(hal' a zone).
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C7H5Cl2NO4S 270.09
Benzoic acid, 4-[(dichloroamino)sulfonyl]-;    
p-(Dichlorosulfamoyl)benzoic acid     [80-13-7].
Halazone contains NLT 91.5% and NMT 100.5% of C7H5Cl2NO4S, calculated on the dried basis.
•  Procedure
Sample:  100 mg
Analysis:  Add the Sample to 5 mL of a sodium bromide solution (1 in 10).
Acceptance criteria:  Bromine is liberated from the mixture.
•  Procedure
Sample:  150 mg
Analysis:  Add the Sample to 10 mL of 2.5 N sodium hydroxide in a 250-mL iodine flask, and stir well to dissolve. Add 75 mL of water, then promptly add 15 mL of potassium iodide solution (1 in 10), and mix. Acidify with 10 mL of 6 N acetic acid, and titrate immediately with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium thiosulfate is equivalent to 6.752 mg of C7H5Cl2NO4S.
Acceptance criteria:  91.5%–100.5% on the dried basis
Organic Impurities 
•  Procedure: Readily Carbonizable Substances Test 271
Sample:  100 mg
Analysis:  Dissolve the Sample in 0.5 mL of sulfuric acid.
Acceptance criteria:  No blackening occurs, although some effervescence may take place.
•  Loss on Drying 731: Dry a sample over phosphorus pentoxide for 4 h: it loses NMT 0.5% of its weight.
•  Packaging and Storage: Preserve in tight, light-resistant containers.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Ahalya Wise, M.S.
Senior Scientific Liaison
(SM12010) Monographs - Small Molecules 1
USP35–NF30 Page 3394
Pharmacopeial Forum: Volume No. 34(5) Page 1163