CALCIUM 219 



radioassay, and therefore the standard procedure with but shght modifica- 

 tion can be utiUzed for both chemical and radioactivity measurements. 

 Details are given in the next section. 



Typical Methods. Dosage Levels. The following dosages have been 

 used in general metabohsm studies with animals and have allowed tissue 

 analyses and bone autoradiograms (higher dosages should be used if there 

 is a particular interest in long-term studies or in tissues of lower accumula- 

 tion, and smaller amounts could be used if there is an interest only in 

 bone) : rats, 1 to 10 mc in about 1 to 10 mg Ca orally or parenterally (Ca-2, 

 Ca-3) ; chicks, 580,000 counts/min in 0.8 mg Ca orally (Ca-4) ; laying hens, 

 15 MC in 1 mg Ca orally (Ca-5); young pigs, 0.75 mc/100 lb intravenously 

 (Ca-6) ; cattle, 2 to 3 mc intravenously and 4 to 6 mc orally in not more 

 than 200 mg Ca for 500- to 1000-lb animals (Ca-7) ; dairy cows, 2 to 15 mc 

 in 40 to 210 mg Ca intravenously and orally (Ca-8) ; cattle, 150 to 300 mc 

 intravenously daily for 10 to 15 days for determination of endogenous 

 fecal calcium by isotope dilution (Ca-9). 



Some levels that have been used in soil and plant work are as follows: 

 For a 1-yr study of leaching and plant uptake, 5.4 juc Ca^^ per gram CaCOs 

 was used in treatments of soil up to an equivalent of 5000 lb CaCOs per 

 acre (Ca-10). In a study of uptake by alfalfa from a Sassafras sandy 

 loam, 43 fxc Ca^^ in various salts was used per pot containing 18 lb of soil 

 (Ca-1 1) . In a study of uptake of Ca^^ by tobacco from band applications 

 of CaCOs, CaS04, and CaH4(P04)2 apphed at rates of 21 to 31 lb Ca per 

 acre, the tagged materials contained 90 mc Ca^^ per gram Ca (Ca-12). 



Analysis. Procedures for combined chemical analysis and radioassay 

 have been described (Ca-13, Ca-14), from which the following is taken, 

 not as representing the best or only methods, but ones that have been 

 satisfactory. 



SOFT TISSUES, BLOOD, AND URINE. It is usually desirable to use a large 

 sample for a yield of as high a content of Ca*^ as possible. However, 

 experience has shown that it is difficult, on account of interfering sub- 

 stances, to precipitate calcium as the oxalate quantitatively from more 

 than 200 mg of tissue ash with the amounts of reagents and the volumes 

 used. In general, the sample is ashed, and calcium oxalate precipitated 

 from the ash solution for titration to give the total calcium content. 

 After titration the solution is neutralized, a standard amount of carrier 

 calcium added, and the calcium oxalate reprecipitated for the counting 

 procedure. This reprecipitation with carrier is necessary because the 

 original sample does not contain enough calcium to yield an amount of 

 precipitate large enough for counting. 



If there is sufficient material available, an alternative to the reprecipita- 

 tion is the use of two samples, one for chemical analysis and one for radio- 

 assay. Details are as follows: The sample is treated with fuming nitric 



