Abstract: A flow injection analysis method for the determination of the lactate anion with enzyme amplification and amperometric detection is described. The system utilizes an oxygen electrode for measurement of changes in the oxygen concentration in the flow stream. Two enzymes, lactate oxidase and lactate dehydrogenase, were randomly coimmobilized on aminopropyl controlled-pore glass (AMP-CPG) and packed into a reactor. β-NADH was used as a coenzyme for the regeneration of lactate from pyruvate. The experimental conditions for the determination of the lactate anion were studied for this system by the simplex and the univariant methods. The results obtained under these two conditions were compared. The simplex experimental condition yielded a calibration curve whose linear portion had a slope that was 1.2 times greater than that of the linear portion of the curve obtained under univariant conditions. The limit of detection under simplex condition was 1.19 x 10^-7 M vs 3.29 x 10^-7 M lactate under univariant conditions. The relative standard deviation obtained for this system at 6 x 10^-6 M lactate (n = 10) was about 2.5% under simplex conditions and 3.6% under univariant maximization conditions.

Abstract: The simple system described is capable of analyzing 70 samples h-1 at a flow rate of 2.2 mL min-1. It involves measurement, in an aqueous solvent system of 0.1 M HNO3, 1.95 mM Na2MoO4 and 30% (v/v) methanol, of the reduction current of previously formed 12-molybdophosphoric acid at a platinum electrode in a commercial amperometric thin-layer detector (Bioanalytical Systems). The peak area is rectilinearly related to PO43- concentration. up to 50 µM, the detection limit (signal-to-noise ratio = 2) is 0.02 µM in the original sample, and the coefficient of variation (n = 5) at the 1 µM level is 2.6%. For the determination of P in 10 samples of urine, results by the proposed method did not differ at the 95% level of confidence from those obtained by a spectrophotometric method. Silicate in a ratio of 10:1 to PO43- interferes substantially, as do Fe(III) at 1:10, Cu(II) at 1:1 and As at 10:1; glucose does not interfere even in a ratio of 100:1.