An easy and general method to quantify Azithromycin dihydrate in a matrix of amorphous Azithromycin

Issue in Honor of Prof. J. Elguero and P. Molina ARKIVOC 2005 (ix) 321-331 In the present work a method is developed for the detection and quantification of low amounts of the dihydrate crystalline form in presence of its amorphous counterpart. The requirements for the dihydrate contents are less than 2%. Our method is based on the increase of the intensity (measured as the area) of the highest peak in the X-ray powder diffraction pattern for the mixtures of amorphous crystal when the amount of the crystalline phase is varied in the range 0–10% (see Figure 2). A very good linear relationship was found between the percentage of crystalline phase and the area of the peak. Figure 2. Powder diffraction patterns of the mixtures of amorphous and crystalline dihydrate Azithromycin (in the amounts 0%, 1%, 2%, 4%, 6%, 8% and 10% of the dihydrate form). Results and Discussion Five samples of amorphous pure Azithromycin were used. The samples, respectively labeled, azt77, le06, le07, le08 and le11, contain different amounts of water and t-butanol H2O: 1–1.5%; t-BuOH: 3.5–5.5%), but this feature does not have an appreciable influence on the powder diffraction pattern (see Figure 3). ISSN 1424-6376 Page 323 ©ARKAT USA, Inc