Eluents suppressed

Ion chromatography has found widespread application for the analysis of inorganic and organic ions with pKa values less than 7. It combines the techniques of ion-exchange separation, eluent suppression, and... 

Ion exchange chromatography with eluent suppression and conductometric detection is referred to as ion chromatography (IC). The ion exchanger consists of a basic structure (the matrix) and... 

The original method for the analysis of mixtures of anions used two columns attached in series packed with ion exchange resins to separate the ions of interest and suppress the conductance of the eluent, leaving only the species of interest as the major conducting species in the solution. Once the ions were separated and the eluent suppressed, the solution entered a conductivity cell, where the species of interest were detected. 

Van Os et al. [41] achieved complete separations in 6min of l-30mg L 1 concentrations of bromide, chloride, nitrite, nitrate and sulphate using a Zipax SAX separation column, with eluent suppression and electrical conductivity detection [42], The necessary high pressure packing techniques for packing the separation column have been described [43], With sample pieconcentration, detection limits were reduced to about 5pg L 1 but calibration graphs for chloride and nitrate were not linear. Sodium adipate and 1.410 3M disodium succinate are used as eluants, both at pH7. 

Shintani and Dasgupta [32] have reported that post-suppression membrane-based ion exchange chromatography with fluorescence detection permits detection limits superior to those obtained by conductivity detection in hydroxide eluent suppressed anion chromatography... 

Figure 9.11. Representation of eluent suppression scheme for ion chromatographic separation of nitrate and sulfate. Reprinted with permission from H. Small, Anal. Chem. 1983,55, 235A. Copyright 1983, American Chemical Society.

The main advantages of eluent suppressed ion chromatography (ESIC) are that a wide range of eluents and columns can be used, the wide dynamic range, and the higher sensitivity the main disadvantage is the periodical necessity for suppressor-column regeneration. 

A method of ion chromatography with conductivity detection of ions after eluent suppression for analysis of phosphites (phosphonate ion), was developed (Glenn et al., 1990 Ouimette and Coffe, 1988). It is rapid and relatively simple and shows recoveries are higher than 95% and a detection limit in grapes of 0.5-1.0 ppm is reported. 

Ion Chromatography with Eluent Suppressed Conductivity Detection... 

Risner, C. H., Quantitation of some tobacco anions by eluent suppressed anion exchange chromatography using conventional liquid chromatographic equipment. Tobacco Set, 1986, 85-90,... 

Figure 15.37 Schematic of the eluent suppression approach for ion chromatography that permits conductometric detection of analytes.

The idea behind eluent suppression has been to convert the moderately conductive Na+ in the eluent to the weakly eonductive H2CO3 while converting the low-conducting analyte NaX to the high-condueting HX. Limiting equivalent conductivity, denoted by A, of some ions in aqueous solution at 25°C are as follows (100) ... 

Commercial ion chromatograph instruments have become available since early 1976. Ion chromatography (IC) is a combination of ion exchange chromatography, eluent suppression and conductimetric detection. For anion analysis, a low capacity anion exchange resin is used in the separator column and a strong cation exchange resin in the H+ form is used in the suppressor column. 

Conductivity detectors are widely used in 1C instruments using eluent suppression detection. The detectors are inexpensive, simple, rugged, and easy to miniaturize. The same type of detectors can be used for any chromatographic process to detect charged species in a nonionic eluent. 

Another suppression device uses a packed-bed suppressor in disposable cartridges. A device with soUd-phase electrochemical cells called Electrically Regenerated Ion Suppression (ERIS) is marketed by Alltech [9]. A degassing unit for removing CO2 from suppression of carbonate is included in a more recent suppressor. Metrohm markets a column suppressor module that uses two suppressor columns. One is regenerated while the other is being used. When the first is exhausted then the other is available for eluent suppression. 

US EPA Method 326.0 allows the combination of suppressed conductivity detection and postcolumn derivatization for UV absorbance detection, as schematically depicted in Figure 8.45. A volume of sample (225 pL) is introduced into an ion chromatography system. After separation and eluent suppression, standard anions and oxyhalide ions are measured using conductivity detection. The suppressed effluent from the conductivity detector is then combined with an acidic solution of potassium iodide (0.26 mol/L) containing a catalytic amoimt of ammonium molybdate tetrahydrate (43 pmol/L). The mixture is heated in the knitted reaction coil to 80 °C to facilitate complete reaction. The formed triiodide is measured by its UV absorption at 352 nm. Because KI is photosensitive, the KI/Mo PCR solution develops a light yellow color with time, even when stored under helium. Therefore, the PCR reservoir has to be protected from light by covering it with aluminum foil and should be pressimzed with helium. Under... 

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