Spectrophotometric method for the determination of microquantities of lactic acid in biological material

A simple spectrophotometric method for the determination of microquantities of lactic acid is described. Lactic acid was quantitatively oxidized to acetaldehyde by cerium(IV) under prescribed conditions. Oxidation was terminated by reducing cerium(IV) to cerium(III) with nitrite. The acetaldehyde was reacted with copper ions and oxalydihydrazide under alkaline conditions to form an intense blue complex which is measured spectrophotometrically. The developed citrate-phosphate-borate-sodium hydroxide alkalizing reagent enhanced color stability by removing cerium from solution and also ensured extremely low blank values. Beer's law was followed over the range 0 to 150 micrograms of lactate. The method was successfully applied to the routine determination of lactate in silage and blood.