Analysis of some dosage forms containing pyridine derivatives using a cyclodextrin bonded stationary phase in HPLC

Study on complex formation of biologically active pyridine derivatives with cyclodextrins by capillary electrophoresis

The capillary electrophoretic separation of the pyridine derivatives pyridoxine, pyridoxal, nicotinamide, nicotinic acid and isonicotinic acid in phosphate buffer using cyclodextrins as buffer additives was studied at pH 2.0 and 3.5. Superior separation was achieved at pH 2.0. Addition of alpha- and beta-cyclodextrin and the respective 2-hydroxypropyl derivatives as well as carboxymethyl-alpha-cyclodextrin to the running buffer did not significantly improve the resolution of the compounds. The interactions of alpha- and beta-cyclodextrin as well as their hydroxypropyl derivatives with the pyridine derivatives were investigated by capillary electrophoresis at pH 2.0. No complex formation was observed between the cyclodextrins and pyridoxine, pyridoxal and nicotinamide. alpha-Cyclodextrin and 2-hydroxypropyl-alpha-cyclodextrin form weak 1:1 complexes with nicotinic and isonicotinic acids in aqueous media at 298.15K, while beta-cyclodextrin and its hydroxypropyl derivative did not form complexes. The apparent stability constants (K) of the complexes calculated from the electrophoretic mobility data ranged between 3 and 33 kg/mol. The negative values of enthalpy and entropy of complex formation obtained from the graphical plot of the van't Hoff equation indicate an important role of van der Waals and electrostatic interactions in the binding of nicotinic acid with alpha-cyclodextrin.

Determination of tropicamide in pharmaceutical formulations using high-performance liquid chromatography

An isocratic, reversed-phase liquid chromatographic method was developed for determination of tropicamide using atropine as an internal standard in a pharmaceutical dosage form. Tropicamide and atropine sulfate were separated using a microBondapak ODS (C18) column by isocratic elution of mobile phase with flow rate of 2.0 ml/min. The mobile phase composition was methanol-50 mM phosphate buffer (pH 4; 30:70, v/v). The eluate was monitored at 257 nm with detector range setting fixed at 0.01 AUFS. Under these conditions, the retention times were 4.81 min for atropine and 11.89 min for tropicamide. The standard calibration curve was linear over a sample concentration range from 2 to 300 microg/ml, with limit of detection of 0.15 microg/ml. The assay linearity was good (typically r2 = 0.9992) and the standard curves were linear in the detection range. The precision of the method (expressed by relative standard deviation) and the accuracy (mean error in percent) were <5% for both intra- and inter-day assays. Recovery at 80-120% of labeled claim ranged from 98.4 to 100.7% for tropicamide. The proposed method was satisfactorily applied to the determination of tropicamide in pharmaceutical preparation and stability indicating studies.

Quantitative determination of piroxicam in a new formulation (piroxicam-beta-cyclodextrin) by derivative UV spectrophotometric method and HPLC

A derivative ultraviolet (UV) spectrophotometric method for the determination of piroxicam in piroxicam--beta-cyclodextrin tablets was developed. Phosphate buffer (pH 7.8, 0.1 M) and ethanol were used as a solvent system throughout the study. In this study, determination of piroxicam was conducted by using first order derivative amplitudes at 261.4 nm (n=4). Standards for the calibration graph ranging from 2.40 to 20.0 microg/ml were prepared from working standard. The proposed method is accurate with 99.70%+/-0.50 recovery value and precise with coefficient of variation (CV) of 1.29. The results were compared with those obtained using a high-performance liquid chromatography (HPLC) procedure. A reversed-phase C(18) column with aqueous phosphate buffer:methanol, 60:40, v/v, mobile phase was used. UV detector was set at 254 nm. Calibration solutions used in HPLC were ranging from 5 to 20 microg/ml. Results obtained in HPLC were comparable to those obtained by derivative UV spectrophotometric method.

Enantiomeric analysis of phenylpropanolamine in plasma via resolution of dinitrophenylurea derivatives on a high performance liquid chromatographic chiral stationary phase

Racemic phenylpropanolamine was resolved on a high performance liquid chromatographic (HPLC) chiral stationary phase (CSP) as the 3,5-dinitrophenyl ureide derivative. The CSP was prepared by a simple in situ procedure in which (R)-(1-naphthyl)ethyl isocyanate was bound to aminopropyl silanized silica through a urea linkage. The enantiomeric ureides were prepared by a room-temperature, 60-second procedure, accomplishing simultaneous extraction and derivatization and utilizing achiral 3,5-dinitrophenyl isocyanate as reagent. Baseline resolution was readily achieved under normal phase conditions, with a separation factor (alpha) of 1.16 and a resolution factor (RS) of 2.2. Elution was complete within 10 min. A limit of detection, by UV at 235 nm, of 250 pg per isomer was established. Feasibility of the procedure for plasma determinations was demonstrated by assay of samples from a canine subject.

Analytical applications of enhanced drug luminescence

Luminescence emission from drugs is strongly dependent on their physicochemical environment. Several biomedically and environmentally important compounds and pharmaceuticals exhibit sufficient intrinsic luminescence properties to allow their determination by high-performance liquid chromatography (HPLC) with fluorimetric, chemiluminescence or room temperature phosphorimetric detection. In the case of weakly fluorescing compounds it is possible to use the dependence of the emitted radiation on the molecular environment at the moment of measurement. The composition of the eluent, i.e. solvents, added salts and buffers, pH and ionic strength, oxygen content and temperature, are of the highest importance for the luminescence detection of drugs in solution (e.g. in liquid chromatography) or adsorbed onto solid surfaces (e.g. in thin-layer chromatography). Post-column or post-plate acid-base manipulation and the use of specific reagents may remarkably enhance the observed luminescence of several molecules. The term "enhancement" of luminescence comprises various sample treatments leading to an increase of the emitted radiation. These treatments include the addition of non-fluorescent compounds to, or the creation of organized media (surfactants, cyclodextrins, heavy atoms) in, the sample to be measured. They may also involve changes in molecular environment, pH, the application of excessive drying conditions, the removal of oxygen, the protection of adsorbed compounds against non-radiative decay mechanisms by means of specific spraying or dipping conditions, amongst others. The use of organized media in luminescence spectroscopy is growing. Many of the recent studies have involved micelles for enhancing the fluorescence, room temperature phosphorescence and chemiluminescence of several chemicals. Cyclodextrins are increasingly used for various analytical applications. Liquid paraffin, triethanolamine, dodecane, Triton X-100 and Fomblin Y-Vac are commonly used fluorescence enhancers in chromatographic assays. Examples of these systems in drug analysis are presented.

Analysis of some dosage forms containing pyridine derivatives using a cyclodextrin bonded stationary phase in HPLC

The high performance liquid chromatography of some pyridine derivatives using a silica column to which beta-cyclodextrin has been bonded, has been investigated. In spite of the low affinity constants of the drugs for cyclodextrin (of the order of 10(2) M(-1)) good separations can be achieved using a mobile phase of methanol and pH 7.0 phosphate. Good analysis of some dosage forms are achieved, including one on a tablet containing pheniramine maleate, pyrilamine maleate and phenylpropanolamine hydrochloride. Extractions and chromatography are quick and simple.