Liquid chromatographic method for the determination of nine phenolic antioxidants in butter oil: collaborative study

Ten laboratories collaboratively studied a liquid chromatographic (LC) method for the determination of propyl, octyl, and dodecyl gallate (PG, OG, and DG, respectively), 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-hydroxy-methylphenol (Ionox-100), and 3,5-di-tert-butyl-4-hydroxytoluene (BHT) in butter oil. The 10 samples analyzed were spiked in matched pairs at about 100, 50, and 10 micrograms/g. In the method studied, antioxidants are extracted as in AOAC LC method 983.15, but different LC eluants are used to separate the 9 antioxidants. Results from 1 laboratory were rejected as not valid and were not included in any calculations. For the remaining 9 laboratories, the overall mean recoveries for PG, THBP, TBHQ, NDGA, BHA, OG, Ionox, BHT, an DG were 100.9, 97.8, 103.4, 95.4, 97.4, 93.6, 95.5, 79.0, and 96.2%, respectively. The overall reproducibility relative standard deviations were 8.55, 17.4, 25.6, 14.5, 6.60, 9.64, 10.8, 11.4, and 7.35%, respectively. The method was adopted first action by AOAC International as a modification of AOAC method 983.15.