EFFECTIVE-MASS SAMPLED BY NIR FIBEROPTIC REFLECTANCE PROBES IN BLENDING PROCESSES

Recent efforts have demonstrated the in situ use of NIR spectroscopy t o determine the homogeneity and potency of powder blends. This work ha s raised questions regarding the effective mass of a powder blend inte rrogated by a fiber-optic probe. The effective mass determined from ex periments described herein is wavelength dependent and ranges from 0.1 54 to 0.858 g with a maximum standard deviation of about 0.16 g. Altho ugh the precision of this estimate is low, it is sufficiently accurate to demonstrate the usefulness of in situ NIR monitoring of blending o perations in the pharmaceutical industry, The method was established b y using the relationship between sample mass and spectral variance, Mi xtures of lactose (50% w/w), microcrystalline cellulose (40% w/w), and sodium benzoate (10% w/w) were manually blended and sampled at select ed intervals, The spectral variance at relevant wavelengths was determ ined as a function of blend homogeneity and sample mass using a standa rd micro-sample cup. The spectral variance obtained from micro-cup mea surements was used to calibrate the effective mass sampled by a fiber- optic reflectance probe. The estimated mass was greatest at wavelength s where the minor constituent contributed most to the overall spectral variance. Typical pharmaceutical tablets have weights in the range of 0.1-1.0 g. According to FDA regulations, the maximum allowed sample m ass for determining the homogeneity of these preparations is 0.3-3.0 g , For many formulations, the effective mass sampled by the fiber-optic probe easily falls below this range.