Analysis of Zinc Dialkyldithiophosphate Additives in Commercial Lubricating Oil using Matrix Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry

Polkit Sangvanich,^a* Jannate Tungcharoen^b and Amorn Petsom^c

^a Research Centre for Bioorganic Chemistry, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, THAILAND
^b Program of Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bangkok, 10330, THAILAND
^c Institute of Biotechnology and Genetic Engineering, Chulalongkorn University, Bangkok, 10330, THAILAND
* Corresponding author: E-mail: Polkit@gmail.com

Abstract
The zinc dialkyl/aryl dithiophosphates (ZDDPs) are multifunctional lubricating oil additives. In this research, the analysis of ZDDPs additive in lubricating oils using Matrix Assisted Laser Desorption/Ionization Time-of-Flight (MALDITof) has been developed. The complexes [Zn(DTP)(DMSO)₂]⁺ from reaction between zinc dithiophosphate with dimethylsulfoxide were prepared. Analysis parameters for MALDI-Tof MS have been investigated; types of matrix and analyte: matrix ratio. The optimum condition of the analysis is dithranol as a matrix with tetrahydrofuran as solvent and the ratio of [Zn(DTP)(DMSO)₂]⁺ to matrix is 1:75 by volume. And then, this developed method is applied for the analysis of ZDDPs additive in a commercial lubricating oil. Moreover, the results also suggested that additives in commercial lubrication oils can be separated to two groups; zinc dialkyldithiophosphates and zinc diaryldithiophosphates. Consequently, the pattern of ZDDPs can be used as a tool for producers of commercial lubricating oil products.

Keywords: MALDI-Tof MS, zinc dialkyldithiophosphate, lubicating oil additive