A compact and high‐resolution version of a capacitively coupled contactless conductivity detector

An all‐in‐one version of a capacitively coupled contactless conductivity detector is introduced. The absence of moving parts (potentiometers and connectors) makes it compact (6.5 cm 3 ) and robust. A local oscillator, working at 1.1 MHz, was optimized to use capillaries of id from 20 to 100 μm. Low noise circuitry and a high‐resolution analog‐to‐digital converter (ADC) (21 bits effective) grant good sensitivities for capillaries and background electrolytes currently used in capillary electrophoresis. The fixed frequency and amplitude of the signal generator is a drawback that is compensated by the steady calibration curves for conductivity. Another advantage is the possibility of determining the inner diameter of a capillary by reading the ADC when air and subsequently water flow through the capillary. The difference of ADC reading may be converted into the inner diameter by a calibration curve. This feature is granted by the 21‐bit ADC, which eliminates the necessity of baseline compensation by hardware. In a typical application, the limits of detection based on the 3σ criterion (without baseline filtering) were 0.6, 0.4, 0.3, 0.5, 0.6, and 0.8 μmol/L for K + , Ba 2+ , Ca 2+ , Na + , Mg 2+ , and Li + , respectively, which is comparable to other high‐quality implementations of a capacitively coupled contactless conductivity detector.