Alpha Lipoic Acid Capsules
DEFINITION
Alpha Lipoic Acid Capsules contain NLT 90.0% and NMT 115.0% of the labeled amount of C8H14O2S2.
IDENTIFICATION
•  The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the test for Content of Alpha Lipoic Acid.
STRENGTH
•  Content of Alpha Lipoic Acid
Mobile phase:  0.025 M phosphoric acid and acetonitrile (62:38)
Standard solution:  0.05 mg/mL of USP Alpha Lipoic Acid RS in acetonitrile and water (1:1)
Sample solution A (for hard gelatin Capsules) Empty and mix thoroughly the contents of NLT 20 Capsules. Transfer a portion of the powder, equivalent to 100 mg of alpha lipoic acid, to a suitable container. Add 70 mL of a mixture of acetonitrile and water (1:1), and shake for 45 min by mechanical means. Transfer to a 100-mL volumetric flask, dilute with the mixture of acetonitrile and water (1:1) to volume, and filter a portion of this preparation, discarding the first 5 mL of the filtrate. Transfer 5.0 mL of the remaining filtrate to a 100-mL volumetric flask, and dilute with acetonitrile and water (1:1) to volume.
Sample solution B (for soft gelatin Capsules) Using a suitable cutting instrument, open a number of Capsules equivalent to 500 mg of alpha lipoic acid from a counted number of opened Capsules. Transfer the contents and the shells to a suitable container with stopper, add 500.0 mL of a mixture of acetonitrile and water (1:1), and shake for 45 min by mechanical means. Filter a portion of this preparation, discarding the first 5 mL of the filtrate. Transfer 5.0 mL of the remaining filtrate to a 100-mL volumetric flask, and dilute with acetonitrile and water (1:1) to volume.
Chromatographic system 
Mode:  LC
Detector:  UV 220 nm
Column:  3.9-mm × 30-cm; packing L1
Flow rate:  1.5 mL/min
Injection size:  20 µL
System suitability 
Sample:  Standard solution
Suitability requirements 
Column efficiency:  NLT 1300 theoretical plates
Tailing factor:  NMT 1.2 for alpha lipoic acid
Relative standard deviation:  NMT 1.0%
Analysis 
Samples:  Standard solution and appropriate Sample solution
Calculate the percentage of alpha lipoic acid in the portion of Capsules taken:
Result = (rU/rS) × (CS/CU) × 100
rU== peak response from Sample solution A or Sample solution B
rS== peak response from the Standard solution
CS== concentration of USP Alpha Lipoic Acid RS in the Standard solution (mg/mL)
CU== nominal concentration of alpha lipoic acid in Sample solution A or Sample solution B (mg/mL)
Acceptance criteria:  90.0%–115.0%
PERFORMANCE TESTS
•  Disintegration and Dissolution of Dietary Supplements 2040: Meet the requirements for Dissolution
Medium:  Water; 900 mL
Apparatus 1 (for hard gelatin Capsules) 100 rpm
Apparatus 2 (for soft gelatin Capsules) 75 rpm
Time:  60 min
Standard solution:  1 mg/mL of USP Alpha Lipoic Acid RS in a mixture of acetonitrile and water (1:1). Dilute with water to obtain a concentration of 0.02 mg/mL.
Sample solution:  Withdraw a portion of the solution under test, and filter, discarding the first portion of the filtrate. Transfer an aliquot to a volumetric flask, and dilute with water to volume to obtain a solution having an expected concentration of 0.02 mg/mL of alpha lipoic acid.
Mobile phase and Chromatographic system:  Proceed as directed in the test for Content of Alpha Lipoic Acid.
Injection size:  50 µL
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of alpha lipoic acid (C8H14O2S2) dissolved:
Result = (rU/rS) × (V × C × D/L) × 100
rU== peak area from the Sample solution
rS== peak area from the Standard solution
V== volume of dissolution Medium, 900 mL
C== concentration of USP Alpha Lipoic Acid RS in the Standard solution (mg/mL)
D== dilution factor of the sample
L== label claim of alpha lipoic acid (mg/Capsule)
Tolerances:  NLT 70% of the labeled amount of C8H14O2S2 is dissolved.
•  Weight Variation of Dietary Supplements 2091: Meet the requirements
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in well-closed containers.
•  USP Reference Standards 11
USP Alpha Lipoic 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 Natalia Davydova
Scientific Liaison
1-301-816-8328
(DS2010) Monographs - Dietary Supplements
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 1367
Pharmacopeial Forum: Volume No. 36(1) Page 145