Phosphoric Acid
H3PO4 98.00
Phosphoric acid
[7664-38-2].
(fos for' ik as' id).
H3PO4 98.00
Phosphoric acid
[7664-38-2].DEFINITION
Phosphoric Acid contains NLT 85.0% and NMT 88.0%, by weight, of H3PO4.
[Caution—Avoid contact, because Phosphoric Acid rapidly destroys tissues.
]
IDENTIFICATION
• A. Identification Tests—General, Phosphate 
191
:
When carefully neutralized with 1 N sodium hydroxide, phenolphthalein TS being used as the indicator, it meets the requirements.
191:
When carefully neutralized with 1 N sodium hydroxide, phenolphthalein TS being used as the indicator, it meets the requirements.
ASSAY
• Procedure
Sample:
1 g
Blank:
120 mL of water
Titrimetric system
(See Titrimetry 541.)
541.)
Mode:
Direct titration
Titrant:
1 N sodium hydroxide VS
Endpoint detection:
Visual
Analysis:
Place the Sample in a tared, glass-stoppered flask, and dilute it with water to 120 mL. Add 0.5 mL of thymolphthalein TS. Titrate with 1 N sodium hydroxide VS to the first appearance of a blue color. Perform a blank determination.
Calculate the percentage of phosphoric acid (H3PO4) in the Sample taken:
Result = {[(VS 
VB) × N × F]/W} × 100
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, 49.00 mg/mEq |
| W | = | = weight of the Sample (mg) |
Acceptance criteria:
85.0%–88.0% by weight
IMPURITIES
• Heavy Metals, Method I 231:
NMT 10 ppm
231:
NMT 10 ppm
• Limit of Nitrate
Sample solution:
Dilute 6 mL of Phosphoric Acid with 14 mL of water.
Analysis:
Mix 5 mL of the Sample solution with about 0.1 mL of indigo carmine TS, then add 5 mL of sulfuric acid.
Acceptance criteria:
The blue color is not discharged within 1 min.
SPECIFIC TESTS
• Chloride and Sulfate, Sulfate 221
221
Sample solution:
Dilute 6 mL of Phosphoric Acid with 90 mL of water.
Analysis:
To the Sample solution add 1 mL of barium chloride TS.
Acceptance criteria:
No precipitate is formed immediately.
• Alkali Phosphates
Sample:
1 mL
Analysis:
Transfer the Sample to a graduated cylinder, and add 6 mL of ether and 2 mL of alcohol.
Acceptance criteria:
No turbidity is produced.
• Phosphorous or Hypophosphorous Acid
Sample solution:
Dilute 6 mL of Phosphoric Acid with 14 mL of water.
Analysis:
Gently warm 5 mL of the Sample solution, and add 2 mL of silver nitrate TS.
Acceptance criteria:
The mixture does not become brownish.
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 1891