– Pure samples were kindly supplied by Misr Company for pharmaceutical industries. The percentage purity was found to be 99.56 ± 0.649% and 99.96 ± 0.767 for ISO and DIF, respectively according to the official method.1
– Travodermal cream, Batch No. 906023, manufactured by Misr Company for pharmaceutical industries and were pur- chased from a local market.
2.4. Standard stock and working solutions
A stock standard solution of ISO and DIF (1 mg/mL) were prepared by dissolving separately ISO and DIF in methanol then completing to 100 mL measuring flask with the same sol- vent. Aliquot of the prepared stock solution was further diluted with methanol to get working solution with final con- centration (100 lg mL 1).
2.5. Procedures
For HPLC method:
Chromatographic conditions:
Chromatographic separation was carried out using isocratic
mode on a Agilant ODS-C18 (4.6 250 mm I.D.) column with a mobile phase consisting of 80% acetonitrile: 20% methanol. (The mobile phase was filtered using 0.45 m membrane filter and degassed by ultrasonic vibrations for 10 min) with a flow rate of 1 mL/min and the eluate was scanned at 230 nm at room temperature. All the injections were run in three repli- cates and the injection volume was 20 lL. The run time was 6 min and the total peak areas were used to quantify the stud- ied components.
2.5.1. Construction of calibration graph for the determination of the binary mixture by HPLC method
Aliquots of ISO and DIF working standard solution (100 lg mL 1) equivalent to 100–900 lg and 20–180 lg, respectively were accurately transferred into a two series of 10-mL volumetric flasks, the volume was completed to the mark with the mobile phase. Analyze the prepared samples using the previously mentioned chromatographic conditions and record the peak area then construct a calibration curve correlating the peak areas of ISO and DIF to the correspond- ing concentrations. Compute the corresponding regression equations.
2.5.2. Construction of calibration graph for the determination of ISO and DIF by TLC-densitometric method
Aliquots equivalent to 0.05–2 mg, 0.05–0.7 mg of ISO and DIF, respectively from stock standard solution (1 mg mL 1) were transferred into 10-mL volumetric flasks and the volume was completed with methanol. 20 lL was applied to thin layer chromatographic plates (20 20) using applicator. Spots were spaced 2 cm apart from each other and 1.5 cm from the bot- tom edge of the plate. The plates were developed in the chro- matographic tank previously saturated with the developing mobile phase, ethyl acetate: chloroform: toluene (60:10:10 by volume), for at least 20 min. The plates were developed by
2.3. Samples