248 



GOLD 



Intake Levels. Gold is primarily of biological interest on account of 

 its use in the treatment of arthritis and the use of radioactive gold colloids 

 for radiation therapy. Toxic effects in rats have occurred from intra- 

 peritoneal administration of 23 to 50 mg/kg of gold as the chloride. 



Radioassay. Au^^^ is apparently the isotope of choice except where 

 material of very high specific activity is recjuired. This preparation has 

 little if any radiocontamination and has been the most widely used. 

 Either beta or gamma measurements are satisfactory. Au^^^ contains 

 Pt^", which could be eliminated by decay, and also Pt^^^"', which would 

 have to be removed chemically or could be prevented from contributing 

 to the counts by using a high-efficiency beta counter. 



Chemistry. Biological materials can be wet- or dry-ashed. A chem- 

 ical method has been described which permits estimation of 0.2 ng (Au-1). 

 Tissues were treated with concentrated H2SO4, dried, and ashed at 550°C 

 for about 2 hr; urine was pretreated with tellurium tetrachloride, stan- 

 nous chloride, and acid before dry-ashing. 



Typical Methods. Simplified devices have been described for dispens- 

 ing conveniently the relatively high activities of Au^^* used for intracav- 

 itary instillation or interstitial injection (Au-2). In a study with dogs, 

 radioactive gold solutions containing 1 to 2 mc Au^^^ were mixed with 4 

 to 5 ml of the animal's serum and then injected intravenously. Blood 

 samples were diluted with water, and 10-ml aliquots counted in a flat dish 

 under an end-window tube. Tissues were heated with HNO3, and at the 

 end of digestion 2 ml concentrated HCl was added to yield ionic gold, 

 which tended to reduce adsorption of radioactivity on the glass walls. 



