Comparison of flow injection analytical biosystems based on open-tube and packed-bed enzyme reactors

Abstract

A comparison between the most widely used enzyme reactors in flow injection analysis (FIA) systems has been realised. These reactors were the open-tube reactors and the packed-bed reactors. The comparison was realised with three different enzymes (urease, creatinine iminohydrolase and creatine amidinohydrolase). The enzymes were covalently immobilised on controlled-pore glass beads (CPG). These beads were used as the filling for the packed-bed reactors. The enzymes were also inmobilised covalently on the inner wall of nylon tube reactors. All three enzymes were used in clinical analysis and they have clearly distinguished activities. All of them produced ammonium ions as a consequence of their interaction with their respective substrates. The single channel FIA system used for the evaluation and the comparison of the reactors worked automatically and included a flow bioreactor and an ammonium-ion sensor. The FIA systems used with the different bioreactors were optimised to obtain the largest signal in the shortest time. Once optimised, the performance of the reactors were evaluated and compared while working with each enzyme. The parameters to evaluate were: calibration parameters ( y-ordinate, slope and linear), reproducibility, conversion ratio (yield) of the enzyme reaction in the reactor, dynamic parameters (response time and analysis time) and lifetime. The comparison of the bioreactors working under optimal conditions showed that the packed reactors had a higher conversion ratio, a higher sensitivity (slope of the calibration curve), a smaller lower detection limit and shorter response times. Open-tube reactors showed a higher reproducibility, a higher upper detection limit and a diminished amount of reagent at the optimal flow rate. Analysis time was lower in open-tube reactors since the packed-bed reactors are difficult to wash after sample injection and the signal took longer to return to the baseline after an FIA peak. In some cases, the baseline value was not fully reached again.