Abstract is one of the major applications of zinc dialkyldithiophosphates (ZnDDPs) is their usage as an anti-wear additive in lubricants including greases, hydraulic oils, and motor oils. ZnDDPs also could be used as corrosion inhibitors and antioxidants. In this study, GC/MS with solid-phase extraction (SPE) pretreatment was used to effectively remove base oils in lubricants and qualitative and quantitative analysis method for ZnDDPs in automotive lubricants. As a pretreatment method, liquid–liquid extraction (LLE) and SPE were applied. The SPE method using mixed absorbent containing 1.0% of active carbon in silica gel base showed the best results in both recovery and reproducibility. The LOD and LOQ of the developed method were 2.2 µg/ml and 6.7 µg/ml, respectively. And this method showed very good reproducibility of less than 0.1% RSD for the standard sample analysis. The developed method was successively applied to qualitative and quantitative analyses of ZnDDP in various real automotive lubricant samples.
Introduction
Oil additives are chemical compounds that improve the lubricant performance of base oil (or oil “base stock”). Manufacturers of many different oils can utilize the same base stock for each formulation and can choose different additives for each specific application. Additives comprised up to 5% by weight of some oil (Bartels et al. 2003). Nearly all commercial motor oils contain additives, no matter whether the oils are synthetic or petroleum-based.
Some of the most important additives include those used for anti-wear additives which are one of the most important oil additives for automotive lubricants. Zinc dialkyldithiophosphates (often referred to as ZDDPs or ZnDDPs) (ZNDDP Engine Oil - Mustang Monthly XXXX) are typically used the most. These uncharged compounds are not the salts. They are soluble in nonpolar solvents, and the longer-chain derivatives easily dissolve in mineral and synthetic oils used as lubricants. The main application of ZnDDPs is anti-wear additives in lubricants including greases, hydraulic oils, and motor oils. ZnDDPs also perform various functions such as corrosion inhibitors, coolants, and antioxidants (Barnes et al. 2001). They can be seen almost anywhere in the lubricants, and usages are usually between 600 and 2000 ppm depending on the type of automobiles.
The analysis of lubricant additives was generally applied to obtain information about the age and condition of the product. Various techniques have been applied to the analysis of oil additives including energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and mass spectrometry (MS) (Çelik et al. 2013; Zhang et al. 2013; Kassler et al. 2011). Using mass spectrometry, highly detailed information about the chemical composition of lubricants can be generated, and quantification of additives is possible. Mass spectrometry is typically hyphenated with chromatographic techniques