Candle soot-smoked electrodes as a natural superhydrophobic material for potentiometric sensors

The application of carbon soot as a solid-contact layer in potentiometric sensor is presented. The preparation method of carbon layer from the candle is inexpensive and as short as 10 s and was optimized and described in the scope of this paper. With the use of the proposed procedure, it is possible to cover not only the glassy carbon disc electrodes, but all surfaces of various shapes and types, like foil or paper. Obtained soot layer was casted with potassium-selective membrane, for the comparison of results with other solutions presented in literature, however by changing the composition of ion-selective membrane it is possible to achieve electrodes sensitive to various cations and anions. By introducing the candle soot into the sensor, the electrical and analytical properties of electrode were significantly improved. Designed candle soot-based sensor exhibit repeatable and reversible Nernstian response towards potassium ions, low detection limit (10^-6.7 M K⁺ ions), remarkable potential stability (drift equals to 15 μV/h) enhanced selectivity (in comparison with coated-disc electrode) and short response time. Designed sensors owe its great analytical properties to high electrical capacity (C = 343 μF) and superhydrophobic properties (proven by the high value of contact angle - 165°). Obtained sensors are insensitive to redox conditions and exhibit long lifetime. Performed tests proved that carbon layer obtained directly from the candle is appropriate material for solid-contact layer in potentiometric sensor and allows to obtain robust potentiometric sensor of competitive parameters using simple and fast procedure.