Carbonate - Δ47
Carbonate clumped isotope analysis starts when 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 Porapak Q trap (50/80 mesh, 122 cm long, 6.35 mm OD) held at -20 °C. The CO2 is transferred through the Porapak Q trap using helium 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 5-8 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 or fossil fuel combustion in Pyrex break seals with South Pole ice core water, local tap water, or 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 box 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 mass / charge (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 are 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 carbon dioxide equilibrium scale (CDES) of Dennis et al. (2011) using CO2 equilibrated with a suite of waters and at three temperatures (4 °C, 60 °C, 1000 °C). We also 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 start with our rates page. This analysis requires Carbonate Prep Line to convert the carbonate to carbon dioxide and Carbon Dioxide - Δ47 to analyze the carbon dioxide for isotopic abundance. 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 triplicates for a sound interpretation (# of samples x # replicates = total analyses). Note, increased replication is at our discretion unless specifically stated upon submission.
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.
Standard Operating Procedures
- Making Phosphoric Acid
- Carbonate Clumped Isotope Preparation
- Carbonate Clumped Isotope Analysis
- Brand WA, Assonov SS, Coplen TB. (2010) Correction for the 17O interference in δ(13C) measurements when analyzing CO2 with stable isotope mass spectrometry. Pure and Applied Chemistry, 82. doi: 10.1351/PAC-REP-09-01-05.
- Daëron M, Blamart D, Peral M, Affek HP. (2016) Absolute isotopic abundance ratios and the accuracy of Δ47 measurements. Chemical Geology 442, 83. doi: 10.1016/j.chemgeo.2016.08.014.
- Eiler JM, Schauble E. (2004) 18O13C16O in Earth’s atmosphere. Geochimica et Cosmochimica Acta 68, 4767-4777. doi: 10.1016/j.gca.2004.05.035.
- Dennis KJ, Affek HP, Passey BH, Schrag DP, Eiler JM. (2011) Defining an absolute reference frame for ‘clumped’ isotope studies of CO2. Geochimica et Cosmochimica Acta 75, 7117-7131. doi: 10.1016/j.gca.2011.09.025.
- He B, Olack GA, Colman AS. (2012) 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. doi: 10.1002/rcm.6436.
- Huntington KW, Eiler JM, Affek HP, Guo W, Bonifacie M, Yeung LY, Thiagarajan N, Passey B, Tripati A, Daëron M, Came R. (2009) Methods and limitations of ‘clumped’ CO2 isotope (Δ47) analysis by gas-source isotope ratio mass spectrometry. Journal of Mass Spectrometry 44, 1318-1329. doi: 10.1002/jms.1614.
- Kelson JR, Huntington KW, Schauer AJ, Saenger C, Lechler AR. (2009) Toward a universal carbonate clumped isotope calibration: Diverse synthesis and preparatory methods suggest a single temperature relationship. Geochimica et Cosmochimica Acta 197. doi: 10.1016/j.gca.2016.10.010.
- Petersen SV, Defliese WF, Saenger C, Daëron M, John CM, Huntington KW, Kelson JR, Bernasconi SM, Colman AS, Kluge T, Olack GA, Schauer AJ, Bajnai D, Bonifacie M, Breitenbach SFM, Fiebig J, Fernandez AB, Henkes GA, Hodell D, Katz A, Kele S, Lohmann KC, Passey BH, Peral M, Petrizzo DA, Rosenheim BE, Tripati A, Venturelli R, Young ED, Wacker U and Winkelstern IZ (2019) Effects of improved 17O correction on interlaboratory agreement in clumped isotope calibrations, estimates of mineral‐specific offsets, and temperature dependence of acid digestion fractionation. Geochemistry, Geophysics, Geosystems 20, 3495–3519. doi: 10.1029/2018GC008127.
- Santrock J, Studley SA, Hayes JM. Isotopic analyses based on the mass spectra of carbon dioxide. Analytical Chemistry 57, 1444–1448. (1985) doi: 10.1021/ac00284a060.
- Schauer AJ, Kelson J, Saenger C, Huntington KW. (2016) Choice of 17O correction affects clumped isotope (Δ47) values of CO2 measured with mass spectrometry. Rapid Communications in Mass Spectrometry 30, 2607–2616 doi: 10.1002/rcm.7743.
- Wang Z, Schauble EA, Eiler JM. (2004) Equilibrium thermodynamics of multiply substituted isotopologues of molecular gases. Geochimica et Cosmochimica Acta 68, 4779-4797. doi: 10.1016/j.gca.2004.05.039