Uffelmann's Test

The best test for lactic acid is made with the Uffelmann1 solution, which has always to be freshly prepared before use. It consists of a two-per-cent. carbolic-acid solution in water, to which is added a drop of sesquichloride of iron. This test solution has an amethyst-blue color. Place about 2 c,c. of this Uffelmann solution in a test tube, and add a few drops of the filtrate. The presence of lactic acid brings on a canary-yellow color; the presence of fatty acids produces an ashy-gray color, whereas inorganic acids decolorize the blue color of the Uffelmann solution.

As some phosphates are liable to give the same reaction with the Uffelmann solution as lactic acid, and as these salts are very often present in the gastric contents, the surest way to discover the presence of lactic acid in the filtrate is the following: 5 or 10 c.c. of the filtrate are well shaken for quite a while in a test tube with a double quantity of ether. Then the tube is allowed to stand a few minutes until the ether has separated from the watery solution. Pour the ethereal portion into another test tube, which is placed in a glass of hot water, so as to allow its contents to evaporate. After evaporation has taken place, only a few drops remain in the test tube. Add 1 to 2 c.c. of distilled water and test for lactic acid with the Uffelmann solution. If a canary-yellow color now arises, the presence of lactic acid is positively shown.

Instead of evaporating the ether Fleischer2 recommends testing the poured off ethereal extract directly with the Uffelmann solution; the presence of lactic acid gives the canary-yellow color above described.

1 Uffelmann: Deutsches Arcliiv f. klin. Med., vol. 26, p. 431. 2Fleischer: "Milchsaurenachweis im directen Aether." Cited from Penzoldt: Deutsch. Arch. f. klin. Medicin, Bd. ii., p. 544.

A new test for lactic acid has been suggested by Arnold.1 The test solution consists of two reagents: (1) A solution of gentian violet (0.2 c.c. saturated alcoholic solution in 500 c.c. distilled water), and (2) 5 c.c. of the tincturaferri perchloridi, U. S. P., diluted with 20 c. c distilled water. A drop of the iron solution strikes a blue color with 1 c.c. of the gentian violet, which changes to a green or yellow-green when a few drops of gastric contents, containing lactic acid, are added.

Boas' Procedure For The Qualitative Determination Of Lactic Acid

The principle of this method consists in the fact that when solutions of lactic acid are treated and heated with oxidizable substances, a splitting of these occurs into acetaldehyde and formic acid, according to the following formula:

CH2 -CH (OH) - COOH = CH2 - CHO + CHOOH. Lactic acid Acetaldehyde Formic acid.

The method of procedure is as follows: Take 10-20 c.c. of the filtrate and evaporate in a porcelain dish over the water-bath to a syrupy consistence. (If hydrochloric acid was present, then the addition of barium carbonate during the evaporation is necessary.) Add a few drops of phosphoric acid, expel the carbonic acid by boiling, and after cooling, extract with small portions of ether (two or three times, 50 c.c. each). After stirring for half an hour pour off the clear layer of ether. The ether is now evaporated; the residue, taken up with 45 c.c. of water, is well shaken and filtered. To the filtrate add 5 c.c. of con-centrated sulphuric acid (sp. gr. 1.89) and a knife-pointful of manganese. The mixture is now distilled and the vapors conducted into a cylinder which contains either 5-10 c.c. of an alkaline solution of iodine (i.e., equal parts of decinormal iodine solution and standard potassium-hydrate solution), or the same quantity of Nessler's reagent. If lactic acid is present, the aldehyde escapes with the vapors and gives rise to the formation of iodoform (turbidity and iodoform smell, Lieben's reaction), or (with Nessler's reagent) of the yellowish-red aldehyde of mercury as shown by the yellow color.

1 Arnold: Journ. Am. Med. Assoc, 1898, vol. viii., p. 21.

On the same principle, Boas also devised a quantitative method for determining the amount of lactic acid. This new test has certainly a scientific value, but thus far it has remained without practical importance. The procedure is quite complicated and hardly gives more accurate results than the usual test of Uffelmann described above.