Apples and pears from trees in several experiments in various sections of the U.S., sprayed with Plictran miticide, were analyzed for residues of total and organic tin. Inorganic tin was calculated as the difference between total and organic tin. Residue levels were similar on the two fruits and a maximum of less than 2 ppm of organotin was found, calculated as tricyclohexyltin hydroxide (Cy3SnOH) on the day of the last of four applications. Organotin decreased to about half of the initial value in 3 to 5 weeks. Most of the residue of total tin remaining 4 weeks after spraying was organic tin, and most of that was the active ingredient Cy:iSnOH. Nearly all the residue was on the peel of the fruit, and up to half of this was removed with a cold water wash.

No abstract

The dithiol colorimetric method has been applied to the determination of trace amounts of tin as residues from the spray treatment of fruit with a miticide containing tricyclohexyltin hydroxide. The samples are prepared by an initial wet combustion to give a sulfuric acid solution of tin in the inorganic form. The tin is separated from other elements in the acid digest by one of two methods. One involves distillation of stannic bromide with a mixture of HBr and HCl. In the second separation method stannic iodide is extracted into n-hexane. Both separation procedures result in a solution of tin in a few milliliters of concentrated H2SO4, which is then measured spectrophotometrically. Data are presented for sensitivity and precision of the measuring system; accuracy and precision of both separation methods are illustrated by duplicate analyses and recovery tests on apples and pears treated with various cyclohexyltin compounds and inorganic tin. The extraction method has been tested for compatibility with 35 elements. Only arsenic (>0.15 mg or 1.5 ppm) and antimony (>2 mg or 20 ppm) are likely to interfere. Procedures are given for elimination of greater amounts of these elements.

No abstract