HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kelley, K. R. Search for Related Content PubMed Articles by Kelley, K. R. Agricola Articles by Kelley, K. R.

Vacuum Apparatus to Concentrate Ammonium Solutions for Nitrogen Isotope-Ratio Analysis

Agric. Res. Dep., F137 NFDC, Muscle Shoals, AL 35660

* Corresponding author.

ABSTRACT

Concentrating NH₄ solutions in preparation for ¹⁵N 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 (NH₄)₂SO₄ samples containing 0.20, 0.50, 1.00, or 2.00 atom % ¹⁵N were acidulated with H₂SO₄ or H₃BO₃ plus H₂SO₄ and evaporated to dryness with the vacuum system, a conventional forced-air system, or a conventional open-air system. No significant contamination by atmospheric NH₃ was found in samples acidulated with H₂SO₄ and dried with the vacuum apparatus. In comparison, absorption of atmospheric NH₃ during evaporative processing of H₂SO₄-acidulated samples with the forced-air or open-air system resulted in dilution of ¹⁵N concentrations in excess of 0.027 and 0.047 atom % ¹⁵N in standards containing 1.00 or 2.00 atom % ¹⁵N, respectively. The atom % ¹⁵N concentrations of evaporated samples containing H₃BO₃ plus H₂SO₄ were inconsistent. No significant N loss, isotopic fractionation, or atmospheric contamination was detected in samples acidulated with H₂SO₄ 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 ¹⁵N concentration that were acidulated with H₂SO₄ and dried under vacuum, indicating that the vacuum apparatus can be used to simultaneously process samples differing in ¹⁵N concentration. The apparatus can accommodate up to 80 samples, depending on sample volume and container size (< 5–250 mL).

Contribution from Agric. Res. Dep., Natl. Fertilizer Development Ctr., Tennessee Valley Authority.

Received for publication May 31, 1988.