A known principle in which triphenylphosphine is allowed to be oxidized by hydroperoxides to triphenylphosphine oxide, was developed into an analytical method for determination of hydroperoxide content in light mineral oils using GCMSdetection and quantification. By suitable choice of reagent solution solvents and internal standard, the method proved to be simple to apply and very rugged. For a series of oven-aged oil samples the developed method gave results with a satisfactory correlation to an established iodometric method (which also gave a higher standard deviation). A mechanistic explanation for interference of high concentrations of added aldehydes on measurements was also suggested, but it was found that the interference is of no practical consequence for oxidized oil samples.

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IEC 61125C, a traditional oxygen-rich material test for determination of oxidation stability of insulating oils, was modified to give continuous data over the entire testing time by application of a logging pH-meter. A complementary oxygen-poor testing method, which may be more relevant to certain power transformer designs, was also developed further. The methods give insight into the chemistry and dynamics of oil oxidation, and may serve as a future means to investigate insulating oil behavior and support development of high performance insulating oils.