Spectrofluorimetric determination of 3-methylflavone-8-carboxylic acid, the main active metabolite of flavoxate hydrochloride in human urine.

A simple, sensitive and selective spectrofluorimetric method has been developed for the determination of 3-methylflavone-8-carboxylic acid as the main active metabolite of flavoxate hydrochloride in human urine. The proposed method was based on the measurement of the native fluorescence of the metabolite in methanol at an emission wavelength 390 nm, upon excitation at 338 nm. Moreover, the urinary excretion pattern has been calculated using the proposed method. Taking the advantage that 3-methylflavone-8-carboxylic acid is also the alkaline degradate, the proposed method was applied to in vitro determination of flavoxate hydrochloride in tablets dosage form via the measurement of its corresponding degradate. The method was validated in accordance with the ICH requirements and statistically compared to the official method with no significant difference in performance.

Different techniques for the determination of tofisopam.

Five simple and sensitive methods were developed for the determination of tofisopam (TF). The first four are stability-indicating depending on the determination of TF in the presence of its degradation product, while the fifth depended on the determination of TF via its degradation product. Method A was based on first and second derivative spectrophotometry, D and 2D, measuring the amplitude at 298 and 332 nm in the case of 1D and at 312 and 344 nm in the case of 2D. Method B depended on measuring the peak amplitude of the first derivative of the ratio spectra 1DD at 336 nm. Method C was based on difference spectrophotometry by measuring deltaA at 366 nm. Method D was a TLC method using silica gel 60 F254 plates, the optimized mobile phase ethyl acetate-methanol-ammonium hydroxide 10% (8.5 + 1.0 + 0.5, v/v/v), and quantification by densitometric scanning at 315 nm. In method E, spectrofluorometry was applied for the determination of TF via its degradation product; maximum emission was 383 nm when excitation was 295 nm. Linearities were obtained in the concentration range 2-20 microg/mL for methods A, B, and C and 2-20 microg/band and 0.2-1.6 microg/mL for D and E, respectively. In method A, the mean recoveries were 99.45 +/- 0.287 and 100.28 +/- 0.277% at 298 and 332 nm, respectively, in the case of 1D and 99.40 +/- 0.245% and 99.50 +/- 0.292% at 312 and 344 nm, respectively in the case of 2D. The mean recovery was 100.03 +/- 0.523% at 366 nm in method B. Method C showed mean recovery of 100.20 +/- 0.642%. Recoveries for methods D and E were 98.98 +/- 0.721 and 100.25 +/- 0.282%, respectively. The degradation product was obtained in acidic stress condition, separated, and identified by IR and mass spectral analysis, from which the degradation product was confirmed and the degradation pathway was suggested. The first four methods were specific for TF in the presence of different concentrations of its degradation product. The five proposed methods were successfully applied for the determination of TF in Nodeprine tablets. Statistical comparison among the results obtained by these methods and that obtained by the official method for the determination of the drug was made, and no significant differences were found.

Different stability-indicating chromatographic techniques for the determination of netobimin.

Two simple, accurate, and sensitive methods were developed for the determination of netobimin in the presence of its degradation product. Method (A) was an HPLC method, performed on C18 column using acetonitrile/methanol/0.01 M potassium dihydrogen phosphate (56 : 14 : 30 by volume) as a mobile phase with a flow rate of 0.5 mL/min. Detection was performed at 254 nm. Method (B) was a TLC method, using silica gel 60 F(254) plates; the optimized mobile phase was toluene/methanol/chloroform/ammonium hydroxide (5 : 4 : 6 : 0.1 by volume). The spots were scanned densitometrically at 346 nm. Linearity ranges were 1-10 µg/mL for method (A) and 0.5-5 µg/band for method (B), and the mean percentage recoveries were 99.3 ± 0.7% and 99.7 ± 0.7% for methods (A) and (B), respectively. The proposed methods were found to be specific for netobimin in the presence of up to 90% of its degradation product. Statistical comparison between the results obtained by these methods and the manufacturer method was done, and no significance difference was obtained.

Stability-indicating methods for the determination of racecadotril in the presence of its degradation products.

Three stability-indicating methods were developed for the determination of racecadotril (RCT) in the presence of its alkaline degradation products. The first was an HPLC method in which efficient chromatographic separation was achieved on a C18 analytical column and a mobile phase of acetonitrile-methanol-water-acetic acid (52:28:20:0.1, v/v/v/v). Linearity was obtained in the range of 4-40 microg/mL with mean accuracy of 99.5 +/- 0.88%. The second method was a densitometric evaluation of thin-layer chromatograms of the drug using a mobile phase of isopropanol-ammonia (33%)-n-hexane (9:0.5:20, v/v/v). The chromatograms were scanned at 232 nm, a wavelength at which RCT can be readily separated from its degradation products and determined in the range of 2-20 microg per spot with mean accuracy of 99.5 +/- 0.56%. The third method is based on the use of first-derivative spectrophotometry (D1) at 240 nm, and the drug was determined in the range of 5-40 microg/mL with mean accuracy of 99.2 +/- 1.02%. The three methods provided satisfactory recovery of the intact drug (100.8 +/- 0.82, 100.4 +/- 0.55, and 99.9 +/- 0.72%, respectively) in the presence of up to 90% of its degradation products. Determination was also successful when analyzing RCT in a formulation in the form of acetorphan packets. Results were statistically analyzed and found to be in accordance with those given by a reported method.