Metrohm 746 VA Trace Analyzer - Manual (Page 52)

3.4 Multi-mode electrode (MME)
746 VA Trace Analyzer / 747 VA Stand
3-25
3.4.9 Cleaning the MME
If the mercury in the multi-mode electrode is contaminated and this leads to distur-
bances (see sections 7.4.2 and 7.4.3), the MME must be cleaned and refilled with
ultrapure mercury. Proceed as follows:
1 Remove multi-mode electrode from 747 VA Stand
• Unscrew FEP tubing 51 51 and 59 59 from the MME, disconnect electrode
cable 37 37 from MME.
• Take multi-mode electrode 38 38 out of measuring head 41 41 while gently
tapping the MME to knock off any mercury drops on the glass capillary
into the measuring vessel.
2 Remove old mercury
• Place multi-mode electrode 38 38 in a horizontal position in the electrode
holder 114 114 (see Fig. 15-3). The slotted screw 101 101 is now at the top.
• Unscrew slotted screw 101 101 using a suitable coin.
• Carefully turn MME and empty mercury through the threaded opening
100 100 into a waste container placed in the drip pan 113 113. While doing so,
gently tap the glass capillary 109 109 and the MME to ensure that all mercury
flows out of the MME.
3 Dismantle MME
• Unscrew retaining nut 108 108.
• Take glass capillary 109 109 out of opening 104 104, the sealing ring 106 106 and the
locking ring 107 107 are removed at the same time. Remove these two parts
from the glass capillary 109 109.
• Remove insert ring 105 105 from the MME.
• Unscrew slotted screw 96 96 with a suitable coin in an anticlockwise direc-
tion from screw thread 98 98.
• Screw locking ring 95 95 onto slotted screw 96 96 and pull out of the MME.
4 Dispose of old capillary
• Connect filling tubing 115 115 with the tubing coupling 118 118 to the two gas
wash bottles 117 117 and the vacuum pump (see Fig. 14).
• Insert glass capillary 109 109 (capillary end) in the filling cone 116 116 of the filling
tubing 115 115.
• Remove mercury from the capillary with the vacuum pump.
5 Clean MME
• Clean inner compartments of the MME, contact pin 102 102 and the screw
threads 98 98, 100 100 and 104 104 with a lint-free cloth.
• Thoroughly rinse all inner compartments of the MME and the unscrewed
individual parts with dist. water and then dry with N
2
.
Do not use any organic solvents.