Metrohm 746 VA Trace Analyzer - Manual (Page 49)

3 Installation
746 VA Trace Analyzer / 747 VA Stand
3-22
10 Pressurize the MME
• Switch on 746 VA Trace Analyzer with mains switch 11 11 (746 VA Trace
Analyzer and 747 VA Stand must first be installed properly as described
in section 3.2 and section 3.3).
• Select dialog page "STAND" and then switch on the inert gas supply to
the 747 VA Stand by pressing the softkey . This pressurizes
the multi-mode electrode 38 38 and the mercury begins to flow slowly out of
the capillary.
• Gently tap the MME with your finger (to remove any air bubbles) and
allow mercury to flow out of the capillary into the empty measuring vessel
for approx. 2 min.
• Fill measuring vessel 28 28 with 10 mL ultrapure water and add 1 drop KCl
solution (in pure water, mercury drops from the capillary only with diffi-
culty).
• Allow mercury to flow out of the capillary for ca. 2 min while checking the
drop formation: The drop time should be ca. 3 s.
11 Adjusting the sealing needle 97 97
• Turn slotted screw 96 96 using a suitable coin slowly in a clockwise direction
until the mercury flow stops.
• Open slotted screw 96 96 slightly in an anticlockwise direction until the
mercury flow restarts.
• Gently tap the MME with your finger and turn the slotted screw 96 96 very
slowly clockwise until the mercury flow just stops. (The tapping action is
used to knock off the mercury drop so that it is easier to see whether
mercury continues to flow.)
• Finally, turn slotted screw 96 96 a quarter of a turn clockwise.
12 Checking the MME for leaks
• Select dialog page "STAND" and then switch on the dropping mercury
electrode by pressing the softkey . The mercury drops freely out of
the capillary for ca. 1 min.
• Press softkey . A single mercury drop is formed. Knock this off by
gently tapping the MME 38 38 with your finger and check that the mercury
flow has really stopped. Repeat this operation several times.
• If mercury continues to flow, turn slotted screw 96 96 still further in a clock-
wise direction and repeat check.
3.4.6 Storing the MME
On completion of the measurements, the MME is stored in the 747 VA Stand so
that the tip of the glass capillary 109 109 is immersed in pure water (or in the solvent
used). This prevents blockage of the capillary by crystallized salts.
An electrode treated in this manner can be taken out of the 747 VA Stand after a
few hours and stored in air for a lengthy period without suffering any damage. Al-
ways store the MME so that the glass capillary 109 109 is horizontal.