Fragmentation rules in plasma desorption mass spectrometry

Abstract

Several studies concerning the analysis and quantification of biological and pharmaceutical compounds have been effected during the past 20-30 years using different techniques of desorption-ionization. In most cases, however, the authors have not been interested in the mass spectrometric fragmentation mechanisms of these products. Plasma desorption mass spectrometry (PDMS) is a powerful technique for analysing, without matrix interferences, solid biological and pharmaceutical compounds. In this work, we use PDMS in order to study the influence of the amine (amide) function on the fragmentation processes of nitrogen-containing compounds. For this work, quaternary ammonium salts, trisubstituted amines, disubstituted amines and a compound with an amide function were chosen. Classical PD mass spectra, accurate mass measurements, transitions in the field free region (FFR), labelled compound spectra and thermodynamical data are reported for the structural study of these compounds. Our results allow us to propose fragmentation rules for positively charged polyfunctional biological nitrogen compounds. These rules relate to a class of structurally informative decomposition reactions that can be applied to the determination and of identification of structural unknowns.In an attempt to apply modern mass spectrometric techniques to direct analysis of biological and pharmaceutical compounds, plasma desorption-ionization was employed. Plasma desorption mass spectrometry, introduced by Macfarlane and Torgerson,' uses energetic fission fragments from the decay of 252Cf to volatilize and ionize a solid sample. This technique was one of the first particle bombardment techniques successfully applied for the formation of gas-phase ions of nonvolatile and thermally labile biomolecules. The PDMS technique has been extensively used for measuring the molecular weights of biopolymers in the mass range 103-3 x lo4 u. Recently, this technique was demonstrated to be very useful for the analysis of small molecules and for obtaining structural information from small and large molecules.' This paper describes the decomposition mechanisms of positively charged ions from biological and pharmaceutical compounds containing several functional groups including, at least, one amine or one amide function and shows that the fragmentation is chargeinduced or charge-remote depending on the substituents of the ionized nitrogen atom. The mechanisms and some applications of charge-remote fragmentations have been studied by Gross.3 We have applied these mechanisms to nitrogen-containing organic compounds of biological and pharmaceutical interest.The compounds studied and presented in Table 1 are: quaternary ammonium salts, namely L-carnitine inner salt l a , L-carnitine hydrochloride l b and thiamine hydrochloride 2; trisubstituted amines, namely chlorpromazine hydrochloride 3, thioridazine hydrochloride 4 and riboflavin 5; disubstituted amines, such as niflumic acid 6; amphetamines, namely fenproporex 7, fenfluramine 8 and methylamphetamine 9; and an amide,...

Analysis of aromatic pesticides by mass spectrometry. Advantage of plasma desorption over electron impact and NH3 or CH4 positive chemical ionization: the competitive formation of M+. and MH+ ions

“…This work on carbamates and phenylureas confirms previous work [3][4][5] showing that PD is an ionization technique very well adapted for obtaining structural information on small polyfunctional molecules.…”

Decarboxylation of Carnitine and α-Cyano-4-Hydroxycinnamic Acid under Particle Bombardment

“…Since these ions are preformed in solution, it is easy to generate gaseous ZH + ions. During earlier mass spectrometry studies using either 252 Cf fission products [Plasma desorption (PD)] 1 or UV photons [laser desorption (LD)] 2 as a primary particle beam to desorb and ionize solid carnitine samples, we observed decarboxylation product ions. Is the decarboxylation observed for carnitine an exceptional or a more general process?…”

Large Molecular Mass Materials in Coal-Derived Liquids by 252Cf-Plasma and Matrix-Assisted Laser Desorption Mass Spectrometry

“…Unlike the case where a powerful Nd:YAG laser had been used, , neither the PAH nor the fullerite mixture displayed carbon cluster sequences. PD-MS operates without a matrix and for standard materials (porcine insulin in this work) and simple molecules can generate a molecular ion. − , A mass spectrum for fullerene (not shown), generated by PDMS, showed a molecular ion at 720 u and C2 fragmentation peaks, but only low-intensity doubly charged ions.

1 MALDI-TOF spectra of the model compounds and (a) rubrene, (b) pyranthrene, (c) the fullerite mixture, and (d) the NMP-solvent blank.

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“…PD-MS operates without a matrix and for standard materials (porcine insulin in this work) and simple molecules can generate a molecular ion. [11][12][13]31 A mass spectrum for fullerene (not shown), generated by PDMS, showed a molecular ion at 720 u and C2 fragmentation peaks, but only low-intensity doubly charged ions. Figure 2a,b, shows MALDI mass spectra of the pyridine-soluble (with no matrix) and pyridine-insoluble (with sinapinic acid as matrix) fractions of the coal tar pitch, respectively.…”

“…Plasma desorption mass spectrometry (PD-MS) normally operates with a thin layer of sample deposited on the target which approximates to a monolayer. The technique has been used to examine peptides and lipids as well as small molecules such as nitrogen-containing pharmaceuticals 12 and alkylaminotriazines . Volatilization and ionization are achieved by collision of a very energetic 252 Cf fission product with the sample.…”