Section 6. Temperature-Stabilized Detector Operation
6.1 Rationale for Use
Thermostatted control of the effluent temperature before it reaches the cell reduces the ef-
fects of ambient temperature change on electrochemical detection. Furthermore, temperature
control of the column protects the separation from the effects of temperature change, and
when the LC-23C cartridge column heater is used with the CC-5 detector package, the dis-
tance between the heated column and cell inlet is quite small and there will be sufficient tem-
perature control to minimize effects on detection. However, in extreme environments (e.g.,
lab temperature changes due to automated heating/cooling shutdown after business hours,
or proximity to vents, ducts, or drafts) or at high detector gain, small fluctuations in tempera-
ture at the detector cell can still produce marked deviations in the detector baseline. In these
cases both a column heater and a cell preheater may be needed. In Figure 6.1 are shown
plots of EC detector background current versus temperature. The slope of the curve (di/dT)
is significant, typically 0.5–1.5 nA per
°
C. Hence it is easy to see how a small change in
eluent temperature (e.g., 0.1
°
C) could still cause appreciable shifts in the baseline at high
gain.
Figure 6.1.
Plot of electrochemical background current versus mobile phase temperature on a glassy carbon electrode oper-
ated at 650 and 800 mV applied potential.
What phenomena are responsible for this dependence? The background current in electro-
chemical detection derives from several contributions, the majority component being the oxi-
dation or reduction of the solvent itself.
2H
2
0
→
0
2
+ 4H
+
+ 4e
-
20
30
40
TEMPERATURE ( C)
o
+650 mV
+800 mV
20
2.0
30
3.0
40
4.0
BACKGROUND CURRENT (nA) AT 800mV
BACKGROUND CURRENT (nA) AT 650mV
Section 6. Temperature-Stabilized Detector Operation
37
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