Environmental Isotope Laboratory | Services

Delta SService analyses for internal and external users include measurement of natural levels of tritium in water, stable isotope analyses of water, carbonates, brines, sulfide and sulfate minerals.

The Radiocarbon Laboratory has closed. For radiocarbon dating, please contact the NSF-Arizona Accelerator facility.

Analytical Service Rates for 2016

Analytical Method Descriptions
 

C and N isotopes in organics, soils etc.

d15N and d13C, as well as carbon and nitrogen content were measured on a continuous-flow gas-ratio mass spectrometer (Finnigan Delta PlusXL) coupled to an elemental analyzer (Costech). Samples were combusted in the elemental analyzer.  Standardization is based on acetanilide for elemental concentration, NBS-22 and USGS-24 for d13C, and IAEA-N-1 and IAEA-N-2 for d15N. Precision is better than ± 0.10 for d13C and ± 0.2 for d15N (1s), based on repeated internal standards.

Carbonate isotopes

d18O and d13C of carbonates were measured using an automated carbonate preparation device (KIEL-III) coupled to a gas-ratio mass spectrometer (Finnigan MAT 252). Powdered samples were reacted with dehydrated phosphoric acid under vacuum at 70°C. The isotope ratio measurement is calibrated based on repeated measurements of NBS-19 and NBS-18 and precision is ± 0.1 ‰ for d18O and ±0.08‰ for d13C (1sigma).

H isotopes in cellulose and minerals

d D was measured on a continuous-flow gas-ratio mass spectrometer (Thermo Electron Delta V). Samples were combusted at 1400 °C using an ThermoQuest Finnigan TCEA (Thermal combustion elemental analyzer) coupled to the mass spectrometer. Standardization is based on a linear calibration curve obtained by measuring three materials -- NIST SRM 8540 (-65.7‰), IAEA CH7 (-110.3‰) and our house standard benzoic acid (-87.6‰) in each set of analyses. Precision is better than ± 2.5 per mil on the basis of repeated internal standards.

H isotopes in organics with exchangeable hydrogen

The counting lab

Samples were equilibrated with ambient water vapor in laboratory air with tracer standards (swan feather). They are then dried with P2O5 for at least 6 hours.

d D was measured on a continuous-flow gas-ratio mass spectrometer (Thermo Electron Delta V). Samples were combusted with excess C at 1400 °C using an ThermoQuest Finnigan TCEA (Thermal combustion elemental analyzer) coupled to the mass spectrometer. Standardization is based on the calibrated house standard benzoic acid (-87.6‰) and Hexatriacontane (-247, University of Indiana) in each set of analyses. A value of 1.120 is used for the fractionation between water vapor and exchangeable hydrogen in calculating the non-exchangeable dD value. Precision is better than ± 2.5 per mil on the basis of repeated internal standards.

O and H isotopes in water

d D and d18O were measured on a gas-source isotope ratio mass spectrometer (Finnigan Delta S). For hydrogen, samples were reacted at 750°C with Cr metal using a Finnigan H/Device coupled to the mass spectrometer. For oxygen, samples were equilibrated with CO2 gas at approximately 15°C in an automated equilibration device coupled to the mass spectrometer.  Standardization is based on international reference materials VSMOW and SLAP.  Precision is 0.9 per mil or better for d D and 0.08 per mil or better for d18O  on the basis of repeated internal standards.

S isotopes in sulfates and sulfides

d34S was measured on SO2 gas in a continuous-flow gas-ratio mass spectrometer (ThermoQuest Finnigan Delta PlusXL). Samples were combusted at 1030 deg. C with O2 and V2O5 using an elemental analyzer (Costech) coupled to the mass spectrometer. Standardization is based on international standards OGS-1 and NBS123, and several other sulfide and sulfate materials that have been compared between laboratories.   Calibration is linear in the range -10 to +30 per mil.  Precision is estimated to be ± 0.15 or better (1s), based on repeated internal standards.

C isotopes in DIC

d13C of DIC was measured on a continuous-flow gas-ratio mass spectrometer (ThermoQuest Finnigan Delta PlusXL) coupled with a Gasbench automated sampler (also manufactured by Finnigan).   Samples were reacted for > 1 hour with phosphoric acid at room temperature in Exetainer vials previously flushed with He gas.  Standardization is based on NBS-19 and NBS-18 and precision is ±0.30‰ or better (1sigma).

O isotopes in sulfate

d18O of sulfate was measured on CO gas in a continuous-flow gas-ratio mass spectrometer (Thermo Electron Delta V). Samples were combusted with excess C at 1350 °C using a thermal combustion elemental analyzer (ThermoQuest Finnigan) coupled to the mass spectrometer. Standardization is based on international standard OGS-1.  Precision is estimated to be  ± 0.3 per mil or better (1s), based on repeated internal standards.

Tritium

Tritium was measured by liquid scintillation spectrometry on samples that were first distilled to remove non-volatile solutes, and then enriched by electrolysis by a factor of about 9.   Enriched samples were mixed 1:1 with Ultimagold Low Level Tritium (R) cocktail, and counted for 1500 minutes in a Quantulus 1220 Spectrometer in an underground counting laboratory at the University of Arizona.    The detection limit under these conditions is 0.6 TU.  Standardization is relative to NIST SRM 4361C, and water from Agua Caliente Spring in Tucson basin is used to determine background.

O isotopes in organics

d18O of cellulose was measured on a continuous-flow gas-ratio mass spectrometer (Thermo Electron Delta PlusXL). Samples were combusted with excess C at 1350 °C using a thermal combustion elemental analyzer (ThermoQuest Finnigan) coupled to the mass spectrometer. Standardization is based on international standards IAEA601, IAEA602 and OGS-1.  Precision is estimated to be  ± 0.3 per mil or better (1s), based on repeated internal standards.

N isotopes in bulk DIN

d15N was measured on bulk residual salt from the gentle evaporation of water to dry; this represents bulk DIN of the sample.  Measurements were made using a continuous flow gas-ratio mass spectrometer (Finnigan Delta PlusXL) coupled to an elemental analyzer (Costech). Samples were combusted in the elemental analyzer.  Standardization is based on IAEA-N-1 and IAEA-N-2 for d15N.  The IAEA standards were used to calibrate d15N  of the laboratory working standard, acetanilide.  Precision is better than ± 0.2 for d15N (1s), based on repeated internal standards.


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David Dettman

Data Repository

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