SCREENING OF CALF URINE FOR 19-NORTESTOSTERONE - MATRIX EFFECT IN SOME IMMUNOASSAYS

The performances of three enzyme linked immunosorbent assays (ELISAs) and one radioimmunoassay (RIA) in 17 alpha-19-nortestosterone (17 alph a-19-NT) analysis of bovine urine have been evaluated. Sample preparat ion was performed by enzymic deconjugation and solid-phase extraction. The main object of the study was the evaluation of the matrix effect, which is generally great in 19-NT immunoassays. Fifty-seven bovine ur ine samples have been analysed by immunoassay and by gas chromatograph y-mass spectrometry (GC-MS). The defection limit of GC-MS analysis was 1 mu g l(-1). The mean sample blank values in urine analysis were clo se to 1.5 mu g l(-1) for one ELISA, and 0.4-0.8 mu g l(-1) for the oth er assays (n = 55, samples coming from several breeds in different geo graphic areas). The detection limits, calculated in compliance to the EEC criteria, were 2.67, 1.97, 2.05 and 5.01 mu g l(-1) for RIA, ELISA s 1, 2 and 3, respectively. The percentage of fate positive results ad opting this criteria were: 1.8, 3.6, 1.8 and 3.6%. The probability of the occurrence of false negative results was evaluated by adding 2 mu g l(-1) of 19-NT to a negative sample, was high in each assay, Two;sam ples from experimentally treated animals gave positive results both in GC-MS and in immunoassays. The results obtained confirm that be emplo ying immunoassay and solid-phase extraction as sample clean-up, it is not possible to apply the action level (2 ppb) suggested by the Europe an Union (EU).