Manometric Method for Quantitative Determination of Lactic Acid.

Abstract

Van Slyke and Neill 1 have recently introduced an apparatus for the determination of blood gases by manometric methods. This manometric blood-gas apparatus has been used by Van Slyke and Sendroy 2 in determining blood Ca. The Ca is precipitated as the Department of Anatomy, Cornell University Medical College, xddition of acidified KMnO₄. The oxalate is oxidized to CO₂ and H₂O, and the CO₂ so produced determined in the usual way.

A modification of the Clausen method for the determination of small amounts of lactic acid was described recently by Friedemann, Cotonio, and Shaffer. 3 These investigators found that the use of manganous salt increases the rate and yield of aldehyde when lactates are oxidized by acid KMnO₄.

The writers have developed a method for the determination of lactates using the manometric apparatus of Van Slyke and Neill, and in part the modified Clausen reagents of Friedemann, Cotonio, and Shaffer.

In selecting a mixture of MnSO₄ and KMnO₄ that would fully oxidize lactic acid to acetaldehyde and CO₂, an excess of MnSO₄ was found to prevent the oxidation or greatly to retard the process and this was also true for equal amounts of MnSO₄ and KMnO₄. When excess KMnO₄ was present good results were obtainecf over a considerable range of ratios of KMnO₄ to MnSO₄ as shown in Table I. Shaffer gives the oxidation-reduction potential necessary to oxidize lactic acid as +1.36 at 25° C. but carries out oxidation at the boiling point, i. e., at an Eh of approximately +1.74. The Eh of our oxidizing agent was about +1.44 in the concentration of sulphuric acid employed, namely Normal and at 20°.

Procedure: The apparatus was the closed manometer type of Van Slyke gas apparatus. Reagents consisted of 5N H₂SO₄, M/10 KMnO₄, M/10 MnS0₄, Standard Lactic Acid, 5 N NaOH.