Determination of phenols and phenates in disinfectant formulations by liquid chromatography with UV detection: collaborative study

Fourteen collaborating laboratories assayed o-phenylphenol (OPP), p-t-amylphenol (PTAP), and o-benzyl-p-chlorophenol (OBPCP) in formulated products, both ready-to-use and concentrates, by RP-HPLC. The actives in the samples ranged from 0.03 to 11% OPP, 0.06 to 4% PTAP, and 0.07 to 10% OBPCP either in free forms or as salts. Seven blind duplicates were analyzed. The samples were diluted/extracted with acidified methanol, filtered, and analyzed by LC on a C18 column using gradient elution and UV detection at 285 nm. The concentration of the active ingredients was calculated from a standard curve. Each laboratory weighed each test sample twice within a single analytical run. The data were analyzed using all 14 laboratory results, with appropriate statistical tests to detect outliers. The repeatability RSDs ranged from 0.98 to 3.40% for the free phenols, and 1.26 to 2.51% for the salts. The reproducibility RSDs ranged from 5.31 to 7.80% for the free phenols, and 5.50 to 8.67% for the salts. The HorRat ranged from 0.86 to 2.17 for the free phenols, and 1.54 to 2.72 for the salts.