Tree-rings were collected from various sites within the United States to investigate the effects of atmospheric deposition on the growth of trees. Three different sample preparations were investigated to maximize detection limits and sample throughput, and to minimize element losses and sample contamination. The preparation methods included dry ashing at 450° C, cryogenic pulverization, and microwave wet digestion. Since PIXE-PIGE was used to determine the elements Li-U in the tree-rings at low concentrations, the method of cryogenic pulverization could not be used. Dry ashing was the preferred method and it was used to analyze the trace element concentrations in individual tree-rings. Detailed sample preparation methods are described along with applications for studying the affects of climate on the uptake of different elements in the rings.