A new method for the colorimetric determination of small concentrations of thymol.

Abstract

In order to evaluate the thymol content of sodium-fluoride, thymol mixtures used for the preservation of blood samples, the following simple method was devised.

Sulphanilic acid is diazotized and then coupled with thymol in alkaline solution. A reddish brown color stable for at least 50 minutes is obtained. The only alkali that gives satisfactory results is NaHCO₃.

METHOD (outline). 3 cc. of a 0.6 per cent sulphanilic acid solution (contains theory HC1 necessary to form sulphanilic acid hydrochloride) and 0.5 cc. of 2.0 per cent HC1 are pipetted into a sugar tube (Myers-Benedict). 0.5 cc. of a 1.5 per cent aqueous solution of NaNO₂ are then added and after one minute 1 to 5 cc. of the thymol solution to be analyzed. (The number of cc. of thymol solution used is diluted so that it will not contain more than 0.5 mg. thymol.) Allow to react 1 minute and then add 2 cc. of a 3.0 per cent NaHCO₃ solution. Set aside in diffused light for 10 minutes and then read in a colorimeter against a standard thymol solution 2 cc. of which contains 0.2 mg. (or 0.5 mg.) thymol. Thymol solutions are best prepared by first dissolving the thymol in a small volume of alcohol and then diluting to volume with distilled water.

In order to obtain the best results by this method the reagents listed above must be prepared and used with an accuracy of at least ±5.0 per cent.