pH 
791
:
between 3.5 and 5.0, in a solution prepared in the following manner. Add 15 mL of boiling water to 3.5 g of Cream in a 50-mL centrifuge tube, and shake vigorously until an emulsion is formed. Loosen the cap, and place in a steam bath for 5 minutes. Centrifuge the hot solution. After cooling to room temperature, collect the lower aqueous solution in a glass tube, and determine the pH.
Related compounds—
Solution A, Solution B, Mobile phase, Solution 1, Solution 2, and Resolution solution—
Prepare as directed in the Assay.
Standard stock solution—
Prepare as directed for Standard stock preparation in the Assay.
Standard solution—
Prepare as directed for Standard preparation in the Assay.
System sensitivity solution—
Dilute 1.0 mL of the Standard solution with dehydrated alcohol to 50.0 mL. Dilute 1.0 mL of the solution thus obtained with Solution A to 20.0 mL.
Test solution—
Prepare as directed for the Assay preparation.
Chromatographic system—
Proceed as directed in the Assay. Chromatograph the System sensitivity solution: the signal-to-noise ratio is not less than 3. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.57 for prednicarbate related compound B, 0.64 for prednicarbate related compound C, 1.0 for prednicarbate, and 1.04 for prednicarbate related compound A.
Procedure—
Inject a volume (about 60 µL) of the
Test solution into the chromatograph, record the chromatogram, and measure the peak responses. Calculate the percentage of each related compound and unknown impurity in the portion of Cream taken by the formula:
100(ri / rs)
in which
ri is the peak response for each individual impurity obtained from the
Test solution, and
rs is the sum of the peak responses obtained from the
Test solution: not more than 2.0% of prednicarbate related compound B and not more than 2.0% of prednicarbate related compound C is found; not more than 0.5% of any individual related compound is found; and not more than 5.0% of total related compounds is found.
Assay—
Solution A—
Prepare a 0.01 M solution of monobasic potassium phosphate in water.
Solution B—
Prepare a mixture of acetonitrile and dehydrated alcohol (2:1).
Mobile phase—
Use variable mixtures of
Solution A and
Solution B as directed for
Chromatographic system. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard stock preparation—
Dissolve an accurately weighed quantity of
USP Prednicarbate RS in dehydrated alcohol, and dilute quantitatively, and stepwise if necessary, with dehydrated alcohol to obtain a solution having a known concentration of 0.3 mg per mL.
Standard preparation—
Transfer 10.0 mL of the Standard stock preparation to a 100-mL volumetric flask, add 15 mL of tetrahydrofuran and 30 mL of Solution B, and dilute with Solution A to volume.
Assay preparation—
Transfer an accurately weighed quantity of Cream, equivalent to about 3.0 mg of prednicarbate, to a 100-mL volumetric flask. Add 15 mL of tetrahydrofuran, shake vigorously, and allow to stand in an ultrasonic bath until the sample has dissolved. Add 20 mL of dehydrated alcohol, and shake vigorously. Add 20 mL of acetonitrile, and shake vigorously. Immediately dilute with Solution A to volume, and shake vigorously. Allow to stand in an ice bath for at least 15 minutes. Shake the samples vigorously, and pass through a folded paper filter. Pass the filtrate through a membrane filter of 0.45-µm porosity.
Solution 2—
Transfer about 15 mg of
USP Prednicarbate Related Compound A RS, accurately weighed, to a 50-mL volumetric flask; add 1.0 mL of
Solution 1, and dilute with dehydrated alcohol to volume.
Resolution solution—
Transfer 10.0 mL of the Standard preparation to a volumetric flask; add 1.0 mL of Solution 2, 1 mL of tetrahydrofuran, and 2 mL of acetonitrile; and dilute with Solution A to 20.0 mL.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 243-nm detector and a 4.0-mm × 25-cm column that contains 5-µm packing L1. The column temperature is maintained at 40
. The flow rate is about 1 mL per minute. The chromatograph is programmed as follows.
Time
(minutes) |
Solution A
(%) |
Solution B
(%) |
Elution |
| 0–5 |
67 |
33 |
equilibration |
| 5–45 |
67®40 |
33®60 |
linear gradient |
| 45–50 |
40 |
60 |
isocratic |
| 50–55 |
40®20 |
60®80 |
linear gradient |
| 55–70 |
20 |
80 |
isocratic |
| 70–75 |
20®67 |
80®33 |
linear gradient |
| 75–85 |
67 |
33 |
isocratic |
Chromatograph the
Resolution solution, and record the peak responses as directed for
Procedure: the resolution,
R, between prednicarbate and prednicarbate related compound A is not less than 1.5. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the tailing factor for the prednicarbate peak is between 0.7 and 1.5; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 60 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the quantity, in mg, of prednicarbate (C
27H
36O
8) in each g of Cream taken by the formula:
100(C/W)(rU / rS)
in which
C is the concentration, in mg per mL, of
USP Prednicarbate RS in the
Standard preparation; W is the weight, in g, of Cream taken; and
rU and
rS are the prednicarbate peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
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