Comparison of Steam-Distillation Apparati and Glassware Cleaning Procedures for Reduction of Nitrogen-15 Cross-contamination

Abstract

Several studies were conducted to evaluate the effectiveness of three types of steam-distillation apparati and condensing columns and various acid-bath cleaning procedures for glassware for reduction of cross-contamination errors after contamination with 50 atom percent excess 15N. Regardless of the procedure used to reduce contamination between samples, a stainless steel apparatus always retained less N than a glass design widely used in N research. However, comparable cross-contamination errors with glass can be achieved by simulating design features that have been recommended for the stainless steel apparatus. The effectiveness of the condensing columns in reducing cross-contamination was in the order: stainless steel > Ag-plated brass > glass where no procedure was performed to reduce cross-contamination. Regardless of the procedure used to reduce contamination, the stainless steel condenser always retained the least amount of N. However, use of a steel condenser in conjunction with a glass steam-distillation head did not reduce cross-contamination errors. Immersion of glassware in 0.01 M HCl for 5 min removed 18 to 80% of residual NH+4-N from contaminated glassware. Longer immersion periods improved contamination errors but did not eliminate residual NH+4-N. Hydrofluoric acid was generally more effective than HCl in removing retained N but offers little advantage during routine N analysis.