An improved dual-channel capacitively coupled contactless conductivity detector with high detection performance

Abstract

Conductivity detectors are widely used electrochemical sensors. It has long been a goal of researchers to improve detection performance. In this contribution, we propose a multi-input capacitively coupled contactless conductivity detector (MIC⁴D) with high sensitivity, and we carry out a detailed theoretical investigation of the detector. In order to overcome the problem of a rising baseline level as a result of sensitivity improvements when using the multi-input detection method, we innovatively combine MIC⁴D with differential detection to propose a further-improved detector (DFMIC⁴D). The detector is composed of two channels, one for the reference and the other for the analyte. The signal output from differential amplification can effectively reduce the high baseline level and detection interference. In KCl solution with a concentration range of 10⁻⁴ to 10⁻⁵ M, the response to the solution is a linear function of the logarithm of the concentration, and this detector has a high slope. The slope of DFMIC⁴D is 1.393, higher than a traditional single-input capacitively coupled contactless conductivity detector (C⁴D: 0.905) and a double-input capacitively coupled contactless conductivity detector (DIC⁴D: 1.314). For 10⁻³ M KCl solution, the response-to-baseline ratio is 1.776 for C⁴D, 1.779 for DIC⁴D, and 12.06 for DFMIC⁴D, with a ratio increase of nearly 6-fold shown by our new detector. At a S/N (signal-to-noise) ratio of 3, the limit of detection (LOD) of DFMIC⁴D is low, reaching 0.7 nM. In addition, DFMIC⁴D can be applied to the detection of low-conductivity solutions and total dissolved solids (TDS) analysis. Compared with a standard conductivity meter, our detector shows better detection performance.