Summary: | Two simple, rapid and cost-effective methods based on titrimetric and spectrophotometric
techniques are described for the assay of RNH in bulk drug and in dosage forms using silver nitrate, mer-
cury(II)thiocyanate and iron(III)nitrate as reagents. In titrimetry, an aqueous solution of RNH is treated
with measured excess of silver nitrate in HNO 3 medium, followed by determination of unreacted silver
nitrate by Volhard method using iron(III) alum indicator. Spectrophotometric method involve the addi-
tion a known excess of mercury(II)thiocyanate and iron(III)nitrate to RNH, followed by the measurement
of the absorbance of iron(III)thiocyante complex at 470 nm. Titrimetric method is applicable over 4-30
mg range and the reaction stoichiometry is found to be 1:1 (RNH: AgNO 3 ). In the spectrophotometric
method, the absorbance is found to increase linearly with concentration of RNH which is corroborated
by the correlation coefficient of 0.9959. The system obey Beer’s law for 5-70 μg mL -1 . The calculated
apparent molar absorptivity and sandell sensitivity values are found to be 3.27 × 10 3 L mol -1 cm -1 , 0.107
μg cm -2 respectively. The limits of detection and quantification are also reported for the spectrophoto-
metric method. Intra-day and inter-day precision and accuracy of the methods were evaluated as per ICH
guidelines. The methods were successfully applied to the assay of RNH in formulations and the results
were compared with those of a reference method by applying Student’s t and F-tests. No interference was
observed from common pharmaceutical excipients. The accuracy of the methods was further ascertained
by performing recovery tests by standard addition method.
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