Simultaneous determination of glucose and L-lactate in rat brain by an electrochemical in vivo flow-injection system with an on-line microdialysis sampling.

An electrochemical in vivo flow-injection system with an on-line microdialysis sampling is proposed for the simultaneous monitoring of L-lactate and glucose in rat brain. In the first stage of the operation, the dialysate from the microdialysis probe is delivered to a sample loop of the six-way autoinjector by perfusing Ringer's solution for 80 s at 5 microl min(-1). In the second stage, the dialysate collected in the sample loop is automatically injected for 10 s into the flow-injection line. Injected dialysate is split into two streams and two portions pass through two channels with two different immobilized enzyme reactors (glucose oxidase and lactate oxidase immobilized reactors) to produce hydrogen peroxide from glucose and L-lactate in the dialysate. After a subsequent confluence of the streams, produced hydrogen peroxide can be detected amperometrically at a downstream poly(1,2-diaminobenzene) film-coated platinum electrode, without any interference from oxidizable species and proteins present in the dialysate. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to L-lactate and the second peak to glucose. The peak current is linearly related to the concentrations of L-lactate between 0.2 and 10 mM and glucose between 0.1 and 20 mM. The present method can be successfully applied to the simultaneous in vivo monitoring of L-lactate and glucose in rat brain. The analytical speed is 45 dialysates h(-1).

Simultaneous determination of orthophosphate and total phosphates (inorganic phosphates plus purine nucleotides) using a bioamperometric flow-injection system made up by a 16-way switching valve.

Orthophosphate and total phosphates (inorganic phosphates plus purine nucleotides) can be determined simultaneously in a novel flow-injection system made up by a 16-way switching valve with two sample loops, acid phosphatase (AcP) immobilized reactor and a delay coil needed to separate two peaks corresponding to two sample portions injected simultaneously. An orthophosphate enzyme electrode with a hybrid membrane of trienzyme film and poly(1,2-diaminobenzene) film was used to selectively detect both the endogenous orthophosphate and orthophosphate generated enzymatically into the AcP immobilized reactor, without any interferences from electroactive species, such as ascorbate and urate. Because two sample portions passed through the flow line with different residence time, two peaks were obtained. The first peak corresponded selectively to orthophosphate and the second peak to the total of inorganic phosphates and purine nucleotides. The maximum currents of both peaks were linearly related to the concentration of orthophosphate and total phosphates (as orthophosphate) in the range 5x10(-7)-8x10(-4) M, respectively; 30 samples per hour can be processed with an R.S.D. <2.5%.