Simultaneous analysis of biologically active pyridines in pharmaceutical formulations by capillary zone...

A capillary zone electrophoretic method using UV detection is developed for the analysis of four biological active pyridines [i.e., nicotine (NIC), cotinine (COT), nicotinic acid (NA), and nicotinamide (NM)]. The separation of the pyridines is achieved in 25 mM sodium dihydrogen phosphate (pH 2.1) using a fused-silica capillary with an effective length of 56 cm and an inner diameter of 50 µm (extended light path), hydrodynamic injection at 50 mbar for 10 s, a temperature of 25°C, applied voltage of 30 kV, and UV detection at 260 nm. These conditions provide baseline separation of all the analytes [resolution (R(s)) > 3.6] in 9.4 min with good linearity (r(2) > 0.998, in ranges of 50-600 µg/mL for NIC, 8-160 µg/mL for NM, and 10-200 µg/mL for COT and NA), precision (relative standard deviation <2.04%), recovery (96.4-101.6%), limits of detection (<3.0 µg/mL), and quantitation (<10 µg/mL). The method is robust upon the alterations of pH of BGE, separating voltage, and injection time [the RSDs of the relative migration time (migration time of the analyte/migration time of the internal standard) and resolution <3.26%]. The method is efficient, reliable, and simple for the routine analysis of NIC, NA, and NM in various products such as gum and tablets and can be applied to determine COT in thermal degradation of NIC gum.