Immunobased elution assay for process control

A flow-injection analysis (FIA) system with an integrated immunobased elution assay was developed for the on-line determination of biotechnological products. This paper describes its application for tissue-type plasminogen activator (rt-PA) and recombinant antithrombin III (r-AT III). The short response time of the immunochemical system allows its use for measurement and control of biotechnological production processes. Immobilized polyclonal antibodies were found to bind rt-PA in the cartridge better than monoclonal antibodies. Sepharose-4B was found to be the best support for the antibodies. The cartridge with immobilized antibodies can be prepared easily, has a high reliability and is stable for more than two weeks. The total time necessary for one assay cycle is in the range of 6–8 min, depending on the conditions. The whole procedure is controlled by a personal computer. The FIA system can be used for automatic analysis as a stand-alone version with a frequency of 7 samples per hour. The standard operation range is from 500 μg/ml down to 2 μg/ml. A comparison with the conventional microtiter ELISA assay shows that this assay can be applied for an accurate determination of undiluted cultivation samples.