Hypromellose Acetate Succinate

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION 

Hypromellose Acetate Succinate is a mixture of acetic acid and monosuccinic acid esters of hydroxypropyl methylcellulose. It contains NLT 12.0% and NMT 28.0% of methoxy groups (–OCH₃), NLT 4.0% and NMT 23.0% of hydroxypropoxy groups (–OC₂HCHOHCH₃), NLT 2.0% and NMT 16.0% of acetyl groups (–COC₃), and NLT 4.0% and NMT 28.0% of succinoyl groups (–COC₂H₄COOH), calculated on the dried basis.

2 IDENTIFICATION 

Change to read: 

2.1 A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197A (CN 1-May-2020) 

Sample: Neat. Do not dry specimen. 

Analysis: Use a Fourier transform IR spectrophotometer tted with a suitable accessory for single bounce attenuated total reectance (see Mid-Infrared Spectroscopy 〈854〉) with a diamond or germanium crystal. Acquire a background single-beam spectrum with a clean diamond or germanium crystal sampling plate in place. Place the sample on the diamond or germanium crystal sampling surface with a microspatula or equivalent. For best results, the sample should cover the crystal surface under the pressure point tip. Using the pressure device, apply pressure to the sample, making sure the sample remains centered under the pressure tip. Acquire a single-beam spectrum of the sample, and make the necessary corrections for the background. Release the pressure device, and clear it from the sample area. Wipe the sample off the crystal and pressure device tip, and rinse both with acetone. 

Acceptance criteria: The IR spectrum of the Sample exhibits maxima only at the same wavelengths as a similarly obtained spectrum of USP Hypromellose Acetate Succinate RS. 

3 ASSAY 

3.1 Acetyl and Succinoyl Groups 

Phosphoric acid solution: 1.25 M phosphoric acid and water (2:98) 

Buffer: 2.72 g/L of monobasic potassium phosphate 

Diluent: Adjust the Buffer with 1 N sodium hydroxide to a pH of 7.5. 

Acetic acid stock solution: Add approximately 20 mL of water to a stoppered, 100-mL volumetric ask, place the ask on a balance, and tare. Transfer 2.0 mL of glacial acetic acid to the ask, and record the weight of the acid added. Fill the ask with water to volume. Transfer 6 mL of the resulting solution into a 100-mL volumetric ask, and dilute with water to volume. 

Succinic acid stock solution: 1.3 mg/mL of succinic acid 

Mobile phase: Adjust the Buffer to a pH of 2.8 by the dropwise addition of 6 M phosphoric acid. Pass through a 0.22-µm nylon lter. Standard solution 1: Transfer 4.0 mL of the Acetic acid stock solution and 4.0 mL of the Succinic acid stock solution to a 25-mL volumetric ask. Dilute with Mobile phase to volume, and mix. 

Standard solution 2: Prepare as directed for Standard solution 1. This solution is prepared as a duplicate. 

Sample solution: Weigh 12.4 mg of Hypromellose Acetate Succinate into a glass vial. Transfer 4.0 mL of 1.0 N sodium hydroxide to the vial, and stir the solution for 4 h. Then, add 4.0 mL of 1.25 M phosphoric acid to the same vial to bring the pH of the solution to 3 or less. Invert the test Sample solution vial several times to ensure complete mixing, and pass through a lter of 0.22-µm pore size. Use the clear ltrate. Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 215 nm 

Column: 4.6-mm × 15-cm; 5-µm packing L1 

Column temperature: 20°–30° 

Flow rate: 1 mL/min 

Run time: 15 min 

Injection volume: 10 µL 

System suitability 

Samples: Standard solution 1 and Standard solution 2 

Suitability requirements 

Column eciency: NLT 8000 theoretical plates, determined from the succinic acid peak, Standard solution 1 

Tailing factor: 0.9–1.5 for the succinic acid peak, Standard solution 1 

Relative standard deviation: NMT 2.0% for each peak from six replicate injections, Standard solution 1 

Peak difference: The difference in peak areas between Standard solution 1 and Standard solution 2 for both acetic and succinic acids peaks does not exceed 2%. 

[Note—After each run sequence, the column should be ushed rst by 50% water and 50% acetonitrile for 60 min and then by 100% methanol for 60 min. The column should be stored in 100% methanol.] 

Analysis 

Samples: Standard solution 1 and Sample solution 

Calculate the percentage of acetic acid, A, in the portion of Hypromellose Acetate Succinate taken: 

A = (r_UA/r_SA) × (C_A/C_U) × 100

r_UA = peak response for acetic acid from the Sample solution  

r_SA = peak response for acetic acid from Standard solution 1 

C_A = concentration of acetic acid in Standard solution 1 (mg/mL) 

C_U = concentration of Hypromellose Acetate Succinate in the Sample solution (mg/mL) 

Calculate the percentage of acetyl groups (–COCH₃) in the portion of Hypromellose Acetate Succinate taken: 

Result = (A − A_free) × (M_r1/M_r2) 

A = dened above 

A_free = percentage of free acetic acid, as determined in the test for Limit of Free Acetic and Succinic Acids 

M_r1 = molecular weight of the acetyl group, 43.04 

M_r2 = molecular weight of acetic acid, 60.05 

Calculate the percentage of succinic acid, S, in the portion of Hypromellose Acetate Succinate taken: 

S = (r_US/r_SS) × (C_S/C_U) × 100

r_US = peak response for succinic acid from the Sample solution 

r_SS = peak response for succinic acid from Standard solution 1 

C_S = concentration of succinic acid in Standard solution 1 (mg/mL) 

C_U = concentration of Hypromellose Acetate Succinate in the Sample solution (mg/mL) 

Calculate the percentage of succinoyl groups (–COC₂H₄COOH) in the portion of Hypromellose Acetate Succinate taken:

Result = (S − S_free) × (M_r1/M_r2) 

S = dened above 

S_free = percentage of free succinic acid, as determined in the test for Limit of Free Acetic and Succinic Acids 

M_r1 = molecular weight of the succinoyl group, 101.08 

M_r2 = molecular weight of succinic acid, 118.09 

Acceptance criteria 

Acetyl groups (–COCH₃): 2.0%–16.0% on the dried basis 

Succinoyl groups (–COC₂H₄COOH): 4.0%–28.0% on the dried basis 

3.2 Content of Methoxy and 2-Hydroxypropoxy Groups 

[Caution—Hydriodic acid and its reaction byproducts are highly toxic. Perform all steps in the preparation of the Sample solution and the Standard solution in a properly functioning hood. Specic safety practices to be followed are to be identied to the analyst performing this test.] 

Hydriodic acid: Use a reagent having a specic gravity of at least 1.69, equivalent to 55% hydrogen iodide. 

Solution A: Methanol and water (10:90) 

Solution B: Methanol and water (85:15) 

Mobile phase: See Table 1. 

Table 1 

[Note—These gradient elution times are established on an HPLC system with a dwell volume of approximately 2.0 mL. The injection time can be adjusted relative to the start of a run to accommodate the change in dwell volume from one HPLC system to another to achieve the separation described.] 

Standard stock solution: Transfer 2 mL of o-xylene into a stoppered, 10-mL volumetric ask, place the ask on a balance, and tare. Add 200 µL of methyl iodide, insert the stopper into the ask, and accurately weigh: the weight of methyl iodide is about 350 mg. Tare the ask again, add 34 µL of isopropyl iodide, and weigh the ask: the recorded weight of isopropyl iodide is 50 mg. Dilute with o-xylene to volume, and mix. 

Standard solution: Transfer 85 mg of adipic acid into an 8-mL vial (or other suitable container), add 2 mL of Hydriodic acid, and add 2.0 mL of the Standard stock solution. Shake and allow the phases to separate. Carefully transfer approximately 1.5 mL of the o-xylene (top) layer to a small vial, making sure that the bottom aqueous layer is not disturbed. Transfer 1.0 mL of the resulting solution to a 10-mL volumetric ask, and dilute with methanol to volume. [Note—This solution is stable for 8 h at 5°.] 

Sample solution: [Caution—Use a cap that has a top safety relief valve, such as a Minniert valve, to prevent accidental explosion of the vial under high pressure when heated.] Weigh 65 mg of Hypromellose Acetate Succinate into a 5-mL reaction vial, and add 2.0 mL of o-xylene and about 100 mg of adipic acid. Add 2.0 mL of Hydriodic acid, and close the vial tightly with a cap. 

Weigh the vial before heating, and place the vial into a heating block at 150°. Shake the vial after 5 min and after 30 min of heating. Remove the vial from the heating block after 1 h of heating, and cool. Weigh the vial. If the weight loss is greater than 10 mg, discard the mixture, and prepare another reaction solution. Carefully transfer approximately 1.5 mL of the top o-xylene layer into a small glass vial, making sure that the bottom aqueous layer is not disturbed. Transfer 1.0 mL of this solution into a 10-mL volumetric ask, and dilute with methanol to volume. [Note—This solution is stable for 8 h at 5°.] 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 254 nm 

Column: 4.6-mm × 15-cm; 5-µm packing L1 

Column temperature: 30° 

Flow rate: 1 mL/min 

Injection volume: 10 µL 

System suitability 

Sample: Standard solution 

Suitability requirements 

Column eciency: NLT 10,000 theoretical plates, determined from the methyl iodide peak 

Tailing factor: 0.9–1.5 for the methyl iodide peak 

Relative standard deviation: NMT 2.0% for each peak 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of methoxy groups (–COCH₃) in the portion of Hypromellose Acetate Succinate taken: 3 

Result = (r_UM/r_SM) × (C_s/C_u) × (M_r1/M_r2) × 100

r_UM = peak response for methyl iodide from the Sample solution 

r_SM = peak response for methyl iodide from the Standard solution 

C_s = concentration of methyl iodide in the Standard solution (mg/mL) 

C_u = concentration of Hypromellose Acetate Succinate in the Sample solution (mg/mL) 

M_r1 = molecular weight of the methoxy group, 31.03 

M_r2 = molecular weight of methyl iodide, 141.94 

Calculate the percentage of 2-hydroxypropoxy groups (–COC₂H₄COOH) in the portion of Hypromellose Acetate Succinate taken: 2 3 

Result = (r_US/r_SI) × (C_s/C_u) × (M_r1/M_r2) × 100

r_US = peak response for isopropyl iodide from the Sample solution 

r_SI = peak response for isopropyl iodide from the Standard solution 

C_s = concentration of isopropyl iodide in the Standard solution (mg/mL) 

C_u = concentration of Hypromellose Acetate Succinate in the Sample solution (mg/mL) 

M_r1 = molecular weight of the 2-hydroxypropoxy group, 75.09 

M_r2 = molecular weight of isopropyl iodide, 169.99 

Acceptance criteria 

Methoxy groups (–COCH₃): 12.0%–28.0% on the dried basis 

Hydroxypropoxy groups (–COC₂H₄COOH): 4.0%–23.0% on the dried basis 

4 IMPURITIES 

4.1 Residue on Ignition 〈281〉 

Analysis: Determine at 600 ± 50°. 

Acceptance criteria: NMT 0.20% 

4.2 Limit of Free Acetic and Succinic Acids 

Phosphoric acid solution, Buffer, Diluent, Acetic acid stock solution, Succinic acid stock solution, Mobile phase, Standard solution, and Chromatographic system: Proceed as directed in the Assay for Acetyl and Succinoyl Groups. 

Sample solution: Weigh 102 mg of Hypromellose Acetate Succinate into a glass vial. Transfer 4.0 mL of Diluent to the vial, and stir the content for 2 h. Then, transfer 4.0 mL of the Phosphoric acid solution to the same vial to bring the pH of the Sample solution to 3 or less. Invert the vial several times to ensure complete mixing, centrifuge, and use the clear supernatant. 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of free acetic acid, A_free, in the portion of Hypromellose Acetate Succinate taken: 

A_free = (r_UA/r_SA) × (C_A/C_U) × 100

r_UA = peak response for acetic acid from the Sample solution 

r_SA = peak response for acetic acid from the Standard solution 

C_A = concentration of acetic acid in the Standard solution (mg/mL) 

C_U = concentration of Hypromellose Acetate Succinate in the Sample solution (mg/mL) 

Calculate the percentage of free succinic acid, S_free, in the portion of Hypromellose Acetate Succinate taken: free 

S = (r_US/r_SS) × (C_s/C_u) × 100

r_US= peak response for succinic acid from the Sample solution 

r_SS = peak response for succinic acid from the Standard solution 

C_s = concentration of succinic acid in the Standard solution (mg/mL) 

C_u = concentration of Hypromellose Acetate Succinate in the Sample solution (mg/mL) 

Acceptance criteria: The sum of free acetic acid and free succinic acid is NMT 1.0%. 

5 SPECIFIC TESTS 

5.1 Loss on Drying 〈731〉 

Analysis: Dry at 105° for 1 h. 

Acceptance criteria: NMT 5.0% 

5.2 Viscosity—Capillary Methods 〈911〉 

Sodium hydroxide solution: Immediately before use, prepare 4.3 mg/mL of sodium hydroxide in carbon dioxide-free water. Analysis: To 2.00 g of Hypromellose Acetate Succinate, previously dried, add Sodium hydroxide solution to make 100.0 g, insert a stopper into the vessel, and dissolve by constant shaking for 30 min. Adjust the temperature of the solution to 20 ± 0.1°, and determine the viscosity in a suitable viscometer. 

Acceptance criteria: 80%–120% of that stated on the label 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers. No storage requirements specied. 

Labeling: Label it to indicate its nominal viscosity type. 

USP Reference Standards 〈11〉 

USP Hypromellose Acetate Succinate RS