Comparison of the performance characteristics of two tubular contactless conductivity detectors with different dimensions and application in conjunction with HPLC

Abstract

Two tubular capacitively coupled contactless conductivity detection (C(4)D) cells with different geometric dimensions were evaluated with regard to their main analytical characteristics under non-separation and separation conditions in conjunction with liquid chromatography. A comparison of the performance of the tubular cells to a previously tested thin-layer detection cell was drawn. Additionally, using a theoretical model the experimental results were compared with sets of calculated values and partially enabled to model the complex behavior of C(4)D detection in combination with high-performance liquid chromatography (HPLC). While cell 1 is characterized by a geometric cell volume of 0.6 μL, a wall thickness of 675 μm, and an inner diameter of 125 μm, the respective values for cell 2 are 2.3 μL, 200 μm, and 250 μm. The main analytical parameters were evaluated using a potassium chloride (KCl) solution. The limits of detection were 0.4 μM KCl (5.7 × 10(-6) S m(-1)) for cell 1 and 0.2 μM KCl (3.2 × 10(-6) S m(-1)) for cell 2, which compares well to the previously found 0.2 μM for the thin-layer cell. A pair of linear ranges was found for both cells in a concentration interval ranging from 1 × 10(-6) to 1 × 10(-4) M (corresponding to 1.5 × 10(-5) to 1.5 × 10(-3) S m(-1)) KCl, respectively. Furthermore, the detector cells were applied to the HPLC separation of a model compound system consisting of benzoic acid, lactic acid, octanesulphonic acid, and sodium capronate. Separation of the compounds was achieved with a Biospher PSI 100 C18 column using 60% aqueous acetonitrile mobile phase. Calibration curves for the examined model system were well correlated (r² > 0.997), and it was found that under separation conditions the arrangement with the lower cell volume (cell 1) yields higher sensitivity and respectively lower limits of detection for all model compounds. Compared with the thin-layer cell, the tubular cells show better overall performance in regard to the determined analytical characteristics.

Contactless conductivity detection for analytical techniques: Developments from 2010 to 2012

“…However, real benefits of this circuitry are not evident, as for a standard cell and circuitry it is readily possible to effectively eliminate the capacitive impedance by simply working at a sufficiently high frequency. Furthermore, the LODs of approximately 5 μM reported are not better than the values routinely achieved for CE‐C 4 D. Mark et al compared the performance of two detectors, which differed in the wall thickness, and essentially confirmed that it is not necessary to strive for thin walls when working with tubular geometries. Yang et al reported an inductively, rather than capacitively, coupled detector, which is of course of high interest for fundamental reasons, but benefits compared to C 4 D are, at least for now, also not apparent.…”

Contactless Impedance Sensors and Their Application to Flow Measurements

“…The detector was applied to the detection of ionic compounds such as benzoic, lactic and octanesulfonic acids, and sodium capronate, after their separation by high performance liquid chromatography (HPLC) [24]. The properties of the thin-layer detector were compared with those obtained by the standard contactless conductivity detector equipped with tubular electrodes [25]. As compared to the thin-layer cell, the tubular cell was substantially simpler and its fabrication was much easier.…”

Investigation of the Effects of Electrode Geometry on the Performance of C4D Sensor with Radial Configuration

“…Researchers have made great efforts to the design of C 4 D sensors, such as optimization of the sensor structure [ 1 , 2 , 3 , 14 , 15 , 17 , 22 ] and improvement of the measurement circuit [ 1 , 7 , 16 , 23 , 24 , 25 ]. The selection of the electrode structure, i.e., the configuration pattern and the geometry (geometrical parameters) is a key point [ 1 , 2 , 3 , 9 , 14 , 15 , 17 , 18 , 22 , 26 ]. The design of electrodes is a basic process for detection and an attractive research aspect for researchers [ 14 , 15 , 17 , 22 ].…”