Spectrophotometric Determination of Niacin, Thiamine, Glibenclamide, Erythromycin and Para Amino Benzo Ic Acid Using 2, 3 – Dichloro – 5, 6 – Dicyano – 1, 4 – Benzoquinone

Abstract

A simple and sensitive spectrophotometric method is described for the assay of the drugs; niacin, glibenclamide, erythromycin, thiamine and 4-aminobenzoic acid. The method is based on charge transfer complexation (CT) reaction of niacin, glibenclamide, erythromycin, thiamine and 4-aminobenzoic acid as n-electron donors with 2,3-dichloro-5,6-dicyno-1,4-benzoquinone(DDQ) as л-electron acceptor in methanol. Intensely coloured charge transfer complexes with niacin (reddish brown, max ;464 nm; εmax, 1.02x103 dm3mol-1cm-1) thiamine (reddish brown ,max ;474 nm; εmax, 1.08x103 dm3mol-1cm-1), glibenclamide (reddish brown , max ;474 nm; εmax,0.99x103 dm3mol-1cm-1) erythromycin(reddish brown , max ;464 nm; εmax, 1.27x103 dm3mol-1cm-1) 4-aminobenzoic acid(reddish brown, max ;474nm; εmax, 1.06x103 dm3mol-1cm-1) all in a 1:1 stoichiometric ratio. Condition for complete reactions and optimum stability of complexes were niacin (70 min, 60 OC) thiamine (25 min, 40 OC), glibenclamide (35 min, 40 OC), erythromycin (15 min, 60 OC) and 4-aminobenzoic acid (15 min, 60 OC) as absorbances of the complexes remained invariant within these conditions. Formation and stability of the complexes of niacin, thiamine, 4-aminobenzoic acid and erythromycin were optimum at pH 8. For glibenclamide pH 2.0 favoured optimum stability and formation. The bands distinguished for the donors to donor-acceptor CT complexes displayed small changes in band intensities and frequency values in the IR spectra ,The –NH2 group vibration occurring at 3609 cm-1 shifted to 3610 cm-1 in thiamine, PABA (3222 cm-1 to 3183 cm-1), ѵ (N-H) occurring at 3331cm-1 shifted to 3371 cm-1 in glibenclamide, ѵ(C=N) occurring at 2936 cm-1 shifted to 2944 cm-1 in niacin, ѵ (CH3-N) occurring at 2948 cm-1 shifted to 2939 cm-1 in erythromycin. The vibration ѵ (C= O) of DDQ observed at 1665 cm-1 shifted to 1669 cm-1 in the CT complex for thiamine, PABA(1665 cm-1 to 1670 cm-1), glibenclamide(1675 cm-1 to 1676 cm-1), erythromycin(1665 cm-1 to 1674 cm-1), niacin(1665 cm-1 to 1655 cm-1) respectively. Adherence to Beer’s Law was within the concentration range for niacin (5-130 μg/cm3), thiamine (5-80 μg/cm3), glibenclamide (9-100 µg/cm3), erythromycin (5-150 µg/cm3), 4-aminobenzoic acid(5-90 µg/cm3). Limit of detection and quantification of the drugs based on this method is niacin (1.78 and 5.4), thiamine (1.23 and 3.37), glibenclamide (3.47 and 10.5), erythromycin (2.11 and 6.40), 4-aminobenzoic acid (0.55 and 1.67) respectively. Evaluation of the degree of interference by excipients used in the drugs manufactured indicates tolerance to certain concentrations. A detailed study on the interference of different excipients was made. No significant interference was observed in magnesium stearate (30 µg/cm3), Talc (15-25µg/cm3, 35-40 µg/cm3) with thiamine-DDQ complex. There were no significant interference in stearic acid (35 µg/cm3) but tolerable interference was seen in magnesium stearate (20 µg/cm3) and calcium phosphate (15 µg/cm3) with niacin-DDQ complex. For glibenclamide – DDQ complex, no significant interference was seen with calcium phosphate (30 µg/cm3) but there were tolerable interference present in stearic acid (40 µg/cm3). In 4-aminobenzoic acid, no significant interference was observed with magnesium stearate (30 µg/cm3) and talc (35 -40µg/cm3) but tolerable interference was observed in corn starch (15 µg/cm3). Also no significant interference was seen in corn starch (35 µg/cm3) with erythromycin-DDQ complex but there was tolerable interference in talc (10 µg/cm3). The Pearson correlation coefficient for the compliance of the method as regards the pure and commercial forms of niacin, thiamine, glibenclamide, erythromycin and 4-aminobenzoic acids are 0.993, 0.977, 0.987, 0.998 and 0.993 respectively which shows significance with p < 0.01. The analysis of variance test revealed the non-significance of niacin, thiamine, glibenclamide, erythromycin and 4-aminobenzoic acid with p > 0.01. The mean percentage recoveries were 98.94 ± 0.016, 96.2 ± 0.016, 98.24 ± 0.011, 107.4 ± 0.023 and 102.35 ± 0.014 for niacin, thiamine, glibenclamide, erythromycin and 4-aminobenzoic acid respectively. Kinetics of the reactions infer that the rate of formation of the CT complexes did not vary significantly with increase in concentration of glibenclamide, erythromycin, thiamine, niacin and 4-aminobenzoic acid indicating likely zeroth order dependence of the rate with respect to concentration of the drugs. However, the linearity of the pseudo-first order plot points to first order dependence of rate on [DDQ].The overall rate equation for the reactions can be given as

-(d[DDQ])/dt=k_(obs ) [DDQ]

Based on the limit of detection and quantification, adherence to Beer-Lambert’s law and low degree of interference, the method is recommended for the analysis of these drugs.