Compliance assay
Mobile phase
Dissolve 2.55g of tetrabutylammonium hydrogen sulfate in 750mLof water,dilute with acetonitrile to 1000mL,and mix.Pass through a filter having a 5-µm or finer porosity,and degas.Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Resolution solution
Dissolve 4mg of
USP Ketoconazole RSin 1.0mLof a solution of potassium sorbate in water (1in 5000),dilute with a mixture of methanol and water (1:1)to 10.0mL,and mix.
Standard preparation
Dissolve an accurately weighed quantity of
USP Ketoconazole RSin a mixture of methanol and water (1:1)to obtain a solution having a known concentration of about 0.4mg per mL.
Assay preparation
[NOTEIf the Oral Suspension has settled,invert the container 10to 15times,and sonicate for about 5minutes,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 5.0mLof homogeneous Oral Suspension,freshly mixed and free from air bubbles,to a 250-mLvolumetric flask,add 100mLof water,and stir for 15minutes to dissolve the xanthan gum.Add 135mLof methanol,and stir for an additional 15minutes.Cool,dilute with methanol to volume,and mix.
Chromatographic system(see Chromatography á621ñ)
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 1mLper minute.Chromatograph the
Resolution solution,and record the peak responses as directed for
Procedure:the relative retention times are about 1.0for ketoconazole and 1.7for 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 5µL)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
Cis the concentration,in mg per mL,of
USP Ketoconazole RSin the
Standard preparation;and
rUand
rSare the ketoconazole peak responses obtained from the
Assay preparation and the
Standard preparation,respectively.