Positive displacement holder for critical point drying of small particle materials*

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Abstract
SUMMARY: A specimen holder has been designed specifically to contain small particulate matter, such as microorganisms, fibres or powders, during the fluid exchange cycle and final evaporation step of the critical point drying process. The mode of fluid exchange is positive displacement rather than diffusion. The holder can accommodate up to ten different samples without loss of material or cross‐contamination during the dehydration process. The samples are separated by silver membrane filters, and fluid exchange is accomplished in minimal time by only slight positive pressure. Experiments with soluble dyes have shown that any fluid can be displaced completely with another in less than 2 min, whereas diffusion requires more than 30 min. The holder and individual capsules have been tested with different materials and a standard water/ethyl alcohol/amyl acetate/carbon dioxide fluid sequence. This paper describes the design, production, and testing of the holder and capsules, and presents selected examples of results.