ARE THIN-LAYER CHROMATOGRAPHIC SCREENING PROCEDURES STILL UP-TO-DATE - CRITICAL COMPARISON WITH IMMUNOCHEMICAL TESTS

The formerly prefered TLC screening procedures are often replaced by i mmunoassays. Many pitfalls must be taken into account when enzyme-immu nological (e.g. EMIT-st, ETS) or fluorescence-polarisation-immunologic al (e.g. ADx, TDx) screening tests are applied. False negative results may be caused by conjugate formation, poor cross-reactivities and/or low concentrations. This article describes typical cases and indicates modifications which enable the toxicologist to obtain valid results. Beside this the advantages of TLC-methods are described and discussed.