Stable Isotope Laboratory

Before mailing any samples, please contact the lab manager, Gregory Cane at gcane@illinois.edu, to discuss sample type, quantity, and analytical needs. Upon agreement, samples can be mailed to:

Illinois State Geological Survey
ATTN: Gregory Cane
615 E. Peabody Drive
Champaign, IL 61820

• Follow the sample requirement guidelines provided in the Samples and Services section below.
• Samples must be clearly labeled.
  • Sample IDs should avoid using special characters, such as: $ ! # & * (these symbols are not compatible with our analytical software).
• Shipments must include a detailed sample manifest, as well as a letter detailing the account number, researcher name, and address for invoicing purposes. We receive many boxes of samples and your letter will help distinguish which samples belong to which client.
• Specify if you wish samples to be returned to you. Samples will be stored for up to 3 months after results have been reported. If you wish samples to be returned, include a FedEx or UPS account number in your correspondence.

Pricing

Please contact the lab manager, Greg Cane, at gcane@illinois.edu, for pricing information.

Billing and Payment

Invoices are generated and sent with analysis results.  U of I researchers should specify U of I funds (i.e., CFOP) to be used for payment during sample submission.

External submitters should receive a UIUC Banner account prior to sample submission. The lab can assist in setting up a Banner account.  Payment can be made online by going to http://go.illinois.edu/paygar and logging in with the UIUC Banner account number assigned to your department, group, or business. Please reference the invoice number during payment.

Payments can also be mailed to:

University of Illinois Payment Center
General A/R
28394 Network Place
Chicago, IL 60673‐1283
ISGS FEIN# 37-6000511

When making out your payment, please be sure to reference the invoice number, your UIUC Banner account number, and University of Illinois Fund number and make payable to University of Illinois, Fund 304203.

Isotope Ratio Mass Spectrometers

• 1 x MAT252 Dual Inlet IRMS
• 1 x Delta V Advantage

Peripherals

• Carlo Erba Elemental Analyzer NC2500
• Thermo Fisher GasBench II
• Thermo Finnigan TCEA
• Thermo Fisher Kiel III

Other Equipment

• Mettler Toledo Microbalance
• 2 x Analytical Balances
• 2 x Drying ovens
• Centrifuge – Exchangeable Bucket Swing Rotor

Extraction Lines

• Multi-Purpose Vacuum Extraction Line

The Illinois State Geological Survey’s (ISGS) stable isotope laboratory (SIL) recently passed a standards proficiency test overseen by the International Atomic Energy Association (IAEA).

Below are links to the SIL results and a guide on how to interpret results.

ISGS SIL Results

IAEA WICO 2020 Report Guide

The Illinois State Geological Survey’s (ISGS) stable isotope laboratory (SIL) passed a standards proficiency test overseen by LGC Axios and the Forensic Isotope Ratio Mass Spectrometry Scheme, related to C13 analysis and comparison between participating laboratories.

ISGS SIL Results

2021 LGC Axios Report

Requirements

• Plant leaves should be washed under DI water to remove dust, soil, and/or any extraneous sources of N and C.
• Plant matter, muds, soils, and any wet samples should be completely dried at 46 °C in a drying oven for several days.
• All samples should be ground to a fine powder and homogenized before sending. Manual grinding is not possible for samples such as grasses, hairs, feathers, and most plant matter. Use a mill if possible.
• Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
• Roughly 5 mg of plant-based samples and 10 to 100 mg of decarbonated soil/sediment sample is needed for analysis (see requirements for submitting soils/sediments for decarbonation technique).
• Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).
• For soils processing, contact Greg Cane for further details.

Methodology

Samples are loaded into tin capsules. Soils/sediment samples require 10 to 100 mg, whereas plant-based samples require anywhere between 2 and 4 mg. Calibration standards and two quality control standards are also weighed. Samples and standards are loaded into a 50-position carousel NC2500 Carlo Erba Instruments Elemental Analyzer. Tin capsules are dropped one at a time into a combustion reactor set at 980 °C, and roughly 5 mL of pure oxygen is added to the reaction which flash combusts the aliquot at 1800 °C. Ultra-high purity helium is used as a carrier gas, which transports analytes of CO₂, N₂, H₂O, and SO₂ through three columns; i) a copper trap to remove excess oxygen and reduce any N₂O to N₂, ii) a magnesium perchlorate trap to remove water, and iii) a GC column to separate the N₂ from the CO₂ phase. Sample gases are then quantified with a TCD (Thermal Conductivity Detector).

Analytical precision for N and C is less than 0.1%.

Turnaround Time

• ≤ 50 samples: 3-4 weeks to process.
• > 50 samples: 4-5 weeks to process.

Requirements

• Solid samples should be ground to a powder and homogenized before sending.
• If samples are moist or wet, they should be dried at 46 °C in a drying oven for several days.
• Samples such as leaves, grasses, and other plant matter may be difficult to grind.
• Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
• Typically, 1 to 2 mg of sample is necessary for analysis.
• Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).

Methodology

Samples are weighed into silver capsules. Benzoic acid and cellulose standards are also weighed into silver capsules and loaded into a Costech Zero blank autosampler. An isolation valve on the autosampler allows for the capsules to be purged with ultra-high purity helium for ten minutes prior to opening to the reactor assembly and the main helium stream. Pyrolysis of the samples is performed by a Thermo Finnigan TCEA, whereby capsules are dropped one at a time into a glassy carbon reactor set at 1400 °C containing glassy carbon chips. The resulting reaction leads any oxygen to interact with the glassy carbon to produce carbon monoxide and water. These analytes pass through a 1.5 m long 5 Å mol sieve GC column and a chemical water trap before proceeding to a Thermo Fisher Scientific Conflo IV-Delta V isotope ratio mass spectrometer for analysis. Quantitative O values are calculated by analyzing a cellulose standard ten times at variable weight and generating a calibration curve of the standard voltage versus the amount of oxygen weighed. Sample O data is then quantified from this curve knowing the weight of the analyzed sample.

Analytical precision for O is less than 0.1%.

Turnaround Time

• 6 weeks but subject to change given batch size.

Requirements

• Samples should be ground to a powder and homogenized before sending.
• If samples are moist or wet, they should be dried at 46 °C in a drying oven for several days.
• Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
• The percentage and carbonate type for each sample must be indicated in any correspondence sent with the shipment, e.g., Calcite 100% or Dolomite 50%.
• Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).

Methodology – Two Options

1. Continuous Flow

Samples and standards are loaded into 12 mL round bottom borosilicate glass Labco exetainer vials (Cat # 938W) and capped. Vials are purged for ten minutes with ultra-high purity helium. Using 1 mL disposable syringes with 25G needle attached, five to ten drops of 100% prepared phosphoric acid (ρ=1.9023 g/cm³) are injected into the exetainer and the samples are allowed to equilibrate for 24 hours at 30 °C. The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler. Sample CO₂ gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) inside a Thermo Fisher GasBench II front-end peripheral, then to a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ¹³C and δ¹⁸O. Isotope data is corrected for any linearity effects displayed by a standard analyzed ten times at variable weight. Precision for δ¹³C is ±0.08‰ and for δ¹⁸O is ±0.23‰.

Turnaround Time:

• • ≤ 40 samples: 2-3 weeks to process.
  • > 40 samples: 6-8 weeks to process.

2. Dual Inlet

Samples and standards are loaded into Kiel vials obtained from VM Glass Company (# VMS-943). A total of 38 samples, in addition to six internationally recognized calibration standards and two internally calibrated quality control standards. Vials are placed in an autosampler tray and placed in a Thermo Fisher Kiel III peripheral set at 70 °C. Samples are processed automatically, one at a time, whereby three drops of 100% prepared phosphoric acid are added to the evacuated vial. Reaction times depend on the type of carbonate mineral submitted, i.e., Calcite=12 minutes, Dolomite=15 minutes, Siderite=20 minutes. Sample CO₂ gas is then transferred to a ThermoFisher MAT252 dual inlet isotope ratio mass spectrometer for analysis of δ¹³C and δ¹⁸O. Although raw isotope data is calibrated to the internally used CO₂ calibration tank, a second calibration is performed using the plotted curve generated by data from the international standards. Precision for δ¹³C is ±0.03‰ and for δ¹⁸O is ±0.07‰.

Turnaround Time:

• • ≤ 40 samples: 2-3 weeks to process.
  • > 40 samples: 6-8 weeks to process.

Requirements

• Plant leaves should be washed under DI water to remove dust, soil, and/or any extraneous sources of N and C.
• Plant matter, muds, soils, and any wet samples should be completely dried at 46 °C in a drying oven for several days.
• All samples should be ground to a fine powder and homogenized before sending. Manual grinding is not possible for samples such as grasses, hairs, feathers, and most plant matter. Use a mill if possible.
• Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
• Glass fiber filters containing filtered material can be sent wrapped in tin foil, but the %N and %C cannot be determined unless the client has indicated the filtered material weight (typically done with “before” and “after” dry weight of the filter).
• Roughly 5 mg of plant-based samples and 10 to 100 mg of decarbonated soil/sediment sample is needed for analysis (see requirements for submitting soils/sediments for decarbonation technique).
• Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).

Methodology

Please note: Carbon and nitrogen results can be obtained on the same analysis for each sample. It is up to the client to specify if either one or both is required. In rare cases, it is not possible to obtain results for both isotopes on a single analysis. The sample must then be analyzed twice, once for the carbon fraction, and then a second time for the nitrogen. In these cases, the client will be notified prior to analysis, as the cost per sample would be two-fold.

Samples are loaded into tin capsules. Soil/sediment samples require 10 to 100 mg, whereas plant-based samples require anywhere between 2 and 4 mg. Calibration standards and two quality control standards are also weighed. Samples and standards are loaded into a 50-position autosampler carousel connected to a Carlo Erba NC2500 elemental analyzer. Tin capsules are dropped one at a time into a combustion reactor set at 980 °C, and roughly 5 mL of pure oxygen is added to the reaction which flash combusts the aliquot at 1800 °C. Ultra-high purity helium is used as a carrier gas, which transports analytes of CO₂, N₂, H₂O, and SO₂ through three columns; i) a copper trap to remove excess oxygen, ii) a magnesium perchlorate trap to remove water, and iii) a GC column to separate the N₂ from the CO₂ phase. Sample gases are then passed on to a Thermo Fisher Conflo IV linked to Delta V Advantage isotope ratio mass spectrometer for analysis of δ¹⁵N and δ¹³C. Soil sample precision for δ¹⁵N is ±0.39‰ and for δ¹³C is 0.10‰. Plant matter precision for δ¹⁵N is ±0.23‰ and for δ¹³C is 0.08‰.

Turnaround Time

• ≤ 25 samples: 3-4 weeks to process.
• > 25 samples: 6-8 weeks to process.

Requirements

• Solid samples should be ground to a powder and homogenized before sending.
• If samples are moist or wet, they should be dried at 46 °C in a drying oven for several days.
• Samples such as leaves, grasses, and other plant matter may be difficult to grind.
• Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
• Typically, 1 to 2 mg of sample is necessary for analysis.
• Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).

Methodology

Samples are weighted into silver capsules. Benzoic acid and cellulose standards are also weighed into silver capsules and loaded into a Costech Zero blank autosampler. An isolation valve on the autosampler allows for the capsules to be purged with ultra-high purity helium for ten minutes prior to opening to the reactor assembly and the main helium stream. Pyrolysis of the samples is performed by a Thermo Finnigan thermal conversion elemental analyzer (TCEA), whereby capsules are dropped one at a time into a glassy carbon reactor set at 1400 °C containing glassy carbon chips. The resulting reaction leads any oxygen to interact with the glassy carbon to produce carbon monoxide and water. These analytes pass through a 1.5 m long 5 Å mol sieve GC column and a chemical water trap before proceeding to a Thermo Fisher Scientific Conflo IV-Delta V isotope ratio mass spectrometer for analysis of δ¹⁸O.

Turnaround Time

• ≤ 25 samples: 4-5 weeks to process.
• > 25 samples: 6-8 weeks to process.

Requirements

• Samples must be sent ground up as well as possible, with no chunks present.
• Roots must be thoroughly removed.
• The decarbonation process requires a minimum of 2 grams of sample; however, we suggest you send at least twice that amount for rock-based carbonate samples.
• Samples can be sent in vials/bags of your choice.
• Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).

Methodology

Samples are processed 24 at a time in graduated 50 mL falcon tubes (Fisher Scientific # 22-171-717) by acidifying 2 grams of the sample with 40 mL of 0.5 N hydrochloric acid. The acidification process is done a minimum of two times over two days, with regular agitation of the vials done several times per day. Tubes are centrifuged at 4,000 RPM for 5 minutes between acidification steps and the acid is decanted. Vials are capped tightly overnight, and any residual pressure upon undoing the cap merits an additional acidification process. This is repeated until no residual pressure is heard or felt. Acid is decanted and the samples are rinsed twice with deionized water or until a pH of 5 to 7 is reached. Again, tubes are centrifuged and the supernatant is discarded between rinse steps. At the end of the final rinse, the supernatant is decanted and the tubes are placed in a drying oven at 46 °C for a week. Dried samples are then crushed by mortar and pestle into a fine powder and stored in 2 dram vials (Fisher Scientific # 14-955-326) until ready for analysis of δ¹³C_org.

Turnaround Time

• ≤ 25 samples: 4-5 weeks to process.
• > 25 samples: 6-8 weeks to process.

Requirements

• Samples should be submitted in 60 mL wide-mouth Amber HDPE bottles (Fisher Scientific Cat # 02-925-3B) – Avoid tin foil lined caps!!
• Samples must be filtered using 0.45 μm luer lock syringe filters (Fisher Scientific Cat # 50-109-8711).
• Bicarbonate alkalinity (HCO3^– mg/L) is a helpful component and should be sent with any correspondence regarding sample submission. This parameter helps us determine how much sample to inject during the methodology phase.
• Bottles must be submitted with as little headspace as possible, ideally with no headspace (loss of DIC via the headspace will occur over a matter of days).
• Soon after collection and prior to shipment, refrigerate samples if possible. DO NOT FREEZE.
• For long term storage of DIC samples on the order of months, a small amount of mercuric chloride can be added to each sample (Fisher Scientific Cat # LC165909). This is to prevent biological buildup, algae formation, and fractionation of the DIC. You must indicate in your correspondence if such a preservative is used.
• Samples should be sent as soon as possible to our facility. Samples will be refrigerated upon arrival.

Methodology

A series of solid standards with known δ¹³C are weighed into 12 mL round bottom borosilicate glass Labco exetainer vials (Cat # 938W) and capped. These vials are purged with ultra-high purity (UHP) helium for ten minutes using an offline purge rack. Using 1 mL disposable syringes with 25G needle attached, five to ten drops of 100% prepared phosphoric acid (ρ=1.9023 g/cm³) are injected into the exetainer and allowed to equilibrate for 24 hours at 30 ^oC. Another series of empty exetainer vials for the samples are labeled, and five to ten drops of the same phosphoric acid is added to each vial, then capped. The sample vials are purged using UHP helium for ten minutes each. Based on the bicarbonate alkalinity, an aliquot of the sample is injected into the corresponding purged exetainer vial, which forces CO₂ and H₂CO₃ from solution to CO₂ gas. The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler with ultra-high purity helium acting as a carrier gas. Sample CO₂ gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) located inside a Thermo Fisher GasBench II front-end peripheral, then onto a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ¹³C. Isotope data is corrected for any linearity effects showed by a standard analyzed ten times at variable weight. Precision for δ¹³C_DIC is ±0.08‰.

Turnaround Time

• ≤ 60 samples: 2-3 weeks to process.
• > 60 samples: 4-6 weeks to process.

Requirements

• Samples can be submitted in 30 mL wide-mouth HDPE bottles (Fisher Scientific Cat # 02-893-5A) or any plastic bottle of your choice – Avoid tin foil lined caps.
• Samples must be filtered using 0.45 μm luer lock syringe filters (Fisher Scientific Cat # 50-109-8711).
• Bottles must be submitted with as little headspace as possible, ideally with no headspace.
• Samples do not need to be refrigerated, although, for long term storage, this is recommended.
• Samples should be sent as soon as possible to our facility, where they will be refrigerated upon arrival.

Methodology – 2 Options

1. TCEA – δ¹⁸O and δ²H Preparation

Water samples and standards are pipetted individually into 2 mL vials sealed with Teflon silicone screw cap septa (Cole-Parmer Cat # SK-98701-90). A series of ten samples are bracketed by standards before and after analysis. Analysis always begins with a set of ten deionized water conditioners to monitor drift, then a set of standards.

Secondary standards include a broad spectrum of depleted and enriched aliquots, from ice core melt water to bottled water from France and Italy. These standards are kept frozen until the day before use, where they are completely thawed at room temperature, then shaken. Secondary standards were calibrated by primary standards of VSMOW2, SLAP2, and GISP obtained from the IAEA, Vienna. Two quality control standards (one internally calibrated, and a medium natural isotope water from EA Consumables # B2193) are also included at various intervals throughout the run.

Sample analysis is performed via automated injections using a CTC Analytics PAL autosampler into a Thermo Finnigan Thermal Conversion Elemental Analyzer (TCEA) set at 1400 °C and linked via continuous flow to a Thermo Fisher Delta V Isotope Ratio Mass Spectrometer. The autosampler syringe is rinsed twice with HPLC grade methanol, then subjected to a vacuum for five seconds to remove residual methanol. The syringe is then rinsed three times with the sample before injecting 0.5 μL into the TCEA reactor. This is repeated three times for each sample and standard. The sample is combusted to produce elemental hydrogen. Glassy carbon in the reactor produces carbon monoxide as the oxygen phase. These two analytes are carried by a continuous helium stream set at 100 mL/min and separated by a 1.5 m long stainless steel GC column before being admitted to the IRMS for isotope analysis of δ²H and δ¹⁸O. Of the three injections performed for each sample and standard, only the third is used for calibration purposes. Memory effect is monitored by calculating the standard deviation of all three peaks.

A set of four secondary water standards are analyzed every ten samples, at the beginning of a run, and at the end. Raw δ²H and δ¹⁸O values are plotted versus their known isotopic values to produce a four-point calibration curve. Sample data is calibrated to this curve and reported to the VSMOW scale. Typical linear regression is 0.9996 or better for both the hydrogen and oxygen calibration curves.

Two quality control standards are analyzed after every ten samples and calibrated to the VSMOW scale. Compiled results of EA Consumables Medium Natural Isotopic Water # B2193 and a Greenland Ice Core water show that sample data can be reported as better than ±0.4‰ for δ²H, and better than ±0.16‰ for δ¹⁸O.

Turnaround Time:

• • ≤ 60 samples: 3-4 weeks to process.
  • > 60 samples: 6-8 weeks to process.

2a. GasBench – δ¹⁸O Preparation

0.5 mL of water sample and standards are pipetted individually into 12 mL Labco exetainer vials (Cat # 938W) and capped. Vials are flushed for five minutes at 100-150 mL/min with a 0.5% carbon dioxide in ultra-high purity helium mixture. Freshwaters are left to equilibrate a minimum of 18 hours, and saline waters for five days at 30 °C, prior to analysis.

A series of ten samples are bracketed by standards before and after analysis. Standards include a broad spectrum of depleted and enriched aliquots, from ice core melt water to bottled water from France and Italy. These standards are kept frozen until the day before use, where they are completely thawed at room temperature, then shaken. Secondary standards were calibrated by primary standards of VSMOW2, SLAP2, and GISP obtained from the IAEA, Vienna. Two quality control standards (one internally calibrated, and a medium natural isotope water from EA Consumables # B2193) are also included at various intervals throughout the run.

The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler with ultra-high purity helium acting as a carrier gas. Sample CO₂ gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) located inside a Thermo Fisher GasBench II front-end peripheral, then onto a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ¹⁸O. Sample and standard chromatography include eight CO₂ samples peaks in the results. However, the first and last sample peaks are dropped from the calibration, and the remaining six are averaged. δ¹⁸O data is corrected by generating a four-point calibration curve of the previously mentioned standards, and raw sample data is corrected to the VSMOW scale. Precision for δ¹⁸O is ±0.08‰.

2b. GasBench – δ²H Preparation

0.5 mL of water sample and standards are pipetted individually into 12 mL Labco exetainer vials (Cat # 938W). ***Note*** The sample aliquot used for analysis of δ¹⁸O can be used for the preparation of δ²H analysis. Activated charcoal (Fisher Scientific Cat # AC403995000), copper wire (EA Consumables Cat # B1016), and a platinum catalyst rod are added to each vial and capped. These are added to remove dissolved organic carbon and sulfur compounds that can interfere with the analysis. Vials are flushed for five minutes at 100-150 mL/min with a 2% hydrogen in ultra-high purity helium mixture. Freshwaters are left to equilibrate a minimum of 40 minutes, and saline waters for 24 hours at 30 ºC, prior to analysis.

A series of ten samples are bracketed by standards before and after analysis. Standards include a broad spectrum of depleted and enriched aliquots, from ice core melt water to bottled water from France and Italy. These standards are kept frozen until the day before use, where they are completely thawed at room temperature, then shaken. Secondary standards were calibrated by primary standards of VSMOW2, SLAP2, and GISP obtained from the IAEA, Vienna. Two quality control standards (one internally calibrated, and a medium natural isotope water from EA Consumables # B2193) are also included at various intervals throughout the run.

The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler with ultra-high purity helium acting as a carrier gas. Sample H₂ gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) located inside a Thermo Fisher GasBench II front-end peripheral, then onto a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ²H. Sample and standard chromatography include eight hydrogen sample peaks in the results. However, the first and last sample peaks are dropped from the calibration, and the remaining six are averaged. δ²H data is corrected by generating a four-point calibration curve of the previously mentioned standards, and raw sample data is corrected to the VSMOW scale. Precision for δ²H is ±0.4‰.

Turnaround Time:

• • ≤ 30 samples: 3-4 weeks to process.
  • > 30 samples: 6-8 weeks to process.

Requirements

• Samples can be submitted in 30 mL wide mouth HDPE bottles (Fisher Scientific Cat # 02-893-5A) or any plastic bottle of your choice – Avoid tin foil lined caps.
• Samples must be filtered using 0.45 μm luer lock syringe filters (Fisher Scientific Cat # 50-109-8711).
• Bottles must be submitted with as little headspace as possible, ideally with no headspace.
• Samples do not need to be refrigerated, although, for long term storage, this is recommended.
• Samples should be sent as soon as possible to our facility where they will be refrigerated upon arrival.

Methodology

5 mL of the saline water sample is transferred to a distillation vial and hooked up to a vacuum line. A second distillation vial that acts as the collector vessel is also hooked up. Sample is gradually frozen with liquid nitrogen, and both vessels are evacuated to baseline. Liquid nitrogen dewar is removed from the frozen sample and placed into the collector vessel, whilst completely submerged and a valve is opened between the two vessels to allow the transfer to take place. Distillation of the sample takes several hours, while leaving behind salt crystals from the sample side vessel. The process is complete when all of the water from the sample side has sublimated to the collector vessel. The collected sample is then thawed and the vessel is removed from the vacuum line, where the sample is then poured into a clean 2 mL screw cap vial and refrigerated.

Sample analysis is performed via automated injections using a CTC Analytics PAL autosampler into a Thermo Finnigan Thermal Conversion Elemental Analyzer (TCEA) set at 1400 °C and linked via continuous flow to a Thermo Fisher Delta V Isotope Ratio Mass Spectrometer. The autosampler syringe is rinsed twice with HPLC grade methanol, then subjected to a vacuum for five seconds to remove residual methanol. The syringe is then rinsed three times with the sample before injecting 0.5 μL into the TCEA reactor. This is repeated three times for each sample and standard. Sample is combusted to produce elemental hydrogen. Glassy carbon in the reactor produces carbon monoxide as the oxygen phase. These two analytes are carried by a continuous helium stream set at 100 mL/min and separated by a 1.5 m long stainless steel GC column before being admitted to the IRMS for isotope analysis of δ²H and δ¹⁸O. Of the three injections performed for each sample and standard, only the third is used for calibration purposes. Memory effect is monitored by calculating the standard deviation of all three peaks.

A set of four secondary water standards are analyzed every ten samples, at the beginning of a run, and at the end. Raw δ²H and δ¹⁸O values are plotted versus their known isotopic values to produce a four-point calibration curve. Sample data is calibrated to this curve and reported to the VSMOW scale. Typical linear regression is 0.9996 or better for both the hydrogen and oxygen calibration curves.

Two quality control standards are analyzed after every ten samples and calibrated to the VSMOW scale. Compiled results of EA Consumables Medium Natural Isotopic Water #B2193 and a Greenland Ice Core water show that sample data can be reported as better than ±0.4‰ for δ²H, and better than ±0.16‰ for δ¹⁸O.

Turnaround Time

Email Greg Cane (gcane@illinois.edu) for discussion.

Requirements

• Samples should be submitted in 250 mL wide mouth HDPE bottles (Fisher Scientific Cat # 14-379-007) or any 250 mL plastic bottle of your choice – Avoid tin foil lined caps. If you suspect low concentration of dissolved sulfate (< 100 mg/L), then submitting 500 mL of sample is required.
• Filtering the samples in the field is not necessary as we will filter after receiving the shipment. This is included in the cost.
• Bottles must be submitted with as little headspace as possible.
• Samples do not need to be refrigerated, although, for long term storage, this is recommended.
• Samples should be sent as soon as possible to our facility where they will be refrigerated upon arrival.

Methodology

The principle by which dissolved sulfate is converted to a useful medium for analysis of sulfur and oxygen isotopes is by the precipitation of barium sulfate. Water samples are gravity filtered using 0.7 μm GFF (glass fiber) filters. Filter is discarded. Using 0.5 N HCl, sample is acidified very slowly until pH reaches 3 to 4. A 0.25 M BaCl₂ solution is prepared and 10 mL is added to the sample upon which a white precipitate is produced. The sample is allowed to precipitate barium sulfate overnight. The next day, the precipitate is collected via vacuum filtration using a 0.45 μm nitrocellulose filter (Fisher Scientific Cat # HAWP04700) and rinsed with 250 mL of deionized water to remove any residual barium chloride. The filter is removed, covered, and placed in a desiccator for several days and allowed to dry. Barium sulfate is then collected by scraping the powder into a 20 mL glass scintillation vial (Fisher Scientific Cat # 03-341-25E).

Sample analysis is done in two parts.

1. δ³⁴S analysis is performed by loading 300 to 400 μg of sample into tin capsules and analyzing these via a Carlo Erba NC2500 series elemental analyzer. Sample δ³⁴S data is calibrated by analyzing, in conjunction with the samples, two barium sulfate standards in triplicate: IAEA-SO-6 and NBS-127 (NIST Ref Mat #8557). δ³⁴S data is calibrated to the VCDT (Vienna Canyon Diablo Troilite) scale. Sample error can be reported as better than ±0.15‰.
2. δ¹⁸O analysis is performed by loading 200 to 300 μg of sample into silver capsules and analyzing these via a Thermo Finnigan thermal conversion elemental analyzer (TCEA). Sample δ¹⁸O data is calibrated by analyzing, in conjunction with the samples, two barium sulfate standards in duplicate: IAEA-SO-5 and IAEA-SO-6, both from the International Atomic Energy Association. δ¹⁸O data is calibrated to the VSMOW (Vienna Standard Mean Ocean Water) scale. Sample error can be reported as better than ±0.21‰.

Turnaround Time

• 8 weeks, possibly longer.