Microspectroscopic FT-IR mapping system as a tool to assess blend homogeneity of drug-excipient mixtures.

In order to prepare a controlled-release tablet by direct compression, a Fourier transform infrared (FT-IR) microspectroscopic mapping system was utilized to assess the blend homogeneity of a pharmaceutical powder blend. The model powder blend was a two-component mixture consisting of captopril as a model drug and micronized ethylcellulose (EC) as a direct-compressible model excipient, which was mixed in a laboratory mill. The two-component mixture was mixed in two different weight proportions (captopril:EC, 1:1 or 10:1). By varying the mixing time, different blend mixtures sampled were determined by a reflectance FT-IR microspectroscopic mapping system to collect successively the IR spectra from the actual analysis area. The results revealed that the blend homogeneity increased gradually with increased mixing times, but the powder began to demix or segregate as mixing continued beyond the time when homogeneity was reached. In addition, the statistical results indicated that the sample mixture proportion had an effect on the uniformity of the powder blend. This study demonstrates that microspectroscopic FT-IR mapping technique can be easily used to determine the blend homogeneity in a powder blend mixture.