Journal of Analytical Sciences, Methods and Instrumentation, 2012, 2, 203-207 Published Online December 2012 ( 203
System for High Throughput Water Extraction from Soil
Material for Stable Isotope Analysis of Water
Timothy S. Goebel, Robert J. Lascano*
Wind, Erosion, and Water Conservation Research Unit, Cropping Systems Research Laboratory USDA-ARS#, Lubbock, USA.
Email: *
Received September 25th, 2012; revised October 26th, 2012; accepted November 2nd, 2012
A major limitation in the use of stable isotop e of water in ecological studies is the time that is required to extract water
from soil and plant samples. Using vacuum distillation the extraction time can be less than one hour per sample. There-
fore, assembling a distillation system that can process multiple samples simultaneously is advantageous and necessary
for ecological or hydrological investigations. Presented here is a vacuum distillation apparatus, having six ports, that
can process up to 30 samples per day. The distillation system coupled with the Los Gatos Research DLT-100 Liquid
Water Isotope Analyzer is capable of analyzing all of th e samples that are generated by vacuum distillatio n. These two
systems allow larger sampling rates making investigations into water movement through an eco logical system possible
at higher temporal and spatial resolution.
Keywords: Isotope; Vacuum Distillation; Soil
1. Introduction
Stable Isotopes of water have been studied in the fields’
of ecology and geology since the 1950’s with increased
attention over the last 30 years [1-6]. Historically the sam-
ples were analyzed using isotope ratio mass spectrometry
(IRMS) that requires the evolution of the sample into a
gas. This process is very sensitive; however, it is also
very time consuming [3]. With the advent of instrument-
tation using off-axis integrated cavity output spectros-
copy (OA-ICOS), such as the Liquid Water Stable Iso-
ope Analyzer (LIWA) DLT-100 from Los Gatos Inc. or
the L2130 from Picarr o Inc., the time required to analyze
samples is no longer the bottleneck in sample pro cessing
for stable isotope analysis [7]. Currently, the major bot-
tleneck for studying stable isotopes has shifted to the
time required for complete extraction of water from soil
samples collected from the field [8]. The larger the num-
ber of samples taken in the field the greater the temporal
and spatial resolution the samples will represent. There
are several different extraction methods currently used to
extract water from plant and soil samples. Examples of
distillation meth ods include azio tropic and cryog enic dis-
tillation techniques [9-12]. The objective was to develop
a multi-port water extraction system capable of produc-
ing unfractionated water samples from multiple soil sam-
ples in a day. Presented here are the details of the design
of a cryogenic vacuum distillation system. This system
follows the port design developed by West et al. [8]
having six ports that allow extraction of several sets of
soil samples in a day. A manifold that allows the iso-
lation of individual ports for troubleshooting and main-
tenance connects these ports.
2. Experimental
2.1. Build Details
2.1.1. Assembly of Extraction Port
The most basic component of the Vacuum Distillation
System is the port as illustrated in Figure 1. The port
connects the ignition tube and the collection test tube to
the vacuum. The ignition tube (Pyrex, Ignition Tube, 25
200 mm, Rimless, Heavy Wall, # 9860-25) contains the
soil or plant material. It is connected to the glass “T” by a
custom made Swagelok adapter (# 8 in Figure 1). The
collection tube (Pyrex, Tube, 12 75 mm, Rimless, #
9820-12) contains the water extracted from the soil sam-
ple. It is connected to the glass “Tee” by another cus-
tom-ma de Sw agelok ad aptor (# 9 in Figure 1). The glass
“Tee” is a custom-made glass piece made by “Q” Glass
*Corresponding a uthor.
#The US Department of Agriculture (USDA) prohibits discrimination
in all its programs and activities on the basis of race, color, national
origin, age, disability, and where applicable, sex, marital status, famil-
ial status, parental status, religion, sexual orientation, genetic informa-
tion, political beliefs, reprisal, or because all or part of an individual’s
income is derived from any publi c assistance program.
Copyright © 2012 SciRes. JASMI
System for High Throughput Water Extraction from Soil Material for Stable Isotope Analysis of Water
II, LLC. It is a 3/8-inch (~10 mm) glass tube connecting
both the sample tube and the collection tube to the vacu-
um manifold. The glass “Tee” is then connected to an-
other Swagelok adaptor (# 3 in Figure 1). The next piece
is a Swagelok Union Tee (# 2 in Figure 1) allowing for
the addition of a thermocoup le gauge tube (# 5 in Figure
1) to the port through the use of another Swagelok adap-
tor (# 6 in Figure 1). The port is then connected to a
Swagelok Plug Valve (# 1 in Figure 1) that can isolate
the port from the manifold.
2.1.2. Assembl y of Mani f ol d
The manifold (Figure 2) was made using seven Swagelok
Plug Valves, one for each port plus one to release vacu-
um. The plug valves were connected using eight 3/8-inch
(~10 mm) copper “Tee”s connected by 4 cm long copper
tubing with the outside “Tee”s fitted with a cap. One of
the copper “Tee”s faces the opposite direction and is
connected to the vacuum (Edwards # 5). All of the cop-
per fittings were sized and assembled prior to soldering.
The completed manifold was then fastened to the frame
to stabilize the system. The assembled port was con-
nected to the manifold using the included swagelok com-
pression ferrule and 3/8-inch (~10 mm) copper tubing
that can be bent to fit multiple ports to the manifold (Fig-
ure 3a).
2.1.3. Construction of Support Base
The base of the system was manufactured from plywood
with the length of the base measuring 3.0 m and the
width measuring 0.6 m (Figure 3b). The platform that
the ports and manifold are fastened to was 0.3 m wide
and 3.0 m long with two braces in th e middle f or sup por t.
Given that the length of the sample tube and the collec-
tion tube are different, wooden 4 4 blocks were cut as
stands for the water beaker and the liquid nitrogen Dewar
(Figure 3b). Adjacent to each port, a heating coil was
fastened to the platform at an appropriate height to main-
tain boiling water in the beaker containing the sample
tube. While cost can vary based on location and time the
total cost for construction of the distillation setup was
less than $10,000 USD, making this a reasonably priced
solution for water extraction from soil samples for iso-
topic analysis.
Figure 1. Diagram of the port assembly with parts list.
Copyright © 2012 SciRes. JASMI
System for High Throughput Water Extraction from Soil Material for Stable Isotope Analysis of Water 205
2.2. Soil Sample Collection and Preparation
Soil samples were collected from a field adjacent to the
USDA-ARS research facility in Lubbock Texas, USA
(33˚3540 N, 101˚54'00 W). The soil texture was a sandy
clay loam and was ground and passed through a 2-mm
sieve before being oven dried at 225˚C for 24 hours.
From the bulk sample, 10 g of soil was weighed and
added to a pre-weighed ignition tube. The ignition tube
was then weighed again. One mL of water was then
added to the soil in the ignition tube and the weight was
taken again. Glass wool was then added to the ignition
tube to prevent soil loss during the ex traction process an d
the ignition tube was weighed again. The ignition tube
was then sealed with a rubber stopper and placed in a
freezer until it is time for extraction.
2.3. Extraction Procedure
The process of extraction begins by removing the sam-
ple-tube from the freezer and placing in LN2 (liquid Ni-
trogen). Next, the collection tube is placed on the port
with a “dummy” sample-tube. The vacuum is applied to
the system and allowed to draw down for 20 minutes to
remove any possible water contamination. During this
process the plug valve on the port was turned off to iso-
late the port from the vacuum to check for leaks. The
port should hold vacuum at <0.013 kPa (100 milliTorr)
or adaptors should be tightened unt i l 0.013 kPa is achi eved
and maintained.
The vacuum is then released and the “dummy” tube is
removed and replaced with sample-tube frozen in LN2.
The LN2 Dewar is placed under the sample-tube to
maintain the temperature at –210˚C preventing any loss
of water from the sample as vacuum is applied to the port.
The vacuum is then drawn down <0.013 kPa and the
system is again checked for leaks. If a leak is present it
must be from the adap tor connected to th e sample tu be as
Figure 2. Diagram of manifold.
the other junctions were tested previously. Once the port
is isolated from the vacuum pump and is holding vacuum
the LN2 Dewar is removed from the sample side of the
port and placed under the collection tube. A 1000 mL
beaker was placed under the sample tube and boiling
water was poured into the beaker up to the top of the
heating mantle and a timer was started.
The amount of time the sample was allowed to distill
was varied between 4 and 90 minutes for each soil sam-
ple. When the distillation ti me was complete the vacuum
was released from the port and the collection tube was
removed from the port, sealed with parafilm®, and placed
in a water bath to thaw. Once the collectio n tube is in the
bath, the sample-tube is removed from the port and al-
lowed to cool before weighing. All water samples that
were collected were then analyzed using a LGR-DLT
100 Liquid Water Isotope Analyzer following the IAEA
procedure for analysis of stable isotopes [13].
3. Results and Discussion
When using vacuum distillation it is imperative that the
resulting water extract be unfractionated. However, the
distillation process follows a Rayleigh distillation curve
where the heaver water (i.e., ) will condense first
and the lighter water (i.e., ) being condensed last.
This process creates a fractionated sample if the distilla-
tion process is stopped before all of the water has been
evaporated from the sample and condens ed in the collec-
tion tube. Calibration of the extraction timing is an es-
sential first step to develop a protocol that can be used in
the extraction system for stable isotope measurements.
As an example of this protocol, results from the calibra-
tion of the different ports are shown in Figure 4. These
results clearly show that the minimum extraction time
required to develop an unfractiona ted water sample from
soil samples is 30 minutes, based on both the isotope
signature as well as the percent water. There was no dif-
ference in the extraction times between the different ports
regardless of the distance from the vacuum source. While
the minimum extraction time was found to be 30 minutes,
in our labor atory we use one h our as our stand ard extrac-
tion time. This allows enough time to start all six ports
and the time necessary to make adjustments to a port
before the hour is up on first po rt.
4. Conclusion
The distillation apparatus described allows for a high
throughput water extraction from soil samples. The sys-
tem has six ports that allow us to extract 30 or more
samples in a 8-hour working day using one hour as the
standard extraction time. This system in conju nction with
the LGR DLT-100 allows for the extraction and analysis
of 30 samples per day making it possible to study water
Copyright © 2012 SciRes. JASMI
System for High Throughput Water Extraction from Soil Material for Stable Isotope Analysis of Water
Figure 3. (a) Diagram of the copper tubing used to connect the manifold to the six ports; (b) Photograph of the assembled
distillation apparatus.
Figure 4. Extraction timing curves for each port. The δ18O is represented by and the water content is represented by .
he dashed line represents the minimum extraction time to obtain an unfractionated water sample. T
Copyright © 2012 SciRes. JASMI
System for High Throughput Water Extraction from Soil Material for Stable Isotope Analysis of Water 207
movement in the soil at a higher spatial and temporal
resolution than has been previously used. Extraction times
may vary based on the soil type, e.g., clay vs. sand, and
as such calibration should be performed for differing soil
types. The system described here can also be used to ex-
tract water form plant material such as leaves and stems;
however, some concern has been noted about the inter-
ference of organics that can co-distill with the water
causing errors in the spectroscopic analysis of these wa-
ter samples [14,15]. More recently, a study has shown
that it is possible to calibrate the instrument for these
types of contaminants and remove the interference from
the measurement [16]. The possibility of using this ex-
traction technique for analysis of samples from both soil
and plant material makes this a simple cost effective sys-
tem for in depth analysis of water movement through an
5. Acknowledgements
This research was supported in part by the Ogallala Aq-
uifer Program, a consortium between USDA-Agricultural
Research Service, Kansas State University, Texas Agri-
Life Research, Texas AgriLife Extension Service, Texas
Tech University, and West Texas A&M University.
We would like to thank Blake Bradley for his help in
developing the drawings of the apparatus. We would also
like to thank Ja mey Deusterhaus and Jill Booker for their
help and insight.
Mention of trade names or commercial products in this
publication is solely for the purpose of providing specific
information and does not imply recommendation or en-
dorsement by the US Department of Agriculture.
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