This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
The following method is described by Villedieu and Hebert1 for the estimation of ethyl alcohol in dilute solutions containing 01 to 1 per cent., and is applied to the estimation of alcohol in urine. It depends upon the fact that, at a definite dilution, the quantity of alcohol converted into iodoform is constant. The iodoform is transformed into potassium iodide and the amount of this estimated volumetri-cally with silver nitrate.
Solutions are prepared containing quantities of alcohol varying from 0.1 to 1 per cent., and these solutions are treated as follows in order to obtain the value of the silver nitrate solution in terms of the different quantities of alcohol.
One hundred c.c. of the alcoholic solution are treated with 10 c.c. of 16 per cent. sodium hydroxide solution, and about 30 c.c. of 105 per cent. iodine solution are then added drop by drop. After three hours, a further small quantity of iodine solution is added, so that the mixture exhibits a yellow coloration. At the end of twenty-four hours the precipitated iodoform is collected on a filter and washed with cold water. With the smaller quantities of alcohol it is necessary to "seed" the mixture with a trace of iodoform in order to promote precipitation.
The filter and precipitate are now transferred to a flask, and boiled for twenty minutes under a reflux apparatus with 30 c.c. of saturated alcoholi- potassium hydroxide solution. The contents of the flask are then acidified with nitric acid, 20 c.c. of N/100-silver nitrate solution are added, and the excess of silver nitrate titrated with N/100-thiocyanate solution. The number of c.c. of
1 J. Pharm. Chim., 1917 (vii), 15, 41.
2 the silver nitrate solution required to precipitate the potassium iodide formed from the iodoform is thus obtained for the respective alcoholic solutions, and the numbers correspond with the quantities of alcohol present in the solutions.
Any dilute alcoholic solution of unknown strength is treated similarly, and the alcohol content ascertained from the volume of silver nitrate required to precipitate the resulting iodide.
To estimate alcohol in urine by this method, 200 c.c. of the sample, which must be free from acetone and aldehydes, are distilled after the addition of 1 c.c. of phosphoric acid, and 100 c.c. of distillate collected. This is treated as above described.