Bigger is NOT Better – Sample Preparation in the Pharmaceutical Industry

The trend is to have small samples having smaller and more controlled particle size and yet remain representative

In the analysis of solid material, the popular adage that ‘bigger is better’ certainly does not apply. The goal is to produce particles that are sufficiently small to satisfy the requirements of the analysis while ensuring that the final sample accurately represents the original material. The ‘particles’ of interest to the analyst generally range from 10µm to 2mm. Additionally there are many applications, where even finer sizes are needed. One example are active ingredients, where it is necessary to grind in the submicron range. Finally for DNA or RNA extraction mechanical cell lysis is well-established.

Materials differ widely in their composition and physical properties. Hence, there are many different grinding principles that can be applied, and this, together with other variables such as initial feed or ‘lump’ size, fineness needed and amount of sample available, results in a wide range of models available to the researcher. Some grinding processes may require aids that will help the size reduction process while at the same time, leave the material uncontaminated or unaltered in any way. The most common example of such an aid is that of cryogenic grinding where soft material (animal tissue/plastics) will not grind unless it is made brittle through the use of dry

ice or liquid nitrogen. Finally, choosing the most appropriate mill will often require the help and support of the manufacturer. This process may include a trial test sample to help finalise the decision.