Sensitive spectrophotometric determination of aceclofenac following azo dye formation with 4-carboxyl-2,6-dinitrobenzene diazonium ion.

The study is a description of a sensitive spectrophotometric determination of aceclofenac following azo dye formation with 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD). Spot test and thin layer chromatography revealed the formation of a new compound distinct from CDNBD and aceclofenac. Optimization studies established a reaction time of 5 min at 30 degrees C after vortex mixing the drug/CDNBD for 10 s. An absorption maximum of 430 nm was selected as analytical wavelength. A linear response was observed over 1.2-4.8 µg/mL of aceclofenac with a correlation coefficient of 0.9983 and the drug combined with CDNBD at stoichiometric ratio of 2 : 1. The method has a limit of detection of 0.403 µg/mL, limit of quantitation of 1.22 µg/mL and is reproducible over a three day assessment. The method gave Sandell's sensitivity of 3.279 ng/cm2. Intra- and inter-day accuracies (in terms of errors) were less than 6% while precisions were of the order of 0.03-1.89% (RSD). The developed spectrophotometric method is of equivalent accuracy (p > 0.05) with British Pharmacopoeia, 2010 potentiometric method. It has the advantages of speed, simplicity, sensitivity and more affordable instrumentation and could found application as a rapid and sensitive analytical method of aceclofenac. It is the first described method by azo dye derivatization for the analysis of aceclofenac in bulk samples and dosage forms.

Solvatochromic behaviours and structure-spectra relationships of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes.

Comprehensive electronic absorption spectra of a new dye series, 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes have been investigated in solvents of varying polarities. The solvent dependent UV-vis spectral shifts were analysed using some solvent physical parameters such as refractive index, dielectric function, hydrogen bonding acceptor ability, orientation of polarization and others. The observed spectral shifts were correlated with different solute-solvent interaction mechanisms using simple and multiple linear regression analyses. The results of the curve fitting coefficients enabled us to classify the various interactions of solvents with the dyes and relate the solvatochromic behaviours to the substituent effects on the dye molecules. Charge-transfer complexation occurring between one of the congeners and N,N'-dimethylformamide was extensively studied and discovered to be both concentration- and temperature-dependent. The electronic character and the chemical nature of the solvents as well as the chemical nature of the other substituents, apart from the common hydroxyl group, are important factors for the observed solvatochromic properties of the 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes.

Computational models for structure-hydrophobicity relationships of 4-carboxyl-2,6-dinitrophenyl azo hydroxynaphthalenes.

Some phenyl azo hydroxynaphthalene dyes (e.g., sunset yellow) are certified as approved colorants for food, cosmetics, and drug formulations. The hydrophobicity of 4 newly synthesized azo dyes of the phenyl azo hydroxynaphthalene class was investigated, as a training set, with the goal of developing models for quantitative structure-property relationships (QSPR). Retention behavior of the molecules reversed-phase thin-layer chromatography (RPTLC) was investigated using liquid paraffin-coated silica gel as the stationary phase. Mobile phases consisted of aqueous mixtures of methanol, acetone, and dimethylformamide (DMF). Basic hydrophobicity parameter (Rmw), specific hydrophobic surface area (S), and isocratic chromatographic hydrophobicity index (phio) were computed from the chromatographic data. The hydrophobicity index (Rm) decreased linearly with increasing concentration of organic modifiers. Extrapolated Rmw values obtained by using DMF and acetone differ significantly from the value obtained by using methanol as organic modifier [P < 0.05, 1-way analysis of variance (ANOVA), Tukey's multiple comparison test]. Structure-property relationships showed that hydrophobicity was dependent on type and position of naphthalene ring substituents. Rm decreased with the presence of a highly polar substituent (e.g., COOH). Owing to intramolecular interaction, Rm increased when the common hydroxyl group (OH) is positioned ortho to the azo group, relative to para positioning, in 2 positional isomers. Pattern recognition data analysis underscores the utility of phio as a more accurate hydrophobicity descriptor than Rmw. Phio is negatively correlated with theoretically calculated density, surface tension, and refractive index for the molecules. These models could be used to predict toxicity (absorption, distribution, metabolism, excretion, toxicity; ADMET) properties of the azo dyes and may also play useful roles in computer-assisted molecular discovery of nontoxic azo dyes.

Rapid colorimetric assay of diclofenac sodium tablets using 4-carboxyl-2,6-dinitrobenzene diazonium ion (CDNBD).

This study describes a novel simple, rapid and sensitive colorimetric assay method for diclofenac sodium tablets. The method is based on a simple aromatic ring derivatization technique using newly developed 4-carboxyl-2, 6-dinitrobenzenediazonium ion (CDNBD) as chromogenic derivatizing reagent with subsequent formation of an azo dye. The diazo coupling reaction was carried out between CDNBD and diclofenac. Optimization studies for time and temperature was conducted using the method of steepest ascent. The UV absorption spectrum was recorded and the stoichiometric ratio for the drug and reagent was done by continuous variation method. Optimal calibration range was fixed (1-way ANOVA) and then the method was applied to dosage form analysis. Comparison of dosage form analysis was done with the BP HPLC method. The diazo coupling reaction is very fast and optimization studies established an optimal reaction immediately after mixing the reaction mixture in a vortex mixer for 10 sec. A new absorption maximum (lambdamax) at 470 nm was selected as analytical wavelength. The assays were linear over 1.35-10.8 microg/ml of diclofenac and the reaction required a 2:1 reagent/drug stoichiometric ratio. The new method has a low limit of detection of 0.27 microg/ml, and was reproducible over a three-day assessment of precision (RSD 2.31%). The method has been successfully applied to the assay of diclofenac sodium slow-release tablets and found to be of equivalent accuracy (p>0.05) with the official (B.P 1998) HPLC method. The new method has distinct advantages of speed, simplicity, sensitivity, and more affordable instrumentation and could find application as a rapid analytical method for diclofenac sodium tablets.

Kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD).

The kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD), an arenediazonium ion newly developed as a derivatizing reagent for drug analysis, are described. The arenediazonium ion, in an optimized concentrated sulfuric acid/orthophosphoric acid medium, was incubated for various time intervals at 30 degrees, 45 degrees, 55 degrees , 65 degrees , 75 degrees, and 85 degrees C. The amount of ion left after each time interval was quantified selectively by colorimetric assay at 490 nm, using mefenamic acid as a model diazo-coupling component. The rate constants for the decomposition were determined graphically. An Arrhenius plot was used to delineate the dependence of the rate constant on temperature and to predict the half-life at 25 degrees C and lower temperatures. The diazonium ion decomposed by first-order kinetics. The rate constants of decomposition, which increased progressively with temperature, were 3.18 +/- 0.41 x 10(-5), 1.19 +/- 0.07 x 10(-4), 4.87 +/- 0.15 x 10(-4), 12.88 +/- 0.73 x 10(-4), and 21.32 +/- 2.74 x 10(-4) (s(-1)) with corresponding half-lives of 363, 97.06, 23.72, 8.97, and 5.42 min at 30 degrees, 45 degrees, 55 degrees, 65 degrees, and 75 degrees C, respectively. CDNBD is highly stable in concentrated acid medium, with half-life values of about 10 h, 10 days, and 7.3 months at 25 degrees, 0 degrees, and -20 degrees C, respectively. The reagent stability profile shows that it could be readily adapted for routine applications in instrumental chemical analysis.

Colorimetric assay of propranolol tablets by derivatization: novel application of diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA).

A novel colorimetric assay of propranolol tablets has been developed. The assay is based on chemical derivatization (aromatic ring derivatization technique) using diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA) as the chromogenic derivatizing reagent and resultant formation of azo dyes. Optimization studies established an optimal reaction time of 5 min at 30 degrees C after mixing on a Vortex mixer the drug/reagent mixture for 10 s. A new absorption maximum (lambda(max)) was found at 470 nm, which was selected as the analytical wavelength. The assays were linear over 1-8 microg/mL propranolol, and the reaction occurred by a 1:1 reagent/drug stoichiometric ratio. The developed method has a low limit of detection of 0.76 microg/mL and is reproducible. It has been applied successfully to the assay of propranolol tablets and is of equivalent accuracy (p > 0.05) with the official (British Pharmacopoeia) ultraviolet spectrophotometric method. The new method has the main advantage of using more affordable instrumentation and could be applied to the in-process quality control of propranolol tablets.