Serine
(ser' een).

C3H7NO3 105.09
l-Serine     [56-45-1].
DEFINITION
Serine contains NLT 98.5% and NMT 101.5% of l-serine (C3H7NO3), calculated on the dried basis.
IDENTIFICATION
ASSAY
•  Procedure
Sample:  100 mg of Serine
Blank:  Mix 3 mL of formic acid and 50 mL of glacial acetic acid.
Titrimetric system
Mode:  Direct titration
Titrant:  0.1 N perchloric acid VS
Endpoint detection:  Potentiometric
Analysis:  Dissolve the Sample in 3 mL of formic acid and 50 mL of glacial acetic acid. Titrate with the Titrant. Perform the Blank determination.
Calculate the percentage of serine (C3H7NO3) in the Sample taken:
Result = {[(VS VB) × N × F]/W} × 100
 VS = = Titrant volume consumed by the Sample (mL) VB = = Titrant volume consumed by the Blank (mL) N = = actual normality of the Titrant (mEq/mL) F = = equivalency factor, 105.1 mg/mEq W = = Sample weight (mg)
Acceptance criteria:  98.5%–101.5% on the dried basis
IMPURITIES
NMT 0.1%
Standard solution:  0.50 mL of 0.020 N hydrochloric acid
Sample:  0.73 g of Serine
Acceptance criteria:  NMT 0.05%
Standard solution:  0.10 mL of 0.020 N sulfuric acid
Sample:  0.33 g of Serine
Acceptance criteria:  NMT 0.03%
•  Iron 241: NMT 30 ppm
NMT 15 ppm
•  Related Compounds
System suitability solution:  0.4 mg/mL each of USP l-Serine RS and USP l-Methionine RS in 0.1 N hydrochloric acid
Standard solution:  0.05 mg/mL of USP l-Serine RS in 0.1 N hydrochloric acid. [Note—This solution has a concentration equivalent to about 0.5% of that of the Sample solution. ]
Sample solution:  10 mg/mL of Serine in 0.1 N hydrochloric acid
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:  System suitability solution, Standard 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.
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
Sample solution:  100 mg/mL in 2 N hydrochloric acid
Acceptance criteria:  +14.0 to +15.6
Dry a sample at 105 for 3 h: it loses NMT 0.2% of its weight.