The Estimation of Sugar in Diabetic Urine, Using Dinitrosalicylic Acid

Dinitrosalicylic acid was introduced by the author in 1921 as a reagent for the estimation of sugar in normal and diabetic urine.1 It has also been found to be a valuable reagent for the detection of aIbumin in urine and has been used for the determination of the titratable alkali of the blood.2 During the past 3 years several improvements have been made in the method for the determination of sugar in diabetic urine. One of the chief errors in copper titration methods is the reoxidation of the cuprous oxide by atmospheric oxygen. With dinitrosalicylic acid, on the contrary, the amount of exposed surface has almost no effect, the same amount of reduction being given with tubes of all diameters. But with dinitrosalicylic acid the oxygen that is dissolved in the solution, while largely incapable of reoxidizing the reduction product, is able to destroy part of the sugar. It has been found that the addition to the reagent of a considerable amount of Rochelle salt largely prevents it from dissolving oxygen and greatly increases the amount of color given by small amounts of glucose. As used in the present modified manner, the amount of color given by 1 mg. of glucose is increased by about 65 per cent. As originally used, dinitrosalicylic acid gave practically no color with as little as 0.1 mg. of glucose, as nearly all of the glucose was oxidized by the dissolved oxygen. With the present modification the reaction is very dependable and the color values show such a good proportionality that the color given