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Vacuum Apparatus to Concentrate Ammonium Solutions for Nitrogen Isotope‐Ratio Analysis
Author(s) -
Kelley K. R.
Publication year - 1989
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1989.03615995005300030022x
Subject(s) - chemistry , evaporation , contamination , analytical chemistry (journal) , nitrogen , dilution , environmental chemistry , meteorology , ecology , physics , organic chemistry , biology , thermodynamics
Concentrating NH 4 solutions in preparation for 15 N analysis usually is accomplished by evaporating samples to dryness with open‐air or forced‐air systems. This paper describes a newly developed drying apparatus that operates under vacuum to facilitate evaporation, prevent sample contamination, and avoid several problems associated with conventional evaporative systems. Standard (NH 4 ) 2 SO 4 samples containing 0.20, 0.50, 1.00, or 2.00 atom % 15 N were acidulated with H 2 SO 4 or H 3 BO 3 plus H 2 SO 4 and evaporated to dryness with the vacuum system, a conventional forced‐air system, or a conventional open‐air system. No significant contamination by atmospheric NH 3 was found in samples acidulated with H 2 SO 4 and dried with the vacuum apparatus. In comparison, absorption of atmospheric NH 3 during evaporative processing of H 2 SO 4 ‐acidulated samples with the forced‐air or open‐air system resulted in dilution of 15 N concentrations in excess of 0.027 and 0.047 atom % 15 N in standards containing 1.00 or 2.00 atom % 15 N, respectively. The atom % 15 N concentrations of evaporated samples containing H 3 BO 3 plus H 2 SO 4 were inconsistent. No significant N loss, isotopic fractionation, or atmospheric contamination was detected in samples acidulated with H 2 SO 4 and heated to 130 °C under vacuum for up to 4 h past dryness. Moreover, no significant cross‐contamination was detected in 4‐mL samples of varying 15 N concentration that were acidulated with H 2 SO 4 and dried under vacuum, indicating that the vacuum apparatus can be used to simultaneously process samples differing in 15 N concentration. The apparatus can accommodate up to 80 samples, depending on sample volume and container size (< 5–250 mL).