Adaptation of Fractionation Techniques to Subzero Temperatures

Fractionation techniques at subzero temperatures require special devices. Commerical apparatus is sometimes adaptable, but in most cases new equipment must be built. In all cases the equipment must satisfy the following requirements it must be able to produce 

Two types of devices, both of which we have helped to develop in this laboratory, can be used to generate stable temperatures in the subzero range devices that generate a constant low temperature, and devices able to produce temperature gradients from room (or higher temperatures) down to subzero temperatures. 

The first type of device is used to cool relatively small sample volumes (a few milliliters). It is especially well adapted to low-temperature spectrophotometry. The liquid cooler is mainly used to cool large volumes (liters). In this case, although temperature variations are possible, they are slow because of the thermal inertia of the system. 

The apparatus is composed of two main parts a temperature regulator, and a programming device for organic solvent addition (Fig. 23) (Balny and Becker, 1971). The regulator is a thermostatted bath (Air Liquide BRT 90) coupled to a C 1319 regulator, which is programmed to cool the bath at various speeds between +20° and — 100°C. 

Another important application of temperature gradients is formation 

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