molecule reactions consistent with the chemistry of these anions. For the longer chains (x > 6), the interactions between the ionized and non-ionized carboxyl groups led to readily formed ion–neutral complexes, which are described as a neutral molecule (ROH, R = H or alkyl) held by a pair of molecular tweezers.Key words: ESI-MS/MS on negative ions, fragmentation pathways of acyclic carboxylic acid monoanions, ion–molecule reactions in an ion trap mass spectrometer, hydrogen–deuterium exchange in a gas-phase anion–neutral complex.

Characterization of multiple fragmentation pathways initiated by collision‐induced dissociation of multifunctional anions formed by deprotonation of 2‐nitrobenzenesulfonylglycine

“…In the present study, the unanticipated loss of HONO observed upon CID of deprotonated Ns amino acids differed from the documented fragmentation behavior of other sulfonamide and carboxylate ions. The collection of functional groups in the Ns derivative of glycine (NsGly) also enabled three other distinct fragmentation pathways of deprotonated NsGly to be observed, indicative of a rich gas‐phase chemistry for multifunctional anions.…”

Online measurements of water-soluble organic acids in the gas and aerosol phase from the photooxidation of 1,3,5-trimethylbenzene

“…2), as suggested by Kirkup and Mulholland (2004). This is due to the formation of dimers and aggregates with water during ESI, especially at higher concentrations, and possibly varying fragmentation (Grossert et al, 2005) at different concentration levels. Limits of detection (expressed in ng) have been defined from the calibration curves and converted to ng m −3 according to the experimental sampling flows of WEDD and AC for each experiment.…”

Unambiguous identification of esters as oligomers in secondary organic aerosol formed from cyclohexene and cyclohexene/α-pinene ozonolysis

“…dehydration (m/z 167) and decarboxylation (m/z 141) of pinic acid and dehydration of hydroxypinonic acid (m/z 181). This fragmentation pattern is significant for dicarboxylic acids (Grossert et al, 2005) in general. The MS 3 -spectra of the daughter ion with m/z 185 of m/z 367 (Fig.…”

“…The intensity seems to be dependent on the molecular weight of the hydroxyl component or the ratio of molecular weights of hydroxyl and dicarboxylic acid component in the ester molecules. Furthermore, always visible in the MS/MS-spectra are low intensities of fragments from losses of water, carbon dioxide and combined losses of water and carbon dioxide of the dicarboxylic acid, which is typical for dicarboxylic acids of different chain length (Grossert et al, 2005). The MS 3 -spectrum of the m/z 131 fragment ion (Fig.…”