Sensitive spectrofluorimetric and spectrophotometric methods for the determination of thonzylamine hydrochloride in pharmaceutical preparations based on coupling with dimethylbarbituric acid in presence of dicyclohexylcarbodiimide.

Two sensitive and selective spectrophotometric and spectrofluoimetric procedures were developed for the determination of thonzylamine hydrochloride (THAH) in tablets and nasal drops. The methods are based on König reaction which resulted in an orange-yellow fluorescent product. The orange-yellow product of the interaction between the dicyclohexylcarbodiimide (DCC), THAH and dimethylbarbituric acid (DMBA) showed an absorption maximum at 492 nm, a first-derivative signal at 494 nm and a fluorescence emission peak at 518 nm (lambda(ex)=492 nm). The orange-yellow color was found to be stable for at least 2 h. The reaction conditions were studied and optimized. The reaction obeys Beer's law over the ranges 8-20 and 0.2-2.0 microg ml(-1) for the derivative spectrophotometric and fluorimetric measurements, respectively. The detection limits were found to be 0.29 and 0.018 microg ml(-1) for the spectrophotometric and fluorimetric measurements, respectively. The proposed methods were applied to the analysis of pharmaceutical formulations containing THAH, either alone or in combination with naphazoline nitrate.

Simultaneous determination of tenoxicam and 2-aminopyridine using derivative spectrophotometry and high-performance liquid chromatography.

Derivative spectrophotometry and high-performance liquid chromatography (HPLC) were used to determine tenoxicam and one of its decomposition products (2-aminopyridine) simultaneously and in the presence of each other. The derivative procedure was based on the linear relationship between the tenoxicam concentration and the second derivative amplitudes at 390-348 nm (peak-to-trough) measurement. The 2-aminopyridine was determined through measuring the second derivative amplitude at 241 nm (zero-crossing for tenoxicam). For the HPLC procedure, a reversed-phase C8 column with a mobile phase composed of 0.02 M sodium acetate-methanol-acetonitrile (11:8:1) with 0.005 M heptane sulfonic acid sodium salt, as an ion pair, was used to separate both compounds with 2,4-dinitrochlorobenzene, as an internal standard, in reasonable time. The flow rate was 1.5 ml min-1 with a programmable ultraviolet (UV) detection at 300 and 375 nm. Both UV derivative spectrophotometric and HPLC approaches were followed for confirming the purity of tenoxicam in bulk and tablets dosage form.

Application of the computerized compensation method and the orthogonal functions method to correct for irrelevant interference in spectrofluorometry.

The computerized compensation method and the orthogonal functions method were applied to correct for the presence of interferences in spectrofluorometric analysis. The methods were demonstrated by the determination of tetracycline (TC) and anhydrotetracycline (ATC) in combination. The calibration graphs were linear in the concentration range 0.02-0.12 mg/100 ml of either TC or ATC.

Spectrophotometric determination of benzene in ethanol.

A rapid, simple spectrophotometric method for the detection and determination of benzene in ethanol is described. Thus, using 1 cm cuvettes and applying the first and/or the second derivative methods, benzene can be determined in ethanol over the concentration range of 5-25 p.p.m. with a CV% less than 1% and with a detection limit of 2 p.p.m. This is considered to be an improvement over the method currently given in the British Pharmacopoeia.

Determination of isothipendyl or dimethothiazine with their sulphoxides using third- and fourth-derivatives spectroscopy on a diode-array spectrophotometer.

Third- and fourth-derivative spectrophotometry (3D + 4D), with a diode-array spectrophotometer, has been used for the assay of mixtures of each of isothipendyl hydrochloride (I) and its sulphoxide (II) or dimethothiazine mesylate (III) and its sulphoxide (IV). The parent compounds have been determined by measuring the 3D at 256 nm, 246-256 nm and 256-264 nm and 4D at 250 nm for (I) and 3D at 255 nm or 283 nm and 4D at 257 nm for (III). The sulphoxides have been assayed by measuring the 3D at 285-290 nm and 4D 285-290 nm for (II) and 3D at 305 nm and 4D at 303-310 nm for (IV). Beer's law is obeyed and the detection limits for the proposed 3D and 4D has been calculated. The recovery of these drugs and their sulphoxides in laboratory-made mixture and dosage forms has been reported.

Spectrofluorimetric assay of tetracycline and anhydrotetracycline in combination.

Spectrofluorimetric methods are described for the assay of tetracycline (TC) and anhydrotetracycline (ATC) in combination, without prior separation. The interference from ATC in the TC assay has been corrected for by forming the aluminium complexes of both drugs and measuring the difference in fluorescence at 475 and 418 nm, with excitation at 393 nm. Similarly, measurement of the fluorescence of the magnesium complexes at 525 and 470 nm (excitation at 440 nm) nullifies TC interference in the ATC assay.

A simple fluorometric method for the determination of salicylic acid in aluminium acetylsalicylate.

A simple, rapid fluorometric method for the determination of salicylic acid in aluminium acetylsalicylate is presented. The method is based on the dissolution of aluminium acetylsalicylate in sodium fluoride-hydrochloric acid solution, filtration and dilution with buffer solution pH = 4 followed by the fluorometric determination of the liberated salicylic acid. The method was applied successfully to the determination of salicylic acid in aluminium acetylsalicylate tablets.