Water content determination of superdisintegrants by means of ATR-FTIR spectroscopy.

Water contents of superdisintegrant pharmaceutical excipients were determined by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy using simple linear regression. Water contents of the investigated three common superdisintegrants (crospovidone, croscarmellose sodium, sodium starch glycolate) varied over a wide range (0-24%, w/w). In the case of crospovidone three different samples from two manufacturers were examined in order to study the effects of different grades on the calibration curves. Water content determinations were based on strong absorption of water between 3700 and 2800 cm⁻¹, other spectral changes associated with the different compaction of samples on the ATR crystal using the same pressure were followed by the infrared region between 1510 and 1050 cm⁻¹. The calibration curves were constructed using the ratio of absorbance intensities in the two investigated regions. Using appropriate baseline correction the linearity of the calibration curves was maintained over the entire investigated water content regions and the effect of particle size on the calibration was not significant in the case of crospovidones from the same manufacturer. The described method enables the water content determination of powdered hygroscopic materials containing homogeneously distributed water.