Spectroscopic Determination of Doxycycline by its Reaction with Schiff Base by Ion Pairing Method

In this study, we developed a novel, sensitive, and rapid method for determining doxycycline in its pharmaceutical formulation using the ion-pairing technique. This method is based on the interaction between doxycycline and a Schiff base, which is synthesized via a microwave-assisted condensation reaction of p-aminophenol with p-N, N-dimethylaminobenzaldehyde. The resulting Schiff base reacts with doxycycline to form a complex that exhibits maximum absorption at a wavelength of 446 nm, in contrast to the blank, which shows a peak at 374 nm. The determination of doxycycline is carried out by allowing the reaction to proceed at room temperature for 10 min, followed by dilution with ethanol and measurement of absorbance at 446 nm. The method follows Beer’s law within the concentration range of 10–17 µg/mL and demonstrates high accuracy, as evidenced by the recovery rate and relative standard deviation. This method was successfully applied to the analysis of doxycycline in its pharmaceutical preparation, specifically doxycycline 100 mg capsules. Graphical Abstract: (Figure presented.)