Polyvinyl Acetate Phthalate
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
1 DEFINITION
Polyvinyl Acetate Phthalate is a reaction product of phthalic anhydride and a partially hydrolyzed polyvinyl acetate. It contains NLT 55.0% and NMT 62.0% of phthalyl (o-carboxybenzoyl, C8H5O3) groups, calculated on the anhydrous, acid-free basis.
2 IDENTIFICATION
A. The Sample solution in the Assay exhibits a maximum at 277 ± 3 nm.
B.
Sample: 10 mg
Analysis: Place the Sample in a small test tube, add 10 mg of Resorcinol, and mix. Add 0.5 mL of sulfuric acid, and heat in a liquid bath at 160° for 3 min. Cool, and pour the solution into a mixture of 25 mL of 1 N sodium hydroxide and 200 mL of water.
Acceptance criteria: The solution shows a vivid green fluorescence.
C.
Sample solution: 100 mg/mL of Polyvinyl Acetate Phthalate in methanol
Analysis: Pour 1 mL of the Sample solution onto a clear glass plate.
Acceptance criteria: A lm is deposited as the methanol evaporates.
3 ASSAY
Phthalyl Content
Standard solution: 0.05 mg/mL of phthalic anhydride in alcohol, prepared as follows. Transfer 50 mg of phthalic anhydride to a 1000-mL volumetric flask. Dissolve with heat in 100 mL of alcohol, dilute with alcohol to volume, and mix.
Sample solution: 0.1 mg/mL of Polyvinyl Acetate Phthalate in alcohol, prepared as follows. Transfer 100 mg of Polyvinyl Acetate Phthalate to a 1000-mL volumetric flask, dissolve in alcohol, and dilute with alcohol to volume.
Instrumental conditions
Mode: UV
Cell: 1 cm
Analytical wavelength: 275 nm
Analysis
Samples: Standard solution and Sample solution
Calculate, on the acid-free basis, the percentage of phthalyl taken:
Result = (AU/A ) × (C /CU ) × 100
AU = absorbance of the Sample solution
AS = absorbance of the Standard solution
CS = concentration of phthalic anhydride in the Standard solution (mg/mL)
CU = concentration of Polyvinyl Acetate Phthalate in the Sample solution (mg/mL)
Acceptance criteria: 55.0%–62.0% of phthalyl (o-carboxybenzoyl, C8H5O3) groups on the anhydrous, acid-free basis
4 IMPURITIES
Residue on Ignition 〈281〉: NMT 1.0%
Free Phthalic Acid
Standard solution: 0.05 mg/mL of phthalic anhydride
Sample solution: 6 mg/mL of polyvinyl acetate phthalate in water prepared as follows. Dissolve 1500 mg of Polyvinyl Acetate Phthalate in 50 mL of a mixture of methylene chloride and methanol (4:1). Transfer the solution to a separator with the aid of 75 mL of water, and swirl, taking care not to shake. Add 100 mL of hexanes, shake, and allow the mixture to stand until it separates into two layers. Transfer the water layer to a 250-mL volumetric flask. Add 100 mL of water to the separator, shake, and allow to stand until the layers separate. Transfer the water layer to the same volumetric flask, and dilute with water to volume. If the solution is cloudy, centrifuge a portion until clear.
Instrumental conditions
Mode: UV
Cell: 1 cm
Analytical wavelength: 277 nm
Analysis
Samples: Standard solution and Sample solution
Calculate the percentage of free phthalic acid in the portion taken:
Result = (AU/AS) × (CS/CU) × (Mr1/Mr2 ) × 100
AU = absorbance of the Sample solution
AS = absorbance of the Standard solution
CS = concentration of phthalic anhydride in the Standard solution (mg/mL)
CU = concentration of Polyvinyl Acetate Phthalate in the Sample solution (mg/mL)
Mr1 = molecular weight of phthalic acid, 166.13
Mr2 = molecular weight of phthalic anhydride, 148.12
Acceptance criteria: NMT 0.6% on the anhydrous basis
Free Acid Other Than Phthalic
Sample solution: Proceed as directed for Sample solution in Impurities, Free Phthalic Acid, but instead of transferring the water extracts to a volumetric flask, transfer them to a 400-mL beaker.
Titrimetric system
(See Titrimetry 〈541〉.)
Mode: Direct titration
Titrant: 0.1 N sodium hydroxide VS
Endpoint detection: Visual
Analysis: Titrate the Sample solution with Titrant to a phenolphthalein endpoint.
Calculate the volume, V , in mL, of 0.1 N sodium hydroxide consumed by the free phthalic acid in the sample taken:
V = (1/Mr ) × (1/N) × P × W
Mr = equivalent weight of phthalic acid, 83.065 mg/mEq
N = actual normality of the Titrant (mEq/mL)
P = percentage of free phthalic acid, previously determined, in decimal form
W = sample weight of Polyvinyl Acetate Phthalate on the anhydrous basis (mg)
Calculate the percentage of free acid other than phthalic, as acetic acid, in the portion taken:
Result = [(V − Vp ) × Mr3 × N]/W × 100
V = total volume of 0.1 N sodium hydroxide used (mL)
Mr3 = equivalent weight of acetic acid, 60.05 mg/mEq
N = actual normality of the Titrant
W = sample weight on the anhydrous basis (mg)
Acceptance criteria: NMT 0.6% on the anhydrous basis
5 SPECIFIC TESTS
Viscosity—Capillary Methods 〈911〉
Sample solution: Dissolve a quantity, equivalent to 15 g on the anhydrous basis, in 85 g of methanol.
Analysis: Determine the viscosity of the Sample solution, using a capillary viscometer at 25 ± 0.2°.
Acceptance criteria: The apparent viscosity is 7–11 mPa · s (centipoises).
Water Determination, Method I 〈921〉: NMT 5.0%
6 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight containers.
