Carbidopa
C10H14N2O4·H2O 244.24
Benzenepropanoic acid,
-hydrazino-3,4-dihydroxy--methyl-, monohydrate, (S)-;
(-)-l--Hydrazino-3,4-dihydroxy--methylhydrocinnamic acid monohydrate
[38821-49-7].
Anhydrous 226.23[28860-95-9].
(kar'' bi doe' pa).
+'&img=../../images/v35300/cas-38821-49-7.gif&casNumber=38821-49-7&usp=35&nf=30&chemicalStructureImage=true&ID='+parent.myID,600,500);)
C10H14N2O4·H2O 244.24
Benzenepropanoic acid,
-hydrazino-3,4-dihydroxy--methyl-, monohydrate, (S)-;
(-)-l-
-Hydrazino-3,4-dihydroxy--methylhydrocinnamic acid monohydrate
[38821-49-7].Anhydrous 226.23
[28860-95-9].DEFINITION
Carbidopa contains NLT 98.0% and NMT 102.0% of C10H14N2O4·H2O.
IDENTIFICATION
• B.
The retention time of the major peak from the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.
ASSAY
• Procedure
Mobile phase:
Alcohol and 0.05 M monobasic sodium phosphate, adjusted with phosphoric acid to a pH of 2.7 (1:19)
System suitability solution:
0.1 mg/mL of USP Carbidopa RS and 0.1 mg/mL of USP Methyldopa RS in Mobile phase
Standard solution:
0.5 mg/mL of USP Carbidopa RS in Mobile phase. [Note—Use gentle heat and ultrasonification, if necessary, to dissolve. ]
Sample solution:
0.5 mg/mL of Carbidopa in Mobile phase
Chromatographic system
Mode:
LC
Detector:
UV 280 nm
Column:
3.9-mm × 30-cm; packing L1
Flow rate:
1 mL/min
Injection size:
20 µL
System suitability
Samples:
System suitability solution and Standard solution
[Note—The relative retention times for methyldopa and carbidopa are about 0.8 and 1.0, respectively. ]
Suitability requirements
Resolution:
NLT 0.9 between methyldopa and carbidopa in the System suitability solution
Relative standard deviation:
NMT 1.5% in the Standard solution
Analysis
Samples:
Standard solution and Sample solution
Calculate the percentage of C10H14N2O4·H2O in the portion of Carbidopa taken:
Result = (rU/rS) × (CS/CU) × 100
| rU | = | = peak response from the Sample solution |
| rS | = | = peak response from the Standard solution |
| CS | = | = concentration of USP Carbidopa RS, as the monohydrate, in the Standard solution (mg/mL) |
| CU | = | = concentration of Carbidopa in the Sample solution (mg/mL) |
Acceptance criteria:
98.0%–102.0%
IMPURITIES
Organic Impurities
• Procedure: Limit of Methyldopa and Carbidopa Related Compound A
Mobile phase, System suitability solution, Standard solution, Sample solution, Chromatographic system, and Suitability requirements:
Proceed as directed in the Assay.
Impurity standard solution:
2.5 µg/mL of USP Methyldopa RS and 2.5 µg/mL of USP Carbidopa Related Compound A RS in Mobile phase
System suitability
Samples:
System suitability solution and Standard solution
[Note—The relative retention times for methyldopa, carbidopa, and carbidopa related compound A are about 0.8, 1.0, and 1.8, respectively. ]
Analysis
Samples:
Sample solution and Impurity standard solution
Calculate the percentage of methyldopa in the portion of Carbidopa taken:
Result = (rU/rS) × (CS/CU) × 100
| rU | = | = peak response of methyldopa or carbidopa related compound A from the Sample solution |
| rS | = | = peak response of methyldopa or carbidopa related compound A from the Impurity standard solution |
| CS | = | = concentration of USP Methyldopa RS or USP Carbidopa Related Compound A RS in the Impurity standard solution (µg/mL) |
| CU | = | = concentration of the Sample solution (µg/mL) |
Acceptance criteria:
NMT 0.5% of methyldopa, and NMT 0.5% of carbidopa related compound A
SPECIFIC TESTS
• Optical Rotation, Specific Rotation 
781S
:
21.0
to 23.5, calculated as the monohydrate
781S:
21.0 to 23.5, calculated as the monohydrate
Sample solution:
10 mg/mL, in 0.7 g/mL of aluminum chloride solution (prepared using the hexahydrate form of the aluminum salt) that has been filtered and adjusted with 0.25 N sodium hydroxide to a pH of 1.5
• Loss on Drying 731
731
Analysis:
Heat 1 g in a suitable vacuum drying apparatus at 100 and a pressure of NMT 5 mm of mercury to constant weight. Cool and weigh.
and a pressure of NMT 5 mm of mercury to constant weight. Cool and weigh.
Acceptance criteria:
It loses 6.9%–7.9% of its weight.
ADDITIONAL REQUIREMENTS
• Packaging and Storage:
Preserve in well-closed, light-resistant containers.
• USP Reference Standards 11
11
USP Carbidopa RS 
') + '&img=../../images/v35300/cas-38821-49-7.gif',600,500);)
USP Carbidopa Related Compound A RS
3-O-methylcarbidopa.
C11H16N2O4 240.26
') + '&img=../../images/v35300/c11rs1596.gif',600,500);)
3-O-methylcarbidopa.
C11H16N2O4 240.26
USP Methyldopa RS
') + '&img=../../images/v35300/cas-41372-08-1.gif',600,500);)
Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
| Topic/Question | Contact | Expert Committee |
|---|---|---|
| Monograph | Ravi Ravichandran, Ph.D.
Principal Scientific Liaison 1-301-816-8330 |
(SM42010) Monographs - Small Molecules 4 |
| Reference Standards | RS Technical Services 1-301-816-8129 rstech@usp.org |
USP35–NF30 Page 2487
Pharmacopeial Forum: Volume No. 35(1) Page 73