Liquid chromatographic detection of Dowtherm A contamination in oleochemicals and edible oils

A rapid and direct liquid chromatographic (LC) technique is described for t he determination of a eutectic mixture of diphenyl oxide and biphenyl such as Dowtherm A thermal heating fluid (THF) in oleochemicals and palm olein, Analysis is performed with an RP-18 column with fluorescence detection (exc itation at 247 nm and emission at 310 nm), The isocratic mobile phase (1.0 mL/min) consists of methanol and water (90 + 10, v/v), A linear calibration model (correlation coefficient = 0.9999) was developed directly from used Dowtherm A THF with the biphenyl peak (4.70 min) as a marker. Average recov eries from spiked glycerin, fatty alcohol mixture, methyl ester mixture, fa tty acids, and palm olein were 90.9-108.7%, with a detection limit of 0.1 m u g/mL, The technique requires no prior sample cleanup nor extraction steps and is good for quality assurance purposes.