Frans_M_Everaerts_Isotachophoresis_378342.pdf

184 DETECTION SYSTEMS
Fig.6.40. Equipment used to characterize the influence of additives and coatings on the micro-sensing
electrode via current-voltage curves. It includes a platinum double electrode, a calomel electrode (S.C.E.)
together with a Luggia capillary filled with agar agar (3%) and potassium chloride (30%) and a counter
electrode in a separate compartment filled with 0.1 Mpotassium chloride solution, provided with a
ceramic filter. AU experiments were carried out in 0.1 Mpotassium chloride solution.
that polyvinyl alcohol (Mowiol) shows little desorption if adsorbed. From our experiments
so far, Mowiol proved to be superior to the other additives, even Triton X-100, especially
if the effect is studied in long runs. Triton X-100 shows a type of saturation effect after
some time, which results in a poor resolution.
Some corrosion inhibitors were also tested in two groups of experiments: (1) small
amounts were added to the leading electrolyte, e.g. , thiourea and benzothiazole;
(2) compounds were used as the buffering counter ions, e.g., pyridine and 0-picoline.
These compounds also sharpened the pattern, but were not better than Mowiol. When
gold electrodes were used, coatings were formed during the analysis that were recognizable
in the electrophoretic recording because coated electrodes become sensitive to doubly
charged ions (Fig.6.47). As usual, the d.c. method, applied as before, gave a slightly
different behaviour. When gold was used as the electrode material, a layer was formed
more easily, possibly containing the sulphur component, as it is known that thiourea can
easily form such layers.
In the experiments in which pyridine and /3-picoline were used as the buffering counter