Hanging Mercury Drop Electrode HMDE
Wiktor Kemula (1902-1985) was a famous Polish chemist, electrochemist, and
polarographist. He greatly contributed to the development of electroanalytical
chemistry, particularly polarography. He developed a hanging mercury drop
electrode (HMDE).
The hanging mercury drop electrode HMDE WK 2 (named after Prof. Wiktor Kemula)
is a spherical stationary mercury mini electrode with surface area of the order
of a square millimeter [1]. A mercury drop is suspended at the end of a glass
capillary and its size is conveniently adjusted with a micrometer screw. The
electrode HMDE WK 2 can be used as a working electrode in various
electroanalytical techniques for studying mechanisms and kinetics of
electrochemical reactions as well as for determination of analytes in an
electrolyte solution.
Construction
The electrode HMDE WK 2 features a very reliable mercury sealing system provided
by two bi-conical gaskets. The combination of this system with a micrometer
screw (Part 12 in Fig. 1), used for mercury proportioning, results in
exceptional reproducibility of a mercury drop surface area. Construction and
design of the electrode HMDE WK 2 are greatly improved over the former electrode
HMDE WK 1 [2]. That is, the electrode weight and dimensions are smaller while
the number of mercury drops (available from a single electrode filling with
mercury) is larger. This is because the plunger (Part 11 in Fig. 1) is longer
and its diameter is larger. Therefore, a working mercury volume is about six
times larger; the mercury reservoir being only slightly longer. Importantly, the
HMDE WK 2 can be mounted in two different configurations of terminal assemblies
(Figs. 2-4). One of them involves a 10/18 or 14/20 PTFE conical sleeve attached
directly to the translucent intermediate joint that allows one to house the
electrode HMDE WK 2 in a typical commercial electrochemical cell. The other
configuration involves a duralumin nut. A thermometer type PTFE adjustable
adapter for a standard tapered glass joint 10/18 or 14/20 (Parts 2, 21 and 22 in
Figs. 3 and 4B) is then used for housing the electrode in a cell. The main body
of the electrode HMDE WK 2 is made of electrochemically colored duralumin. Both
the mercury reservoir and the precision-bore capillary (Part 4 in Figs. 1-4) are
made of borosilicate glass.
Features
Total length 240 mm
Outer diameter 14 mm
Weight 52 g
Plunger diameter 1.6 mm
Working length of plunger 45 mm
Pitch of thread 0.35 mm
Glass capillary inner diameter 0.127 mm or 0.178 mm
Glass tubing and capillary length 100 mm (or customized)
Volume of working mercury 96.5 mm3
Reproducibility of the electrode surface area a 0.60 %
a Determined as relative standard deviation of a peak current of the linear
potential scan voltammetry curves for the Cd2+/Cd(Hg)0 electroreduction in 1 mM
Cd(NO3)2, 0.5 M KCl for an electrode area of ca. 2 mm2 (Fig. 7).
Caution. Mercury is a poison. If you swallow it accidentally, then contact your
physician immediately.
References
1. Głód, B. K., Kemula, W., Chem. Anal. (Warsaw), 1985, 30, 665.
2. Kemula, W., Zawadowska, J., Fresenius Z. Anal. Chem., 1980, 300, 39.
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