Intake Levels. Rubidium is widespread in nature. It is taken up 

 rapidly by plants and has been found at levels of 3.4 and 5.7 ppm in beans 

 and barley, respectively. It has been found in most human tissues 

 examined except bone. Human livers have been reported to contain as 

 much as 14 ppm fresh weight. Rubidium is of interest in relation to its 

 similarity to potassium. 



Radioassay. Routine hard-beta or gamma counting is satisfactory on 

 account of the energetic radiations. 



Chemistry. Little information is available in regard to ashing or 

 analytical procedures. However, it would be expected that methods for 

 potassium would also be satisfactory for rubidium. Ashing will usually 

 not be reciuired when only radioassays are needed. Chemical estimation 

 in biological material will recjuire development of procedures. 



Typical Methods. One miUicurie of labeled Rb2C03 in 1 liter of 5 per 

 cent KCl was introduced into a watertight trough constructed around 

 part of a tree trunk (yellow birch and white pine) (Rb-1). The KCl was 

 used to facilitate the entrance and movement of the rubidium in the trans- 

 location stream. The incision was made underwater to a depth of 1 in. 

 using a ^^-in. chisel with its face parallel to the vertical axis. A portable 

 scintillation counter was used for detection of the radioactivity in various 

 parts of the tree. In another study, carrier-free Rb^^ from cyclotron 

 production was used to study the uptake by barley roots from a solution 

 of the order of 10~^ mole Rb per liter (Rb-2). The solution contained 

 about 12 mc Rb**^ per liter and was adjusted to pH 5.5. A 2-cm apical 

 segment from a 3-week-old plant was placed in the stirred solution for a 

 measured time, removed, w^ashed thoroughly with distilled H2O, counted 

 with a Geiger tube, and then replaced in the solution for continuation of 

 the uptake study by repetition of the process. The uptake of Rb^" by 

 disks of rutabaga tissue as affected by auxins was studied using a wet- 

 ashing technique (Rb-3). In a study with dogs, using cyclotron-produced 

 activity, about 300 jjlc in 10 to 15 ml of isotonic Rb^^Cl (2 per cent) was 

 injected intravenously. Samples of spinal fluid and plasma were meas- 

 ured into 10-ml Coors ashing capsules and evaporated without boiling 

 (Rb-4). The radioactivity was measured with a Lauritsen electroscope. 



