ION EXCHANGE 401 



mination of traces of metals other than copper in any food or hi()h)f2;ical 

 materials that can be converted to liciuid form. It may be particularly 

 helpful for the radioassay of soft-beta emitters when necessary to increase 

 the radioactivity/mass ratio in (he sample counted. In this method the 

 milk copper was converted to the cupric form by adjustment of the pH to 

 less than 3 with perchloric acid, which also precipitated the i)r()teiii and 

 carried the fat into the curd so that these substances could be eliminated 

 by filtration. The filtrate was neutralized with amuKjuia to pH 5 and 

 passed through a cation exchanger (Amberlite IR-lOO, H+ form), which 

 retained the copper and other cations. After washing with distilled 

 water, the cations were eluted with 3 A^ HCl for conventional anal3'sis. 

 As in any low-level determination of copper, it is essential that the filter 

 paper and reagents be essentially copper-free. 



Another useful application is illustrated by the paper of Schubert et al. 



(22) on the isolation of radioelements from urine. It is of considerable 

 importance to be able to detect low levels of various radioisotopes, partic- 

 ularly fission products, in urine; such data may be related to the exposure 

 or body burden of an individual. The procedure for yttrium employed 

 70 g of Amberlite IR-1 resin and may be described by a listing of the 

 solutions used in sequence: 



1. 1000 ml of urine, 12.5 ml concentrated HCl, 500 ml HoO; the acid- 

 ification of the urine prevents the precipitation of calcium salts and keeps 

 the yttrium in ionic form. 



2. 1500 ml of 0.4 M HCl; this removes some adsorbed organic matter, 

 monovalent cations, and divalent cations. 



3. 1000 ml of 7 M HCl; this elutes the yttrium quantitatively in a small 

 volume. 



4. 500 ml HsO. 



5. 1500 ml of 95 per cent alcohol, then 100 ml H2O; this removes the 

 remaining organic matter so that the column can be used again. 



If necessary to remove the last traces of salt, the yttrium eluate can be 

 passed through another resin column with a similar sequence of solutions. 

 Similar procedures have been described for the determination of radium 



(23) and barium, strontium, and rare earths in urine (24). 



Exchange methods have been convenient for the concentration of trace 

 substances from natural waters. Abrahamczik (25) has described a pro- 

 cedure in w'hich a number of exchange tubes, as in Fig. 9-7, were taken 

 into the field along with one funnel and one stopcock section. Two hun- 

 dred and fifty liters of water was passed through each column, which was 

 then taken back to the laborator}^ foi- (^lution. This procedure eliminated 

 the need for carrying a large amount of water from the field to the lal)- 

 oratory. The separation and concentration of trace metals from natural 

 waters have also been accomplished by an interesting inolhod (2()) which. 



