Metrohm 797 VA Computrace - Manual (Page 25)

2.2 Installation of the 797 VA Computrace Stand
797 VA Computrace / Hardware-Manual 8.797.8001EN
17
6 Install auxiliary electrode
• Insert auxiliary electrode 43 (6.0343.000 Pt auxiliary electrode or GC auxil-
iary electrode, see section 2.6) in opening 54.
• Attach electrode cable 41 (AE) to auxiliary electrode: push cable lug under
the screw and then tighten screw firmly.
• Turn auxiliary electrode 39 so that the electrode cable 37 points to the rear
and not to the side (in the latter position it may become kinked and dam-
aged when cover 2 is closed).
7 Install MME or dummy stopper
in operation with MME:
• Carefully insert Multi-Mode Electrode 21 (6.1246.020) in opening 58 (the
underside of the capillary must not touch the measuring head during inser-
tion) and push in as far as it will go.
• Screw FEP tubing 34 (6.1805.180) for inert gas supply into connection 71
of the MME.
• Screw FEP tubing 42 (6.1805.180) for inert gas supply into connection 72
of the MME.
• Attach electrode cable 20 (WE) to screw connection 88 of the MME: push
cable lug under the screw and then tighten screw firmly.
in operation with RDE:
• Insert stopper 97 (6.2709.040, option) into opening 58 as far as it will go
so that the two blind holes point to the rear of the stand.
• Screw FEP tubing 34 (6.1805.180) into upper hole of stopper 97.
• Screw FEP tubing 42 (6.1805.180) into lower hole of stopper 97.
8 Install measuring vessel
• Tilt back measuring head arm 23.
• Slide measuring vessel 7 into holder 5 from the front and fill with analyte
solution or dist. H
2
O (storage solution) until the tips of the MME or RDE and
the reference electrode are immersed in the liquid.
• Lower measuring head arm 23 and cover 2.
2.2.5 Inert gas connection
Nitrogen (N
2
) is generally used as the inert gas to de-aerate the analyte solution and
for operation of the MME. The nitrogen must be of sufficient purity.
w(N
2
) ≥ 0.99996 (= 99.996%)
for general polarography/voltammetry
w(N
2
) ≥ 0.99999 (= 99.999% = "5 × 9")
for analyses in organic solvents; for determinations involving very high
current amplification (e.g. in the determination of very low concentra-
tions without preceding enrichment)
For electroplating bath applications, using CVS or CPVS, no inert gas connection is re-
quired.
The scheme for de-aeration of the analyte solution and the inert gas connections at
the 797 VA Computrace Stand needed for operation of the MME is shown in Fig. 7.
The inert gas connections are established as follows: