GC/MS Determination of Pyrogallol and Gallic Acid in Biological Matrices as Diagnostic Indicators of Oak Exposure

A selective and sensitive method was developed for the quantitative determination of pyrogallol and detection of gallic acid in biological samples. Pyrogallol was measured as a metabolite of gallotannin in bovine urine and serum samples. Gallic acid was formed by hydrolysis of the gallotannins in blue oak (Quercus douglasii) leaves, tannic acid standards, and rumen contents. Acid hydrolyzed or acidified samples were extracted with 5% ethanol in ethyl acetate (v/v), followed by evaporation and derivatization with Deriva-sil. The trimethylsilyl derivatives were analyzed by gas chromatography/mass spectrometry using selected ion monitoring. Method detection limits for gallic acid and pyrogallol were 0.5 ppm in urine and serum samples and 5 ppm in rumen contents. The diagnostic utility of the method was tested by analyzing samples from heifers dosed with blue oak leaves and commercial tannic acid. Keywords: Pyrogallol; gallic acid; gallotannins; GC/MS determination