COMPARISON OF PROCEDURES FOR REDUCING CROSS-CONTAMINATION DURING STEAM DISTILLATIONS IN NITROGEN-15 TRACER RESEARCH.

A study was conducted to compare the effectiveness of various procedures for reduction of cross-contamination errors when unenriched samples of (NH//4)//2SO//4 containing 0. 5 mg of N were steam-distilled in a glass distillation apparatus following samples enriched with 50 atom % **1**5N. Twelve procedures were compared in this study, including most of those previously proposed in the literature. None of the procedures completely eliminated cross-contamination; however, some were considerably more effective than others. The results suggest that, when a glass distillation apparatus is used in **1**5N-tracer research, the best way to reduce cross-contamination error is to distill two aliquots of each sample whenever possible, discarding the first distillate and retaining the second for isotope-ratio analysis.