Structural determination of zinc dithiophosphates in lubricating oils by gas chromatography-mass spectrometry with electron impact and electron-capture negative ion chemical ionization

Pentafluorobenzyl ester derivatives were used to identify zinc dialkyldithi ophosphates and diaryldithiophosphates antiwear engine oil additives by GC- electron impact ionization (EI) MS and GC-electron-capture negative ion che mical ionization (ECNCI) MS analysis. GC-EI-MS of the dialkyldithiophosphat e -pentafluorobenzyl derivatives afforded characteristic fragment ions corr esponding to the cleavage of one and two alkyl radicals. In most cases, inf ormation was only obtained on one alkyl chain. Additional and complete info rmation was obtained with retention time indices using synthetic derivative s and with GC-ECNCI-MS analysis. ECNCI afforded characteristic dithiophosph ate anions which allowed the determination of the total number of carbon at oms in the alkyl radicals. The diastereoisomer mixtures of 2-hydroxy-sec.-a lkyl radicals were completely separated on GC analysis. (C) 2001 Elsevier S cience B.V. All rights reserved.