Sensitive Spectrophotometric Assay of Isoniazid in
Pharmaceuticals using Cerium(IV)
and Two Acid Dyes
Nagaraju SWAMY, Kanakapura BASAVAIAH° and Kudige Nagaraj PRASHANTH
Department of Chemistry, Manasagangothri, University of Mysore, Mysore-570 006, Karnataka, India
° Corresponding Author E-mail: kanakapurabasavaiah@gmail.com
Summary
Two simple, rapid, selective and sensitive spectrophotometric
methods are proposed for the assay of isoniazid (INH) in pure
form and in tablets. The methods are based on the oxidation of
INH by a measured excess of Ce(IV) in acid medium followed
by determination of surplus oxidant by reacting with a fixed
quantity of methyl orange (method A) or indigo carmine
(method B) and measuring the absorbance at 520 or 610 nm.
In both methods, the amount of Ce(IV) reacted corresponds
to the amount of INH. The experimental parameters for
the assay have been carefully optimized. In these methods,
the absorbance is found to increase linearly with the
concentration of INH at the respective wavelengths. Beer’s
law is obeyed over the ranges 0.3–3.0 and 0.5–7.0 µg mL-1 for
method A and method B respectively and the respective molar
absorptivity values are 3.71×104 and 3.12×104 L mol-1 cm-1.
The limits of detection and quantification are reported for
both methods. The performance of the methods was validated
according to the current ICH guidelines. The repeatability
and intermediate precision, expressed as the RSD was less
than 2%. The accuracy of the methods expressed as relative
error was satisfactory. The proposed methods were applied
to the analysis of tablet form of INH and the results agreed
well with the label claim. No interference was observed from
the common additives normally added to tablets. The results
were statistically compared with those of an official method
by applying the Student’s t-test and F-test. The accuracy
and validity of the methods were further ascertained by
performing recovery studies using spike method.
Key Words :
Isoniazid, assay, spectrophotometry, pharmaceuticals,
spike.
