400 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



Removal of Impurities or Interfering Substances. A simplified ion- 

 exchange procedure has been described for the removal of metal contam- 

 ination from adenosine triphosphate preparations (18). The purified 

 barium salt was passed through Amberlite IR-100 resin, which removed all 

 the barium as well as all traces of metal. Before use the resin was acti- 

 vated with 4 per cent NaoCOs, then washed free of excess alkali with dis- 

 tilled water. The barium salt was dissolved in a minimum amount of 

 0.1 iV HCl and washed through the resin column in proportions of 2 to 3 g 

 of dry resin per 100 mg of the monobarium salt of ATP. The resin was 

 then washed with double-distilled water. 



Wolfrom et al. (19) were able to isolate a galactogen from beef lung by 

 a procedure that included passage through an acid-cation exchange col- 

 umn (Amberlite IR-100), followed by passage through an anion column 

 (Amberlite IR-4). Piatt and Glock (2) employed a mixed bed of cation 

 and anion exchangers to remove creatine, creatinine, and other interfering 

 substances from extracts of animal tissues prior to the determination of 

 inositol. 



The flame photometer is now being widely used in determination of the 

 alkali metals. A major difficulty has been the mutual interference of 

 sodium and potassium and the effect of sodium on the photometer read- 

 ings for calcium. Sutton and Almy (20) have described exchange proce- 

 dures for the complete separation of sodium, potassium, magnesium, and 

 calcium in milk ash prior to the flame-photometric determination. The 

 general procedure follows: A 100-g sample of milk was treated with a few 

 drops of glacial acetic acid, evaporated to dryness, and muffled at 550°C, 

 and the ash extracted in 0.7 .V HCl. Colloidal Dowex 50, used in a 

 23-mm-diameter by 61-cm column, was converted to the hydrogen form, 

 and the ash solution passed through and eluted with 0.7 N HCl. Prelim- 

 inary trials based on a simple flame test served to approximate the limits 

 of sodium and potassium elution. After complete elution of potassium, 

 a 1.0 A^ HCl treatment was commenced in order to elute the magnesium 

 and calcium. The eluate fractions were evaporated to dryness on a steam 

 bath to remove all uncombined HCl, and each residue was extracted iu 

 oO ml of distilled water for estimation of the metal cation. 



Concentration of Trace Constituents. A major difflculty in the deter- 

 mination of copper in dairy products has resulted from the extremely 

 small amounts naturally present. In the usual methods the practice has 

 been to destroy the organic matter by ashing; this has hmited the size of 

 sample that can be used for routine determinations. Cranston and 

 Thompson (21) have described an ion-exchange procedure that concen- 

 trates the copper from milk and serves to increase the over-all sensitivity 

 of the determination while at the same time eliminating the tedious ashing 

 step. This type of procedure should have wide application for the deter- 



