Spectrophotometric determination of doxycycline hyclate using oxidative coupling reaction

A simple spectrophotometric technique has been developed for the determination Doxycycline hyclate (DCH) in pure and pharmaceutical formulations. The proposed method is based on the oxidative coupling reaction using sodium periodate and hydrazine dihydrochloride (HZD) producing an orange colored complex with maximum absorption at 420 nm. The Beer′s law is obeyed over the concentration range of (3.0 –72.0) µg ml-1, while the detection limit and quantification limit are 0.0631 and 0.1912 µg ml-1 respectively, with a correlation coefficient (r) of 0.9999 and a molar absorptivity of 3.0562× 103 L mol-1cm-1 with Sandell′s sensitivity index of 0.1678 µg cm-2. The precision and accuracy of the method are checked by calculating relative standard deviation (RSD) (≤ 2.27%) and average recovery (98.913 %). The value of the stability constant has been calculated and found to be 1.89×108 L mol-1. Different experimental parameters affecting the development and stability of the formed color product are carefully studied and optimized. Possible interferences that related to the determination of (DCH) in pharmaceutical capsules are studied and the results showed that the method is successfully applied for determination of DCH in pharmaceutical formulation.