Der Pharma Chemica
Journal for Medicinal Chemistry, Pharmaceutical Chemistry and Computational Chemistry


“Solid as solvent”- Novel spectrophotometric analysis of indomethacin capsules using melted phenol as solvent

Author(s): R. K. Maheshwari and R. Dahima

Each and every substance present on the earth possesses solubilizing power (mixed-solvency concept proposed by Maheshwari). All substances i. e. gases, liquids and solids have solubilizing power. All substances which are liquids at room temperature are known as solvents and this is very well known to us. Supercritical fluid technology is a good proof that gases have solubilizing power. In this technology, liquefied carbon dioxide gas acts as solvent to perform various functions like extraction of active constituents from herbal drugs, purification, production of nanoparticles etc. Similarly, solids also possess solubilizing power. The solubility of nalidixic acid in ethanol is 0.198 % w/v while its solubility in a solution containing 20 % w/v ibuprofen in ethanol was found to be 2.689 % w/v. This 13 fold enhancement in solubility is due to solubilizing power of ibuprofen (a solid). Also, the solubility of nalidixic acid in a solution containing 20 % w/v ibuprofen and 20 % w/v benzoic acid combinedly, in ethanol was found to be 5.753 % w/v. Again, this further enhancement in solubility of nalidixic acid is due to the solubilizing power of benzoic acid (a solid). These all proofs show that solids also have solubilizing power (or solvent character). The present investigation is an attempt to show that solids can also be wisely used to act as solvent precluding the use of organic solvents. In a separate study, author has attempted soxhelation using phenol as solvent. The vapours of boiling phenol got condensed in extraction chamber to effect the extraction of active constituents from powder of crude drugs. The main objective of the present study is to demonstrate the solvent action of solid. Solid excipients can nicely be employed as solubilizers in the development of pharmaceutical dosage forms in solution form of poorly soluble drugs (mixed solvency concept). Present study describes the application of solvent character of melted phenol (at 50-60°C) for spectrophotometric estimation of indomethacin capsules. Solubility of indomethacin in distilled water was found to be 0.36 mg/ml at room temperature. More than 380 mg of indomethacin dissolves in one gram of melted phenol (at 50-60°C). In the present investigation, melted phenol (at 50-60°C) was utilized to extract out (dissolve) the drug from the fine powder of indomethacin capsules. Distilled water was used for dilution purpose. Absorbances of standard solutions containing 15, 30, 45 and 60 μg/ml were noted at 320 nm against reagent blanks to obtain calibration curve. Proposed method is novel, economic, ecofriendly, rapid, free from toxicity of organic solvent, accurate and reproducible. Recovery studies and statistical data proved the accuracy, reproducibility and precision of the proposed method. The presence of tablet excipients and phenol did not interfere in the spectrophotometric estimation of indomethacin at 320 nm. Phenol does not interfere above 300 nm in spectrophotometric analysis.

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