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USP–NF Online: <191> Identification Tests—General, Chloride

Type of Posting: Publication Correction
Posting Date: 20–Nov–2018

USP recently discovered an error with <191> as it appears in USP–NF Online. A future PF version was inadvertently published in the USP–NF Online on November 1, 2018 (  

The correct text of the <191> Identification Tests-General, Chloride is available below. The file will be corrected and the updated version made available via the monthly posting on November 30, 2018.


With silver nitrate TS, solutions of chlorides yield a white, curdy precipitate that is insoluble in nitric acid but is soluble in a slight excess of 6 N ammonium hydroxide.
When testing amine (including alkaloidal) hydrochlorides that do not respond to the above test, add 1 drop of diluted nitric acid and 0.5 mL of silver nitrate TS to a solution of the substance being examined containing, unless otherwise directed in the monograph, about 2 mg of chloride ion in 2 mL: a white, curdy precipitate is formed. Centrifuge the mixture without delay, and decant the supernatant layer. Wash the precipitate with three 1-mL portions of nitric acid solution (1:100), and discard the washings. Add ammonia TS dropwise to this precipitate. It dissolves readily.
When a monograph specifies that an article responds to the test for dry chlorides, mix the solid to be tested with an equal weight of manganese dioxide, moisten with sulfuric acid, and gently heat the mixture: chlorine, which is recognizable by the production of a blue color with moistened starch iodide paper, is evolved.

USP apologizes for any inconvenience this may have caused.

Should you have any questions, please contact Caroline Martin, Director, Publications (301-816-8521 or