Identification—
Place a quantity of finely powdered Tablets, equivalent to about 24 mg of ephedrine hydrochloride, in a 15-mL centrifuge tube, add 4.0 mL of a mixture of chloroform and methanol (4:1), mix by sonication for 10 minutes, and filter to obtain the test solution. Prepare separate Standard solutions containing known concentrations of about 36 mg of
USP Theophylline RS per mL, about 9.6 mg of
USP Ephedrine Sulfate RS per mL, and about 5 mg of
USP Phenobarbital RS per mL, respectively, in the mixture of chloroform and methanol (4:1). Apply 2 µL of the test solution and of each of the three Standard solutions at equidistant points about 2.5 cm above one edge of a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a suitable chamber previously equilibrated with a solvent system consisting of a mixture of chloroform, acetone, methanol, and ammonium hydroxide (50:10:10:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, air-dry, and locate the spots on the plate by viewing under short-wavelength UV light: the
RF values of the spots obtained from the test solution correspond to those obtained from the Standard solutions.
Dissolution, Procedure for a Pooled Sample 711—
Medium:
water; 900 mL.
Apparatus 1:
100 rpm.
Time:
30 minutes.
Determine the amounts of theophylline, ephedrine hydrochloride, and phenobarbital dissolved using the following procedure.
Mobile phase—
Dissolve accurately weighed quantities of monobasic potassium phosphate and sodium 1-hexanesulfonate in water, and dilute quantitatively with water to obtain a solution having concentrations of 0.953 mg per mL (0.007 M monobasic potassium phosphate) and 0.564 mg per mL (0.003 M sodium 1-hexanesulfonate), respectively. Adjust, if necessary, with 0.3 M phosphoric acid or 0.2 M monobasic potassium phosphate to a pH of 3.0 ± 0.05, to obtain a Phosphate buffer. The Mobile phase is a mixture of Phosphate buffer and methanol (75:25).
Standard preparation—
Dissolve accurately weighed quantities of
USP Theophylline RS,
USP Ephedrine Sulfate RS, and
USP Phenobarbital RS in water, and dilute quantitatively and stepwise with water to obtain a solution having known concentrations of about 145 µg of anhydrous theophylline per mL, 28 µg of ephedrine sulfate per mL, and 9 µg of phenobarbital per mL.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 215-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 3.0 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the resolution,
R, between the theophylline and phenobarbital peaks is not less than 4.0, the tailing factors for the ephedrine and phenobarbital peaks are not more than 3.0 and 2.0, respectively, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Inject an accurately measured volume (about 75 µL) of a filtered portion of the solution under test into the chromatograph, record the chromatogram, and measure the responses for the major peaks. The elution order is theophylline, ephedrine, and phenobarbital (last). Calculate the quantity, in mg, of C
7H
8N
4O
2 dissolved by the formula:
(0.9C)(rU / rS),
in which
C is the concentration, in µg per mL, of
USP Theophylline RS in the
Standard preparation, and
rU and
rS are the peak responses for theophylline obtained from the solution under test and the similarly chromatographed
Standard preparation, respectively. Calculate the quantity, in mg, of C
10H
15NO·HCl dissolved by the formula:
(201.69/214.27)(0.9C¢)(r¢U / r¢S),
in which 201.69 is the molecular weight of ephedrine hydrochloride, 214.27 is one-half the molecular weight of ephedrine sulfate,
C¢ is the concentration, in µg per mL, of
USP Ephedrine Sulfate RS in the
Standard preparation, and
r¢U and
r¢S are the peak responses for ephedrine obtained from the solution under test and the similarly chromatographed
Standard preparation, respectively. Calculate the quantity, in mg, of C
12H
12N
2O
3 dissolved by the formula:
(0.9C¢¢)(r¢¢U / r¢¢S),
in which
C¢¢ is the concentration, in µg per mL, of
USP Phenobarbital RS in the
Standard preparation, and
r¢¢U and
r¢¢S are the peak responses for phenobarbital obtained from the solution under test and the similarly chromatographed
Standard preparation, respectively.
Tolerances—
Not less than 75% (Q) of the labeled amounts of C7H8N4O2, C10H15NO·HCl, and C12H12N2O3 are dissolved in 30 minutes.
Assay—
Mobile phase—
Mix 240 mL of acetonitrile with 760 mL of 0.01 M, pH 7.8 phosphate buffer (see Buffer Solutions under Solutions in the section Reagents, Indicators, and Solutions).
Internal standard solution—
Dissolve 25 mg of butabarbital sodium in 50 mL of dibasic potassium phosphate solution (17 in 1000). Mix 40 mL of this solution with 10 mL of sodium metaperiodate solution (1 in 100).
Standard preparation—
Transfer about 120 mg of
USP Theophylline RS, about 8 mg of
USP Phenobarbital RS, and about 25 mg of
USP Ephedrine Sulfate RS, each accurately weighed, to a 200-mL volumetric flask. Add 10 mL of methanol and 100 mL of chloroform, mix to dissolve, add chloroform to volume, and mix. Pipet 15 mL of this solution into a 50-mL volumetric flask, add chloroform to volume, and mix. The concentrations of anhydrous theophylline, phenobarbital, and ephedrine sulfate in the
Standard preparation are about 180 µg per mL, 12 µg per mL, and 37.5 µg per mL, respectively.
Assay preparation—
Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 120 mg of anhydrous theophylline, to a 200-mL volumetric flask, and shake by mechanical means for 20 minutes with a mixture of 10 mL of methanol and 100 mL of chloroform. Add chloroform to volume, mix, and filter. Pipet 15 mL of the clear filtrate into a 50-mL volumetric flask, dilute with chloroform to volume, and mix.
Standard solution
and Assay solution—Pipet 10-mL portions of the Standard preparation and the Assay preparation into separate glass-stoppered, 25-mL conical flasks, and treat each as follows: Evaporate in a warm-water bath with the aid of a current of air to dryness. Add by pipet 4 mL of Internal standard solution, insert the stopper in the flask, mix to dissolve the residue, and allow to stand at room temperature for 30 minutes. Pipet 1 mL of propylene glycol solution (1 in 100) into the flask, insert the stopper, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 241-nm detector and a 30-cm × 4-mm stainless steel column that contains packing L1. Set a flow rate of 1.0 mL per minute for the
Mobile phase, and allow the system to equilibrate until a stable baseline is obtained on the recorder. Chromatograph a 10-µL portion of the
Standard solution, and record the peak responses as directed for
Procedure: the peaks are completely resolved, and the resolution factors between each two neighboring peaks are not less than 1.5. Five replicate injections of the
Standard preparation show a relative standard deviation of not more than 2.0%.
Procedure—
Separately inject equal volumes (about 10 µL) of the Standard solution and the Assay solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. In the order of increasing elution times, the five peaks correspond to the reagent (iodate), theophylline, phenobarbital, butabarbital, and benzaldehyde (from ephedrine). Designate the peak response ratio of each component to the internal standard in the Standard solution as RS, and that of each component to the internal standard in the Assay solution as RU.
Calculation for theophylline—
Calculate the quantity, in mg, of anhydrous theophylline (C
7H
8N
4O
2) in the portion of Tablets taken by the formula:
0.667C(RU / RS),
in which
C is the concentration, in µg per mL, of
USP Theophylline RS in the
Standard preparation.
Calculation for ephedrine hydrochloride—
Calculate the quantity, in mg, of ephedrine hydrochloride (C
10H
15NO·HCl) in the portion of Tablets taken by the formula:
(201.69/214.27)(0.667C)(RU / RS),
in which 201.69 is the molecular weight of ephedrine hydrochloride, 214.27 is one-half the molecular weight of ephedrine sulfate, and
C is the concentration, in µg per mL, of
USP Ephedrine Sulfate RS in the
Standard preparation.
Calculation for phenobarbital—
Calculate the quantity, in mg, of phenobarbital (C
12H
12N
2O
3) in the portion of Tablets taken by the formula:
0.667C(RU / RS),
in which
C is the concentration, in mg per mL, of
USP Phenobarbital RS in the
Standard preparation.
