Valproic Acid Capsules
DEFINITION
Valproic Acid Capsules contain NLT 90.0% and NMT 110.0% of the labeled amount of valproic acid (C8H16O2).
IDENTIFICATION
•  A. The retention time ratios of the valproic acid peak to the internal standard peak from the Standard solution and from the Sample solution as obtained in the Assay do not differ by more than 2.0%.
•  B. Procedure
Sample:  Equivalent to 250 mg of valproic acid
Analysis:  Place the Sample in a separator, add 20 mL of 1 N sodium hydroxide, shake, and allow layers to separate. Transfer the aqueous layer to a second separator, add 4 mL of hydrochloric acid, mix, and extract with 40 mL of n-heptane. Filter the n-heptane layer through glass wool into a beaker, and evaporate the solvent completely on a steam bath with the aid of a current of air. Transfer 2 drops of the residue to a test tube containing 0.5 mL each of potassium iodide solution (1 in 50) and potassium iodate solution (1 in 25), and mix.
Acceptance criteria:  A yellow color is produced.
ASSAY
•  Procedure
Internal standard solution:  5 mg/mL of biphenyl in n-heptane
Standard stock solution:  2.5 mg/mL of USP Valproic Acid RS in n-heptane
Standard solution:  Combine 10.0 mL of Standard stock solution and 4.0 mL of Internal standard solution in a container equipped with a closure.
Sample stock solution:  Transfer NLT 20 Capsules to a blender jar or other container. Add 150 mL of methylene chloride, and cool in a solid carbon dioxide–acetone mixture until the contents have solidified. If necessary, transfer the mixture of Capsules and methylene chloride to a blender jar, and blend with a high-speed blender until all the solids are reduced to fine particles. Transfer the mixture to a 500-mL volumetric flask, add n-heptane to volume, mix, and allow solids to settle. Transfer a measured volume of the supernatant to a 100-mL volumetric flask, and dilute with n-heptane to volume to obtain a 2.5 mg/mL solution.
Sample solution:  Combine 5.0 mL of the Sample stock solution and 2.0 mL of the Internal standard solution in a container equipped with a closure.
Chromatographic system 
Mode:  GC
Detector:  Flame ionization
Column:  2-mm × 1.8-m glass column packed with 10% phase G34 on 80- to 100-mesh support S1A
Temperature 
Column:  150
Injector port:  250
Detector:  250
Carrier gas:  Dry helium
Flow rate:  40 mL/min
Injection size:  2 µL
System suitability 
[Note—The relative retention times for valproic acid and biphenyl are 0.5 and 1.0, respectively. ]
Sample:  Standard solution
Suitability requirements 
Resolution:  NLT 3.0 between valproic acid and biphenyl
Relative standard deviation:  NMT 2%
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of C8H16O2 in the portion of Capsules taken:
Result = (RU/RS) × (CS/CU) × 100
RU == peak response ratio of valproic acid to internal standard from the Sample solution
RS == peak response ratio of valproic acid to internal standard from the Standard solution
CS== concentration of USP Valproic Acid RS in the Standard solution (mg/mL)
CU== nominal concentration of valproic acid in the Sample solution (mg/mL)
Acceptance criteria:  90.0%–110.0%
PERFORMANCE TESTS
•  Dissolution 711
Medium:  5 mg/mL of sodium lauryl sulfate in simulated intestinal fluid TS (prepared without the enzyme and with monobasic sodium phosphate instead of monobasic potassium phosphate), adjusted with 5 M sodium hydroxide to a pH of 7.5; 900 mL
Apparatus 2:  50 rpm
Time:  60 min
Internal standard solution, Chromatographic system, and System suitability:  Proceed as directed in the Assay.
Standard solution:  Prepare a solution of USP Valproic Acid RS having a concentration similar to that of the Sample solution. Transfer 10.0 mL to a suitable container, add 3.0 g of sodium chloride, and mix on a vortex mixer for 5 min. Add 1 mL of 6 N hydrochloric acid and 5.0 mL of the Internal standard solution, and shake for 2 min. Allow the phases to separate, remove the n-heptane layer, and filter. Discard the aqueous layer.
Sample solution:  Transfer 10.0 mL of the solution under test to a suitable container, add 3.0 g of sodium chloride, and mix on a vortex mixer for 5 min. Add 1 mL of 6 N hydrochloric acid and 5.0 mL of the Internal standard solution, and shake for 2 min. Allow the phases to separate, remove the n-heptane layer, and filter. Discard the aqueous layer.
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of C8H16O2 taken:
Result = (RU/RS) × CS × (V/L) × 100
RU == peak response ratio of valproic acid to internal standard from the Sample solution
RS== peak response ratio of valproic acid to internal standard from the Standard solution
CS== concentration of USP Valproic Acid RS in the Standard solution (mg/mL)
V == volume of Medium (mL)
L == label claim of Capsules (mg)
Tolerances:  NLT 85% (Q) of C8H16O2 is dissolved.
•  Uniformity of Dosage Units 905: Meet the requirements, chloroform being used as the solvent in the procedure for Soft Capsules
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers, and store at controlled room temperature.
•  USP Reference Standards 11
USP Valproic Acid RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Hariram Ramanathan, M.S.
Associate Scientific Liaison
1-301-816-8313
(SM42010) Monographs - Small Molecules 4
711 Margareth R.C. Marques, Ph.D.
Senior Scientific Liaison
1-301-816-8106
(GCDF2010) General Chapters - Dosage Forms
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 4993
Pharmacopeial Forum: Volume No. 35(3) Page 591