Extraction-colorimetric method for the determination of erythromycin and its esters in dosage forms using chromotropic acid azo dyes

Accurate, rapid and sensitive extraction-colorimetric method for the determ ination of erythromycin and its esters, depending on the formation of an io n-pairs with chromotropic acid (I), chromotrope 2B (II), chromotrope 2R (II I), arsenate I(IV), arsenate III (V), bentocaprol red (VI) and acid ethyl b lue (VII) is described. The calibration curves resulting from the measureme nts of absorbance-concentration relations (at the optimum reaction conditio ns) of the extracted ion-pairs are linear over the concentration range 0.4- 56 mug ml(-1) with a relative standard deviation (RSD) of 1.3% for 25 mug m l(-1) erythromycin. The detection limit, quantification limit, the molar ab sorptivity and Sandell sensitivity for erythromycin ion-pairs were evaluate d. The interference from excipients commonly present in dosage forms and co mmon degradation product was studied. The method is highly specific for the determination of stearate and succinate esters in dosage forms. The method has been compared to the official method and found to be simple, accurate (t-test) and reproducible (F-test). The developed method was applied for bu lk drug, esters and some of their dosage forms without interferences from a dditives and excipients.