Enzyme-linked immunosorbent assays are usually performed by running standard and Unknown concentrations together on the same microtiter plate, because the standard curve is known to vary considerably from one assay to the next. Here we examine experimentally the sources and nature of this variation, and discuss the possibility of reducing the cost of the assay by using a batch of plates, only one of which is used to generate the calibration curve. We present a method for doing this, and test it empirically.

An immunochemical method for simultaneous analysis of cross-reacting analytes is presented. We demonstrate the general principle using triazine herbicides as the model system. The analysis is based on a combination of individual enzyme immunoassays (immunoarray) for triazine herbicides using antibodies with different cross-reactivity patterns towards the selected analytes. The assay signals obtained can be mathematically evaluated to estimate concentrations of each analyte out of a ternary or quaternary mixture. The mathematical model utilizes an extension of the empirical four parameter log-logistic fit. Using mono- and polyclonal antibodies it was possible to quantify the four analytes atrazine, simazine, cyanazine, and prometon in the low to sub-ppb range simultaneously.