Metrohm 757 VA Computrace - Manual (Page 28)

3 Installation
757 VA Computrace – Hardware
24
2 Draw up mercury
• Attach needle 91 to syringe 90.
• Draw up 6 mL ultrapure mercury slowly and carefully using syringe 90.
3 Add mercury to MME
• Lower syringe needle 91 into the top opening of the MME 17 between
sealing ring 85 and sealing needle 76.
• Expel mercury slowly and carefully from the syringe to allow it to flow into
the Hg reservoir 82.
The Hg reservoir 82 must never be filled more than 2 /
3
full with mer-
cury.
3.3.3 Mounting the capillary
The glass capillaries 88 for the multi-mode electrode 17 are supplied separately in
a protective plastic package. After they have been unpacked, avoid any contact
whatsoever with the sensitive capillary tip. The capillary 88 is mounted in the MME
filled with mercury as described in section 3.3.2 as follows:
1 Insert retaining nut
• Screw retaining nut 87 into screw thread 83 until a slight resistance is
noticeable (on no account screw in retaining nut fully!).
2 Insert capillary
• Cut open plastic package containing the glass capillary 88 on the side of
the large capillary opening using scissors (do not tear open), leave capil-
lary in the package.
• Insert glass capillary 88 directly from its protective plastic package
through the retaining nut 87 into the sealing ring 85 and push in as far as
it will go.
3 Tighten retaining nut
• Firmly tighten retaining nut 87 by hand (do not use a tool). The glass
capillary 88 should then be centered in the opening of the retaining nut
87.
• If this is not the case, undo retaining nut 87 by one full turn and then
retighten by hand. When tightening, move glass capillary 88 in a circle so
that it is centered in the feedthrough of the retaining nut 87.
3.3.4 Filling the capillary without vacuum
The glass capillary 88 can normally be filled with mercury by the method described
here without vacuum. However, if difficulties regarding stability or reproducibility
arise with a capillary filled in this manner, try to fill the capillaries by the alternative
method with vacuum (section 3.3.5).
To fill the mounted glass capillary 88 (section 3.3.3) with Hg without vacuum, pro-
ceed as follows: