Metrohm 757 VA Computrace - Manual (Page 38)

3 Installation
757 VA Computrace – Hardware
34
3.4 Rotating disk electrode (RDE)
The rotating disk electrode (RDE) is available as an option and can be used in
place of the MME in the 757 VA Computrace Stand with different electrode tips as a
working electrode. The following accessories have to be ordered (see also section
6.2):
• 6.1246.000 Drive shaft for rotating electrode
• 6.1204.XXX Electrode tip for rotating electrode
6.1204.100 Ultra Trace Graphite
6.1204.110 GC (Glassy Carbon)
6.1204.120 Pt
6.1204.130 Ag
6.1204.140 Au for Hg determination
6.1204.150 Au for As determination
• 6.2709.040 Stopper for closing the MME opening
• 6.2802.000 Polishing kit for 6.1204.XXX Electrode tips
(Pt, Ag, Au, GC)
• 6.2827.000 Trimming tool for 6.1204.100 Electrode tip
(Graphite)
It is recommended to use RDE tips (except Pt) only together with a
glassy carbon auxiliary electrode!
3.4.1 Construction and startup of the RDE
The rotating disk electrode RDE comprises the two parts drive shaft 100
(6.1246.000) and electrode tip 99 (6.1204.XXX), which must be screwed together.
The procedure for installing the RDE in the measuring head arm of the 757 VA
Computrace Stand is described in detail in section 3.2.4. The fully equipped meas-
uring head arm with the RDE is illustrated in Fig. 12.
3.4.2 Regenerating the RDE
The RDE is a solid electrode with a stationary surface. This becomes contaminated
with the products of the electrode redox processes with increasing use. The surface
of the 6.1204.XXX electrode tips (Pt, Ag, Au, GC) must therefore be regenerated
from time to time by mechanical cleaning with extremely fine aluminum oxide pow-
der. Proceed as follows:
• Affix polishing cloth (part of 6.2802.000 Polishing kit) to a flat surface (e.g. to the
bottom of a Petri dish) then add a little Al
2
O
3
powder (part of 6.2802.000 Polish-
ing kit) and dist. H
2
O to form a thick paste.
• Polish electrode tip by hand in the paste for ca. 10 s with small, circular move-
ments.
• Rinse electrode tip with dist. H
2
O, immerse in diluted HCl for ca. 10 s, rinse
again with dist. H
2
O and then dry with a cloth or filter paper.
Regeneration of the 6.1204.100 Ultra Trace Graphite Electrode Tip depends on its
use (mercury film or adsorptive stripping voltammetry). The procedure is described
in detail in the Application Bulletins available for the determinations with this elec-
trode.