APPLICATION OF FACTORIAL DESIGN TO IMPROVE A FIA SYSTEM FOR PENICILLIN DETERMINATION

A potentiometric FIA system for penicillin determination, employing pe nicillinase [E.C. 3.5.2.6] immobilized on silica gel, packed into a re actor, was improved by the use of statistically designed experiments. A two-level and three-factor factorial was used to find the best worki ng conditions evaluating the influence of some parameters on the signa l response of the system and the number of determinations per hour. Th ese parameters were analyzed individually obtaining two level of the v ariables to be used in the factorial design: length of the reactor (1. 5 and 2.0 cm), carrier flow rate (1.6 and 2.2 mi min(-1)) and sample v olume (100 and 150 mu l). The pure error on the measurements was estim ated by authentic repetitions. The ideal working conditions taking int o account a compromise between the best response signal and the number of determinations per hour (with the same importance) being chosen th e level of factors: length of reactor 1.5 cm, carrier flow rate 2.2 ml min(-1) and sample volume of 150 mu l. Under these conditions the sys tem allowed to analyze was about 45 samples per hour, during 73 days, with a standard deviation of 2.4% at concentration range between 10(-1 ) and 10(-3) mol l(-1).