The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 1832 is to determine the δ(15N/14N), abbreviated as δ15N, and the δ(13C/12C), abbreviated as δ13C, of total nitrogen and carbon in a solid sample. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen and carbon in a solid sample into N2 and CO2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines the relative difference in stable nitrogen isotope-amount ratio (15N/14N) of the product N2 gas and the relative difference in stable carbon isotope-amount ratio (13C/12C) of the product CO2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in tin capsules and loaded into a Costech Zero Blank Autosampler on the EA. Under computer control, samples then are dropped into a heated reaction tube that contains an oxidant, where combustion takes place in a helium atmosphere containing an excess of oxygen gas. Combustion products are transported by a helium carrier through a reduction furnace to remove excess oxygen and to convert all nitrous oxides into N2 and through a drying tube to remove water. The gas-phase products, mainly CO2 and N2, are separated by a gas chromatograph. The gas is then introduced into the IRMS through a Finnigan MAT (now Thermo Scientific) ConFlo II interface. The Finnigan MAT ConFlo II interface is used for introducing not only sample into the IRMS but also N2 and CO2 reference gases and helium for sample dilution. The flash combustion is quantitative; no isotopic fractionation is involved. The IRMS is a Thermo Scientific Delta V CF-IRMS. It has a universal triple collector, two wide cups with a narrow cup in the middle; it is capable of measuring mass/charge (m/z) 28, 29, 30 or with a magnet current change 44, 45, 46, simultaneously. The ion beams from these m/z values are as follows: m/z 28 = N2 = 14N/14N; m/z 29 = N2 = 14N/15N primarily; m/z 30 = NO = 14N/16O primarily, which is a sign of contamination or incomplete reduction; m/z 44 = CO2 = 12C16O16O; m/z 45 = CO2 = 13C16O16O primarily; and m/z 46 = CO2 = 12C16O18O primarily.
Additional publication details
USGS Numbered Series
Determination of the δ15N and δ13C of total nitrogen and carbon in solids; RSIL lab code 1832
Techniques and Methods
Version 1.0 - 2006, Version 1.1 - 2007, Version 1.2 - September 2012
U.S. Geological Survey
Reston Stable Isotope Laboratory
viii, 31 p.
Larger Work Type:
Larger Work Subtype:
USGS Numbered Series
Larger Work Title:
Chapter 5 of Book 10, Methods of the Reston Stable Isotope Laboratory, Section C, Stable Isotope-Ratio Methods