Identification—
Place in a separator a volume of Ophthalmic Solution, equivalent to about 25 mg of naphazoline hydrochloride, add 5 mL of 1 N sodium hydroxide, saturate with sodium chloride, and extract with two 25-mL portions of ether. Wash the ether solution with 5 mL of water, pass the ether through a small paper filter, evaporate the filtrate to about 5 mL, transfer the residual solution to a 10- to 15-mL beaker, allow to evaporate spontaneously, and dry the residue at 80
for 1 hour: the naphazoline so obtained melts between 115
and 120
when determined as directed for
Class Ia under
Melting Range or
Temperature 
741
.
Assay—
Phosphate buffer—
Transfer 3 g of monobasic potassium phosphate to a 1-liter volumetric flask, dissolve in 1000 mL of water and 3 mL of triethylamine, and mix. Adjust with phosphoric acid to a pH of 3, and mix.
Mobile phase—
Prepare a filtered and degassed mixture of
Phosphate buffer and acetonitrile (80:20). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Naphazoline Hydrochloride RS in water, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 0.05 mg per mL.
Assay preparation—
Transfer an accurately measured volume of Ophthalmic Solution, equivalent to about 5.0 mg of naphazoline hydrochloride, to a 100-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 285-nm detector and a 4.6-mm × 15-cm column that contains packing L11. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 40
. Chromatograph the
Standard preparation, and record the peak responses as directed under
Procedure: the column efficiency is not less than 5000 theoretical plates, the tailing factor is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C
14H
14N
2·HCl in the portion of Ophthalmic Solution taken by the formula:
100C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Naphazoline Hydrochloride RS in the
Standard preparation, and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
