Sulfuric Acid
(sul fure' ik as' id).

H2SO4 98.08
Sulfuric acid     [7664-93-9].
DEFINITION
Sulfuric Acid contains NLT 95.0% and NMT 98.0%, by weight, of sulfuric acid (H2SO4).
[Caution—When sulfuric acid is to be mixed with other liquids, always add it to the diluent, and exercise great caution. ]
IDENTIFICATION
•  A. Identification Tests—General, Sulfate 191: Meets the requirements
ASSAY
•  Procedure
Sample solution:  Place 1 mL of Sulfuric Acid in a weighed, glass-stoppered flask containing 20 mL of water, and weigh again to obtain the weight of the Sulfuric Acid. Dilute with 25 mL of water, and cool.
Titrimetric system 
(See Titrimetry 541.)
Mode:  Direct titration
Titrant:  1 N sodium hydroxide VS
Blank:  45 mL of water
Endpoint detection:  Visual
Analysis:  To the Sample solution add methyl orange TS, and titrate with 1 N sodium hydroxide VS. Perform a blank determination. Calculate the percentage of sulfuric acid (H2SO4) taken:
Result = {[(VS VB) × N × F]/W} × 100
VS== Titrant volume consumed by sulfuric acid in the Sample solution (mL)
VB== Titrant volume consumed by the Blank (mL)
N== Titrant actual normality (mEq/mL)
F== equivalency factor, 49.04 mg/mEq
W== weight of sulfuric acid in the Sample solution (mg)
Acceptance criteria:  95.0%–98.0%
IMPURITIES
•  Residue on Ignition 281
Sample:  22 mL (40 g)
Analysis:  Evaporate the Sample to dryness, and ignite.
Acceptance criteria:  NMT 2 mg of residue remains (0.005%).
•  Chloride and Sulfate, Chloride 221: A dilution of 1.1 mL (2.0 g) in water shows no more chloride than corresponds to 0.15 mL of 0.020 N hydrochloric acid (50 ppm).
•  Arsenic 211
Test preparation:  Add 1.6 mL (3.0 g) to a mixture of nitric acid and water (3:20). Evaporate the solution until dense fumes of sulfur trioxide form. Cool, and cautiously wash the solution into an arsine generating flask with 50 mL of water.
Analysis:  Proceed as directed in the chapter, omitting the addition of the 20 mL of 7 N sulfuric acid.
Acceptance criteria:  NMT 1 ppm
•  Heavy Metals 231
Test preparation:  Add 2.2 mL (4.0 g) to 10 mg of sodium carbonate dissolved in 10 mL of water. Heat until almost dry. Add 1 mL of nitric acid, and evaporate to dryness. Add 2 mL of 1 N acetic acid to the residue, and dilute with water to 25 mL.
Analysis:  Proceed as directed in the chapter.
Acceptance criteria:  NMT 5 ppm
SPECIFIC TESTS
•  Reducing Substances
Sample:  4.4 mL (8.0 g)
Analysis:  Carefully dilute the Sample with 50 mL of ice-cold water, keeping the solution cold during the addition. Add 0.10 mL of 0.10 N potassium permanganate.
Acceptance criteria:  The solution remains pink for 5 min.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers.
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
USP35–NF30 Page 2001