Determination of corproporphyrin in urine by using stopped-flow fluoroimmunoassay

A simple and fast stopped-flow fluoroimmunoassay method for the direct determination of coproporphyrin in urine is described, which is the first attempt to apply the immunoassay methodology for this analytical purpose. The method is based on the use of the initial rate of the immunochemical reaction as the analytical parameter, which is measured in only 0.5 s through the fluorescence quenching of the porphyrin caused by its reaction with monoclonal antibodies. Stopped-flow mixing technique allows this high initial rate to be easily measured and facilitates the automation of the method. The dynamic range of the calibration graph is 7–100 nM and the relative standard deviation is 1.1–4.0%. Potential interferences from the sample matrix are avoided or minimized by the use of kinetic methodology, so that the pretreatment of the sample is not required. The analytical recoveries obtained by applying the method to urine samples ranged from 88 to 113%