Role of Anthranilic Acid in Background Levels of Sulfonamide in Porcine Livers when Determined by the Tishler Method

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Abstract
Anthranilic acid occurs in excised swine livers as a result of temperature abuse before and/or after freezing. The tryptophan metabolite is the major source of the variable non-sulf onamide background level frequently encountered in the Tishler method for determining sulfonamide residues in swine livers. Diazotized anthranilic acid reacts slowly with N-( naphthyl)ethylenediamine [k(s-1) = 5.79 (±0.07) × 10-5] and the final background level depends on the time elapsed between addition of the coupling agent and spectrophotometric determination. Kynurenine was tentatively identified as a minor source of the non-sulfonamide background level.