Passive Conductivity Detection for Capillary Electrophoresis

Abstract

A passive electrochemical detection principle that can be applied to capillary electrophoresis is presented. The separation electrical field is used to generate a potential difference between two electrodes located along the channel. For constant-current electrophoresis, the generated signal is proportional to the resistance of the solution passing between the two electrodes. Contrary to conductivity detectors that are ac driven and need to be decoupled from the separation field, the passive detection directly takes advantage of the separation field. The signal is simply measured by a high-impedance voltmeter. The detection concept has been validated by numerical simulations showing how the magnitude of the signal is related to the ratio between the electrode distance and the length of the sample plug. As a proof of the principle, this detection concept has been demonstrated by the electrophoretic separation of three alkali ions on a polymer microchip. Based on preliminary results, a detection limit of 20 microM and a dynamic range of up to 3 orders of magnitude have been achieved.

On‐column conductivity detection in capillary‐chip electrophoresis

“…Here, conductivity detection is achieved by measuring the potential difference with external macro reference electrodes placed in the reservoirs located at the extremity of the side detection channels. In this way, a reliable galvanic contact was achieved, and problems due to electrode poisoning [19] was avoided. This design is advantageous as it is easy to implement in term of microfabrication, as there is no limit to the choice of substrate material and as there is no restriction to the size of the sensing electrodes.…”

“…The electric coupling of the high voltage necessary for the electrophoretic separation and the low electric signals used for the electrochemical detection has been a major technological hurdle and has limited the wider development and applications of electrochemical detection. Conductivity detection was one of the main electrochemical detection methods investigated in micro-TAS [9][10][11][12][13][14][15][16][17][18][19]. Both for end-of-column and for in-column conductivity measurements, electric-coupling may cause polarization at the sensing electrodes, bubble generation, or damage to the detection circuit.…”

“…For example, Bai et al [19] reported a passive conductivity detection method by integrating two carbon paste electrodes in a separation channel, and the detection was achieved by measuring the potential difference between the two sensing electrodes in contact with the flowing solution. Potential gradient detection also takes advantage of the electrophoresis voltage, and detection is carried out by measuring the potential disturbance caused by the passage of a sample band of different conductivity [21][22][23][24].…”

Conductivity detection for conventional and miniaturised capillary electrophoresis systems

“…The carbon paste electrodes were connected to a commercially available conductivity meter and used for detection in a CE separation of 1 mM K 1 , Na 1 , and Li 1 in a poly(allyamine) hydrochloride-coated channel. The same group presented a paper on potential gradient detection (PGD) in CE, where this detection technique was named "passive conductivity detection" [126]. The microfabrication method was identical to the one described above, incorporating a second detection electrode in parallel with the other electrode.…”

Determination of inorganic ions using microfluidic devices

“…The NO 2 2 produced from this reaction was detected amperometrically with a LOD of 1.0 mM. Recently, Girault and co-workers [72] described the use of passive conductivity detection on a poly(-ethlyleneterephthalate) (PET) chip. Rather than isolating the detector from the field, the separation field was used to induce a potential difference across two electrodes placed perpendicular to the separation channel.…”