Quantification limits immunoassay development

Much effort has been made to detect steroids in biological fluids. Even simple TLC methods have been used for qualitative analysis [38], One method that been used for quantification involves an immunoassay, but several problems exist with that method, most notably cross-reactions and interference with other substances [39], On the other hand, a number of chromatographic methods have been developed to overcome these problems. The majority of analytical methods involved GC, which has good detection limits, but requires previous derivatization [40] of the steroids to accomplish volatilization. Many methods have also been reported using HPLC with UV detection or LC-MS [40, 41], Previously used stationary phases for LC was e.g., Sephadex LH-20, Celite and Lipidex, but they could not be operated with high pressure [42], These columns were therefore slow to run and the separation of steroids was very time-consuming [43], Nowadays applications mainly use HPLC as a separation method with both normal-phase and re-versed-phase chromatography. 

A commercially available RIA developed as a screen for tetracycline antibiotics in serum, urine, milk, and tissue of livestock has been adapted by Meyer and co-workers to analyze water samples. The interest in pharmaceutical compounds in the enviromnent is relatively new. Immunoassays for pharmaceutical compounds are commonly used in biological media where the concentrations are quite high. Therefore, in this RIA the lower limit of antibiotic detection had to be modified to enable quantification of antibiotic levels as low as one part per billion in water samples. 

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