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7 Troubleshooting
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45
7 Troubleshooting
7.1
General rules for voltammetric trace analysis
7.1.1
Sampling
The analysis is only as good as the sample.
￭
Make sure that the sample is representative.
￭
Be aware of contamination risks.
7.1.2
Measuring solution
￭
The analyte must be in ionic form, e.g. AsO
4
3-
, Hg
2+
or Cu
2+
.
￭
The measuring solution must have a sufficient conductivity. Take care
that the used electrolyte is sufficiently concentrated. Check Metrohm
application documentation, e.g. Application Bulletins, for detailed
information on the electrolyte.
￭
Some components of the electrolyte, e.g. organic buffers or complex-
ing agents, may not be stable over a longer period of time. Take care
that the electrolyte is prepared freshly in appropriate intervals.
￭
The measuring solution must be free of interfering substances. Possible
interferences are:
– Substances producing interfering voltammetric signals, such as
• Oxygen, H
2
O
2
, other metal ions
• Organic compounds (e.g. nitro compounds)
• Anions (e.g. nitrite, sulfite)
– Substances complexing the analyte ions, such as
• Organic complexing agents (e.g. EDTA, humic acids, etc.)
• Anions or cations forming hardly soluble salts with the analyte
(e.g. As
2
S
3
or As
2
S
5
, Hg(CN)
2
)
– Substances blocking the surface, such as
• Surfactants
Organic interferences can be destroyed by e.g. UV digestion.
￭
Be aware of contamination risks, interfering substances as well as the
analyte itself (keyword: blank)
– Every surface, measuring vessel, electrode and other equipment
in contact with sample or reagents, can be contaminated.
– Reagents as well as the water used for the preparation of
reagents can contain impurities. Make sure to use only reagents
of highest quality, e.g. Merck suprapur
®
or Honeywell/Fluka
TraceSelect
®
. The water for preparation of reagents and for rins-
ing should have ultrapure quality (resistivity >18 M
Ω·
cm (25 °C),
type I grade (ASTM D1193)).
Summary of Contents for 2.946.0010
Page 1: ...946 Portable VA Analyzer 2 946 00x0 Manual 8 946 8003EN ...
Page 2: ......
Page 8: ......
Page 12: ...1 4 Symbols and conventions 4 Note This symbol marks additional information and tips ...
Page 79: ... 8 Technical specifications 71 8 8 Connection Connection USB version 1 1 or higher ...
