Comparison of Procedures for Reducing Cross-contamination During Steam Distillations in Nitrogen-15 Tracer Research1
- R. L. Mulvaney2
A study was conducted to compare the effectiveness of various procedures for reduction of cross-contamination errors when unenriched samples of (NH4)2SO4 containing 0.5 mg of N were steamdistilled in a glass distillation apparatus following samples enriched with 50 atom % 15N. 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 15N-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. When this is not possible, it is recommended that 1 mL of 1M formic acid be distilled for 1 min and 25 mL of 16.4 M (95%) ethanol be distilled for 3 min between samples. This procedure can be made more effective by increasing the amount of formic acid used and extending distillation beyond 1 min.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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