Developments in Scanning Electron Microscopy for Tablet and Granule Characterization - Pharmaceutical Technology

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Developments in Scanning Electron Microscopy for Tablet and Granule Characterization
Recent advances in SEM, particularly the incorporation of automation and software, have made simpler, lower-end SEM instruments easy to operate and have improved the capabilities of larger, sophisticated instruments.

Pharmaceutical Technology


Simple SEM. Traditional SEM analysis required trained operators who knew how to find and sharpen images using various controls on the instrument. "A lot of these labs are spending thousands of dollars looking at samples; and the lead time and preparation time needed to take these samples to contract labs is likely quite time consuming," says Joe Fillion, FEI (Hillsboro, OR). In 2007, FEI launched "Phenom," a tabletop point-and-shoot version of a traditional SEM. "We redesigned the entire user interface to be very intuitive. Operators simply touch the area you want to look at and you click a picture. Whereas a traditional method you may be turning dials for many minutes or hours in some cases. We're finding that pharmaceutical companies are using this in place of outsourcing their SEM work to analytical laboratories," says Fillion.

Traditional optical microscopes are incapable of capturing an image of the ever-smaller particles the industry is currently producing. "You can go to about 1000, but it's very featureless and very flat," says Fillion. "Most of our customers want to see particles in the 3000–8000 range, where most of our customers use it. As these grain sizes get smaller, we're seeing a lot more interest in SEM. I've been told on a number of occasions that, as these particles get smaller and smaller, scientists want to be able to see the samples they are evaluating. They can do laser scattering to determine the distribution, but a picture is a powerful thing to see."

SEM–software combination. Sophisticated SEM instruments generate images uses low-energy secondary electrons "pulled" from the sample surface after impact with the electron as well as electron back scattering (elastic scattering from the high-energy electron beam) to generate an image. Trained operators use this combination to obtain detailed images and elemental information (see Figures 4, 5). Gaining clear definition of particle edges allows measurement of various parameters characterizing particle size, including the diameter and particle shape measurements encouraged in USP ‹776› "Microscopy."

Resent advances in high-end SEM instruments include the coupling of SEM visualization with statistical software. The software automatically provides direct measurements for several characterization parameters ("Quanta Morphologi," FEI Company and Malvern Instruments). The data for each particle can be stored with the image in a database and viewed at a later time.


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