Compliance assay
Mobile phase
Dissolve 2.55 g of tetrabutylammonium hydrogen sulfate in 750 mL of water, dilute with acetonitrile to 1000 mL, and mix. Pass through a filter having a 5-µm or finer porosity, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Resolution solution
Dissolve 4 mg of
USP Ketoconazole RS in 1.0 mL of a solution of potassium sorbate in water (1 in 5000), dilute with a mixture of methanol and water (1:1) to 10.0 mL, and mix.
Standard preparation
Dissolve an accurately weighed quantity of
USP Ketoconazole RS in a mixture of methanol and water (1:1) to obtain a solution having a known concentration of about 0.4 mg per mL.
Assay preparation
[NOTEIf the Oral Suspension has settled, invert the container 10 to 15 times, and sonicate for about 5 minutes, or stir on a magnetic stirrer until the suspension appears homogeneous. Examine the mixture for the presence of bubbles and unsuspended solids prior to sampling.] Transfer 5.0 mL of homogeneous Oral Suspension, freshly mixed and free from air bubbles, to a 250-mL volumetric flask, add 100 mL of water, and stir for 15 minutes to dissolve the xanthan gum. Add 135 mL of methanol, and stir for an additional 15 minutes. Cool, dilute with methanol to volume, and mix.
Chromatographic system (see Chromatography 621)
The liquid chromatograph is equipped with a 223-nm detector, a 4.6-mm × 25-cm analytical column that contains 5-µm packing L1, and a guard column containing 5-µm packing L1. The column temperature is maintained at 30
, and the flow rate is about 1 mL per minute. Chromatograph the
Resolution solution, and record the peak responses as directed for
Procedure: the relative retention times are about 1.0 for ketoconazole and 1.7 for sorbate; and the resolution,
R, between the sorbate and ketoconazole peaks is not less than 2.0. 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%.
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. Calculate the quantity, in mg, of ketoconazole (C
26H
28Cl
2N
4O
4) in the portion of Oral Suspension taken by the formula:
250C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Ketoconazole RS in the
Standard preparation; and
rU and
rS are the ketoconazole peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.