Labeling—
In addition to meeting the requirements for
Labeling under
Injections 
1
, fused-seal containers of the Injection in concentrations of 250 mg per mL and greater are labeled to indicate that since pressure may develop on long storage, precautions should be taken to wrap the container in a protective covering while it is being opened.
Identification—
A:
To a volume of Injection, equivalent to 40 mg of ascorbic acid, add 4 mL of 0.1 N hydrochloric acid, then add 4 drops of
methylene blue TS, and warm to 40
: the deep blue color becomes appreciably lighter or is completely discharged within 3 minutes.
B:
The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that of the Standard preparation, obtained as directed in the Assay.
C:
It responds to the flame test for
Sodium 191.
Limit of oxalate—
Dilute a volume of Injection, equivalent to 50 mg of ascorbic acid, with water to 5 mL. Add 0.2 mL of acetic acid and 0.5 mL of
calcium chloride TS: no turbidity is produced in 1 minute.
Assay—
Mobile phase—
Dissolve 15.6 g of dibasic sodium phosphate and 12.2 g of monobasic potassium phosphate in 2000 mL of water, adjust with phosphoric acid to a pH of 2.5 ± 0.05. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Ascorbic Acid RS in
Mobile phase, and mix to obtain a solution having a known concentration of about 0.5 mg per mL.
[NOTE—Refrigerate and store protected from light until use. The solution is stable for at least 24 hours. Inject within 3 hours after removal from the refrigerator.
]
Assay preparation—
Dilute the Injection, quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a concentration of about 0.5 mg per mL. [NOTE—Refrigerate and store protected from light until use. The solution is stable for at least 24 hours. Inject within 3 hours after removal from the refrigerator.]
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 245-nm detector and a 6-mm × 150-mm column that contains packing L39. The flow rate is about 0.6 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency is not less than 3500 theoretical plates, the tailing factor is not more than 1.6, and the relative standard deviation for replicate injections is not more than 1.5%.
Procedure—
Separately inject equal volumes (about 4 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peak. Calculate the quantity, in mg, of ascorbic acid (C
6H
8O
6) in each mL of the Injection taken by the formula:
CD(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Ascorbic Acid RS in the
Standard preparation; D is the dilution factor; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
