Nitrogen isotopic analyses by isotope-ratio-monitoring gas chromatography/mass spectrometry

• Published in: Journal of the American Society for Mass Spectrometry Vol. 5; no. 5; pp. 387 - 397
• Main Authors: Merritt, Dawn A., Hayes, J.M.
• Format: Journal Article
• Language: English
• Published: Headquarters Elsevier Inc 1994
• Subjects: Amino Acids - analysis; Carbon Dioxide - chemistry; Chemistry Techniques, Analytical - instrumentation; Chemistry Techniques, Analytical - methods; Copper - chemistry; Exobiology; Gas Chromatography-Mass Spectrometry - instrumentation; Gas Chromatography-Mass Spectrometry - methods; Gases - analysis; Nickel - chemistry; Nitrogen - analysis; Nitrogen Isotopes; Space life sciences; Non-Nasa Center; Nasa Discipline Exobiology; NASA Discipline Exobiology; Non-NASA Center
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/1044-0305(94)85054-2

Amino acids containing natural-abundance levels of
15N were derivatized and analyzed isotopically using a technique in which individual compounds are separated by gas chromatography, combusted on-line, and the product stream sent directly to an isotope-ratio mass spectrometer. For samples of N
2 gas, standard deviations of ratio measurement were better than 0.1%
0 (Units for δ are parts per thousand or per million (%
0).) for samples larger than 400 pmol and better than 0.5%
0 for samples larger than 25 pmol (0.1%
0
15N is equivalent to 0.00004 atom %
15N). Results duplicated those of conventional, batchwise analyses to within 0.05%
0. For combustion of organic compounds yielding CO
2/N
2 ratios between 14 and 28, in particular for N-acetyl
n-propyl derivatives of amino acids, δ values were within 0.25%
0 of results obtained using conventional techniques and standard deviations were better than 0.35%
0. Pooled data for measurements of all amino acids produced an accuracy and precision of 0.04 and 0.23%
0, respectively, when 2 nmol of each amino acid was injected on column and 20% of the stream of combustion products was delivered to the mass spectrometer.