3. Results and discussion
3.1. Apparatus and procedures
A significant reduction in sample volume while retaining the
standard three electrode configuration should overcome severe
geometric constrains. Three electrodes plus the stirrer and the
purging gas tube must be soaked into the sample volume: they all
have a roughly cylindrical shape with diameters ranging from
1 mm (purging gas tube and counter electrode) to 2–3 mm (working
and reference electrodes plus stirrer). Moreover, the mercury
drop electrode needs a minimum sample volume to be operated:
the Hg drop should be well submersed and the capillary free to
swing when the drop is removed by the knocker.
Accordingly, the minimum sample volume was rationally
determined as the minimum sample surface and height. The first
one was determined by positioning the electrodes, the stirrer and
the purging tube at the same height and measuring the minimum
surface necessary to accommodate all of them. The minimum
sample height was set to the lowest figure required to work the
mercury drop electrode properly. As a result, the minimum
required volume was precisely defined in terms of diameter
(20 mm) and height (minimum 1.6 mm).
Several prototypes with different designs were manufactured
from different materials according to these constrains: the geometry
combining the simplest design and best usability was
chosen. Our new low volume cell is a cylindrical quartz vessel
(20 mm internal diameter, 6 mm height, 2 mm wall thickness) and
it is designed as an insert to be placed inside the standard glass
cell (see Fig. 1). Operationally, the sample holder was blown and
subsequently lathed from quartz: a small handle was added to the
cell rim to easily manipulate it. Quartz was chosen to ensure
minimum memory effects and contamination.
The standard stirrer, although fitting into the small sample
volume, did not provide an efficient stirring because of its slash cut
end and its overall dimensions unnecessary for the small volume.
Accordingly, a new, smaller agitating rod was lathed from polytetrafluoroethylene
with a length of 55 mm, a diameter of 8 mm
and a smaller, 1 mm diameter tip: a threaded inner hole in the
upper part enabled the fastening to the rotor in the voltammetric
stand. Furthermore, a polytetrafluoroethylene stand was lathed
and placed at the bottom of the standard cell to keep the small
3. Results and discussion
3.1. Apparatus and procedures
A significant reduction in sample volume while retaining the
standard three electrode configuration should overcome severe
geometric constrains. Three electrodes plus the stirrer and the
purging gas tube must be soaked into the sample volume: they all
have a roughly cylindrical shape with diameters ranging from
1 mm (purging gas tube and counter electrode) to 2–3 mm (working
and reference electrodes plus stirrer). Moreover, the mercury
drop electrode needs a minimum sample volume to be operated:
the Hg drop should be well submersed and the capillary free to
swing when the drop is removed by the knocker.
Accordingly, the minimum sample volume was rationally
determined as the minimum sample surface and height. The first
one was determined by positioning the electrodes, the stirrer and
the purging tube at the same height and measuring the minimum
surface necessary to accommodate all of them. The minimum
sample height was set to the lowest figure required to work the
mercury drop electrode properly. As a result, the minimum
required volume was precisely defined in terms of diameter
(20 mm) and height (minimum 1.6 mm).
Several prototypes with different designs were manufactured
from different materials according to these constrains: the geometry
combining the simplest design and best usability was
chosen. Our new low volume cell is a cylindrical quartz vessel
(20 mm internal diameter, 6 mm height, 2 mm wall thickness) and
it is designed as an insert to be placed inside the standard glass
cell (see Fig. 1). Operationally, the sample holder was blown and
subsequently lathed from quartz: a small handle was added to the
cell rim to easily manipulate it. Quartz was chosen to ensure
minimum memory effects and contamination.
The standard stirrer, although fitting into the small sample
volume, did not provide an efficient stirring because of its slash cut
end and its overall dimensions unnecessary for the small volume.
Accordingly, a new, smaller agitating rod was lathed from polytetrafluoroethylene
with a length of 55 mm, a diameter of 8 mm
and a smaller, 1 mm diameter tip: a threaded inner hole in the
upper part enabled the fastening to the rotor in the voltammetric
stand. Furthermore, a polytetrafluoroethylene stand was lathed
and placed at the bottom of the standard cell to keep the small
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