High performance liquid chromatographic determination of seven antioxidants in oil and lard: collaborative study

A high performance liquid chromatographic procedure for the determination of propyl gallate (PG), 2,4,5-trihydroxybutyrophenone (THBP), tert-butylhydroquinone (TBHQ), nordihydroguaiaretic acid (NDGA), 2- and 3-tert-butyl-4-hydroxyanisole (BHA), 2,6-di-tert-butyl-4-hydroxymethylphenol (Ionox-100), and 3,5-di-tert-butyl-4-hydroxytoluene (BHT) was collaboratively studied by 8 laboratories. The 14 samples analyzed consisted of 10 vegetable oil samples spiked in matched pairs at about 200, 100, and 20 ppm and 4 lard samples spiked in matched pairs at about 100 and 40 ppm for each antioxidant except NDGA which was spiked only at the 2 lower levels in oil. In the method studied, the samples were dissolved in hexane and the antioxidants were partitioned into acetonitrile. The acetonitrile was concentrated and diluted with isopropanol to give isopropanol-acetonitrile (1 + 1). The antioxidants were separated by reverse phase gradient elution and detected at 280 nm. The results from one laboratory were rejected as outlying and were not considered in any calculations. For the remaining 7 laboratories, the overall mean recoveries for PG, THBP, TBHQ, NDGA, BHA, Ionox-100, and BHT were 93.2, 95.1, 95.6, 95.5, 98.3, 95.8, and 84.8%, respectively, and the overall mean coefficients of variation were 5.02, 7.74, 19.3, 4.36, 3.75, 6.33, and 3.45%, respectively.