Tubes used in purge and trap analyses generally are packed with multiple beds of adsorbent materials, so that a broad range of polar and nonpolar, high and low molecular weight compounds can be trapped in a single tube. Each bed protects the next, increasingly active bed, by preventing compounds from being held so strongly that they cannot be desorbed quickly without decomposition. During the purge phase of sampling, lower molecular weight compounds pass through the initial adsorbent beds but are trapped by succeeding beds. During desorption, the carrier gas passes through the trap in the reverse direction of purge flow, so that higher molecular weight compounds never come in contact with the stronger (innermost) adsorbents.
The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society, 67(5), 351-360 (2019-01-10)
Modern electron microscopy offers a wide variety of tools to investigate the ultrastructural organization of cells and tissues and to accurately pinpoint intracellular localizations of macromolecules of interest. New volumetric electron microscopy techniques and new instrumentation provide unique opportunities for
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