Metrohm 746 VA Trace Analyzer - Manual (Page 39)

3 Installation
746 VA Trace Analyzer / 747 VA Stand
3-12
3.3.3 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 concentrations without
preceding enrichment)
The scheme for deaeration of the analyte solution and the inert gas connections at
the 747 VA Stand needed for operation of the MME is shown in Fig. 11. The inert
gas connections are established as follows:
1 Fill gas wash bottle
• Unscrew gas wash bottle 27 27 from measuring head arm 40 40.
• Fill gas wash bottle 27 27 half full with dist. H
2
O (for long-term measure-
ments 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 27 27 back on measuring head arm 40 40.
2 Connect inert gas supply
• Attach one end of 6.1801.080 PVC tubing to connection 32 32 of the 747 VA
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 30 30 for inert gas lead-off.
• Route the other end of the lead-off tubing to a fume cupboard.
Additional VA Stands are attached in exactly the same manner. If only one inert gas
bottle for all stands is desired, the 6.1807.000 Y-Connections available as an option
can be used for the connection of PVC tubings.