Metrohm 746 VA Trace Analyzer - Manual (Page 46)

3.4 Multi-mode electrode (MME)
746 VA Trace Analyzer / 747 VA Stand
3-19
• 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 drops so that it is easier to see whether
mercury continues to flow.)
• Finally, turn slotted screw 96 96 a quarter of a turn clockwise.
5 Checking the MME for leaks
• Select dialog page "STAND" then switch on the dropping mercury elec-
trode 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.
3.4.5 Filling the capillary using vacuum
Filling of the glass capillary 109 109 with vacuum is advisable in all cases where diffi-
culties have been found with the method without vacuum described in section
3.4.4. Filling with vacuum is especially recommended when no ultrapure Hg is
available.
To fill the mounted glass capillary 109
109 (section 3.4.3) with Hg with vacuum, pro-
ceed as follows:
1 Set up filling station
• All actions involving the electrode and the mercury vessels must be
performed in or over the drip pan 113 113 supplied (see Fig. 14).
• The MME 38 38 is placed in the electrode holder 114 114 for filling.
2 Connection for vacuum pump
• For filling the capillary 109 109, the filling tubing 115 115 is required. At one end it
is fitted with a filling cone 116 116 for mounting on the capillary 109 109, and at
the other end with the tubing coupling 118 118 for attachment to the line for
the vacuum pump.
• To avoid possible mercury losses, two gas wash bottles 117 117 are attached
to the filling tubing 115 115.
3 Vacuum pump
• To draw up mercury a suitable vacuum pump is required (e.g. water jet
pump). The partial vacuum ∆p should be around 25 mbar.
• A vacuum release tap must be installed at the vacuum pump or in the line
between the gas wash bottle and the pump for slowly releasing the vac-
uum.
4 Mount filling tubing
• Mount filling tubing 115 115 with filling cone 116 116 on glass capillary 109 109.
• Connect filling tubing 115 115 with tubing coupling 118 118 to the two gas wash
bottles 117 117 and the vacuum pump (see Fig. 14).