Cysteine Hydrochloride
C3H7NO2S·HCl·H2O 175.64
C3H7NO2S·HCl 157.62
l-Cysteine hydrochloride monohydrate
[7048-04-6].
Anhydrous[52-89-1].
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C3H7NO2S·HCl·H2O 175.64
C3H7NO2S·HCl 157.62
l-Cysteine hydrochloride monohydrate
[7048-04-6].Anhydrous
[52-89-1].DEFINITION
Cysteine Hydrochloride is l-cysteine hydrochloride monohydrate and contains NLT 98.5% and NMT 101.5% of l-cysteine hydrochloride (C3H7NO2S·HCl), calculated on the dried basis.
IDENTIFICATION
ASSAY
• Procedure
Sample:
250 mg of Cysteine Hydrochloride
Blank:
Proceed as directed in the Analysis without the Sample.
Titrimetric system
(See Titrimetry 
541
.)
541.)
Mode:
Residual titration
Titrant:
0.1 N iodine VS
Back titrant:
0.1 N sodium thiosulfate VS
Endpoint detection:
Visual
Analysis:
Transfer the Sample to an iodine flask. Add 20.0 mL of water and 4 g of potassium iodide, and mix. Cool the solution in an ice bath, and add 5 mL of 3 N hydrochloric acid and 25.0 mL of 0.1 N iodine VS. Insert the stopper, and allow to stand in the dark for 20 min. Titrate the excess iodine with the Back titrant. Add 3 mL of starch TS as the endpoint is approached. Perform the Blank determination. Calculate the percentage of cysteine hydrochloride (C3H7NO2S·HCl) in the Sample taken:
Result = {[(VB 
VS) × N × F]/W} × 100
VS) × N × F]/W} × 100| VB | = | = Back titrant volume consumed by the Blank (mL) |
| VS | = | = Back titrant volume consumed by the Sample (mL) |
| N | = | = actual normality of the Back titrant (mEq/mL) |
| F | = | = equivalency factor, 157.6 mg/mEq |
| W | = | = Sample weight (mg) |
Acceptance criteria:
98.5%–101.5% on the dried basis
IMPURITIES
• Residue on Ignition 281:
NMT 0.4%
281:
NMT 0.4%
• Chloride and Sulfate, Sulfate 221
221
Standard solution:
0.10 mL of 0.020 N sulfuric acid
Sample:
0.33 g of Cysteine Hydrochloride
Acceptance criteria:
NMT 0.03%.
• Iron 241:
NMT 30 ppm
241:
NMT 30 ppm
• Heavy Metals, Method I 231:
NMT 15 ppm
231:
NMT 15 ppm
• Related Compounds
N-Ethylmaleimide solution:
40 mg/mL of N-ethylmaleimide in alcohol
Standard stock solution:
Dissolve 20 mg of USP l-Cysteine Hydrochloride RS in 10.0 mL of water. Add 10.0 mL of N-Ethylmaleimide solution, and mix. Allow the solution to stand for 5 min before using.
Standard solution:
0.05 mg/mL from Standard stock solution in water. [Note—This solution has a concentration equivalent to 0.5% of that of the Sample solution. ]
System suitability solution:
Transfer 10 mg of USP l-Tyrosine RS and 10 mL of the Standard stock solution to a 25-mL volumetric flask. Dilute with water to volume.
Sample stock solution:
Transfer 0.2 g of Cysteine Hydrochloride to a 10-mL volumetric flask, dissolve, and dilute with water to volume.
Sample solution:
To 5.0 mL of the Sample stock solution add 5.0 mL of N-Ethylmaleimide solution, and mix. Allow the solution to stand for 5 min before using.
Chromatographic system
Mode:
TLC
Adsorbent:
0.25-mm layer of chromatographic silica gel mixture
Application volume:
5 µL
Developing solvent system:
Butyl alcohol, glacial acetic acid, and water (3:1:1)
Spray reagent:
2 mg/mL of ninhydrin in a mixture of butyl alcohol and 2 N acetic acid (95:5)
System suitability
Suitability requirements:
The chromatogram of the System suitability solution exhibits two clearly separated spots.
Analysis
Samples:
Standard solution, System suitability solution, and Sample solution.
After air-drying the plate, spray with Spray reagent, and heat between 100
and 105 for 15 min. Examine the plate under white light.
and 105 for 15 min. Examine the plate under white light.
Acceptance criteria:
Any secondary spot of the Sample solution is not larger or more intense than the principal spot of the Standard solution.
Individual impurities:
NMT 0.5%
Total impurities:
NMT 2.0%
SPECIFIC TESTS
• Optical Rotation, Specific Rotation 781S
781S
Sample solution:
80 mg/mL in 6 N hydrochloric acid
Acceptance criteria:
+5.7 to +6.8
to +6.8
• Loss on Drying 731:
Dry a sample at room temperature at a pressure not exceeding 5 mm of mercury for 24 h: it loses 8.0%–12.0% of its weight.
731:
Dry a sample at room temperature at a pressure not exceeding 5 mm of mercury for 24 h: it loses 8.0%–12.0% of its weight.
ADDITIONAL REQUIREMENTS
• Packaging and Storage:
Preserve in well-closed containers.
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Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
| Topic/Question | Contact | Expert Committee |
|---|---|---|
| Monograph | Huy T. Dinh, M.S.
Scientific Liaison 1-301-816-8594 |
(DS2010) Monographs - Dietary Supplements |
| Reference Standards | RS Technical Services 1-301-816-8129 rstech@usp.org |
USP35–NF30 Page 2798
Pharmacopeial Forum: Volume No. 30(5) Page 1598