A novel long drop time mercury electrode has been constructed from common fused-silica capillary (50 μm I.D., 360 μm E.D.). Proposed device provides reproducible mercury drops with typical lifetime 40-120 s. The electrode was used for a set of electrocapillary measurements aimed at determination of critical micelle concentration of anionic surfactants by a convection controlled drop-time technique. A critical micelle concentration of sodium dodecyl sulfate 5.6 ± 0.4 mmol L(-1) and 4.3 ± 0.4 mmol L(-1) were obtained in 1 mmol L(-1) and 5 mmol L(-1) phosphate buffer (pH 7.0), respectively. The values were comparable to those obtained from conductometric measurements under the same conditions (7.0 ± 0.1 mmol L(-1) and 5.2 ± 0.1 mmol L(-1), respectively) and the difference was explained in accordance with theory of hemi-micelle formation.

Department of Analytical Chemistry Faculty of Science Palacký University 17 Listopadu 1192 12 77146 Olomouc Czech Republic

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