A validated laser diffraction (LD) wet dispersion method developed for the Mastersizer2000 was copied onto the Masterszer3000 instrument from Malvern Instruments Ltd, keeping as many parameters as possible the same. These two methods were tested using a series of powder blends from a range of inhalation powders to demonstrate the sensitivity of the methods to detect small changes in particle size distribution (PSD).

Blending experiments demonstrate these methods on these instruments are capable of measuring a shift in the d(0.1), d(0.5) and d(0.9) PSD for this powder of 0.04 micron, 0.05 micron and 0.3 micron respectively, with statistical confidence. This sensitivity analysis of an analytical method is important when considering the suitability of product specifications.  It is also important to recognise that there may be a bias when comparing data from one instrument to another, even when manufactured by the same manufacturer, and this needs to be taken into consideration when transferring methods from one instrument to another.