208 ARSENIC 



when dry-ashing was used. Wet-ashing with a mixture of HNO3 and 

 H2SO4 has been employed, with care taken to avoid charring (As-2). As 

 a precaution, the Hquid driven off at first can be condensed for recovery 

 of any volatilized arsenic. Estimation of arsenic in the acid digest can 

 be accomplished by distillation of pentavalent arsenic after addition of 

 l)romide, followed by colorimetric evaluation of a molybdenum blue reac- 

 tion. The general literature should be consulted for methods of handling 

 biological samples that are difficult to oxidize. 



Typical Methods. Potassium arsenite was prepared to contain As^^ 

 from a germanium target and was made isotonic with NaCl for subcuta- 

 neous injection as a 0.1 per cent solution (As-1). Five daily doses were 

 given at about the following levels, expressed in milligrams per kilogram 

 of arsenic: rats, 0.6; guinea pigs, 1.6; rabbits, 0.9; apes, 0.14; and some 

 human beings were given up to 4 mg/day. Fluid samples were evapo- 

 rated onto filter paper, tissue samples were mashed into a thin layer and 

 dried, and bone marrow samples were digested and then placed on paper. 

 The filter paper was wrapped around the counter tube for measurement. 



In another study (As-3) carrier-free cyclotron-produced As^^ was pre- 

 pared in an isotonic solution of pH 6 to 7 for intramuscular administration 

 of about 7 jjLC to rats. The tissues were dried at 60 to 70°C for 48 hr, then 

 ground to a powder and transferred to a dish of 10-cm- area for counting 

 with an end-window tube. Mass corrections were made from an experi- 

 mentally determined self-absorption curve. In a study with As^'^, sodium 

 arsenite was administered in buffered isotonic solution at the following 

 levels: rat, 47 nc; rabbit, 235 yuc; man, 3 mc (As-4). Tissue samples were 

 wet-ashed in fuming HNO3, and the solution evaporated to dryness for 

 counting with an end-window tube. Stool samples were measured 

 directly with a high-pressure gamma ionization chamber. 



In a study with the silkworm, As^Mabeled solutions of sodium arsenate, 

 calcium arsenate, and lead arsenate were prepared (As-5). The solution 

 was injected directly into the fore-gut of the insect with a hypodermic 

 syringe with a calibrated micrometer. Some groups received 0.01 to 

 0.02 mg arsenic per gram of insect, and others received 0.06 mg/g. The 

 insect samples were digested for a short time in concentrated HNO3, and 

 measurements made on 1-ml aliquots with a dipping counter. The dis- 

 tribution of arsenic trioxide labeled with As'^'^ was studied in insect larvae 

 (As-6). Using a dipping counter on an acid tissue digest, it was possible 

 to detect 10~'^ g arsenic. 



to 



As-1. Hunter, F. T., A. K. Kip, and J. \V. Irvine, Jr.: Radioactive Tracer Studies on 

 Arsenic Injected as Potassium Arsenite. I. Excretion and Localization in 

 Tissues, J. Pharmacol. Exptl. Therap., 76: 207-220 (1942). 



As-2. Sandell, E. B.: "Colorimetric Determination of Traces of Metals," 2d ed., 

 Interscience Publishers, Inc., New York, 1950. 



