CN-EA-iRMS results guide
A CN-EA-iRMS results file includes up to four tabs. A results summary is in the fourth and last Final Report tab.
All data are observed directly and recorded by Thermo Scientific Isodat software during automated analysis. This output is recorded in the first Export tab. These C and N data are normalized (also called corrected) to international reference scales according to the calculations explained below. These calculations are documented in the second and third C and N Corrections tabs. A comprehensive understanding of the contents of the first three tabs is generally unnecessary for appropriate application of CN-EA-iRMS results in the results summary in the Final Report tab.
Quality control (QC) standards are standard reference materials with measured and normalized with identical treatment of standard materials. These results are checked for internal consistency (precision) and external consistency with established calibrated or reference values (accuracy). Any CN-EA-iRMS run at UCSC SiL will include IU Acetanilide, and some runs may include USGS41, 61, 62, and/or 63.
Identifier
Identifier 2
Amount
This is the information you provide for each submitted sample. In a results file, identifier 2 usually indicates the sample tray identifier and well location of the submitted sample. In some cases identifier 2 may also indicate sample pretreatment. For example, sediment or soil samples where inorganic carbon has been removed will be indicated as 'Decarbonated' in identifier 2.
Row
Run
Row is the run position of a measurement. For larger projects with multiple runs, results may be organized with an additional column indicating the run number.
C amount (µg)
wt%C
C amount for each measurement is calculated from carbon C peak area observed in the iRMS via regression of sample amount vs. carbon sample peak area for a size array of weighed standard reference materials, usually PUGel. If sample weight is known then wt%C is calculated as µg C / µg sample * 100. Errors for routine samples are ≤ 5 µg C, which corresponds to ≤ 1 wt%C for a routine animal protein tissue sample measurement.
N amount (µg)
wt%N
N amount for each measurement is calculated from carbon N peak area observed in the iRMS via regression of sample amount vs. carbon sample peak area for a size array of weighed standard reference materials, usually PUGel. If sample weight is known then wt%N is calculated as µg N / µg sample * 100. Errors for routine samples are ≤ 1 µg N, which corresponds to ≤ 0.2 wt%N for a routine animal protein tissue sample measurement.
C:N (wt:wt)
C:N (atom:atom)
Ratios of carbon to nitrogen (wt:wt) are directly calculated from C and N amounts. Atomic C:N is calculated via mass balance:
C:N (atom:atom) = C:N (wt:wt) * 14.0067 µg N / 12.0107 µg C
Because errors in C and N amount are coordinated to an extent, C:N is even more accurate than C amount and N amount.
δ13C (‰ VPDB)
C isotope ratios are typically reported as δ13C as calculated according to the principles outlined by Fry et al. (1992). These calculations always account for offset from VPDB and size effects. For a given run, this may also inclue an arbitrary correction for temporal drift. Typical δ13C precision is ≤ 0.1 ‰ VPDB.
C isotope ratio results for measurement of 13C-labelled samples with unnatural 13C that deviate >~100 ‰ from -35 ‰ VPDB will usually be reported as atom%13C. Precision for atom%13C is high with even relatively small C yields.
Other isotope ratio notation results are available by request. For example, results for respiration studies may be reported as R13 (13C/12C).
δ15N (‰ AIR)
N isotope ratios are typically reported as δ15N as calculated according to the principles outlined by Fry et al. (1992). These calculations always account for offset from AIR and size effects including blank-mixing. For a given run, this may also inclue an arbitrary correction for temporal drift. Typical δ15N precision for >25 µg N is ≤ 0.2 ‰ AIR.
N isotope ratio results for measurement of 15N-labelled samples with unnatural 15N that deviate >~100 ‰ from 0 ‰ AIR will usually be reported as atom%15N. Precision for atom%15N is high with even relatively small N yields.
N isotope ratio results may be omitted from results for measurements where N yield is too low for accurate δ15N.