Sodium Benzoate
(soe' dee um ben' zoe ate).
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C7H5NaO2 144.10
Benzoic acid, sodium salt;    
Sodium benzoate     [532-32-1].
DEFINITION
Sodium Benzoate contains NLT 99.0% and NMT 100.5% of C7H5NaO2, calculated on the anhydrous basis.
IDENTIFICATION
•  A. Infrared Absorption 197M: On the undried specimen
•  B. Identification Tests—General, Sodium 191: Meets the requirements
•  C. Identification Tests—General, Benzoate 191: Meets the requirements
ASSAY
•  Procedure
Sample:  600 mg
Titrimetric system 
Mode:  Direct titration
Titrant:  0.1 N perchloric acid VS
Blank:  100 mL of glacial acetic acid
Endpoint detection:  Visual
Analysis:  To the Sample add 100 mL of glacial acetic acid, and stir until completely dissolved. Add 2 drops of crystal violet TS, and titrate with 0.1 N perchloric acid VS to a green endpoint. Perform a blank determination.
Calculate the percentage of sodium benzoate (C7H5NaO2) in the Sample taken:
Result = [(VS VB) × N × F]/W × 100
VS== volume of Titrant consumed by the Sample (mL)
VB== volume of Titrant consumed by the Blank (mL)
N== actual normality of the Titrant (mEq/mL)
F== equivalency factor, 144.1 mg/mEq
W== weight of the Sample (mg)
Acceptance criteria:  99.0%–100.5% on the anhydrous basis
IMPURITIES
•  Heavy Metals 231
Test preparation:  4.0 g in 40 mL of water
Analysis:  To the Test preparation add dropwise with vigorous stirring 10 mL of 3 N hydrochloric acid, and filter. Use 25 mL of the filtrate.
Acceptance criteria:  NMT 10 ppm
SPECIFIC TESTS
•  Alkalinity
Sample solution:  2 g in 20 mL of hot water
Analysis:  To the Sample solution add 2 drops of phenolphthalein TS.
Acceptance criteria:  The pink color produced, if any, is discharged by the addition of 0.20 mL of 0.10 N sulfuric acid.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in well-closed containers.
•  USP Reference Standards 11
USP Sodium Benzoate RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, M.S.
Scientific Liaison
1-301-816-8335
(EXC2010) Monographs - Excipients
Reference Standards RS Technical Services
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USP35–NF30 Page 1950
Pharmacopeial Forum: Volume No. 31(3) Page 818