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Menlo
Park Stable Isotope and Tritium Labs
BEMIS. Bryan Bemis (650-329-5603, bebemis@usgs.gov). Bryan is an isotope geochemist post-doc. His main interests are applying isotopic ratio techniques to solving environmental problems, including using compound specific isotopic ratio techniques for tracing sources of nutrients to the base of aquatic food webs, food chain reconstructions, mercury bioaccumulation, characterizing sources of DOC to wetlands, and correlating THM formation potential with DOC type.
CHANG. Cecily Chang (650-329-4471, ccchang@usgs.gov): Cecily divides her time between methods development work, and working with WEBB, NAWQA, and other nitrate-related projects. Cecily developed an improved method for collecting and analyzing nitrate for 18O from very dilute, DOC rich waters that was used in many watershed nitrate studies. She is currently focusing on nitrate sources and cycling in big river systems.
DOCTOR. Dan Doctor (650-329-4544), dhdoctor@usgs.gov): Dan is a new NRC post-doc who is working on sources and cycling of carbon (DIC and DOC) at one of the WEBB program sites (Sleepers River VT) using our new automated TIC/TOC analyzer connected to an IsoPrime mass spectrometer.
KENDALL. Carol Kendall (650-329-4576, ckendall@usgs.gov): Chief of the Isotope Tracers Project. Carol's main field of interest is watershed biogeohydrochemistry. Other interests include: the impact of isotopic fractionations and heterogeneity in shallow hydrologic systems on determination of water and solute sources; nitrate sources and cycling; the use of biota isotopes as indicators of nutrient sources, landuses, and redox reactions; and the development of new analytical methods and practical applications for CHNOS stable isotopes. She also coordinates the bi-annual Isotope Hydrology course taught at the National Training Center in Denver.
MICHEL. Bob Michel (650-329-4547, rlmichel@usgs.gov): Chief of the Tritium Lab. Bob's main fields of interest are alpine and arid zone hydrology. He is actively working on improving methods for collecting sulfate on anion exchange resins, extracting the sulfate, and analyzing it for 35S. This method has been applied to age-dating very young waters in a number of locations and appears very promising. This information combined with 34S data will improve our knowledge of sulfur cycling in shallow systems.
RADYK. John Radyk (650-329-4469, jradyk@usgs.gov): John's main duties are to help with the processing of tritium samples, assist with 35S procedures, distill waters from soils and plant materials, log in samples, and keep track of the flux of tritium samples through the project. John's main interest is the use of isotopes in understanding arid zone hydrology.
SILVA. Steve Silva (650-329-4538, srsilva@usgs.gov): Steve divides his time between methods development research, and several research projects related to nutrient sources. Steve developed a new method for concentrating nitrate on anion exchange resins in the field, and analyzing this for 15N and 18O, which was the central focus of our WEBB and NAWQA collaborations for ~ 7 years. Most of his current methods development research has been on devising new ways to expand project analytical capabilities. He is currently focused on tracing nitrate and POM sources in big river systems using a multi-isotope approach.
WANKEL. Scott Wankel (650-329-4303, sdwankel@usgs.gov): Scott divides his time between managing our laboratory database and helping with method development and ongoing ecological projects, with his thesis work (at Stanford, in collaboration with Adina Paytan). He is especially interested in foodweb ecology at the bottom of the foodweb. His dissertation focuses on nutrient sources and cycling in Monterey Bay
WHITE. Doug White (650-329-4509, ldwhite@usgs.gov): Doug's main duty has been to keep 4 mass spectrometers, 4 tritium counters, 2 vacuum lines, and all sorts of equipment working, and fixed promptly when they fail. Doug is responsible for data quality assurance and data reduction for waters and carbonates, and handles much of the responsibility for safety issues, monitoring equipment performance, supervising junior team members in the labs, and helping NRP colleagues with sampling problems. Doug also helps in the automation of the laboratory so we can do more and different types of analyses with less manpower, loads the dual inlet mass spectrometers, and helps with various preparations.
There is more information about the "Isotope Tracers" project, including project goals and recent publications, on the NRP homepage.
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.
Database requirements: No waters are analyzed for 18O, 2H, or 3H without submission of specific sample collection information, similar to the requirements for submission to the NWQL (National Water Quality Lab) in WRD. All 18O/2H data are entered in NAWID (North American Water Isotope Database) for eventual release to the public. Other types of samples have different submission information requirements; eventually, submittal requirements will resemble those for waters (but with more required information about water chemistry).