Development of two spectrophotometric methods in determination of tetracycline

Abstract

    Two spectrophotometric methods have been developed for the estimation of tetracycline as pure and in its pharmaceutical preparations. They were based on a reaction of tetracycline with concentrated sulphuric acid to produce a yellow product of tetracycline – sulphonic acid shows maximum absorption at 435 nm with a molar absorptivity of 8.31x10³ l./mol.cm. Sandell's sensitivity index, limit of detection (LOD) and limit of quantitation (LOQ) equal to 0.0534 μg /cm²,0.108 and 0.360 μg/ml respectively. Beer's law is obeyed over the concentration range of 2-40 μg/ml, the relative error is from - 4 to 0.8 %. Method B included the same reaction principle as in method A, except the estimation via calculation of the area under the curve instead of the absorbance. The linearity is from 2 to 50 μg/ml with a molar absorptivity of 1.511x10³ l./mol.cm and Sandell's sensitivity index equal to 0.0294 μg /cm².The RSD% is not more than 0.142% and RE% not more than -3.4%. The proposed methods are characterized by simplicity and they are economical. The two methods used only one reagent, which is sulphuric acid, and thus reduce the possibility of contamination with organic materials and reagents.  The two methods were successfully applied to the estimation of tetracycline in pharmaceutical preparations(capsules).