Calibration standards, prepared by gravimetric addition of TPPO to a peroxide-free oil, were handled in
the same manner, and a linear calibration equation relating the concentration of TPPO (expressed as the equivalent PV) to the absorbance of
TPPO at 542 cm−1 relative to a baseline at 530 cm−1 in the reconstituted spectra was obtained, with a regression S.D. of ±0.15 meq/kg oil.