Identification—
A:
Thin-Layer Chromatographic Identification Test 
201
—
Test solution—
Transfer a portion of Oral Solution, equivalent to about 100 mg of theophylline, to a separatory funnel. Extract with two 25-mL portions of chloroform, collecting the extracts in a 100-mL volumetric flask. Dilute with methanol to volume, and mix.
Standard solution—
Prepare a solution of
USP Theophylline RS in methanol containing about 1 mg per mL.
Application volume:
20 µL.
Developing solvent system:
a mixture of chloroform, methanol, and acetic acid (89:10:1).
Procedure—
Apply the Standard solution and the Test solution as directed in the chapter, and dry the plate in a current of cool air. Place the plate in a suitable chromatographic chamber lined with filter paper and previously equilibrated with the Developing solvent system. Upon removing the plate from the chamber, dry with a current of warm air in a suitable hood.
B:
The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.
Microbial limits 61—
It meets the requirements of the tests for absence of
Salmonella species and
Escherichia coli. The total aerobic microbial count does not exceed 100 cfu per mL, and the total combined molds and yeasts count does not exceed 50 cfu per mL.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of water, methanol, and acetic acid (76.5:22.5:1) containing 200 mg of sodium 1-octanesulfonate in each 1000 mL of solution. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
System suitability preparation—
Dissolve accurately weighed quantities of
USP Theophylline RS and caffeine in water to obtain a solution containing about 0.68 mg of each per mL.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Theophylline RS in water to obtain a solution having a known concentration of about 0.68 mg per mL.
Assay preparation—
Transfer an accurately measured volume of Oral Solution, equivalent to about 68 mg of theophylline, to a 100-mL volumetric flask. Dilute with water to volume, and mix.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 254-nm detector and a 4.0-mm × 30-cm column that contains packing L1. The flow rate is about 2.0 mL per minute. Chromatograph the
System suitability preparation, and record the peak responses as directed for
Procedure: the relative retention times are about 0.6 for theophylline and 1.0 for caffeine; the resolution,
R, between theophylline and caffeine is not less than 2.0; the tailing factor is not more than 2; and 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 peaks. Calculate the quantity, in mg, of theophylline (C
7H
8N
4O
2) in the portion of Oral Solution taken by the formula:
100C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Theophylline RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
