Metrohm 757 VA Computrace - Manual (Page 23)

3.2 Installation of the 757 VA Computrace Stand
757 VA Computrace – Hardware
19
3.2.5 Inert gas connection
Nitrogen (N
2
) is generally used as the inert gas to deaerate 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 con-
centrations without preceding enrichment)
The scheme for deaeration of the analyte solution and the inert gas connections at
the 757 VA Computrace Stand needed for operation of the MME is shown in Fig. 7.
The inert gas connections are established as follows:
1 Fill gas wash bottle
• Unscrew gas wash bottle 4 from measuring head arm 19.
• Fill gas wash bottle 4 half full with dist. H
2
O (for long-term measurements
with supporting electrolytes such as HAc buffer or NH
3
buffer, fill with
supporting electrolyte; for measurements in organic solvents fill with the
used solvent).
• Screw gas wash bottle 4 back on measuring head arm 19.
2 Connect inert gas supply
• Attach one end of 6.1801.080 PVC tubing to connection 10 of the 757 VA
Computrace Stand.
• Attach the other end of the 6.1801.080 PVC tubing to connection of the
inert gas bottle.
• Set inert gas pressure at gas bottle using the reducing valve to
p = 1 ± 0.2 bar.
• Open gas supply line at gas bottle.
3 Connect inert gas lead-off (option)
• Attach a length of suitable tubing (e.g. Metrohm 6.1805.030, length
150 cm) to connection 8 for inert gas lead-off.
• Route the other end of the lead-off tubing to a fume cupboard.