Antec Scientific VT-03, Руководство пользователя

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14 VT03 flow cell user manual, ed. 8
Fig. 7. Schematic representation of the Ag/AgCl reference electrode.
Salt bridge Ag/AgCl reference electrode
The reference electrode of the Ag/AgCl type with salt bridge consists of a
silver rod, coated with solid AgCl, immersed in a solution of saturated KCl,
containing KCl crystals. Electrical contact with the other electrodes in the flow
cell is made through a salt bridge consisting of a wetted cotton wool frit,
which is electrically conducting and slows down leakage of KCl. This REF for
the VT-03 flow cell is factory filled with KCl. For certain applications another
chloride salt is to be preferred. In case of perchlorate containing mobile
phases, sodium chloride is mandatory, because potassium perchlorate
precipitates and will clog the cotton wool frit. At high modifier percentages,
the REF must be filled with lithium chloride for similar reasons.
HyREF reference electrode
The HyREF is a hydrogen reference electrode, its potential depends on the
pH of the mobile phase. The HyREF is fully comparable with the standard
Ag/AgCl REF as to baseline stability and S/N ratio. The HyREF is more user-
friendly and in principle this REF is completely free of maintenance. Trapping
of air bubbles like in the salt bridge Ag/AgCl type is impossible because of
the absence of a salt bridge. Consequently, refilling the REF with saturated
KCl is not longer required. Due to the absence of a salt bridge and its
inertness, the HyREF is an excellent alternative for the Ag/AgCl REF,
especially in case of high modifier concentrations (i.e. analysis of fat-soluble
vitamins) or high pH (analysis of carbohydrates, PAD).
Depending on the pH of the mobile phase, the potential setting of the working
electrode vs. the HyREF may differ significantly compared to Ag/AgCl.
I/E curves show a shift of more than 200 mV at pH 3.1 (e.g. catecholamines),
no shift appears at pH 12 (e.g. PAD of carbohydrates). Therefore, it is