Nitrogen isotopic analyses by isotope-ratio-monitoring gas chromatography/mass spectrometry.
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 N2 gas, standard deviations of ratio measurement were better than 0.1% (Units for delta are parts per thousand or per million (%).) for samples larger than 400 pmol and better than 0.5% for samples larger than 25 pmol (0.1% 15N is equivalent to 0.00004 atom % 15N).  Results duplicated those of conventional, batchwise analyses to within 0.05%. For combustion of organic compounds yielding CO2/N2 ratios between 14 and 28, in particular for N-acetyl n-propyl derivatives of amino acids, delta values were within 0.25% of results obtained using conventional techniques and standard deviations were better than 0.35%.  Pooled data for measurements of all amino acids produced an accuracy and precision of 0.04 and 0.23%, 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.
Merritt
D A
DA
Department of Chemistry, Indiana University, Bloomington, USA.
Hayes
J M
JM
D000596:Amino Acids / Q000032:analysis*; D002245:Carbon Dioxide / Q000737:chemistry; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation / Q000379:methods*; D003300:Copper / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D005740:Gases / Q000032:analysis; D009532:Nickel / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes
D000596:Amino Acids; D005740:Gases; D009587:Nitrogen Isotopes; D002245:Carbon Dioxide; D003300:Copper; D009532:Nickel; C028007:nickel monoxide; D009584:Nitrogen; C030973:cupric oxide