COMPARISON OF FLOW-INJECTION ANALYTICAL BIOSYSTEMS BASED ON OPEN-TUBEAND PACKED-BED ENZYME REACTORS

A comparison between the most widely used enzyme reactors in flow inje ction analysis (FIA) systems has been realised, These reactors were th e open-tube reactors and the packed-bed reactors. The comparison was r ealised with three different enzymes (urease, creatinine iminohydrolas e and creatine amidinohydrolase). The enzymes were covalently immobili sed on controlled-pore glass beads (CPG). These beads were used as the filling for the packed-bed reactors. The enzymes were also immobilise d covalently on the inner wall of nylon tube reactors. All three enzym es were used in clinical analysis and they have clearly distinguished activities. All of them produced ammonium ions as a consequence of the ir interaction with their respective substrates; The single channel FI A system used for the evaluation and the comparison of the reactors wo rked automatically and included a flow bioreactor and an ammonium-ion sensor. The FIA systems used with the different bioreactors were optim ised to obtain the largest signal in the shortest time. Once optimised , the performance of the reactors were evaluated and compared while wo rking with each enzyme. The parameters to evaluate were: calibration p arameters (y-ordinate, slope and linear), reproducibility, conversion ratio (yield) of the enzyme reaction in the reactor, dynamic parameter s (response time and analysis time) and lifetime. The comparison of th e 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 r esponse times. Open-tube reactors showed a higher reproducibility, a h igher 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. (C) 1 998 Elsevier Science B.V. All rights reserved.