Electrospray mass spectrometry of zinc dithiophosphate derivatives and its application to the analysis of engine oil antiwear additives

Terence J. Cardwell, Ray Colton, Nick Lambropoulos, John C. Traeger, Philip J. Marriott

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37 Citations (Scopus)


Electrospray mass spectrometry (ES-MS) has been applied to a variety of zinc O,O′-dialkyldithiophosphate (DTP) derivatives. The neutral Zn(DTP)2 compounds were converted to the [Zn(DTP)3]- anions by reaction with excess DTP- and these principal anions are readily observed by ES-MS. Exchange reactions between two different zinc tris(DTP) anions leads to the simultaneous observation of zinc anions containing all possible combinations of ligands even though the species in solution are exchanging rapidly on the NMR timescale. Similar mass spectra are observed upon mixing Zn(DTP)2 with a different DTP- anion. Reaction of Zn(DTP)2 with dimethylsulfoxide (DMSO) in methanol solution gives [Zn(DTP)(DMSO)1,2]+ and free DTP- ions which are observed in the positive ion and negative ion ES mass spectra respectively. This latter reaction provides a convenient method for the characterisation and qualitative analysis of engine oil inhibitor and antiwear additives, which contain zinc dithiophosphates with alkyl and aryl substituents.

Original languageEnglish
Pages (from-to)239-244
Number of pages6
JournalAnalytica Chimica Acta
Issue number2
Publication statusPublished - 16 Aug 1993
Externally publishedYes


  • Antiwear additives
  • Engine oils
  • Mass spectrometry
  • Zinc dithiophosphate

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