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Characterization of Glass Delamination


a glass composition ( Figure 6b ). It is unlikely that a particle this small and thin would have had sufficient contrast to be found by SEM, even if it had it been isolated directly onto a polycarbonate filter.


Other types of small particles were found in glass delamination samples filtered onto TEM grids. In one sample, small heterogeneous particles containing elements typical of silicate and steel were found ( Figures 7 a– 7 c), in addition to glass delamination fl akes.


Discussion


Examination by SEM/EDS is an accepted technique for elemental analysis of glass delamination fl akes and other thin particles and residues that form during glass dissolution. SEMs are readily available in many laboratories, and mounting of filters containing isolated particulate is straightforward. However, thin particles and residues may lack suffi cient contrast to be easily located by SEM imaging. Because the beam/sample interaction volume in the SEM includes the thin sample and the substrate below it, SEM/EDS spectra obtained from glass delamination products are typically dominated by signals from the support materials, even when a low accelerating voltage is used. Peaks for major components of the particles, such as silicon, may be barely distinguishable above background, and peaks for minor and trace elements will typically not be detected.


Previous work has shown that TEM/EDS analysis is a more suitable approach, given that glass delami- nation particulate is thin enough to be electron transparent. Examinations of as-received grids and blank grids prepared by filtration of particle- free water indicate that background particulate is minimal and is unlikely to impact identification of materials associated with glass delamination processes. Good quality x-ray spectra containing major, minor, and trace element peaks are easily acquired and may allow for better identifi cation of glass product composition. Smaller particles and flakes that might be missed in an SEM survey of a filter are more likely to be found in the TEM, where high-resolution imaging, high-spatial-resolution EDS, and electron diff raction techniques can be brought to bear on the challenge of small particle identifi cation.


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Figure 6 : (a) Small cluster of glass delamination fragments captured on grid fi lm by fi ltration directly onto TEM grid. (b) TEM/EDS spectrum from small glass delamination fragments in (a) revealing glass components Si, O, Na, Ca, Al, and K.


Figure 7 : (a–b) Small particles of silicate and steel isolated from drug product by fi ltration directly onto TEM grid. (c) TEM/EDS spectrum from silicate (Si, O)/steel (Fe, Cr, Ni, Mn, Mo) particle.


The current work addresses the difficulty of removing thin particulate and residues from a filter for transfer to a TEM grid. Liquid suspected of containing glass delami- nation particulate can be representatively sampled by filtration onto a holey carbon-coated TEM grid placed on a polycarbonate filter on a standard filtration apparatus. This approach allows TEM and SEM samples to be prepared simultaneously, which adds both efficiency and consis- tency to isolation and characterization of delamination particulate.


www.microscopy-today.com • 2017 January


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