Flow impedance detector

Bubble electrodes — Mercury electrodes constructed in such a way that an electrolyte solution is entering a mercury-filled vessel through one or many small orifices in the bottom (cf. Fig. 1). The solution bubbles grow and will finally ascend in the mercury. The counter and the reference electrode have to be situated in the tubing fed to the orifice. Bubble electrodes have been developed as flow-through detectors for HPLC and FIA [i-iii,vi], as electrodes to generate ESR-active species [iii-iv], for - tensammetry [vii], and for electrosynthesis [v]. The fact that they are mercury based impeded further developments of this electrode type. 

The pressure sensitivity defined as that pressure equivalent to the noise level is very important as it determines both the limits of pressure and flow variation that can be tolerated from the pump. The specification of the maximum working pressure is also important where multidimensional column systems are required to be employed since there is a significant flow impedance subsequent to the detector cell,... 

Electrical conductivity detector is commonly use. The sensor of the electrical conductivity detector is the simplest of all the detector sensors and consists of only two electrodes situated in a suitable flow cell. The sensor consists of two electrodes sealed into a glass flow cell. In the electric circuit, the two electrodes are arranged to be the impedance component in one arm of a Wheatstone bridge. When ions move into the sensor cell, the electrical impedance between the electrodes changes and the out of balance signal from the bridge is fed to a suitable electronic circuit. The out of balance signal is not inherently linearly related to the ion... 

The conductivity detector measures the conductivity of a solution containing an electrolyte. When current is allowed to pass through two electrodes, there is resistance (or better impedance) to the flow of current... 

The electrical conductivity detector measures the conductivity of the mobile phase. Conductivity detectors are universal and nondestructive and can be used in either direct or indirect modes. The conductivity sensor is the simplest of all the detectors, consisting of only two electrodes situated in a suitable flow cell. The basis of conductivity is the forcing of ions in solution to move toward the electrode of opposite charge on the application of a potential. To prevent polarisation of the sensing electrodes, AC voltages must be used and so it is the impedance (not the resistance) of the electrode system that is actually... 

Due to the stmcture of the Ranter meter, the correlation between output and gas density is nonlinear. Data characteristics are given in Figure 8. The speed of response of the Ranter meter is relatively high, because specimen gas flow is high and diffusion of gas in the detector does not impede measurement. 

Flow controllers Many detectors are flow sensitive and, thus, a flow controller may be essential. The controllers are simple pneumatic devices that will maintain a constant mass flow rate independent of the column temperature or column impedance. 

When the detector is in thermal equilibrium with the heat sink, the rms fluctuation in the power flowing through the thermal impedance into the detector is (Smith et al. [3.7])... 

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