Batch and Flow Injection Spectrophotometric Determination of Tetracycline Hydrochloride and Doxycycline Hyclate in Pharmaceutical Preparations

New, simple and accurate batch and flow injection spectrophotometric methods have been developed for the determinationsof tetracycline hydrochloride (TCH) and doxycycline hyclate (DCH) in pharmaceutical preparations. The methods are based on diazotization of metchlopramide and coupling reaction with either TCH or DCH in alkaline medium to form yellow–orange water soluble dye with absorption maxima at 414 and 436 nm for TCH and DCH, respectively. A graphs of absorbance versus concentration show that Beer’s law was obeyed over the concentration ranges of 1 –52 μgmL^-1 TCH and DCH for batch method and of 8 – 240 μg mL^-1 TCH and 5 – 350 μgmL^-1 DCH for FIA method. The limits of detection in batchmethods were 0.333 and 0.235μgmL-1for TCH and DCH respectively, and in FIA methods were 0.895, 0.612 μgmL^-1for TCH and DCH respectively. Samplethroughputs in FIA procedures were 120 and 80samples per hour for TCH and DCH, respectively. Different chemical and physical experimental parameters affecting on the development and stability of the colored product were carefully studied and the proposed methods were successfully applied for determination of TCH and DCH in pharmaceutical preparations.