Owner's manual

2.3 Multi-Mode Electrode (MME)
797 VA Computrace / Hardware-Manual 8.797.8001EN
29
2.3.6 Storing the MME
On completion of the measurements, the MME is stored in the 797 VA Computrace
Stand so that the tip of the glass capillary
87 is immersed in pure water (or in the sol-
vent used). This prevents blockage of the capillary by crystallized salts.
An electrode treated in this manner can be taken out of the 797 VA Computrace
Stand after a few hours and stored in air for a lengthy period without suffering any
damage. Always store the MME so that the glass capillary is horizontal (see
Fig. 11-3).
2.3.7 Replenishing the mercury (without changing capillary)
The Multi-Mode Electrode 21 can also be refilled with mercury without having to re-
move the glass capillary
87.
1 Dismantle Multi-Mode Electrode
• Unscrew FEP tubing 34 and 42 from the MME. Disconnect electrode cable
20 from the MME.
• Take Multi-Mode Electrode
21 out of the measuring head 24 and tap the
MME gently to knock off any mercury drops on the glass capillary into the
measuring vessel.
• Place Multi-Mode Electrode horizontally in the electrode holder
92 (see Fig.
11-3). The slotted screw 79 is now at the top.
2 Replenish mercury
• Unscrew slotted screw 79 using a suitable coin. If the slotted screw can not
be loosened by hand, screw on locking ring 73 and pull out of the MME.
• Draw up mercury using the syringe
89 with attached needle 90 and expel
into the Hg reservoir
81.
The Hg reservoir must never be filled more than
2
/
3
full with mercury.
• Reinsert slotted screw into screw thread
78 and screw flush to surface
using a suitable coin (this action may expel a few drops of mercury from
glass capillary).
Do not turn so tightly that the cemented-in steel threaded ring
78 be-
comes loose and hence jeopardizes the tightness and safety of the
MME!
2.3.8 Changing capillary
The capillary has a limited life time due to mechanical wearout of and chemical con-
tamination of the capillary tip. This results in irreproducible drop fall in DME mode,
fall-off of the drop in stripping voltammetry using HMDE or increased noise or high
background currents. If the MME is stored for a longer period of time, it is possible
that the capillary is blocked by mercury salts. In such cases, exchange the capillary.
We also recommend exchanging the sealing needle regularly. After a longer period of
use the surface can be covered with mercury oxides and/or glass particles from the
capillary. Both produce high noise during the measurement. Damaged sealing needles