and noise. At negative potentials, the use of platinum electrodes is severely limited by the
specific ease of reducing hydrogen ions to hydrogen gas. For metal electrodes, the formation of
metal oxides is a limiting factor for running oxidative measurements.
Table 14–1: Some features of different working electrode (WE) materials
WE material
Limits of working potential vs. Ag/AgCl (V)
Application
example
alkaline
acidic
Glassy carbon
-1.50
+0.60
-0.80
+1.30
Catecholamines
Gold
-1.25
+0.75
-0.35
+1.10
Carbohydrates,
thiols
BDD
-
-
-1.00
+2.00
Iodide, disulfides,
phenols
Platinum
-0.90
+0.65
-0.20
+1.30
Alcohols, glycols
Silver
-1.20
+0.10
-0.55
+0.40
Halides, cyanide
Copper
-
+0.20
-
+0.60
Amino acids,
carbohydrates
14.1.4.3 Boron-doped diamond (BDD) electrodes
Boron-doped diamond (BDD) is the most recent addition to the list of available FlexCell working
electrodes. The BDD electrode comprises an ultra-thin film of boron-doped diamond material
deposited on a Si-wafer. The electrode is anodized and is capable of detecting oxidized
components at 1.5–2 V, which would otherwise require a reductive step before detection under
oxidative conditions. Other special properties of BDD electrodes are inertness and excellent
response stability, which make them well suited to detect phenols—an application where
electrode fouling is an issue when glassy carbon is used.
Chemical compatibility:
The BDD electrode operational lifetime is severely reduced when
exposed to fluorinated acids, such as tri-fluoroacetic acid. Even at relatively low concentrations
(2% in aqueous solution), significant damage to the diamond electrode can be seen within days
of operation.
14.1.5 Reference electrode
14.1.5.1 HyREF
The maintenance-free HyREF is the most commonly used reference electrode for a FlexCell.
This reference electrode is most suitable for use with high concentrations (>20%) of organic
modifier in the mobile phase or when running alkaline mobile phase. An important characteristic
of the HyREF is the pH dependence of the reference potential.
December 16, 2021, 715007395 Ver. 00
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