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ABB Los Gatos ResearchTriple Isotope Water Analyzer (TIWA)

ABB’s Triple Isotope Water Analyzer (TIWA) participates in IAEA WICO Intercomparison

Measurement made easy

Summary

The Isotope Hydrology Laboratory of the International Atomic Energy Agency (IAEA) recently organized a water isotope inter-comparison (WICO) for international laboratory performance assessment of stable isotope determination (δ18O and δ2H) in natural water with various technologies (www.iaea.org/water). ABB Los Gatos Research (LGR) participated in that intercomparison using its Triple Isotope Water Analyzer (TIWA).

Eight unknown water samples were measured by ABB LGR; the assigned isotope values for the samples were determined by IAEA by consensus of four dual-inlet isotope-ratio mass spectrometry international reference laboratories and revealed following participation and reporting of results. The TIWA δ18O and δ2H readings were within 0.06 ‰ and 0.6 ‰ of the assigned values of the standard water samples, respectively, and within the convoluted uncertainties of the measured and assigned values. The optional depleted, enriched, and salinized water δ18O and δ2H TIWA measurements were within 0.05 ‰ and 1.2 ‰ of the assigned values, respectively, and within the uncertainty of the assigned values.

Finally, by using ABB LGR’s proprietary Spectral Contaminant Identifier, the methanol contaminated water sample was identified. The isotope reading was corrected and the TIWA measurements of δ18O and δ2H were within 0.26 ‰ and 0.3 ‰ of the uncontaminated values, respectively, despite the level of contamination (and without any pretreatment). These results indicate that ABB LGR’s TIWA is capable of measuring a wide array of water samples, including contaminated, depleted, enriched, and salinized waters.

(Although not the focus of the present study, for those interested in extremely enriched deuterated waters, please see http://onlinelibrary.wiley.com/doi/10.1002/rcm.v30.3/issuetoc).

—ABB LGR Benchtop Triple Isotope Water Analyzer

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—Experimental Method

The IAEA WICO test comprised 5 core and 3 optional test samples sourced from natural water sources. Water samples were prepared by IAEA as described in the 2016 WICO intercomparison information provided to participants.1 Sample descriptions from the IAEA are provided in Table 1.1

Sample Description

WICO 1 Danube River Water, Austria, filtered

WICO 2 Neusiedler Sea (Lake Water), Austria, filtered

WICO 3 Bow River Water, Canada, filtered

WICO 4 Ground Water Mix, Egypt, Austria, filtered

WICO 5

Vienna Tap water and WICO-6 Mix, research grade methanol was added gravimetrically to produce a 0.05 % methanol/water volumetric ratio of contaminated water sample

WICO 6 Depleted Greenland Ice Sheet fern melt, unfiltered

WICO 7Enriched Vienna groundwater with 99 % D2O and 99.9 % H2

18O mixed to ensure a normal d-excess and isotopically enriched result, unfiltered

WICO 8 Synthetic seawater to 30 g/L (commercial Red Sea salt), mixed with WICO-6 to produce a slightly depleted result with a normal d-excess, unfiltered

Table 1 IAEA WICO sample descriptions

The assigned δ18OVMSOW and δ2HVMSOW values for WICO samples for proficiency testing purposes were determined by a consensus of expert laboratories approach, according to ISO 13528. Assigned δ18OVMSOW and δ2HVMSOW values were established from results reported by four dual-inlet isotope-ratio mass spectrometry international reference laboratories. Further details are available from the Isotope Hydrology Laboratory at IAEA.1

The WICO samples were measured blind (the isotope values of the samples were unknown to anyone outside of the WICO team at the time) at ABB LGR using a Triple Isotope Water Analyzer (TIWA) in liquid water mode. The TIWA simultaneously measured δ2H, δ17O, and δ18O on a single water sample. The water samples in the natural isotopic range (WICO 1 – 5 and WICO 8) were measured against the USGS46, USGS47, and USGS48 standards. WICO 6, the depleted water sample, was measured against USGS46, USGS47, and SLAP2. The enriched water sample, WICO 7, was measured against USGS47, USGS48, and ABB LGR internal working standard ES1.

The assigned values for the standards are shown in Table 2. The assigned values of δ2H and δ18O for the USGS standards are provided by USGS, whereas the δ17O values are taken from previously published values.2

The assigned values of δ2H and δ18O for SLAP2 are provided by IAEA, whereas the δ17O value is taken from previously published work.3 The assigned values for ES1 were measured at ABB / LGR against VSMOW2 and Sercon Medium Enriched standard.

Standard δ2H (‰) δ17O (‰) δ18O (‰)

USGS46 –235.8 –15.85 –29.80

USGS47 –150.2 –10.47 –19.80

USGS48 –2.0 –1.15 –2.224

SLAP2 –427.5 –29.6986 –55.5

ES1 89.9 –4.40 9.36

Table 2 Assigned values for standards used throughout this study

Each measurement involved 10 injections of a sample (or standard) to account for memory effects due to the wide span of isotope values and to allow for improved measurement precision. Samples and standards were run with a 2:1 interleave such that 2 sample measurements were made between each standard measurement except for the saline sample WICO8, which used a 1:1 interleave of samples and standards to improve syringe lifetimes. Using this configuration, 40 – 45 unknown samples could be measured per day. Each WICO sample was repeatedly measured between 30 – 60 times to gauge the TWIA’s accuracy, precision, and repeatability.

The output file from the TWIA was analyzed using ABB LGR’s Post-Analysis Software package which analyzes the results for all three stable isotopes (δ2H, δ17O, and δ18O). The Spectral Contaminant Identifier (SCI)4 has been integrated into the latest version of the Post-Analysis Software to immediately flag contaminated samples (see below). Other improvements include the ability to gauge an internal control sample, an injected volume (linearity) correction, multiple fit methods, and integration with established LIMS systems. For the WICO analysis, many of the new features were utilized including an injected volume correction, cubic spline fitting of calibration standards, and internal control monitoring.

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1 2016 WICO intercomparison information provided by IAEA to participants.http://www-naweb.iaea.org/napc/ih/IHS_programme_wico2016.html2 Berman, Elena SF, et al. “Measurement of δ18O, δ17O, and 17O-excess in water by off-axis integrated cavity output spectroscopy and isotope ratio mass spectrometry.” Analytical chemistry 85.21 (2013): 10392-10398.3 Schoenemann, Spruce W., et al. “Measurement of SLAP2 and GISP δ17O and proposed VSMOW-SLAP normalization for δ17O and 17O excess.” Rapid Communications in Mass Spectrometry 27 (2013): 582-590.4 Leen, J. Brian, et al. “Spectral contaminant identifier for off-axis integrated cavity output spectroscopy measurements of liquid water isotopes.” Review of Scientific Instruments 83.4 (2012): 044305.

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—Results

30 individual δ2H and δ18O measurements of WICO 1 are shown in Figure 1. The averaged measured value is very precise and in excellent agreement with the assigned value to within the error bars that represent the 1-sigma precision per measurement.

The measurements of natural, uncontaminated waters (WICO 1 – 4) are summarized in Table 3. The TWIA and assigned values of δ2H, δ18O, and d-excess agree to within 0.6 ‰, 0.06 ‰, and 0.5 ‰ respectively for all samples. Assigned δ17O for the WICO samples were not provided and thus could not be compared to the measured values.

Figure 1 30 individual measurements of WICO 1

Assigned Values

TIWA Measured Values

Sample δ2H [‰] δ18O [‰] d-excess [‰] δ2H [‰] δ18O [‰] d-excess [‰]

WICO 1 –77.4 ± 0.9 –10.80 ± 0.02 9.0 –77.6 ± 0.1 –10.83 ± 0.01 9.0

WICO 2 –41.7 ± 1.1 –5.11 ± 0.03 –0.8 –42.3 ± 0.1 –5.13 ± 0.02 –1.3

WICO 3 –168.3 ± 1.0 –22.01 ± 0.05 7.8 –168.9 ± 0.0 –22.07 ± 0.02 7.6

WICO 4 0.5 ± 1.1 –0.50 ± 0.05 4.5 –0.1 ± 0.2 –0.55 ± 0.08 4.3

Table 3 Intercomparison between ABB LGR TIWA measured values and assigned IAEA values for natural water samples

The precisions of the measured and assigned values are similar; however, the TIWA measures all three isotopes simultaneously, faster, and with substantially less maintenance than an isotope-ratio mass spectrometer.

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—…Results

The Post-Analysis Software also includes the Spectral Contaminant Identifier (SCI) that has been described in detail previously3. The SCI can be used to flag and discard contaminated samples, or, after characterizing the TIWA response curves, the SCI metrics can be used to correct the measured values for spectral contamination.

Figure 2 Post-Analysis Software results indicating the large narrowband metric detecting spectral interference in WICO 5

This process has been extensively vetted on plant5 and wine6 samples. The Post-Analysis Software clearly flagged the WICO 5 contaminated sample (Figure 2).

More specifically, the large narrowband metric and minimal broadband metric further suggested that the contaminant was methanol.

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5 Schultz, Natalie M., et al. “Identification and correction of spectral contamination in 2H/1H and 18O/16O measured in leaf, stem, and soil water.” Rapid Communications in Mass Spectrometry 25.21 (2011): 3360-3368.6 Gupta, Manish, et al. “Laser-based measurements of 18O/16O stable isotope ratios (δ18O) in wine samples.” International Journal of Wine Research 2013:5 (2013): 47 – 54

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The measured values for WICO 5 were then corrected to account for alcohol contamination using the methods described previously5. Specifically, natural water of known isotopic ratio was intentionally contaminated with methanol to produce contaminated water samples with a relatively small span of the narrowband metric output around the narrowband metric measured for WICO 5. A plot (see for example Figure 3) was created with the difference between the measured and the known delta values on the y axis and the measured narrowband metric on the x axis. This was repeated separately for δ2H and δ18O. A best fit function was fit to the data: in this case a double exponential.

The functions thus created were then used to calculate adjustments to the measured isotope values of WICO 5 based on the measured narrowband metric. WICO 5 was measured multiple times, the function applied to each measurement, and then the corrected measurements

averaged to get a final value. For WICO 5 δ2H, the analyzer originally measured an average of –100.1‰; this was corrected using the above procedure to an average of –114.0 ‰. The assigned value was –114.3 ‰.

The measured and corrected isotope ratios for WICO 5 are shown in Table 4. Despite the level of methanol contamination, the corrected measurements are in good agreement with the assigned values. Similar quality results6 have also been shown for broadband absorbers.

Assigned (‰)

Measured uncorrected (‰)

Measured corrected (‰)

δ2H –114.3 ± 1.1 –100.1 ± 0.3 –114.0 ± 0.2

δ18O –15.68 ± 0.02 –6.36 ± 0.06 –15.42 ± 0.21

d-excess 11.1 –49 9.4

Table 4 Assigned, measured, and corrected values for WICO 5

Figure 3 Creation of a correction function for δ2H based on measurement of water of known isotopic ratio intentionally contaminated with methanol

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—…Results

Note that these results highlight the need to use the SCI to confirm that the samples are not contaminated. If the SCI were not used, the incorrect, raw mea-sured values would have been reported.

Measured results for the highly depleted WICO 6 sample are shown in Table 5. As noted above, a different set of standards were used to span the necessary isotope range. Despite the isotope depletion, the TIWA provided excellent results, indicating that sample-to-sample memory effects were appropriately mitigated.

Similar measurements of the enriched WICO 7 are also shown in Table 5. Since international water reference materials were not available at the time, an internal ABB LGR working standard was used in conjunction with the USGS standards. The measured values were in agreement with the assigned values to within the stated errors. Again, sample to sample memory issues did not make the results erroneous.

Finally, measurements of WICO 8, a sample containing sea salt, are also included in Table 5. The measurements are in good agreement with the assigned values, and there is no evidence to suggest that the salt effects the TIWA. However, it should be noted that when measuring salty samples7, the injection block should be cleaned more frequently and an internal control should be implemented to confirm that the block is sufficiently clean.

Assigned Values

TIWA Measured Values

Sample δ2H [‰] δ18O [‰] d-excess [‰] δ2H [‰] δ18O [‰] d-excess [‰]

WICO 6 –323.7 ± 0.9 –41.41 ± 0.04 7.6 –323.7 ± 0.0 –41.44 ± 0.01 7.9

WICO 7 55.7 ± 1.6 5.61 ± 0.08 10.8 54.6 ± 0.1 5.63 ± 0.03 9.5

WICO 8 17.6 ± 1.2 –3.45 ± 0.10 10.0 –18.8 ± 0.1 –3.50 ± 0.04 9.2

Table 5 Intercomparison between ABB LGR TIWA measured values and assigned IAEA values for depleted, enriched, and salty samples

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7 Berman, Elena SF, et al. “Direct analysis of δ2H and δ18O in natural and enriched human urine using laser-based, off-axis integrated cavity output spectroscopy.” Analytical chemistry 84.22 (2012): 9768-9773.

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—Conclusion

ABB LGR’s TIWA has been shown in an international, blind laboratory test to perform accurately and precisely for measurement of δ2H and δ18O from natural, enriched, depleted, and salinized waters. Furthermore, we have demonstrated that with the SCI, contaminated water samples can also be measured accurately and precisely.

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