The automated measurement of δ13C and δ18O from solid carbonate samples has been demonstrated using a ThermoScientific™ Delta Ray™ IRIS with URI Connect. The measurement of certified reference materials confirms the high achievable accuracy and a precision of <0.1‰ for both δ13C and δ18O

Mandic, M.

Smajgl, D.

Stöbener, N.

OceanRep

ABSTRACT  The automated measurement of δ13C and δ18O from solid carbonate samples has been demonstrated using a Thermo Scientific™ Delta Ray™ IRIS with URI Connect. The measurement of certified reference materials confirms the high achievable accuracy and a precision of <0.1‰ for both δ13C and δ18O.  INTRODUCTION  Stable carbon and oxygen isotopic compositions (δ13C and δ18O) of carbonates have been widely used for reconstruction of paleoenvironments.    The isotopic signature of carbon, δ13C is significant as a tracer for the origin of carbon. Variations of δ18O in oxygen bearing minerals have been used as proxies for various environmental records, especially temperature.   For many decades different instrumental methods involving generations of the Thermo Fisher Scientific isotope ratio mass spectrometers with Kiel Carbonate device, or the continuous flow Gas Bench II with the Carbonate-Option in conjunction with an CTC GC PAL or Combi PAL autosampler, offered the scientifically required high precision, and high throughput of samples for these applications.   The Delta Ray IRIS with URI Connect and TELEDYNE Cetac  ASX-7100 autosampler now extends the traditional offerings with a system that can be used in the laboratory or the field and offers high precision and throughput of samples.           Fig 1. Thermo Scientific™ Delta Ray™ IRIS with URI Connect and Cetac ASX-7100 with heated sample rack. 1Thermo Fisher Scientific, Bremen, Germany Using Isotope Ratio Infrared Spectrometer to determine δ13C and δ18O of carbonate samples  Danijela Smajgl1*, Nils Stöbener1, Magda Mandic1 METHOD  The preparation of the samples for analysis on the Delta Ray IRIS with URI Connect is similar to the previously mentioned Gas Bench II method. Samples are put into vials and  phosphoric acid is added. The resulting sample-acid chemical reaction releases CO2 gas, which is then  introduced into the Delta Ray IRIS via the Variable Volume.  Three international standards of carbonate materials (NBS-18, NBS-19 and IAEA-CO-1) were analyzed. NBS-18 and NBS-19 were used as standards for calibration, and IAEA-CO-1 was treated as unknown. The Principle of Identical Treatment was applied in sample and standard preparation, in measurement procedure, as well as in the evaluation of the results.  RESULTS  The obtained isotope ratios for NBS-18 and NBS-19 were averaged and used to generate two-point calibration curves for the 13C/12C and 18O/16O ratios. The calibration functions were then applied to the measured isotope ratios of the samples. The resulting numbers are in perfect agreement with the values certified by IAEA. Fig 5 shows the obtained δ13C and δ18O values for all IAEA-CO-1 standards and mean, median, minimum and maximum, as well as the second and third quartile. For comparison, the certified values plus their uncertainty are also indicated.                               CONCLUSIONS  The Thermo Scientific™ Delta Ray™ IRIS with URI Connect  allows determination of δ13C and δ18O values from carbonates with a precision comparable to IRMS. In addition, the Delta Ray IRIS allows the researcher also to obtain these data directly in the field. The workflow for analysis of carbonates and other samples is fully automated.  REFERENCES 1. IAEA Reference Material Online Catalog:  https://nucleus.iaea.org/rpst/referenceproducts/ReferenceMaterials/index.htm Step by Step Sample Preparation  a) 400 – 500 μg per sample was used for analysis. b) Residual air was removed from the vials by an automated autosampler-assisted flushing procedure. Flushing procedure is carried out at a flow of 30 mL/min for 3 minutes.  c) Samples were manually acidified using 3 droplets of 104% phosphoric acid (H3PO4).  d) Reaction time was 60 minutes at a constant temperature of 80°C. e) Start of measurement                  Measurement Procedure  Sampling and measurement procedure were driven automatically from Qtegra ISDS  Software with the Labbook shown in Figure 4. The built-in method "Transfer Sample" executes sample collection from the autosampler, CO2 concentration determination prior to measurement, and optimization of the measurement conditions. Each sample measurement was followed by a measurement of a working standard gas to correct for instrument drift. Prior to each sample transfer, the Variable Volume and plumbing was flushed twice with Carrier by means of an Action Script ("Preclean D").            EXPERIMENTAL SETUP  The URI Connect contains a Variable Volume (VV) of up to 100 mL in size. The CO2 gas released in vials by reaction of samples with phosphoric acid is flushed into the VV through a Nafion based built-in water trap. CO2 free synthetic air is used as a Carrier. During measurement, the VV is decreased, resulting in a continuous gas flow of diluted sample CO2 into the measurement cell (Fig 2). Prior to measurement, a fraction of the VV is used to determine the present CO2 concentration. The Thermo Scientific™ Qtegra™ Intelligent Scientific Data Solution™ (ISDS) Software automatically adjusts the dilution of the CO2 to achieve the desired concentration (e.g., 400 ppm) in the Delta Ray. As part of the workflow, reference gases are regularly measured at the same concentration as the sample to allow for automatic drift correction.                Fig 2. Workflow of the sample handling within the URI Connect.  a) Flushing of the vial headspace into the Variable Volume (VV) b) VV increases  c) headspace transfer completed  d) release of sample gas from the VV into the Delta Ray and dilution with synthetic air.  a) b) c) d) Fig 3. Sample Preparation. Fig 4. Qtegra Labbook Layout.   Label Flush time [sec.] Measurement time [sec.] Concentration[ppm] Dilution flow [ml/min] Smart Ref. Source Action Sample Processing Type Rack Vial 1 AS cleaning 0 600 380 40  None None UNKNOWN 1 60 2 Ref. 1 60 180 380 0  None None STD Standard 1 3 NBS 18 40 180 380 0  Preclean D Transfer Sample UNKNOWN 1 1 4 Ref. 1 60 180 380 0  None None STD Standard 1 5 NBS 19 40 180 380 0  Preclean D Transfer Sample UNKNOWN 1 2 6 Ref. 1 60 180 380 0  None None STD Standard 1 7 IAEA-CO-1  40 180 380 0  Preclean D Transfer Sample UNKNOWN 1 3 8 Ref. 1 60 180 380 0  None None STD Standard 1 9 IAEA-CO-1 40 180 380 0  Preclean D Transfer Sample UNKNOWN 1 4 10 Ref. 1 60 180 380 0  None None STD Standard 1 11 IAEA-CO-1 40 180 380 0  Preclean D Transfer Sample UNKNOWN 1 5 12 Ref. 1 60 180 380 0  None None STD Standard 1 13C/12C Rexpected Rmeasured Calibration function NBS-18 0.0111241 0.0111998 Rexpected = 0.998347 × Rmeasured + 2.07438×10-5 NBS-19 0.0112020 0.0111218 18O/16O Rexpected Rmeasured Calibration function NBS-18 0.00201920 0.0020334 Rexpected = 1.02488 × Rmeasured  - 6.47652×10-5 NBS-19 0.00206261 0.0020757  IAEA-CO-1 Measured 1 SD Certified* δ13C(‰ VPDB) 2.46 0.03 2.49 ± 0.03 δ18O (‰ VPDB-CO2) -2.42 0.06 -2.4 ± 0.1  Table 1: Expected and measured Isotope Ratios of NBS 18 and NBS 19, as well as derived Calibration functions. Table 2: Resulting δ13C and  δ18O values for ten IAEA-CO-1 standard samples. * Recommendation only for  δ18O Fig 5. δ13C and  δ18O values of ten IAEA-CO-1 standard samples. The green and pink vertical lines indicate the position of NBS 18 and NBS 19 standards used for scale calibration. The blue line and shading refers to the value and uncertainty certified (δ13C) or recommended (δ18O) by the IAEA1. *danijela.smajgl@thermofisher.com 

Using Isotope Ratio Infrared Spectrometer to determine δ13C and δ18O of carbonate samples

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Using Isotope Ratio Infrared Spectrometer to determine δ13C and δ18O of carbonate samples

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