Identification of Foreign Particulates in pMDI products by SEM-EDS mapping

Chris Blatchford

Summary
There is a requirement to identify the foreign particulates from pharmaceutical inhalation products, but with modern improved valve materials and better controlled manufacturing facilities this becomes an increasingly difficult analytical challenge. This publication describes Scanning Electron Microscopy – Energy-dispersive X-ray spectroscopy (SEM-EDS) element-specific mapping methodology which can positively identify up to 99 Mass% of foreign particulates from a pMDI product. The initial sample preparation is identical to a validated light obscuration method and therefore sample integrity is considered to be good. The sample is then filtered onto a gold-coated filter for SEM-EDS mapping. The identification provides better selectivity for typical pMDI particulates than Raman spectroscopy and the selection rules required for identifying foreign particulates were validated by Fourier Transform Infrared (FTIR) microscopy. The accurate estimate of particle size provided by SEM allows the data to be converted to mass% by a density correction factor. This can facilitate an accurate toxicity assessment on material which is orders of magnitude below the level required to ensure patient safety.

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