Resources that we have developed for compound specific isotopic analysis.
How to derivatize fatty acids for CSIA work?
To derivatize fatty acids e.g. long chain n-alkanoic acids for GC work we methylate the fatty acids to fatty acid methyl esters. To do so, we use HCl and methanol*, for more information, read a paper by Hyejung Lee and co-authors Lee et al., 2017, RCM.
*Purchase a batch of GC-grade methanol for derivatization (4L), bottle it in aliquots (we use 500 mL bottles) and teflon tape to seal. Mark it for isotope use only, not general lab use. Find out the isotopic composition of the methyl in the methanol by derivatizing a known standard. Phthalic acid of known isotopic composition can be acquired from A. Schimmelmann, U. Indiana (many OG stds here). But wait, it’s not that easy!!
Methylation of phthalic acid requires more care and skill, and slightly different protocols, than long chain (e.g. leaf wax) FAME preparation, see Hyejung’s protocol accompanying her paper that should guide you to success. NB. Beware evaporation of your PAME product. Good luck!!
Then you can correct your FAME CSIA data for the added methyl group to determine the value of the FA. It is all in the paper: full RCM article here.
Make your own combustion reactor
Video: How to pack your own combustion reactor for the GC Isolink
by Sarah Feakins
Parts list (excel file) – parts we order to pack our own combustion reactors as well as other common consumables for the PTV-GC-Isolink
ISL Scripts for Isodat software
For the GC Isolink:
The GC Isolink from Thermo has a computer controlled furnace to heat the pyrolysis and combustion reactors. Here we provide an isl script that can be opened and run in workspace that will heat/cool the HTC reactor at a slow rate. The goal is to minimize the development of leaks at solder points, leaks at fittings and microcracks in the reactor. The rate, and set-point temperature can be modified in the script. The script could be modified for the combustion reactor.
Details on how to save and run scripts in Isodat:
*Please note that you use and implement the scripts and these instructions at your own risk.*
- Save the files in the same directory along with Thermo ISL scripts C:\Thermo\Isodat NT\Global\ISL\GC Isolink.
- Open the ISL script in workspace set the temperature in the script to the target temperature (endT) and then click ‘! Run’ tab.
- Leave the script open in workspace. Switch over to Instrument control and you can see the temperature ramp happening (slowly) in the GC Isolink window.
Instrumentation in the Feakins lab
GC-IRMS – Gas Chromatography Isotope Ratio Mass Spectrometry
We use a Thermo Scientific Trace GC equipped with a Rxi®-5ms (30m x 0.25mm, film thickness 1mm); a PTV inlet; a TriPlus autosampler; connected via GC Isolink with parallel combustion furnace (at 1000 °C) and pyrolysis furnace (at 1420 °C) together with a Conflo IV to a Delta V Plus mass spectrometer. Combustion is used for the analysis of 13C/12C and pyrolysis is used for the analysis of D/H.
GC-MS/FID – Gas Chromatography – Mass Spectrometry – Flame Ionization
We use an Agilent 6890 GC equipped with a Rxi®-5ms (30m x 0.25mm, film thickness 0.25mm); and a 7683 programmable injector connected to an Agilent 5973 MSD mass spectrometer and an FID flame ionization detector. The Agilent GC-MS provides mass spectral information for biomarker identification and FID provides quantification.
Here we all are learning how to clean the MSD! Source cleaned, reinstalled, working & 4 students trained!
EA-IRMS – Elemental Analyzer & Isotope Ratio Mass Spectrometry
We use a Costech EA in standalone mode or coupled via a Conflo IV to a Delta V Plus mass spectrometer for TC, TOC, TIC, TN, C/N, d13C TC, d13C TOC, d13C TIC, d15N TC.
Preparative facilities in the Feakins lab
We use a Virtis 2k freeze drier, including secondary cold trap (organic clean) to dry sediment and plant tissue prior to solvent extraction.
Cryogenic Vacuum Line Extraction
We have a vacuum line and offline batch distillation apparatus, to enable efficient extraction of plant leaf waters.
We use Accelerated Solvent Extraction (ASE) by Dionex Corporation, which completes solvent extraction and filtration under high temperature (100°C) and pressure (1500psi).