ENZYME IMMUNOASSAYS FOR THE DETERMINATION OF S-TRIAZINES IN WATER SAMPLES - 2 INTERLABORATORY TESTS

Interlaboratory tests on the applicability of enzyme immunoassays in the analytical chemistry of water have not been reported to date. The Immunoassay Study Group has therefore prepared two extensive interlaboratory tests on the determination of s-triazines. A total of 13 laboratories from the application, research, and industry sectors participated in the first test, partly with assays of their own. Most of the participants used atrazine equivalents as the measuring unit. A total of ten samples of ground water, drinking water and surface water were analyzed in the native state and after supplementation with various s-triazines for comparison. Accompanying GC/MS analyses were carried out by the Central Laboratory of Gelsenwasser AG. The atrazine contents could be precisely determined by only a few laboratories on the basis of various enzyme immunoassays. As the results showed, none of the assays tested were suitable for the group determination of s-triazines. In spite of the encouraging overall performance of some of the involved enzyme immunoassays, the performance of several participating laboratories proved to be rather poor. This was in general related to insufficient training. A second interlaboratory test was then performed under more rigorous conditions. A total of 12 laboratories participated with three enzyme immunoassays, which turned out to be the most successful ones at the previous interlaboratory test. This time, six samples of drinking water and surface water (river Rhine) were analyzed in the native state and after supplementation with atrazine and deethyl-atrazine. Two of the spiked surface water samples were identical. Three laboratories carried out GC or GC/MS analyses for comparison. Information such as the composition and origin of the samples or the kind of supplementation was kept secret from all participants. All immunoassays correctly recognized the zero sample (drinking water) and they generally yielded the same results for the identical samples 3 and 4 (water from the river Rhine, supplemented with atrazine). On the average, one immunoassay yielded fairly accurate results for the atrazine concentrations whereas the other two tests were more suitable for the group determination of s-triazines. This can be explained by different cross-reactivities of the applied antibodies. The second interlaboratory test proved the principal qualification of immunoassays for the detection of environmental chemicals. However, several conditions must be met which are contained in the following recommendations of the Immunoassay Study Group: The participation of trained personnel in certified laboratories seems to be necessary. An exact description of the assay including the calibration curves, the detection limits, the cross-reactivities and informations on matrix effects should be available. The working range of the immunoassays should be close to the middle of the test. At least six calibration points should be provided. Four of them should be contained in the respective working range. At least four parallel measurements per calibration point or sample are recommended. If the matrix of the samples is not known, the samples should be spiked with known standards. Under these conditions, immunoassays are to be considered as rapid and relatively simple screening procedures which provide a valuable contribution to the analysis of pesticides.