TIN 



315 



Intake Levels. Only traces of tin occur naturally in biological mate- 

 rial. It is not considered an essential element and is of interest on 

 account of possible entrance into foods from tin plate. Up to 4 ppm on a 

 dry basis has been reported in grain, and levels of about 286 ppm in food 

 are considered dangerous. The fatal dose of tin chloride for the dog has 

 been given as 4 to 6 g, and 1 g of tin salts fed every 6 or 10 days killed 

 rabbits in 1 or 2 months (Sn-1). 



Radioassay, Samples should be allo\ved to stand about 170 hr after 

 being taken from the biological system in order to permit the attainment 

 of equilibrium between Sn"^ and the In"^ daughter. Information should 

 be obtained from the supplier as to how much Sn^'-^ is present, since this 

 will determine the amount of interference to result from the Sb^-^ and 

 'Pgi25m daughters. 



Chemistry. Several methods are available in the literature for estima- 

 tion of tin in foods. Dry-ashing is not recommended, since an insoluble 

 oxide may be formed. Although nitric acid may tend to produce insol- 

 uble metastannic acid, most procedures do call for oxidation with a mix- 

 ture of sulfuric and nitric acids. In one method the acid digest is 

 extracted with dithizone to remove copper, the tin reduced with thio- 

 glycohc acid, and a dithiol reagent added to produce a color for photo- 

 metric evaluation (Sn-2). 



Sn-l. Alonier-Williams, G. W., "Trace Elements in Food," John Wiley & Sons, Inc., 



New York, 1950. 

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



Interscience Publishers, Inc., New York, 1950. 



