Contactless Capacitive Coupled Conductivity Detection (C4D) systems
C4D is a technique for detection of chemical species that cannot be detected with standard chromatography detectors, for example inorganic ions commonly found in water.
eDAQ supplies several products for Capacitively-Coupled Contactless Conductivity Detection (C4D) which can be used for:
Capillary Electrophoresis (CE)
Microchip Electrophoresis (MCE)
Ion Chromatography (IC) and High-Performance Liquid Chromatography (HPLC)
Flow Injection Analysis (FIA)
How does C4D work?
C4D detects changes in the conductivity of the solution containing the analytes without getting in contact with the electrolyte. The technique offers several advantages:
Contactless – no fouling of electrodes
Small size – can be adapted to thin capillaries or microchips
Does not interfere with flow
Detects inorganic ions
An excitation voltage from 10V to 200Vpp at a frequency from 50 to 1500KHz is applied to input electrodes.
This signal couples capacitively to the detection electrodes through the solution under test.
The amplitude of the detected signal will depend on the conductivity of the solution in the volume between the excitation and detection electrodes. Variations in solution conductance due to different analytes passing will result in variation of the detected current.
The detected signal is an AC sdignal with an amplitude depending on the sample conductivity, as well as on the buffer conductivity and the stray capacitance between the electrodes and between electrodes and ground.
The AC signal is demodulated in the signal processing electronics to a DC signal, which is recorded and analysed like any other chromatography detector signal.
As analyte ions pass into the detection region they cause small changes to the overall sample conductivity. Continous monitoring of the conductivity signal will show a series of peaks, the areas (or heights) of which are related to analyte concentration. The signal is processed like a conventional chromatogram.
The C4D electrodes do not make direct contact with the sample. Thus they are electrically isolated from the sample (ideal for electrophoresis detection), and electrode fouling is eliminated.
Since the the vast majority of analytes for CE are ionic, a C4D system functions as a 'universal' method of detection requiring minimal sample preparation. The technique can also be used in parallel with UV-visible absorbance or fluorescent detection. Sensitivity is typically similar to UV-visible absorption detection.