[US Geological Survey]Menlo Park Stable Isotope and Tritium Labs

WHO'S WHO

ABDOLLAHIAN.  Nina Abdollahian (nabdollahian@usgs.gov):  Nina’s main duties are to prepare organic matter samples for C-N-S isotopic analysis, process field samples, prepare media for the microbial nitrate isotope method, and assist with tritium sample distillations.

ARTHUR.  Christa Arthur (carthur@usgs.gov):  Christa’s main duties are to prepare organic matter samples for C-N-S isotopic analysis, process field samples, prepare media for the microbial nitrate isotope method, and assist with tritium sample distillations.

B.  TB is the lead technician in the tritium laboratory, sharing responsibility for keeping the tritium laboratory running smoothly at maximum capacity; he also prepares organic matter samples for C-N-S isotopes, processes field samples, and prepares nitrate isotope samples.

CHOY.  Doug Choy (650-329-4316, dchoy@usgs.gov):  Doug handles much of the responsibility for training and supervising junior team members in the labs, database management, safety issues, instrument maintenance, ordering supplies, running the laser spec and TIC-TOC, and preparing for field trips. Doug also oversees the daily operation of the tritium lab.

KENDALL. Carol Kendall (650-329-4576, ckendall@usgs.gov):  Chief of the Isotope Tracers Project. Carol's main field of interest is watershed biogeohydrochemistry, especially in large human-impacted basins. Other interests include: nitrate and organic matter sources and cycling in aquatic systems, the development of new analytical methods and practical applications for CHNOS stable isotopes, and teaching about applications of isotopes for water quality and ecological studies.

MICHEL. Bob Michel (650-329-4547, rlmichel@usgs.gov):  Former chief of the Menlo Park Tritium Lab, now retired from the USGS but still part of the team. Bob's main fields of interest are alpine and arid zone hydrology.

MIXON.  Rachel Mixon (650-329-5603, rmixon@usgs.gov):  Rachel splits her time between field work in the Sacramento Bay, preparing and analyzing ammonium isotope samples, distilling samples for tritium analysis, and helping with data corrections.

PEEK.  Sara Peek (650-329-4509, speek@usgs.gov):  Sara divides her time between method development, instrument maintenance, analyzing nitrate and other samples for isotopic composition, database management, and helping with ongoing ecological projects.

SILVA.  Steve Silva (650-329-4538, srsilva@usgs.gov):  Assistant Project Chief. Steve divides his time between methods development research, several research projects related to nutrient sources and organic matter sources, instrument maintenance, and budget and personnel paperwork. Most of his current methods development research has been on devising new ways to expand project analytical capabilities.

TU.  Ying Tu (ytu@usgs.gov): Ying’s main duties are to prepare organic matter samples for C-N-S isotopic analysis, process field samples, prepare media for the microbial nitrate isotope method, and help prepare nitrate isotope samples.

YOUNG.  Megan Young (650-329-4544, mbyoung@usgs.gov): Megan specializes in isotope biogeochemistry research, with a focus on nutrient source and cycling dynamics.  She also runs the Menlo Park Tritium Laboratory, providing tritium analysis for groundwater age dating and contaminant tracing within the USGS. She is currently working on several different projects using multiple stable isotopes to trace interactions between groundwater, surface water, and anthropogenic nutrient inputs.

There is more information about the "Isotope Tracers" project, including project goals and recent publications, on the NRP homepage.

ANALYTICAL CAPABILITIES

Equipment:

Micromass Optima continuous flow mass spectrometer with electromagnet and universal triple collectors; capable of analyzing CO2, O2, N2, CO, N2O, and SO2. Peripherals include: Carlo Erba C-N-S elemental analyzer preparation system, diluter, 3-gas reference box, and separate small-sample and large-sample multi-tray carousels for solids and dense liquids, for analysis for C, N, and S isotopes; a HP 5890 GC-combustion system for C-N isotopes of volatiles and gases; a Tekmar 16-port purge and trap mounted on the GC.  All the Micromass peripherals are mounted on wheels so that they can be used on any of the three mass specs.

Micromass IsoPrime continuous flow mass spectrometer with electromagnet, electrostatic sector, universal triple collectors, H collectors, Cl collectors -- capable of analyzing CO2, O2, N2, CO, N2O, SO2, H2, and MeCl isotopes. Peripherals include: Carlo Erba C-N-S elemental analyzer preparation system, diluter, 2-gas reference box, and multi-tray carousels for solids and dense liquids, for analysis for C, N, and S isotopes; MultiFlow (Gilson-type) automated headspace-gas analyzer, used for H2-H2O and CO2 - H2O equilibrations (by CF), analysis of DIC, and analysis of N2O samples prepared using the Sigman-Casciotti microbial denitrifier method; and Eurovector high temperature pyrolysis unit for the analysis of organics, inorganics (esp. nitrates and phosphates), and waters for H and O (usually used for solid samples).

Micromass IsoPrime dual inlet/continuous flow mass spectrometer with electromagnet, electrostatic sector, universal triple collectors, H, Cl, and Br collectors -- capable of analyzing CO2, O2, N2, CO, N2O, SO2, H2, MeCl, and MeBr isotopes. Peripherals include: automatic dual inlet coldfinger, diluter, 2-gas reference box, valve-top assembly (a 30-port multi-port for samples in glass tubes), Eurovector high temperature pyrolysis unit for the CF analysis of  waters for H (either manually or with the Eurovector liquid autosampler); MultiPrep used for H2-H2O and CO2 - H2O equilibrations and analysis of carbonates (by dual inlet analysis); and an HP 5890 GC-combustion system for C-N-Cl-Br isotopes of volatiles and gases.  A new peripheral, a TIC-TOC analyzer (from OI, designed for analyzing DIC and DOC samples) provides automated analyses of d13C of DIC and DOC.

Finnigan MAT 251 dual inlet, permanent magnet, mass spectrometer, capable of analyzing CO2, N2, H2, and SO2 for stable isotope composition (used mainly for CO2 and N2). Peripherals include: automated inlet system (separate 12-port manifold and 12-port tube-cracker manifold), and an automated, 48-port, CO2 - H2O equilibrator.

Finnigan MAT Delta E dual inlet mass spectrometer, capable of analyzing CO2, N2, H2, and SO2 for stable isotopic composition (used mainly for H2). Peripherals include: automated inlet system (20-port manifold, usually configured with tube-crackers for manual cracking Zn technique), and an automated, 48-port, H2 - H2O equilibrator (this mass spec is not in use and will be decomissioned sometime in 2002).
 
 

Vacuum lines: carbonate/water extraction line, zinc method preparation line, "Craig-type" CO2-CH4 line, reference gas-standard preparation line w/ 400 split capacity.

Tritium lab: 4 liquid scintillation counters for tritium and 35S, 3H extraction systems (distillation and electrolysis).

Capabilities:

Waters for 2H and 18O: Standard sample size for water equilibrations is 2.0 ml per analysis (for both H and O isotopes); 0.1 ml is the minimum size for automated equilibrator preparation. We have 3 different types of equilibrators on 3 different mass specs, and a new pyrolysis unit (with autosampler) on the newest IsoPrime.  Zinc reduction samples require only 5 ml per analysis. The new pyrolysis unit requires only a few ml per analysis.  Water is extracted from soils and plants by distillation with toluene; recommended sample size is 1-5 ml water per analysis. Analytical precision is 0.05 to 0.1 ‰ for 18O, and 0.3 to 2.0 ‰ for 2H, depending on method and sample matrix.

Waters for 3H: Tritium concentrations are measured on raw unfiltered (RU) waters collected and stored in either glass or high density polyethylene bottles. The size of the bottle depends on the level of precision desired.
 

Two sigma detection limit

+/- 8 TU

+/- 1.2 TU

+/- 0.6 TU

+/- 0.3 TU

Suggested volume

25 ml

500 ml

500 ml

1000 ml

Electrolyzed

No

Yes

Yes

Yes

13C of DIC: Samples can be precipitated with SrCl2 in a NH4OH solution, filtered, rinsed, acidified, and the purified CO2 analyzed; recommended sample size is >50 m moles of C (200 uM DIC concentrations are sometimes required to get adequate precipitation of SrCO3 with this method). Alternatively, organic-free precipitates can be combusted on the elemental analyzer connected to the Optima mass spectrometer, or organic-bearing precipitates can be baked to remove organics and then combusted. These combustion methods only require a few umoles of C. Analytical precison: 0.1 to 0.2 ‰. Alternatively, use the Multiflow or MultiPrep autosamplers to do headspace analysis of dissolved CO2. This requires only a few m moles of C and produces precisions better than 0.1 ‰.  Or more recently, use the new automated TIC/TOC for d13C.

13C of DIC:  Samples are analyzed using the new automated TIC/TOC.

13C/18O of carbonates: Manual single-sample preparation system; samples are acidified, purified, and the resultant CO2 samples loaded on the automated inlet manifold and analyzed. Recommended sample size >50 mmoles of C. Analytical precision: 0.05 to 0.1 ‰.  Samples can also be analyzed using the MultiFlow or MultiPrep autosamplers, where sample sizes are usually on the order of a mmole.

13C/15N of solids and dense liquids: Samples are loaded into tin boats 100-200 samples in a batch, combusted, and analyzed for bulk elemental and isotopic composition on the elemental analyzer connected (usually) to the Optima. Recommended sample size is 2-10 m moles of N if both C and N isotopes are to be measured (this is about 1-2 mg for typical organic samples). Actual minimum sample size is about 0.01 m moles. Maximum sample weight is about 300 mg. Both C and N isotopes can be determined on the same sample if the %C and the C:N ratio are known (so that the correct sample size is weighed and the diluter adjusted correctly). Analytical precision: 0.1 to 0.2 ‰.

15N/18O of nitrate: Several methods are in use.  For our old method (published in Silva et al., 2000), samples are collected on anion exchange columns in the field. Recommended sample size is 100-200 mmoles N. In the lab, the nitrate is eluted, precipitated as silver nitrate, purified, and divided into separate aliquots for 15N and 18O analysis (using the original method). For 15N, the nitrate is handled about the same as other solid samples. For 18O, the nitrate is processed to remove all other O-bearing materials, combusted in sealed tubes, and the resulting CO2 processed similarly to carbonates. Analytical precision (pure samples): <0.1 ‰ for 15N and 0.5 ‰ for 18O; often 2-3 times this for real samples. Solid silver nitrate samples can also be analyzed for 18O and 15N simultanously using the Eurovector pyrolysis system, which drops our sample sizes by about a factor of 10, with about the same precision.  We are now using a new method (the Sigman-Casciotti microbial denitrifier method) to convert nitrate to N2O, which is then analyzed for 18O and 15N simultaneously. This method requires only about 50 nanomoles of N per aliquot, has no interference with other N-bearing substances, and can be used on saline samples. We are currently modifying this method for d17O of nitrate.

15N of ammonium: Samples can be collected on cation exchange resins in the field, or samples can be sent to us untreated but chilled. For column samples, samples are eluted, dried, and processed like other solid samples in the lab. We are still working out the bugs on high-DOC samples but can handle other samples fine. Recommended sample size is 50 mmoles, and our analytical precision is about 0.2 ‰.  We also analyze untreated samples using a micro-diffusion method; recommended sample size is >10 mmoles.

18O of phosphate: Aqueous samples are collected on anion exchange resins in the field, and processed similarly to nitrate. Our method can handle low phosphate, high sulfate, and high DOC concentrations, and requires about 50 m moles of PO4 per analysis using sealed tiube combustions and about 5 m moles of PO4 for pyrolysis analyses. We get precisions of  about 0.2 ‰ for solid samples and 0.2 to 0.5 ‰ for aqueous samples.

18O of organics and inorganics: Can be analyzed on the automated pyrolysis system, for samples sizes on the order of a few micromoles of O per sample.

18O of O2 gas:  Samples are collected in vacutainers and are purified and analyzed on an EA using the Wassenaar method..

13C, 15N, 18O of gases: Currently, such samples are injected manually into either the elemental analyzer or GC combustion system, and analyzed for one or more constituents at a time. Future plans: analyze such samples (and dissolved gases) using the Microgas automated headspace system.

13C of hydrocarbon and other gas mixtures: Volatile materials are injected manually into the GC combustion system where constituent peaks are separated using the appropriate GC column, combusted to CO2, purified online, and then each peak is analyzed for 13C. Minimum sample size is in the range of 1-10 nanomoles per peak, with precisions of 0.1 to 0.3 ‰.

15N of volatile organics and gas mixtures: Materials are handled similarly to above, but the samples are instead combusted to N2, reduced and purified, and then constituent peaks through the GC are analyzed for 15N. Minimum sample size is in the range of 1-10 nanomoles per peak, and precisions are 0.1 to 0.5 ‰.

34S of solids (organics and inorganics): Samples are loaded into tin boats 100-200 samples in a batch, combusted, and analyzed for bulk elemental and isotopic composition on the elemental analyzer connected to the IsoPrime or Optima. Recommended sample size is 2-10 m moles. If needed, C-N-S isotopes can all be measured on the same sample, but it is much easier to do separate S and C+N determinations. Analytical precision: <0.2 ‰.

35S of sulfate: Samples are collected on ion exchange resins in the field. Approximately 20 liters of sample water is passed thru the resin. The samples are returned to the laboratory for elution, preparation, and counting in a liquid scintillation counter. For best analytical results, sulfate concentrations should be less than 0.002 moles/L. For very low concentrations (0.0001 mole/L and less), a sodium sulfate carrier is provided by the laboratory.


Please direct all comments, corrections, and additions to ckendall@usgs.gov.
This page was last changed on August 2014