Collaboration with AstraZeneca leads to a new generation particle sizing analyser from HEL

For over 15 years HEL has been supplying laboratory automation tools to AstraZeneca. This relationship has led to many projects, the latest of which was the development of the SAS solids particle analyser.

AstraZeneca had been using the Fisher Sub Sieve Sizer (FSSS) for obtaining development and QC data for over 30 years; this instrument works on the principle of particle sizing by air permeability which was established in the 1940’s and has proved to be a very reliable way for many companies to prove the batch to batch consistency of their products.

John Sherwood, AstraZeneca‘s associate principle scientist explains: ‘The technique gives a measure of the SSA (Specific Surface Area) of a compound. Invariably with the measurement of particle size one is interested in a property of the particles not necessarily the particle size distribution itself. Hence when assessing the bioavailability or lubricating properties of a compound, one is interested in the surface properties of the particle size distribution of the compound; such as the ‘envelope’ surface area, which is measured directly by the permeability technique. This, along with the ease of use of the technique, is the reason why AstraZeneca has historically used the Fisher. Although the Fisher is an excellently designed instrument, it has always been a desire to update it, so that it could be more easily calibrated, reduce the operator’s involvement and to produce an automated electronic report.”

Last year, when Sherwood approached the manufacturer to purchase a new FSSS system he found out that it had been discontinued. ‘This had wide implications for AstraZeneca, as the SSA (Specific Surface Area) has become one of the key batch release parameters for over 50% of our compounds’, said Sherwood. ‘Alternative particle sizing techniques were considered. However, to change to another type of technique, such as light scattering, would be both expensive in capital costs and resources, and would need significantly more work to validate.”

It was then that a colleague who was supplied by HEL with a bespoke automated system for producing micro particles recommended HEL to Sherwood.

After initial discussions it became clear that HEL had the internal capabilities to take on this development. Having in-house software, mechanical and electrical development engineers, Mr Sherwood was confident that the company was able to take this product from initial design through to manufacture.

‘Finally, I consider that the new Subsieve AutoSizer (SAS) – a result of this collaboration effort - meets HEL’s and my vision for the instrument,’ said Sherwood.

The SAS is the basis of a new generation of measurement of particle sizing by air permeability, improving on the FSSS’s performance and bringing the technology to the 21st century by offering easy to use automated functions together with electronically recorded data. It reports particle sizes in the range 0.2 to 75 µm and calculates the resulting SSA and does this based on the pressure drop across a packed bed of powder. By varying the sample height and hence the ‘porosity’ of the bed, average surface area and hence particle size can be determined as a function of pressure drop in accordance with the Carmen equation.

‘The SAS is operated by HEL’s superior automation software’, explains John Lee, project manager at HEL. ‘When we designed it, we took on board AstraZeneca’s comments and experiences and created a touch screen interface that makes operation and report generation simple and intuitive.’