Chemistry Reference
In-Depth Information
ronment where numerous sources can have a serious contribution to the
noise signal.
Different methods are described to construct ultramicro electrodes
48-62
such as insulation in glass or epoxy resin, the construction of ultramicro
electrode arrays (an array of individual ultramicro electrodes to increase
the current signal without losing the benefits of ultramicro electrode behav-
iour) by template synthesis, metal depositions in pores of membranes and
by using the connecting wires in microchips. The latter has the advantage
that each ultramicro electrode is individually addressable.
Insulation of microfibres of platinum, gold and graphite in glass is the
best-known method for the construction of ultramicro electrodes. Ultrami-
cro electrodes used in the work described in this topic are also obtained by
insulation in glass according to the following procedure (Fig. 1.11): a wire
of platinum with
r
= 25 mm is deposited in a glass capillary with 5 mm outer
and 0.5 mm inner diameter. One tip of the glass tube is heated, while the
other side of the tube is connected to a vacuum pump. When the glass tube
starts to soften during heating, its internal volume reduces because of the
vacuum, which results in the insulation of a piece of the platinum, gold or
graphite wire. A portion of this sealed tube is analysed under the micro-
scope, and a piece of about 4 mm is cut for further use. Both sides of this
small piece are polished on emery paper in order to obtain a smooth surface
and to allow electrical contact to the insulated microwire. This small piece
is then positioned in a glass tube with an inner diameter of 5 mm and, with
Microwire
Platinum wire
Glass
tube
Capillary
tube
Ag
epoxy
Sealed microwire
1.11
Scheme of the construction of ultramicro electrodes according to
a procedure described in the text.
