240 COBALT 



estimation of cobalt in biological material, including a description of dry- 

 ashing procedures, has been reported as follows (Co-3) : Samples were 

 ashed overnight in silica dishes at 450 to (500°C. If ashing was not com- 

 plete, HNO3 and KNO3 were added and taken to dryness, and the sample 

 ashed again at 600 to 650°C. The nitric acid treatment was repeated if 

 necessary. With samples high in silica, platinum dishes were used, and 

 treatment with hydrofluoric and perchloric acids was employed. The ash 

 solution was extracted with dithizone to eliminate iron interference, the 

 complex oxidized, and the cobalt treated with o-nitrosocresol, which was 

 extracted from the aqueous phase by ligroin for colorimetric evaluation. 

 The following procedure has been described for the electroplating of radio- 

 cobalt (Co-4) : The ash solution was prepared so as to contain a minimum 

 of acid, and an aliquot was added to the electroplating cell containing the 

 plating solution (100 g ammonium sulfate, 180 ml concentrated ammo- 

 nium hj^droxide, and 5 g ammonium hypophosphite per liter). If neces- 

 sary, carrier cobalt was added to provide about 10 mg of the element to 

 be plated out. The cobalt was plated onto copper at 27 ma/cm- for 

 several hours. If the sample contained salts that precipitated out under 

 alkaline conditions, it was necessary to make a preliminary separation of 

 the cobalt; this was done by reaction with Q:-nitroso-/3-naphthol. 



Typical Methods. In studies with normal and diabetic rats, about 1 nc 

 Co*^" in 52 Mg of the element was injected intraperitoneally (Co-5) ; tissues 

 were ashed and made to volume, and aliquots dried for counting with a 

 Geiger tube. In work with cyclotron-produced Co^^'^*, the following 

 approximate dosages were used: rats, 20 ^g, 25 ^tc; rabbits, intravenous, 

 2.4 fjLg, 20 fjLc; rabbits, oral, 60 ng, 600 mc; swine, 60 jug, 600 mc; calves, 

 60 fig, 600 mc; cattle, 2 mg, 500 mc (Co-6, Co-7). In these studies the 

 electroplating procedure as described above was used for the preparation 

 of samples. In a study with swine, the radioisotope was incorporated in 

 the ration at a level of 13 ^c Co^" per kilogram of feed. The animals 

 were on experiment for 43 days, each pig consuming about 61 kg. Tissues 

 were digested in a mixture of HNO3 and H2SO4 plus cobalt carrier, and 

 aliquots were liquid-counted (Co-8). In a study of vitamin B12 biosyn- 

 thesis, 2 mc Co*^" containing about 1.6 mg cobalt was administered orally 

 and intravenously to sheep (Co-9). Samples of high activity were 

 counted directly with an end-window counter using an 89.5-mg/cm^ 

 absorber, so that only gamma activity was measured ; with lower activ- 

 ities, the samples were wet-ashed in concentrated HNO3 and made to 

 volume, and the liquid counted directly; with still smaller amounts, the 

 samples were dry-ashed at 550°C in porcelain dishes, and the ash was 

 spread with HNO3, dried, and counted directly with a thin-window tube 

 or an internal counter. All samples were separated into a vitamin-Bir 

 like fraction, an inorganic fraction, and a bound residue. 



