The influence of different additives on the performance of a bienzyme carbon paste electrode for the detection of L-lactate was investigated. The influence of the pH during the adsorptive coimmobilization of lactate oxidase and horseradish peroxidase on heat pretreated carbon particles was determined in the presence and in the absence of polyethylenimine (PEI). In the absence of PEI the highest H 2 0 2 and lactate sensitivities can be achieved after using a pHi of around 7. In the presence of PEI the response to background ratio can be increased considerably by using pH, values higher than 8.5. The lactate sensitivity is relatively independent of the pH,.
The influence of the additives poly-L-lysine, poly-L-arginine, spermine, and spermidine was also investigated. The use of positively charged poly-aminoacids improves both the sensitivity/background ratio and the long-term stability of L-lactate and Hz02 detection.
Also the choice of both the carboneous powder and the pasting liquid has a considerable influence on the sensor characteristics. A heat treatment of the carboneous powder at 700 "C for 15 s improves the sensitivity of HRP modified CPEs in most cases. The replacement of the organic pasting liquid by organic solids, e.g., octadecane, heneicosane, and naphthene opens up a way to prepare robust and sensitive lactate sensors.
The considered influences of the carbon paste composition and the immobilization conditions were discussed both with respect to the H202 and the L-lactate responses.