Electron impact mass spectra of some salts of carboxylic acids with alkali (group Ia) metals

Abstract

Thirteen of the salts of the alkali metals (Li, Na, K, Rb, Cs) with acetic, 2,2-dimethylpropionic, trifluoroacetic and heptafluorobutyric acid have been found to be sufficiently volatile to give mass spectra under normal electron impact conditions. The metal containing ions observed include ( Electron impact mass spectra have been observed for a number of organo derivatives of the alkali (Group Ia) metals, including ethyllithiurn,' lithiomethyltrimethylsilane,' lithium' and potassium" t-butoxide, 1,3-diketone chelates; and some N-alkyl and N,Ndialkyldithio~arbamates.~ The carboxylate salts have generally been assumed to be insufficiently volatile to give electron impact spectra and have therefore been studied by other techniques such as radio frequency spark source6 and field desorption7.' mass spectrometry even though studies on cuprousg and argentous" (Group Ib) carboxylates have appeared. The reported exceptions are a mention of the similarity of the electron impact and field desorption spectra of sodium acetate by Schulten and Beckey' and the interesting studies by Chamberlin and Agtarap" on the sodium, potassium and rubidium salts of Monensin and related antibiotics in which the metal atom is coordinated by oxygen atoms within the molecule in a way very similar to the crown ether complexes. The spectrum of potassium benzoate under chemical ionization conditions using a field desorption emitter as a solid probe has also been reported."We have examined the behavior under normal electron impact conditions of the salts of the five alkali metals with four simple carboxylic acids chosen to maximize the volatility of the salts and to be representative of acids which may be present after the processing of biological samples. When metal containing ions were observed, the temperature is that required for an intense spectrum. Relative intensities changed somewhat during the course of the evaporation of the sample. RESULTS AND DISCUSSION Volatility and decomposition" Decomposition began at the indicated temperature. No metal containing ions were observed. decompose cleanly to give CO, and C,F,, and the trifluoroacetates decompose to give COz and material with a spectrum similiar to that of mixed perfluoroalkanes. In all cases, a white residue remains which is assumed to be the metal fluoride. This is supported in the case of the cesium salts by the observation of the spectrum of cesium fluoride when the residue is heated to 400°C.For all the acetates except potassium acetate (the least volatile), for all the 2,2-dirnethylpropionates7 and for lithium heptafluorobutyrate the spectrum was independent of the rate of heating and remained unchanged throughout evaporation of the entire sample, thus strongly indicating that these salts volatilize without decomposition. The temperatures needed are surprisingly low with vaporization occurring within or only modestly above the temperature range generally used for nonionic compounds. As expected, the temperatures required to volatilize the salts decrease when the bulky less polar 2...

Electron, chemical, and thermal ionization mass spectra of alkali halides

“…Several years ago we pointed out (7) that a slightly modified commercial quadrupole mass spectrometer could be Used to determine isotopic ratios in lithium. Hunt and co-workers (8) obtained excellent Cl spectra with intense molecular ions from potassium benzoate, and White (9) obtained El spectra of alkali metal salts of several organic acids, the spectra containing the metal cation and clusters involving the metal cation. Rosenstock and co-workers (10) using a noncommercial mass spectrometer found in 1955 that copper halide salts placed on an electrically heated platinum filament evaporated sufficiently in the mass spectrometer source to give rise to characteristic spectra.…”