Conductivity detectors electrolytic suppressor

To minimize the mobile phase s contribution to conductivity, an ion-suppressor column is placed between the analytical column and the detector. This column selectively removes mobile-phase electrolyte ions without removing solute ions, for example, in cation ion-exchange chromatography using a dilute solution of HCl as... 

The most commonly employed detector in ion chromatography is the conductivity detector, which is used with or without a suppressor system. The main function of the suppressor system as part of the detection unit is to chemically reduce the high background conductivity of the electrolytes in the eluent, and to convert the sample ions into a more conductive form. In addition to conductivity detectors, UV/Vis, ampero-metric and fluorescence detectors are used, all of which are described in detail in Chapter 6. 

We wish only to remind readers that there are three main methods of electrochemical re-vealment conductivity, direct current (d.c.) amperometry, and integrated amperometry (pulsed amperometry is a form of integrated amperometry). In revealment by conductivity, the analytes, in ionic form, move under the effect of an electric field created inside the cell. The conductivity of the solution is proportional to the mobility of the ions in solution. Since the mobile phase is itself an electrolytical solution, in order to increase the signal/noise ratio and the response of the detector, it is very useful to have access to an ion suppressor before the revealment cell. By means of ionic exchange membranes, the suppressor replaces the counterions respectively with H+ or OH , allowing only an aqueous solution of the analytes under analysis to flow into the detector. 

Fig. 5. An analysis of a coarse atmospheric aerosol extract by CE and IC [49]. CE conditions a 57 cmX75 xm I.D. capillary, distance to detector, 50 cm. Electrolyte 2.25 mM PMA (pyromel-litic acid), 0.75 mM HMOH (hexamethonium hydroxide), 6.50 mM NaOH and 1.60 mM TEA (triethanolamine), pH 7.7 or 2.0 mM NDC (2,6-naphthalenedicarboxylic acid), 0.5 mM TTAB (tetradecyltrimethylammonium bromide) and 5.0 mM NaOH, pH 10.9 30 kV (PMA) or 20 kV (NDC) pressure injection for 10 s indirect UV detection at 254 nm (PMA) or 280 nm (NDC). IC conditions an IonPac-ASlO column with an IonPac-AGlO guard precolumn conductivity detection using an anion self-regenerating suppressor (ASRS-I) in the recycle mode. Analytes 2, chloride 3, sulfate 5, nitrate 6, oxalate 7, formate 10, hydrocarbonate or carbonate 11, acetate 12, propionate 14, benzoate.

For suppressed conductivity detection, the end of the separation column is connected to a tubular ion exchange membrane suppressor surrounded by a reservoir of regenerant solution [512,513]. The electrodes for conductivity detection are located in a separate capillary downstream of the suppressor. The high voltage electrode for the separation is located in the regenerant reservoir. In this way, the detector is decoupled from the electric field for the separation, and the electroosmotic flow generated in the separation column is used to drive the electrolyte solution through the suppressor and detector. The function of the suppressor (see section 5.7.4.1) is to neutralize electrolyte solution ions. 

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