Determination of thiocolchicoside in its binary mixtures (thiocolchicoside-glafenine and thiocolchicoside-floctafenine) by TLC-densitometry.

The proposed method is based on TLC separation of thiocolchicoside from its binary mixtures (thiocolchicoside-glafenine and thiocolchicoside-floctafenine) followed by densitometric measurement at 375 nm. Separation was carried out on silica gel plates GF(254) using ethyl acetate:methanol:acetic acid (84:13:3%, v/v/v). Various conditions affecting separation and measurement were studied and optimized. Calibration was performed using third-order polynomial equation. It was found superior to first-order with respect to quantification range (0.25-25 microg per spot), correlation coefficient and standard error of estimation. The proposed method was successfully applied for the determination of thiocolchicoside in its synthetic binary mixtures and commercial tablets. Results were compared with those obtained by reference methods and non-significant difference was obtained regarding accuracy and precision. Assay precision using two-way ANOVA was performed on results of inter- and intra-day applications of the method.

Kinetic study of alkaline induced hydrolysis of the skeletal muscle relaxant chlorzoxazone using ratio spectra first derivative spectrophotometry.

2-Amino-4-chlorophenol was found to be the alkaline induced degradation product and the synthetic precursor of chlorzoxazone. The aim of this work is to study different factors affecting the degradation process due to the high toxicity of 2-amino-4-chlorophenol. Chlorzoxazone was found to follow pseudofirst order kinetics. Ratio spectra first derivative spectrophotometry (DR(1)) was developed for monitoring the change in chlorzoxazone concentration during the degradation process. Kinetic parameters (rate constant (K) and half-life (t(0.5))) were calculated at different temperatures (40-120 degrees C) and different sodium hydroxide concentrations (3-10 M). Activation energy at 3 and 8 M sodium hydroxide concentration and alkaline induced catalysis constant at 60, 70 and 80 degrees C were also calculated.

Electroreduction of nifedipine.

At pH greater than 6, the nitro group of nifedipine is reduced in a four-electron step to a hydroxylamino group. At pH less than 6, the hydroxylamino derivative undergoes an acid-catalyzed dehydration, and the rate of this reaction governs the limiting current. Resulting quinonemethide is further reduced, and a six-electron reduction step results. Formation and reducibility of the quinonemethide is favored by conjugation with the 1,4-dihydropyridine ring. Further reduction of the hydroxylamino derivative is confirmed by the absence of the anodic oxidation peak on the reverse scan at pH less than 6.5. At potentials more negative than that of the nitro group, the protonated form of the hydroxylamino derivative is reduced between pH 4 and 8 in direct current (dc) polarography and between pH 6 and 11 in cyclic voltammetry, the difference resulting from the difference in the measurement time window. The yields and fate of the hydroxylamino derivative obtained in controlled potential electrolysis with a hanging mercury drop electrode (HMDE) differ from those in dc polarography, indicating the presence of different competing reactions. For analyses, pH 2 and 11 are most suitable.

Stability-indicating method for determination of some acid-stable penicillins.

A proposed titrimetric procedure for determining some acid-stable penicillins is investigated. The procedure has been used for both pure substances and dosage forms and was fairly accurate. A study of the mechanism of the reaction of the suggested stability-indicating method is presented.

Polarographic and colorimetric methods for determination of cyclophosphamide.

Polarographic and colorimetric methods for analysis of cyclophosphamide and its dosage forms were investigated. Both methods are based on the reaction of cyclophosphamide with nitrous acid. A single cathodic diffusion-controlled wave was used for dc polarographic determination of cyclophosphamide, with an accuracy of 99.98 +/- 1.09%. The wave was well defined and irreversible. By differential pulse polarographic analysis, as little as 10 ppm cyclophosphamide was determined; overall accuracy at 10-60 ppm was 100.16 +/- 0.99%. The linear relationship between absorbance for the lemon-yellow nitroso derivative and the concentration of cyclophosphamide was further used in colorimetric analysis; overall accuracy was 100.2 +/- 0.99%.

Colorimetric analytical study of oxyphenbutazone.

A procedure was developed for the colorimetric determination of oxyphenbutazone by treatment with dilute nitrite and dilute hydrochloric acid solutions for 10 min, then rendering alkaline with potassium hydroxide. By this simple colorimetric measurement, quantities of oxyphenbutazone from 2.5 to 10 mg/100 ml are determined with an accuracy of 98.80 +/- 1.33%. Application of the suggested method to different pharmaceutical preparations has shown no significant difference compared with the Brit. Ph. 1980 method. A colour reaction mechanism is discussed.

Polarographic analytical study of oxyphenbutazone.

The polarographic behaviour of the widely used anti-inflammatory agent, oxyphenbutazone, was studied. It is determined polarographically by conversion to the nitroso derivative characterized by a cathodic, irreversible, diffusion-controlled wave. The method is applied to the determination of 2.5-10 mg/100 mL of oxyphenbutazone, with an accuracy of 99.9 +/- 1.38%. By differential pulse polarographic analysis, as little as 10 ppm oxyphenbutazone can be determined with an accuracy of 99.70 +/- 0.99% in pure powder and in some pharmaceutical formulations.

A voltammetric study of trimethoprim.

With a dropping-mercury electrode well-developed dc. polarographic reduction waves of trimethoprim (1) were obtained with 0.1 M H2SO4, citrate buffers (pH = 3--4) and acetate buffers. The solutions contain 25% ethanol as co-solvent. The reduction process is irreversible and the limiting currents are directly proportional to the concentration of I within the range from 5.10(-5) to 10(-3)M. Coulometric measurements indicate that 4 electrons are consumed per molecule. The reduction process is initiated by the reduction of the 3, 4 double bond in the pyrimidine moiety but results in the final splithing-off of two amino groups. In acetonitrile with 0.1 M LiClO4 as supporting electrolyte, two concentration-proportional anodic oxidation waves are obtained with a rotated gold disk electrode.

A spectrophotometric and polarographic investigation of three new cyclohexene-substituted benzodiazepines.

Three recently introduced benzodiazepine derivatives, tetrazepam (I), nortetrazepam (II) and menitrazepam (III) have been subjected to spectral and polarographic investigation. From the ultraviolet spectral data their pK(a)-values have been determined: 4.28 (I), 4.3 (II) and 3.5 (III). From the polarographic measurements it can be concluded that in I and II the 4,5 CN double bond is reduced with 2 electrons. For the first time for the benzodiazepine series it has been observed that in slightly alkaline solutions this process takes place in two separate 1-electron steps. In III, first the aromatic nitro group is reduced to a hydroxylamine group, then at more negative potentials the CN double bond is also reduced; its reduction wave mostly coalesces with that for the 6-electron reduction of the nitro group to an amino group. A differential pulse polarographic method is presented, for the determination of I, II, III at concentrations as low as 10(-7)M.

Differential pulse polarography of some benzodiazepines and their determination in urine.

A differential pulse polarographic method has been applied to the determination of diazepam, oxazepam, nitrazepam and flurazepam down to 2 x 10(-7)M (0.14 mug/ml). The method can also be used with biological materials such as urine, without prior extraction. Only a 2-ml volume of urine is necessary.