Liquid samples are analyzed for δ²H and δ¹⁸O using a Los Gatos Research T-LWIA-45-EP liquid water isotope analyzer.

Method

Between 0.5 and 1.5 mL of filtered sample* are pipetted into a septum-capped vial. Nine separate 1.2 μL injections introduced into the analyzer cavity for direct measurement. The first four injections are ignored to account for potential memory effects, and the last five injections are averaged to produce a raw isotope value.

QA/QC

Raw data are currently normalized using USGS49 and USGS50. Prior to normalization in LIMS, raw data are checked for spectral contamination using Los Gatos’ Post Analysis Software. Final δ²H and δ¹⁸O values are expressed in permil relative to Vienna Standard Mean Ocean Water (VSMOW).

Long-term standard deviations of δ²H and δ¹⁸O measurements, as assessed by repeated analyses of blind standards (USGS45, LGR 3E and 4E) are 0.2 and 0.1 permil, respectively.

Sample Size

Minimum sample amount for analysis: 0.5 mL

Ideal unprepared sample amount: 2 mL

We strongly recommend a 10% duplication of samples for accurate precision determination. 

Further Reading

Coplen TB, Wassenaar LI. 2015. LIMS for Lasers 2015 for achieving long-term accuracy and precision of δ²H, δ¹⁷O, and δ¹⁸O of waters using laser absorption spectrometry. Rapid Communications in Mass Spectrometry 29: 2122-2130.

Wassenaar LI, Coplen TB, Aggarwal PK. 2014. Approaches for achieving long-term accuracy and precision of δ¹⁸O and δ²H for waters analyzed using laser absorption spectrometers. Environmental Science & Technology 48: 1123-1131.

Tian C, Wang L, Novick KA. 2016. Water vapor δ²H, δ¹⁸O and δ¹⁷O measurements using an off-axis integrated cavity output spectrometer – sensitivity to water vapor concentration, delta value and averaging-time. Rapid Communications in Mass Spectrometry 30: 2077-2086.

IAEA. 2009. Laser spectroscopic analysis of liquid water samples for stable hydrogen and oxygen isotopes: performance testing and procedures for installing and operating the LGR DT-100 liquid water stable isotope analyzer. Training Course Series 35. Vienna: 49 pages.

*Samples must be filtered to at least 0.45 microns prior to submission. If this is not possible, we can filter samples for you. Please see the pricing tab for current rates. Other liquids (biological fluids, alcoholic and non-alcoholic beverages, plant waters, wastewaters) can be analyzed but may require specialized preparation. Contact KSIGL staff to discuss sample preparation in your lab or ours.

Analysis of δ¹⁷O in water samples is carried out in the same fashion as above, but requires – at a minimum – duplicate measurements of each sample with 18 (4 ignored + 14 measured) injections each.

QA/QC

Raw data are currently normalized using LGR 1E and LGR 5E. Prior to normalization in LIMS, raw data are checked for spectral contamination using Los Gatos’ Post Analysis Software. Final δ¹⁷O values are expressed in permil relative to Vienna Standard Mean Ocean Water (VSMOW).

Long-term standard deviation of δ¹⁷O measurements are still under evaluation.

Sample Size

Minimum sample amount for analysis: 0.5 mL

Ideal unprepared sample amount: 5 mL

We strongly recommend a 10% duplication of samples for accurate precision determination. 

Further Reading

Coplen TB, Wassenaar LI. 2015. LIMS for Lasers 2015 for achieving long-term accuracy and precision of δ²H, δ¹⁷O, and δ¹⁸O of waters using laser absorption spectrometry. Rapid Communications in Mass Spectrometry 29: 2122-2130.

Wassenaar LI, Coplen TB, Aggarwal PK. 2014. Approaches for achieving long-term accuracy and precision of δ¹⁸O and δ²H for waters analyzed using laser absorption spectrometers. Environmental Science & Technology 48: 1123-1131.

If desired, the δ¹⁸O of water can also be determined using a GasBench II interfaced with a Thermo Finnigan DELTA^plus XP IRMS.

Method

1 mL of water sample is injected into a 12 mL Labco Exetainer, flushed with ultra high purity (99.999% pure) helium and equilibrated at 25 °C with research grade (99.998% pure) CO₂. Oxygen exchange between the CO₂ and H₂O produces headspace CO₂ with a δ¹⁸O representative of the water sample. After equilibration, seven individual injections of headspace CO₂ are then transferred on a stream of UHP helium to the IRMS for measurement.

QA/QC

Raw data are currently normalized using USGS49 and USGS50. During normalization, the first two injections are ignored while the last 5 injections are averaged to produce a raw isotope value. Long-term standard deviation of δ¹⁸O measurements, as assessed by repeated analyses of blind standards (USGS45) is 0.2 permil or better.

Sample Size

Minimum sample amount for analysis: 1 mL

Ideal unprepared sample amount: 2 mL

We strongly recommend a 10% duplication of samples for accurate precision determination. 

Further Reading

Epstein S, Mayeda T. 1953. Variation in O¹⁸ content of waters from natural sources. Geochimica et Cosmochimica Acta 4: 213-224.

Thermo GasBench II Operating Manual.

The δ¹³C of headspace CO₂ evolved from carbonate-bearing water samples*^† is measured using a Thermo GasBench II interfaced with a Thermo Finnigan DELTA^plus XP IRMS.

Proper sample collection and storage is critical for accurate δ¹³C_DIC measurements. See the liquid sample submission page for more details.

Method

100 uL of 85% H₃PO₄ is added to an acid-washed 12 mL Labco Exetainer and the Exetainer is capped and flushed with ultra high purity (99.999% pure) helium^‡. One milliliter of aqueous sample is then injected via gas tight syringe and reacted in a temperature-controlled heating block at exactly 25 °C for at least 24 hours to produce CO₂.

After reacting, the Exetainers are agitated using a vortex mixer to ensure that evolved CO₂ moves into the headspace, then centrifuged at low RPM to remove any condensation from the bottom of the septa. Once the reaction period is complete, seven individual injections of headspace CO₂ are transferred by autosampler on a stream of UHP helium to the IRMS for measurement.

QA/QC

Raw data are currently normalized using two sodium bicarbonate working standards (SB1, SB2) prepared as solutions prior to each analytical session. A third aqueous sodium bicarbonate solution (SB3), prepared in the same way, is used as a blind standard. All three sodium bicarbonates have been tied to the VPDB scale through repeated measurement (as powder) against NBS-18 and NBS-19 both at KSIGL and other facilities. Long-term standard deviation of δ¹³C measurements, as assessed by repeated analyses of blind standards (NIST SRM 915b or SB3) is 0.2 permil or better.

Sample size: waters containing between 0.002 to 0.05 mg of dissolved inorganic carbon can be analyzed. Contact KSIGL staff prior to sample submission if concentrations outside this range are expected. We strongly recommend a 10% duplication of samples for accurate precision determination. 

Further Reading

Spӧtl C. 2005. A robust and fast method of sampling and analysis of δ¹³C of dissolved inorganic carbon in ground waters. Isotopes in Environmental and Health Studies 41(3): 217-221.

Torres ME, Mix AC, Rugh WD. 2005. Precise δ¹³C analysis of dissolved inorganic carbon in natural waters using automated headspace sampling and continuous-flow mass spectrometry. Limnology and Oceanography: Methods 3: 349-360.

Zhou Y, Guo H, Lu H, Mao R, Zheng H, Wang J. 2015. Analytical methods and application of stable isotopes in dissolved organic carbon and inorganic carbon in groundwater. Rapid Communications in Mass Spectrometry 29: 1827-1835.

*Water samples for δ¹³C_DIC must be filtered to at least 0.45 microns prior to submission to remove carbon-bearing particulates. Alternatively, we can perform filtration immediately after the samples arrive. Please see the pricing tab for current rates.

^†We cannot accept samples preserved with mercuric chloride (HgCl₂).

^‡For local customers, we can provide helium-flushed, H₃PO₄-filled vials free-of charge for direct sample injection in the field.

δ¹³C_DOC in water samples is also measured using a Thermo GasBench II interfaced with a Thermo Finnigan DELTA^plus XP IRMS.

Proper sample collection and storage is critical for accurate δ¹³C_DOC measurements. See the liquid sample submission page for more details.

Method

In addition to normal cleaning, Labco Exetainers used for δ¹³C_DOC measurements are baked at 500 °C for at least five hours to remove trace organic contamination. The baked Exetainer is capped and flushed with ultra high purity (99.999% pure) helium to remove atmospheric CO₂ and 1 to 5 mL of water sample is injected from a headspace-free, septum-sealed vial and a further 0.1 mL of 100% H₃PO₄ is injected into the Exetainer.

CO₂ produced from the reaction of inorganic carbon with H₃PO₄ is then flushed from the vial, again using ultra high purity (99.999% pure) helium. An oxidant (Na₂S₂O₈ + H2O) is then injected, and the Exetainers are placed into a heating block at 99.6 °C for one hour.

After cooling, the Exetainers are agitated using a vortex mixer to ensure that evolved CO₂ moves into the headspace, then centrifuged at low RPM to remove water droplets from the bottom of the septa. The Exetainers are loaded into the autosampler tray and seven individual injections of headspace CO₂ are transferred by autosampler on a stream of UHP helium to the IRMS for measurement.

δ¹³C_DIC and δ¹³C_DOC analysis on the same sample is possible but are charged as separate analyses.

QA/QC

Raw data are currently normalized using two in-house standards (UK-ALA, UK-GLY) that have been normalized to the VPDB scale via EA-IRMS using USGS40 and USGS41. During normalization, the first injection is ignored while the last 6 injections are averaged to produce a raw carbon isotope value. Long-term standard deviation of δ¹³C measurements is still under assessment, but is generally better than 0.4 permil.

Sample size: waters containing between 0.003 to 0.05 mg of dissolved organic carbon can be analyzed. Contact KSIGL staff prior to sample submission if concentrations outside this range are expected. We strongly recommend a 10% duplication of samples for accurate precision determination. 

Further Reading

Gandhi H, Wiegner TN, Ostrom PH, Kaplan LA, Ostrom NE. 2004. Isotopic (¹³C) analysis of dissolved organic carbon in stream water using an elemental analyzer coupled to a stable isotope ratio mass spectrometer. Rapid Communications in Mass Spectrometry 18: 903-906.

Lang SQ, Bernasconi SM, Früh-Green GL. 2012. Stable isotope analysis of organic carbon in small (μg C) samples and dissolved organic matter using a GasBench preparation device. Rapid Communications in Mass Spectrometry 26: 9-16.

Zhou Y, Guo H, Lu H, Mao R, Zheng H, Wang J. 2015. Analytical methods and application of stable isotopes in dissolved organic carbon and inorganic carbon in groundwater. Rapid Communications in Mass Spectrometry 29: 1827-1835.