392 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



cedure has been recommended for the fractional precipitation of blood 

 plasma proteins (2), in which case the salt content is reduced stepwise to 

 precipitate the specific globulin fractions. 



The column itself may be improvised from a burette or any kind of 

 glass tube. For general analytical work, columns 8 to 15 mm in diameter 

 are employed with a length/diameter ratio of about 10 to 20 (2), A 

 typical and widely used arrangement is shown in Fig. 9-6. A plug of 

 glass wool is placed at the bottom of the column to support the resin bed. 

 The resin is slurried and then washed into the column, care being taken to 

 keep the bed covered with water so as to prevent the entrance of air. 

 The outlet tube should be much narrower than the column, and the outlet 



Funnel 



Exchanger 



Class wool 



'Funnel 



Glass wool- 



Exchanger- 



Class wool- 



Cround glass 

 joint 



Fig. 9-6. Typical ion-exchange apparatus. Fig. 9-7. Typical ion-exchange apparatus. 



is located above the top of the resin bed so as to avoid a siphoning action 

 in the event the upper funnel goes dry with inadvertent entry of air during 

 the operation. The test solution is placed in the funnel, and the stopcock 

 adjusted to give the proper flow rate. After the test solution has passed 

 onto the resin bed, an appropriate amount of water is added to displace 

 the test solution. The regeneration solution is then added to the funnel 

 and allowed to pass down through the resin bed. Another modification for 

 use with small columns is shown in Fig. 9-7. In this case the upper 

 glass-wool plug should be well packed. 



In some procedures it is desirable to use both downflow and upflow 

 operations on account of the specific gravities of the solutions or to avoid 

 moving the ions through the whole column in the elution or regeneration 

 step. Figure 9-8 shows a convenient and easily assembled arrangement, 

 as described by Applezweig (6), in which the sorption step can be accom- 



