Content of potassium lactate

Weigh accurately a quantity of solution of lactic acid powder, potassium lactate equivalent to 500mg, placed in a suitable flask, add acetic anhydride: acetic acid = 1:5 mixed solution of 60ml, the mixture Sodium lactate to stand for 20min. With 0.1mol / L perchloric acid in glacial acetic acid solution by the potentiometric titration of its endpoint. While doing a blank test and make the appropriate corrections. Per Ml 0.1mol / L perchloric acid potassium lactate equivalent to 12.82mg.