Acidity—
Dissolve about 1 g in 50 mL of carbon dioxide-free water, and add 1 drop of
bromothymol blue TS: not more than 0.2 mL of 0.01 N sodium hydroxide is required in order to produce a color change.
Chromatographic purity—
Perchloric acid solution and Mobile phase—
Prepare as directed in the Assay.
System suitability solution—
Dissolve accurately weighed quantities of caffeine and
USP Pentoxifylline RS in
Mobile phase to obtain a solution containing about 0.0007 mg per mL and 0.35 mg per mL, respectively.
Standard solution—
Dissolve an accurately weighed quantity of
USP Pentoxifylline RS in
Mobile phase to obtain a solution having a known concentration of about 0.0007 mg per mL.
Test solution—
Dissolve an accurately weighed quantity of Pentoxifylline in Mobile phase to obtain a solution having a concentration of about 0.35 mg per mL.
Chromatographic system (see Chromatography 
621
)—
Proceed as directed in the
Assay. Chromatograph the
System suitability solution, and record the peak responses as directed for
Procedure: the resolution,
R, between caffeine and pentoxifylline is not less than 10.0. Chromatograph the
Standard solution, and record the peak responses for pentoxifylline as directed for
Procedure: the relative standard deviation for replicate injections is not more than 5.0%.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard solution and the
Test solution into the chromatograph, and allow the chromatogram to run five times longer than the retention time for the pentoxifylline. Measure the areas of all the peaks in the
Test solution, except that for pentoxifylline. Calculate the percentage of each impurity in the portion of Pentoxifylline taken by the formula:
286C(ri / rS),
in which
C is the concentration, in mg per mL, of
USP Pentoxifylline RS in the
Standard solution; ri is the peak area response for each impurity obtained from the
Test solution; and
rS is the peak area response for pentoxifylline obtained from the
Standard solution: not more than 0.2% of any individual impurity is found, and not more than 0.5% of total impurities is found.
Assay—
Perchloric acid solution—
Dissolve 1.0 g of perchloric acid in 1000 mL of water, and mix.
Mobile phase—
Prepare a filtered and degassed mixture of
Perchloric acid solution, acetonitrile, tetrahydrofuran, and methanol (80:15:2.5:2). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
System suitability solution—
Dissolve suitable quantities of caffeine and
USP Pentoxifylline RS in
Mobile phase to obtain a solution containing 0.024 mg per mL and 0.048 mg per mL, respectively.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Pentoxifylline RS in
Mobile phase, 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 about 25 mg of Pentoxifylline, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix. Pipet 5.0 mL of the solution so obtained to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 273-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 0.7 mL per minute. Chromatograph the
System suitability solution, and record the peak responses as directed for
Procedure: the resolution,
R, between caffeine and pentoxifylline is not less than 10.0. 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 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major pentoxifylline peaks. Calculate the quantity, in mg, of C
13H
18N
4O
3 in the portion of Pentoxifylline taken by the formula:
500C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Pentoxifylline RS in the
Standard preparation; and
rU and rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
;)
for 3 hours: it loses not more than 0.5% of its weight.