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

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 ((MICD)-D-4) 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 (MICD)-D-4 with differential detection to propose a further-improved detector ((DFMICD)-D-4). 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 (DFMICD)-D-4 is 1.393, higher than a traditional single-input capacitively coupled contactless conductivity detector ((CD)-D-4: 0.905) and a double-input capacitively coupled contactless conductivity detector ((DICD)-D-4: 1.314). For 10(-3) M KCl solution, the response-to-baseline ratio is 1.776 for (CD)-D-4, 1.779 for (DICD)-D-4, and 12.06 for (DFMICD)-D-4, 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 (DFMICD)-D-4 is low, reaching 0.7 nM. In addition, (DFMICD)-D-4 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.