HPLC WITH COULOMETRIC ELECTRODE ARRAY DETECTION - DETERMINATION OF O-TYROSINE AND M-TYROSINE FOR IDENTIFICATION OF IRRADIATED SHRIMPS

Irradiation of dissolved phenylalanine and of phenylalanine-containing proteins with ionizing radiation (gamma-rays, high-energy electrons) leads to the formation of o- and m-tyrosine, in yields proportional to the absorbed dose, in addition to other compounds. The tyrosine isome rs can potentially be used as markers in order to detect irradiated fo od. Based on this fact a method for qualitative and quantitative deter mination of free o- and m-tyrosine in shrimps has been developed. For this purpose the isomers were extracted from non-irradiated as well as irradiated samples with trichloroacetic acid, then separated isocrati cally (methanol/0.05 M trichloroacetic acid, 5:95, v:v, pH 3.4) on a r eversed-phase column (Inertsil ODS-2) and detected by a coulometric el ectrode array detector [potential: +300 to +860 mV (in increments of 80 mV) against a modified palladium electrode]. The oxidative detectio n mode guarantees a reliable determination of o-tyrosine as well as m- tyrosine. The concentrations of o- and m-tyrosine are proportional to the absorbed radiation dose in the range of 0.5 to 6 kGy. Because of t he sensitivity of this method, it was possible to identify irradiated shrimps down to a dose of 0.5 kGy. The concentrations of both tyrosine isomers in nonirradiated samples were found to be rather low.