Studies on the Permeability of Human Oral Mucosa I. Gravimetric Determination of Biological Fluids at Microgram Levels

Abstract

The variation from the determination of small water quantities in standardised discs of ash-free filter paper in closed polyethylene containers and weight determinations with a microbalance have been studied. Mean weight differences of +7 micrograms or less were obtained for antistatic containers with dry filter paper discs after use of a pre-weighing period of 60 minutes and an inactivity period of 30 minutes after manipulation and closure of the containers. Weight determination of moistened filter paper was carried out using a microsyringe for water transfer. The syringe showed a uniform discrepancy between its scale indications and the corresponding weight determinations, which was attributed to an erroneous graduation level. The evaporative water loss from moistened filter paper at varying air humidity occurred at a constant rate at amounts of 500 micrograms or above. Closed weighing bottles containing 100–1,000 micrograms of water in the filter paper showed a mean loss of 7.5 micrograms after 30 minutes' standing and 20.8 micrograms after 60 minutes'. The mean recovery value after 30 minutes' standing was 99.1 % after correction for the evaporative water loss. The variation caused by direct sampling of water was estimated to 10 micrograms.