ZINC 319 



Intake Levels. The normal intake for human beings is 12 to 20 mg/ 

 day, and rats require at least 0.04 mg/day. Some values for zinc content 

 are: liver, 40 to 140 ppm; blood, 6 to 9 ppm; milk, 3 to 5 ppm; crop plants, 

 10 to 200 ppm on a dry basis. A recommended nutrient solution for 

 plants contains 0.02 ppm, whereas 60 ppm is toxic. The health of rats 

 was impaired by 1 per cent zinc carbonate in the diet, and a fatal dose for 

 rabbits was 34 mg/kg dail.y for 11 days. 



Radioassay. Preparation Zn-65-P-l appears to be the one of choice 

 unless very high specific activity is reciuired and the cost of cyclotron- 

 produced Zn-6o-P-2 can be justified. Gamma counting is preferred, since 

 complicated separations may be avoided and the tissues counted directly 

 or in solution. 



Chemistry. Routine dry- or wet-ashing may be used. Zinc may be 

 estimated by dithizone methods. A method has been described for blood 

 and tissues (Zn-1, Zn-2) which consists in ashing at 6f)0°C, dissolving in 

 HCl, and, after buffering to pH 5.5, extracting with dithizone in CCU and 

 measuring the color photometrically. In order to measure Zn^^ on the 

 same sample as used for total zinc, the zinc dithizonate is returned to a 

 clean separatory funnel, a drop of concentrated H2SO4 added, followed by 

 10 ml H2O, and the mixture shaken until all the zinc has gone into the 

 aqueous phase, as shown by the return of green color in the CCI4 phase. 

 A method for plant material (Zn-3) has been described which is similar 

 but involves a "mixed-color"' dithizone method that eliminates interfer- 

 ence from other elements. 



Typical Methods. A preparation of cyclotron-produced Zn^^ was 

 tested for the presence of radiocontaminants of cobalt, nickel, lead, and 

 cadmium by adding a small (juantity of these elements to aliquots of the 

 preparation, separating the added metal from the zinc, and testing the 

 recovered metal for radioactivity (Zn-4). If there had been any of the 

 radiocontaminant in the original Zn^^ preparation, it would have shown 

 up in the separated sample. Mice were injected intravenously with 

 about 0.33 ng of labeled zinc, and dogs with about 6 ^g- Mice excreta 



