Partitioning Evapotranspiration into Evaporation and Transpiration fluxes using Stable Isotopes of Oxygen and Hydrogen

1. Progress Report
Partitioning Evapotranspiration into Evaporation and Transpiration fluxes
using Stable Isotopes of Oxygen and Hydrogen
April 12, 2023
Presented
by
Pankaj Kumar Thakur
(Project Associate-I) GWHD
National Institute of Hydrology,
Roorkee (Uttarakhand)
Under the supervision
of
Dr. Gopal Krishan
(Principal Investigator)
Scientist ‘D’ GWHD
National Institute of Hydrology,
Roorkee (Uttarakhand)

2. Content
Soil Water Extraction:
Azeotropic Distillation
Our Findings and Future Directions…

3. Standard Dean-Stark Apparatus
Setup
Source: Sunshine Scientific
Equipments
Conical Flask
(500 ml capacity)
Soil Sampling
Condenser
>90°C
Heating mantle
Sample collection

4. 𝑯𝟐𝑶 +
Principle
Azeotropic mixture
@ 84.1°C
Completely immiscible at
ambient temperature
B.P. = 100°C
Density = 1
gm/cc
B.P. = 110°C
Density = 0.867
gm/cc
Traces of Toluene can
be separated by
adding wax
Discussion: Though, 𝐶6𝐻5𝐶𝐻3 is completely immiscible with water at
ambient temperature (condenser) therefore, toluene should dip back into the flask
and water should be collected at sampling bottle but heavy toluene traces used to
come with water. Since toluene has lower density than water therefore it floats above
water can be separated using paraffin wax. But, it was found tedious task to do.
It is suggested to adopt freezing technique to separate water from toluene since toluene
has freezing point -95°C. Water can be freeze at 0°C and toluene can be taken out easily.

5. Since, toluene has H-ion therefore it might mix with water. So there is a
need for azeotropic distillation with reagent with no hydrogen or oxygen
ion such as 𝐶𝐶𝑙4
𝑯𝟐𝑶 +
Azeotropic mixture
@ 66.8°C
Completely immiscible at
ambient temperature
B.P. = 100°C
Density = 1
gm/cc
B.P. = 76.8°C
Density = 1.59
gm/cc
Since water has lower
density in comparison
to 𝐶𝐶𝑙4 therefore it
will float at the top

6. 𝑯𝟐𝑶 + Azeotropic mixture
@ 78.2°C
B.P. = 100°C
Density = 1
gm/cc
B.P. = 78.37°C
Density = 0.789
gm/cc
Freezing point = -114.1°C
Traces of ethanol can
be separated by
freezing

7. • Though, Azeotropic Distillation is Simple, inexpensive, fast and widely usable approach
to extract water from soil for isotopic analysis but it is not a precise and effective
approach since getting a water sample at the end is very tedious task.
• Heating unit (Heating mantle, Hot plate, Water bath, Sand bath) must be very precise,
accurate and temperature sensitive to perform the distillation otherwise apparatus does not
perform well.
• Coating of condenser and funnel with a solution of dimethyldichlorosilane compound to
change the surface from hydrophilic to hydrophobic is very important otherwise water
droplets get stuck on walls of the apparatus.
• There are so many other reagents besides toluene which forms azeotrope with water such
as ethanol, benzene, 𝐶𝐶𝑙4 etc. are also be tried.
• Freezing can also be used as an alternative in place of paraffin wax to remove traces of
reagent from the water sample.
Findings and Concluding Remark on
Azeotropic Distillation

8. References
 Jusserand, C., 1980. Extraction de l'eau interstitielle des sediments et des sols. Catena, 7:87 96.
 Stewart, G.L., 1972. Clay-water interaction, the behavior of 3H and 2H in absorbed water, and the isotope effect. J.
Soil Sci. Soc. Am., 36: 421-426.
 Orlowski, N., Pratt, D. L., & McDonnell, J. J. (2016). Intercomparison of soil pore water extraction methods for
stable isotope analysis. Hydrological Processes, 30(19), 3434-3449.
 Allison, G.B. and Barnes, C.J., 1983. Estimation of evaporation from non-vegetated surfaces using natural
deuterium. Nature, 301: 143-145.
 Dewar, W.A. and McDonald, P., 1961. Determination of dry matter in silage by distillation with toluene. J. Sci. Food
Agric., 12: 790-795.
 Revesz, K. and Woods, P.H., 1990. A method to extract soil water for stable isotope analysis. J. Hydrol., 115: 397-
406.
 Millar, C., Pratt, D., Schneider, D.J., and McDonnell, J.J.: A comparison of extraction systems for plant water stable
isotope analysis, Rapid Commun. Mass Spectrom., 32, 1031-1044, https://doi.org/10.1002/rcm.8136, 2018
 Zuecco, G., Amin, A., Frentress, J., Engel, M., Marchina, C., Anfodillo, T., Borga, M., Carraro, V., Scandellari, F.,
Tagliavini, M. and Zanotelli, D., 2022. A comparative study of plant water extraction methods for isotopic analyses:
Scholander-type pressure chamber vs. cryogenic vacuum distillation. Hydrology and Earth System Sciences, 26(13),
pp.3673-3689.

9. Thank you!
Thanks for your gift of time…