Metrohm 797 VA Computrace - Manual (Page 33)

2.3 Multi-Mode Electrode (MME)
797 VA Computrace / Hardware-Manual 8.797.8001EN
25
PUTRACE CONTROL window and clicking on . The mercury drops
freely out of the capillary.
• Select
HMDE and click on . A single mercury drop is formed.
Knock this off by gently tapping the MME 21 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 74 still further in a clock-
wise direction and repeat check.
• If it is not possible to stop the mercury flow, both the glass capillary 87 and
the sealing needle 75 have to be replaced (see section 2.3.9).
2.3.5 Filling the capillary using vacuum
Filling of the glass capillary 87 with vacuum is advisable in all cases where difficulties
have been found with the method without vacuum described in section 2.3.4 Filling
with vacuum is especially recommended when no ultra pure Hg is available.
To fill the mounted glass capillary (section 2.3.3) with Hg with vacuum, proceed as
follows:
1 Set up filling station
• All actions involving the electrode and the mercury vessels must be per-
formed in or over the drip pan 91 supplied (see Fig. 10).
• The MME 21 is placed in the electrode holder 92 for filling.
2 Connection for vacuum pump
• For filling the capillary 87, the filling tubing 93 is required. At one end it is
fitted with a filling cone 94 for mounting on the capillary, and at the other
end with the tubing coupling 96 for attachment to the line for the vacuum
pump.
• To avoid possible mercury losses, two gas wash bottles 95 are attached to
the filling tubing
3 Vacuum pump
• To draw up mercury a suitable vacuum pump is required (e.g. water jet
pump). The partial vacuum Δ
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 va-
cuum.
4 Mount filling tubing
• Mount filling tubing 93 with filling cone 94 on glass capillary 87.
• Connect filling tubing with tubing coupling 96 to the two gas wash bottles
95 and the vacuum pump (see Fig. 10).