A colorimetric reaction of chloride ion.

Specificity of Reactions-Several alkaloids were tested for their reaction with chloride, bromide, and iodide ions. The test system was as follows: From 0.01 to 0.05 milliequivalent of the halogen compound (sodium salt) was placed in calorimeter cuvettes. Water was added to make a volume of 5 ml. and then 2 ml. of 50 per cent phosphoric acid were added. 1 ml. of a 1 per cent solution of the alkaloid (in 5 per cent phosphoric acid) was added; the solution was mixed and 0.5 ml. of a 1.0 per cent solution of potassium persulfate was added. The tubes were placed in a boiling water bath for 30 minutes, allowed to cool at room temperature for 30 minutes, and diluted to the original volume. The amount of color development was measured at 540 rnp in a Coleman spectrophotometer, model 6-A. The results with brucine, strychnine, and cinchonidine are summarized in Table I. From the results given in Table I it is seen that chloride cannot be determined in the presence of bromide or iodide with brucine alone. It is possible, barring interference, to determine chloride in solutions containing no bromide or iodide, to determine bromide in the presence of chloride and in the absence of iodides, and to determine iodides in the presence of chlorides and bromides. Chloride Method-The method is essentially that given above; a solution of brucine is used but the period of heating is extended to 1 hour. The usable range is from about 0.005 to 0.05 milliequivalent (or from 0.1 to 2.0 mg.) of chloride ion in 5 ml. of sample. With suitable modification and small colorimet,er cuvettes, the sensitivity can be increased to 0.01 to 0.1