A new colorimetric method for the determination of nifedipine tablets by derivatization using 4-carboxyl-2,6-dinitrobenzene diazonium ion

A new sensitive colorimetric determination of nifedipine has been developed following azo dye formation with 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD). Judging from the various generic brands currently now available, this research was conceived as a means of developing an alternative cost-effective and readily adaptable method for the assay of nifedipine in tablets and for which official high performance liquid chromatographic technique may not be readily available. Results Nifedipine was reduced with Zn/HCl reduction system and then the diazo coupling reaction was carried out with the CDNBD reagent to generate a new azo adduct with optimal wavelength at 470 nm representing a bathochromic shift relative to nifedipine, reduced nifedipine and CDNBD reagent. Optimal temperature and time for coupling were selected as 50 oC and 15 minutes. A linear response was observed over 2.9 -14.5 µg/mL of nifedipine with a correlation coefficient of 0.9985 and the drug combined with CDNBD at a stoichiometric ratio of 2:1. The method has limits of detection and quantitation of 0.1344 µg mL-1 and 0.4074 µg mL-1 respectively. The Sandell’s sensitivity obtained is 4.673 ng/cm2 and the method was reproducible over a three day assessment. Intra- and inter-day accuracies (in terms of errors) were of the order -0.008 to 3.22 % while precisions were generally less than 3.1 % (RSD). Conclusions The developed spectrophotometric method is of equivalent accuracy (p > 0.05) with USP 2007 HPLC method. It has the advantages of speed, simplicity, sensitivity and more affordable instrumentation and could find application as a rapid and sensitive analytical method for nifedipine. It is the first described method by azo dye derivatization for the analysis of nifedipine in bulk samples and dosage forms.