Purpose: To evaluate laboratory performance through an inter-laboratory study for quantitation of melamine and cyanuric acid in fish tissue samples to meet U.S. action level of 2.5 mg/kg in animal feed.
Methods: Incurred fish tissues were prepared by feeding catfish melamine (10, 20 mg/kg) and/or cyanuric acid (10, 20, or 40 mg/kg) followed by euthanizing 1 or 3 days after feeding. The concentrations of melamine and cyanuric acid in these fish tissue samples were determined using LCMS. One control fish and five dosed fish fillets containing melamine/cyanuric acid at concentrations of (<0.1/1.2, 0.29/<0.1, 1.6/<0.1, 2.5/0.1 and 3.6/<0.1 mg/kg) were used to prepare the proficiency test (PT) samples. Fish fillets were processed by cutting into slices and then homogenizing together with dry ice in a blender. The resulting powder was subdivided and samples were stored frozen prior to the shipment to six participating laboratories. A total of twelve blind coded test samples (15 g each) were shipped to each participating laboratory. The results from five laboratories that used suitable methods were statistically analyzed according to the internationally harmonized protocol ISO 13528:2005.
Results: The consensus values (n = 10) of melamine/cyanuric acid obtained for the dosed samples were <0.1/1.5, 0.28/<0.1, 1.9/<0.1, 2.8/0.1 and 4.2/<0.1 mg/kg with corresponding relative standard deviation of na/18.7, 51/na, 17.5/na, 14.6/76.7 and 22.4/na %. The melamine/cyanuric acid concentrations obtained were in agreement with the pre-determined values.
Significance: These data showed that the participating laboratories were able to accurately measure melamine and cyanuric acid in fish tissues at action level.