Double Input Capacitively Coupled Contactless Conductivity Detector with Phase Shift

A double input capacitively coupled contactless conductivity detector (DIC⁴D) device which gets higher sensitivity has been described in this paper. The detector consists of two input electrodes and one output electrode. When two alternating current (AC) voltages with the same amplitude and different phases are imposed on each input electrode, the equivalent resistance of the output electrode is reduced because of the interference of the two signals with different phase angles. For a capacitively coupled contactless conductivity detector (C⁴D), the ratio of the response of KCl solution to that of distilled water is 1.6. However, for DIC⁴D, the ratio is 1.55 at a phase difference of 0° and increases to 1.8 at the phase difference of 170°, respectively. For C⁴D, the response of KCl solution is a linear function of the logarithm of concentrations from 10^–5 M to 10^–2 M, and the slope is 5.58. However, the slope of the response increases to 7.13 in DIC⁴D, and the limit of detection (LOD) of DIC⁴D is estimated to be 5 × 10^–8 M. The slope of the three-way DIC⁴D is increased to 69.78. A flow injection device is employed for the evaluation of the applicability of DIC⁴D with the same range, and good reproducibility is confirmed through flow injection of the same solution 10 times. The relative standard deviation (RSD) is 0.7%, which demonstrates a promising application to capillary electrophoresis (CE).