sbornik_s_2011.pdf

XI. Workshop of Physical Chemists and Electrochemists´11 Brno
4. WET CHEMISTRY LAB
The wet chemistry lab (WCL) sensor assembly and leaching solution were designed
and built by Thermo Fisher Scientific. The WCL actuator assembly was designed and built
by Starsys Research in Boulder, Colorado. Tufts University developed the reagent pellets,
barium ISE, ASV electrodes, and performed the preflight characterization of the sensor
array [9-13].
The robotic arm scooped up some soil, put it in one of four wet chemistry lab cells,
where water was added, and while stirring, an array of electrochemical sensors measured
a dozen dissolved ions such as sodium, magnesium, calcium, and sulfate that have leached
out from the soil into the water. This provided information on the biological compatibility
of the soil, both for possible indigenous microbes and for possible future Earth visitors
[14]. Every wet chemistry cell has 26 chemical sensors and a temperature sensor. The
polymer Ion Selective Electrodes were able to determine the concentration of ions by
measuring the change of electric potential within the sensor, which is separated from the
wet chemistry cell by an ion selective membrane. The two gas sensing electrodes for
oxygen and carbon dioxide work on the same principle and are separated from the wet
chemistry cell by a gas permeable membrane. A gold micro-electrode array is used for the
Cyclic voltammetry and Anodic Stripping Voltammetry. Cyclic voltammetry is a method
to study ions by applying a waveform of varying potential and measuring the currentvoltage
curve. Anodic Stripping Voltammetry first deposits the metals onto the gold
electrode with an applied potential. After the potential is reversed, the current is
measured while the metals are stripped off the electrode. The first measurement indicated
that the surface layer contained water soluble salts and had a pH between 8 and 9.
Additional tests on soil composition revealed the presence of perchlorate [14].
Later publication of results in the journals Science and JGR reported that chloride, bicarbonate,
magnesium, sodium potassium, calcium, and possibly sulfate were detected in the samples. The pH
was narrowed down to 7.7 + or – 0.5 [9-11]. Further data analysis has indicated that the soil contains
soluble sulfate at a minimum of 1.1% wt % SO3 and provided a refined formulation of the soil [9].
5. ACKNOWLEDGEMENT
The work was by NanoBioTECell GA ČR P102/11/1068.
6. REFERENCES
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