Rapid electroenzymatic measurement of lactate in microsamples of spinal fluid

A lactate sensor, which makes possible rapid direct measurement of L-lactate in small samples of spinal fluid, has been developed. This enzyme electrode gives a linear current output as a function of hydrogen peroxide generated by a lactate oxygen oxidoreductase sandwiched between two membranes. The membranes serve to support the oxidase, prevent the diffusion of soluble electroactive species such as urate, ascorbate, and phenolic drugs such as acetaminophen, and to form a diffusion-limited path for the lactate. A 10 or 25 microL sample of spinal fluid is injected into a 350 microL thermostated chamber containing a suitable buffer and the electrode's sensing surface. The method has been tested by analysis of spinal fluid, with amounts of lactate up to 15 mmol/L, by comparison with a photoenzymatic method. A correlation coefficient of 0.999 was found. With a new cellulose ester membrane, acetaminophen levels up to 10 mmol/L did not interfere. A YSI glucose analyzer can be converted to a lactate analyzer by changing the O-ring mounted enzyme transducer membrane.