We use an offline preparation vacuum line to digest and clean carbonate powders into pure carbon dioxide. Flame sealed pyrex tubes are analyzed automatically and sequentially with a Thermo MAT253 multiport dual-inlet Isotope Ratio Mass Spectrometer.
We correct all samples to the absolute reference frame (carbon dioxide equilibrium scale) using carbon dioxide equilibrated with a suite of water types and at three temperatures (4 °C, 60 °C, 1000 °C). We use a suite of internal carbonate standards as well as the four ETH carbonates to track precision and accuracy in Δ47, δ13C, and δ18O.
We accept samples for Δ47 analysis on a collaborative basis. We will work with you to design an appropriate analysis strategy. You can choose to visit IsoLab and perform analyses yourself, or we can analyze the samples for you. We will then work together when interpreting the data. We would discuss the plan at length and make sure the data make sense for you to interpret. We are not able to do “contract” work (i.e., analyze samples without knowing what they are or taking part in the interpretation) because the method is so time consuming, and it is new enough that issues of standardization and calibration are rapidly evolving and important to work out with an expert on a case-by-case basis. But as long as it involves scientific collaboration and we get to do quality control on the final dataset, we welcome visitors and/or samples. We typically schedule analyses ~4-6 months in advance. If we feel our timeline or expertise do not align well with your project, we would be happy to suggest alternative labs with whom you may wish to collaborate.
To calculate costs please visit our rates page.
If you send someone here to learn the method and do the analyses, the cost is calculated using the "Off Campus Funding, Lab Provided Labor" lane for the first three days then the "Off Campus Funding, User Provided Labor" for every day after that. If we run your samples for you, use the "Off Campus Funding, Lab Provided Labor" lane.
These rates are per analysis not per sample and we require at least duplicates for a sound interpretation (# of samples x # replicates = total analyses).
If your samples are accepted, they must be ground to a fine powder and you must know the percent carbonate for samples below 90 %. At this time, we require 6-8 mg of pure carbonate for a single analysis.
Exhaustive description of analysis
Carbonate samples (6-8 mg) are digested in a common bath of phosphoric acid (specific gravity 1.9-1.95) held at 90 °C for 10 minutes. The evolved CO2 is cryogenically separated from water on an automated nickel / stainless steel vacuum line using an ethanol-dry ice slush trap, isolated in a liquid N2 trap, and passed through a Porapaq Q trap (50/80 mesh, 122 cm long, 6.35 mm OD) held at -20 °C. The CO2 is transferred through the Poropaq Q trap using He as the carrier gas with a flow rate of ~35 mL / min for a total transfer time of 20 minutes then isolated cryogenically and transferred into a Pyrex break seal. Every 4-5 carbonate sample unknowns, a solid carbonate standard (C64, C2, coral, or ETH 1-4) or CO2 reference frame gas is purified on the vacuum line and transferred into a Pyrex break seal. The reference frame gases were created by equilibrating CO2 that originated from corn fermentation and fossil fuel combustion in Pyrex break seals with South Pole ice core water, local tap water, and evaporatively-enriched water (such that the Δ47 range is approximately 80 ‰) held at 4 °C and 60 °C, or by heating CO2 in quartz break seals in a muffle furnace at 1000 °C. Break seals containing CO2 purified on the vacuum line are loaded into an automated 10-port tube cracker inlet system on a Thermo MAT 253 configured to measure m/z 44-49 inclusive. To start each sample analysis, sample bellows are fully expanded and evacuated. Sample gas is expanded into the sample bellows and pressure is measured. Following sample gas filling, evacuated reference bellows at 100% expansion is filled to a pressure equal to that measured in the sample bellows with UW ‘fermented corn’ reference CO2 (δ13C VPDB = -10.2‰, δ18O VPDB = -6.0‰; values calibrated by NBS-19 international carbonate standard). Following bellow fill, the m/z - 45 signal is used for peak centering and bellows are compressed for pressure adjustment that produced a m/z 44 signal of 16 V (equivalent to ~ 2500 mV for m/z 47). Pressure baseline (PBL) is automatically measured similar to the method of He et al. (2012) with the measurement made 0.08 kV left of peak center. Sample CO2 m/z 44-49 is measured against reference CO2 for 6 acquisitions of 15 sample-reference comparison cycles with 26-second integration times. Masses 44-46 are measured with standard amplification (3x108, 3x1010, 1x1011, respectively); masses 47-49 were measured with 1x1012 Ω amplification. At the end of each 6-acquisition sample measurement, water backgrounds are measured by peak centering on the mass-45 faraday collector and measuring m/z 18 of both sample and reference. Δ47 values are calculated using established methods (Santrock et al., 1985; Eiler and Schauble, 2004; Huntington et al., 2009, Brand et al. 2010, Daëron et al. 2016, Schauer et al. 2016) and are corrected to the absolute reference frame (ARF) of Dennis et al. (2011) using heated gas (1000°C) and CO2-water equilibration (4 and 60°C) lines constructed during the corresponding analysis period.
- Brand WA, Assonov SS, Coplen TB. Correction for the 17O interference in δ(13C) measurements when analyzing CO2 with stable isotope mass spectrometry. Pure and Applied Chemistry, 82 (2010).
- Daëron M, Blamart D, Peral M, Affek HP. Absolute isotopic abundance ratios and the accuracy of Δ47 measurements. Chem. Geol. 2016, 442, 83.
- Eiler JM and Schauble E. 18O13C16O in Earth’s atmosphere. Geochimica et Cosmochimica Acta, 68, 4767-4777. (2004).
- Dennis KJ, Affek HP, Passey BH, Schrag DP, Eiler JM. Defining an absolute reference frame for ‘clumped’ isotope studies of CO2. Geochimica et Cosmochimica Acta, 75, 7117-7131. (2011).
- He B, Olack GA, Colman AS. Pressure baseline correction and high-precision CO2 clumped-isotope (Δ47) measurements in bellows and micro-volume modes. Rapid Communications in Mass Spectrometry, 26, 2837-2853. (2012).
- Huntington KW, Eiler JM, Affek HP, Guo W, Bonifacie M, Yeung LY, Thiagarajan N, Passey B, Tripati A, Daëron M, Came R. Methods and limitations of ‘clumped’ CO2 isotope (Δ47) analysis by gas-source isotope ratio mass spectrometry. Journal of Mass Spectrometry, 44, 1318-1329. (2009).
- Santrock J, Studley SA, Hayes JM. Isotopic analyses based on the mass spectra of carbon dioxide. Analytical chemistry, 57, 1444–1448. (1985).
- Schauer AJ, Kelson J, Saenger C, Huntington KW. Choice of 17O correction affects clumped isotope (Δ47) values of CO2 measured with mass spectrometry. Rapid Communications in Mass Spectrometry, 30, 2607–2616 (2016).