Controlled-delivery vapor generator for animal exposures.
A vapor generation system is described which provides long-term stable vapor concentrations for inhalation bioassay tests with laboratory animals. Liquid is pumped from a reservoir by a micrometering pump to the surface of a cylindrical vaporizer covered with a glass fiber wick. An 80-watt heater and temperature sensor, embedded in the cylinder, control the vaporizer temperature. Pump rates of 0.01 to 20 mL/min and surface temperatures greater than 100 degrees C can be achieved. To minimize condensation on delivery-tube walls, the vaporizer is positioned in the dilution air inlet tube leading directly into the 2-m3 exposure chamber. During exposure of rats, mice and rabbits to eleven different chemicals for periods ranging from 4 hours to over 400 daily 6-hour exposure periods, concentrations from 25 to 10,000 ppm were achieved with a dilution air flow of 280 L/min. Chamber concentrations were routinely maintained within 10% of target levels. Stable pump rates provide a method of calculating vapor concentration independent of chemical analysis. Long-term generation stability and ease of operation reduce labor requirements compared to previous generation techniques.
D000818:Animals; D001273:Atmosphere Exposure Chambers; D051379:Mice; D009330:Nebulizers and Vaporizers; D011817:Rabbits; D051381:Rats