Metrohm 2.946.0010, Руководство пользователя

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7 Troubleshooting
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63
NOTICE
Similar effects can be observed with other anions forming complexes
with the working electrode material, e.g. other halides, pseudo-halides,
and hydroxides.
Besides the influence on the working electrode the concentration of chlor-
ide also affects the potential of the reference electrode. The following
table shows the potential difference measured versus a classical Ag/AgCl
reference electrode (6.0728.040; LL-Ag/AgCl, c(KCl) = 3 mol/L; standard
potential (25 °C) vs. NHE 206.3 mV). The potentials versus Normal Hydro-
gen Electrode (NHE) shown in the table are calculated based on the stan-
dard potential of the Ag/AgCl electrode.
Table 1 Reference potential scTRACE Gold electrode against chloride
concentration
c(KCl) Potential vs.
Ag/AgCl (3 mol/L KCl) Potential vs. NHE
0.005 mol/L 154 mV 360 mV
0.01 mol/L 134 mV 340 mV
0.025 mol/L 118 mV 324 mV
0.05 mol/L 102 mV 308 mV
0.1 mol/L 85 mV 291 mV
0.25 mol/L 63 mV 269 mV
0.5 mol/L 47 mV 253 mV
1 mol/L 30 mV 236 mV
3 mol/L 1 mV 207 mV
Influence of oxygen
The influence of oxygen can be observed in section
Ⓑ
of the curve shown
in Figure 18 . Section
Ⓐ
and
Ⓒ
are not affected by the presence of oxy-
gen. These sections are discussed in the subchapters Influence of chloride
and Influence of pH .
At potentials more negative than -0.2 V the first step of the oxygen reduc-
tion takes place: O
2
+ 2 H + + 2 e -
→
H
2
O
2
. The second step would be at
more negative potentials and cannot be registered under these conditions
(electrode type, electrolyte).