A Quick Evaporator for Small Sample Volumes Using Heated Nitrogen A design of a device
(see figure) that produces a stream of heated gasses for laboratory purposes is described. Especially in cases where an inert atmosphere is needed and the usual fan-type hot-air blowers cannot be used, this device proved to be very useful. Ever since it was first developed several years ago, it has become standard equipment in some of our labs and was used routinely in the daily tasks of drying spats on TLC chromatograms or evaporating small amounts of solvents (up to 10 ml) in an inert atmosphere. In the latter case c a r e should be taken if flammable solvents a r e used. As a precaution, we routinely start the flow of nitrogen before turning on the heater and turn it off before we turn off the nitrogen. The heater utilizes the electricaliystem of a commercially available aquarium heater, which should be in the low-power range of 25-50 w. Its manufacture requires only minimum glass-blowing skills. The original glass body of the aquarium heater is replaced by a 1-X 8-in. Pyrex test tube because in many brands the soft glass of the original is not compatible with thePyrex tubing that is used in laboratories. A piece of glass tubing is then attached to the side of the test tuhe anywhere between the top and 3 in. down from the top. This is the gas inlet. Another piece of glass tubing is attached to the bottom of the tube. The length of the tube and the diameter of its orifice areto he adaptedto the intended use. Theseal on top of the system depends on the construction characteristics of the aquarium heater. The original heat control elements cannot be used because they are not designed for this kind of operation and may be removed. In a very basic eonstruetion, only the heating element is left from the original unit and is connected directly to the power cord, which is fitted with an on-off switch. The cord enters the system through a bore in a cork that is then sealed eas-tieht with silicone rubber sealant. However, if retaining the control Lamp that comes with the original aquarium heater is desired, the assembly is left intact wherever the construction leaves enough room to do so. In this ease, again the silicon-rubber-sealed cork is used to close the tube. In some brands', a rubber cap that very conveniently allows the system to be used as it is seals the electrical cord and the temperature adjusting knobs. A plastic assembly that is designed to clamp the heater onto the aquarium is preferably removed. In operation, the inlet tubing is connected to a gas tankvia aneedle valve, and the power cord is plugged into a voltage regulator. This external power regulation is very important since the system's bimetal thermostat cannot be used and has to stav shorted all the time. Above a certain voltaee the l a m in this nasition will light up and can he used to monitor whether [he nitrogen heater is turned on. However, &re it is shorted, thk heater will function at all voltage levels, regardless of whether the control lamp ison, and is usually reset ro lower voltage IeveLs to which thr control lamp does not respond. 'l'hesgstrnn has been used errlurively with nitrogen, but other inert gases suchas helium or argon may also be used. lu use w t h air is not recommended because adeterioration of the coils is possible. Furthermore,if used toevaporatesolvenls, the combination of heater coils, hot air, and flammable liquids is potentially dangerous.
' For example, Thermal Flow" "E" mntrol by PennPlax. Inc.. Yonkers City. NY. Karl-Helm A. Rosler DBpamnent of Medicinal Chemistry/PhBnnacognwy
Unlvmlty of Maryland Schocl of Pharmacy 20 N. Pine Street BBnlmore, MD 21201
1006
Journal
of Chemical Education
