- If I select direct submission of my water samples
instead of NWQL (National Water Quality Laboratory) submission, can
the RSIL add the isotope results to my District computer?
The RSIL does not have access to District computers; therefore,
the RSIL is unable to add isotope ratio results to District computers.
These results can only be emailed to sample submitters.
- Tips on how to collect
a sample.
- How can I pay in advance for samples to be
collected and submitted next fiscal year?
Sample submitters can request isotopic analyses of samples that have
been planned for collection in a multi-year program but have not yet
been collected. The analytical services must satisfy the “bona
fide need” rule. This rule states: “A fiscal year appropriation
may be obligated only to meet a legitimate, or bona fide, need arising
in the fiscal year for which the appropriation was made.” In making
this request, a sample submitter is certifying that a bona fide analytical
services need exists. Download
form for Advanced Request of Analytical Services
- What is LIMS for Light Stable Isotopes?
LIMS for Light Stable Isotopes is a Laboratory Information Management
System (LIMS) based on Microsoft Access for managing samples, analyses,
and other data in a stable isotope (and tritium, carbon-14, and chlorofluorocarbon)
laboratory. For
more information and to download LIMS
- What is the turn-around time for samples submitted
to RSIL?
Processing time on samples submitted for determination of stable hydrogen
and oxygen isotopic composition is is usually about 3 to 5 weeks. During
peak summer season it is 2 to 3 months. Priority service is also available.
If you need to request sample processing status, please refer to our
laboratory ID, such as W-53218 or G-9857.
- How long is the shelf life of a sample?
Samples collected in glass bottles for determination of stable hydrogen
and oxygen isotopic composition with conical insert Polyseal caps have
been stored for up to 10 years before analysis was performed.
- Does algae growing in a sample affect the stable
hydrogen or oxygen isotope ratio analysis?
Tests indicate that the presence of algae in a water sample does not
affect the stable hydrogen or oxygen isotope ratio results.
- How are hydrogen isotope ratios measured on
water samples?
Since May 1, 1990, hydrogen-isotope-ratio analyses have been performed
using a hydrogen equilibration technique (at 30°C) (Coplen et al,
1991), rather than the zinc technique used prior to that date (Kendall
and Coplen, 1985). The hydrogen equilibration technique measures deuterium
activity, whereas the zinc technique measures deuterium concentration.
For the majority of WRD samples, the difference in reported isotopic
compositions between the two techniques is not significant. However,
in brines, the difference may be significant (Sofer and Gat, 1972, 1975).
Reported delta hydrogen-2 values of activity are more positive than
delta hydrogen-2 values of concentration, and this difference is proportional
to molalities of the major dissolved solids. Some examples of the differences
between activity ratios and concentration ratios for delta hydrogen-2
and delta oxygen-18 in 1 molal salt solutions are as follows (Horita
et al, 1993). The data for individual salts may be multiplied by molality
to obtain adjustments to delta values based on concentration.
| Solution |
Delta H-2 (activity)
- Delta H-2 (conc.) |
| (1 molal) |
(30°C) |
| |
| NaCl |
+2.07 per mill |
| KCl |
+2.42 per mill |
| CaCl2 |
+5.31 per mill |
| MgSO4 |
+1.12 per mill |
- How are oxygen isotope ratios of water samples
measured?
Water samples are measured for delta oxygen-18 using the carbon dioxide
equilibration technique (25°C) of Epstein and Mayeda (1953). Therefore,
both oxygen and hydrogen isotopic ratio measurements are reported as
activities.
- How are hydrogen and oxygen isotope ratios
of water samples reported?
Oxygen and hydrogen isotopic results are reported in per mill relative
to VSMOW (Vienna Standard Mean Ocean Water) and normalized (Gonfiantini,
1984; Hut, 1987; Coplen, 1988 and 1994) on scales such that the oxygen
and hydrogen isotopic values of SLAP (Standard Light Antarctic Precipitation)
are -55.5 per mill and -428 per mill, respectively. Oxygen isotopic
results of a sample Z can be expressed relative to VPDB (Vienna Peedee
belemnite) using the equation:
Delta O-18 of Z relative to VPDB =
(0.97001 times delta O-18 of Z relative to VSMOW) - 29.99
- What are the uncertainty of hydrogen and oxygen
isotope ratios reported by the laboratory?
The 2-sigma uncertainty of oxygen and hydrogen isotopic results is 0.2
per mill and 2 per mill, respectively, unless otherwise indicated. This
means that if a sample is resubmitted for analysis at a later date,
there is a 95% probability that the oxygen and hydrogen isotopic result
reported will be within 0.2 per mill and 2 per mill, respectively, of
that originally reported.
Back to Top
|
