Specific rotation 781S:
between +21
and +27
.
Test solution
In a 25-mL volumetric flask mix 1.25 g with 1 mL of edetate disodium solution (1 in 100), add 7.5 mL of sodium hydroxide solution (1 in 25), and mix to dissolve. Dilute to volume with pH 7.0 buffer (prepared by mixing 29.5 mL of 1 N sodium hydroxide, 50 mL of 1 M monobasic potassium phosphate, and sufficient water to make 100 mL and, using a pH meter, adjusting to a pH of 7.0 ± 0.1 by adding, as necessary, more of either solution).
Residue on ignition 281
Transfer to a tared fused silica dish about 2 g, weigh accurately, heat on a hot plate until thoroughly charred, cool, add 1 mL of sulfuric acid, and heat gently until fuming ceases. Ignite at 600
until the carbon is consumed. Not more than 0.5% is found.
Assay
Mobile phase
Dissolve 6.8 g of monobasic potassium phosphate in 1000 mL of water, pass through a membrane filter having a 0.45-µm porosity, and degas. Adjust with phosphoric acid to a pH of 3.0.
Internal standard solution
Dissolve about 1 g of USP l-Phenylalanine RS in 200 mL of freshly prepared sodium metabisulfite solution (1 in 2000).
Standard preparation
Dissolve an accurately weighed quantity of
USP Acetylcysteine RS in sodium metabisulfite solution (1 in 2000) to obtain a solution having a known concentration of about 10 mg per mL. Pipet 10.0 mL of this solution and 10.0 mL of
Internal standard solution into a 200-mL volumetric flask, dilute with sodium metabisulfite solution (1 in 2000) to volume, and mix to obtain a
Standard preparation having a known concentration of about 0.5 mg per mL of
USP Acetylcysteine RS.
Assay preparation
Transfer about 1000 mg of Acetylcysteine, accurately weighed, to a 100-mL volumetric flask. Dissolve in and dilute with sodium metabisulfite solution (1 in 2000) to volume, and mix. Pipet 10.0 mL of this solution and 10.0 mL of Internal standard solution into a 200-mL volumetric flask, dilute with sodium metabisulfite solution (1 in 2000) to volume, and mix.
Chromatographic system (see Chromatography 621)
The liquid chromatograph is equipped with a 214-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the relative standard deviation for replicate injections is not more than 2.0%; and the resolution,
R, between acetylcysteine and
dl-phenylalanine is not less than 6.
Procedure
Separately inject equal volumes (about 5 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.5 for acetylcysteine and 1.0 for
l-phenylalanine. Calculate the quantity, in mg, of C
5H
9NO
3S in the portion of Acetylcysteine taken by the formula:
2000C(RU / RS)
in which
C is the concentration, in mg per mL, of
USP Acetylcysteine RS in the
Standard preparation; and
RU and
RS are the ratios of the peak response of acetylcysteine to that of
l-phenylalanine obtained from the
Assay preparation and the
Standard preparation, respectively.