Non-Suppressed-Ion Chromatography

Ion chromatography with suppressed conductivity detection has been extremely successful in filling a large gap that previously existed in inorganic analysis. However, the necessity for a suppressor device does add to the complexity of the instrumentation. It also restricts the type of eluent that can be used and to some extent limits the separating ability of the method. 

Non-suppressed ion chromatography employs a conventional liquid chromatographic system with a conductivity detector cell connected directly to the outlet end of an ion-exchange separation column. No suppressor unit is required. The successful development of this method was made possible by three principal innovations (1) the use of an anion- or cation-exchange resin of very low capacity (initially 0.007 to 

04 mequiv/g), (2) an eluent with a low ionic concentration and hence a low conductivity, and (3) an eluting ion in the eluent that has a significantly lower equivalent conductance than the analyte ions. 

A separation of eight anions with a more contemporary IC system is shown in Fig. 6.10. Quantitative results are possible in the low-to-medium ppm concentration range for each of the anions. 

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It is appropriate to refer here to the development of non-suppressed ion chromatography. A simple chromatographic system for anions which uses a conductivity detector but requires no suppressor column has been described by Fritz and co-workers.28 The anions are separated on a column of macroporous anion exchange resin which has a very low capacity, so that only a very dilute solution (ca 10 4M) of an aromatic organic acid salt (e.g. sodium phthalate) is required as the eluant. The low conductance of the eluant eliminates the need for a suppressor column and the separated anions can be detected by electrical conductance. In general, however, non-suppressed ion chromatography is an order of magnitude less sensitive than the suppressed mode. 

Poovey HG, Rando RJ. 1995. Determination of chlorine and chlorine dioxide by non-suppressed ion chromatography and application to exposure assessment in the paper industry. J Liquid Chromatogr 18(2) 261-275. 

Amin M., Lim L. W Takeuchi T. Determination of common inorganic anions and cations by non-suppressed ion chromatography with column switching. Journal of Chromatography A 2008 1182 (2) 169-175. 

Erupe M. E., Liberman-martin A., Silva P. J., Malloy Q. G. J., Yonis N., Cocker D. R. Purvis-Roberts K. L. Determination of methylamines and tiimethylamine-N- oxide in particulate matter by non-suppressed ion chromatography. Journal of Chromatography A 2010 1217(13) 2070-2073. 

Bucholz et al. [91] have described a procedure for the determination of less than 1 pg L 1 of chloride, nitrite and sulphate in 2ml of rainwater sample using non-suppressed ion chromatography. Detection limits are less than 0. lmg L 1 for chloride and nitrate and 0.25mg L 1 for sulphate. The method can accomplish the simultaneous analysis of chloride, nitrate, nitrite and sulphate in less than 25min. 

For non-suppressed ion chromatography to be successful, the ion exchanger used in the separation column must have a low exchange capacity and a very dilute eluent must be used. In the separation of anions, the resin must have an exchange capacity between about 0.005 mequiv/g and 0.10 mequiv/g. Typical eluents are 1.0 x 10 M solutions of sodium or potassium salts of benzoic acid, hydroxybenzoic acid, or phtha-lic acid. These eluents are sufficiently dilute that the background conductivity is quite... 

Non-Suppressed Ion Chromatography Table 6.10. Background conductances of eluents l... 

P. R. Haddad and R. C. Foley, Aromatic bases as eluent components for conductivity and indirect ultraviolet detection of inorganic cations in non-suppressed ion chromatography. Anal. Chem., 61, 1435,1989. 

Chen, Z. L., Megharaj, M. Naidu, R. (2007). Speciation Of lodate And Iodide In Seawater By Non-Suppressed Ion Chromatography With Inductively Coupled Plasma Mass Spectrometry. Talanta, Vol.72, No.5, pp 1842-1846, ISSN0039-9140... 

Modem ion chromatography was first reported in 1975 in a landmark paper by Small, Stevens, and Bauman. At present, there are two main types of ion chromatography suppressed ion chromatography and non-suppressed ion chromatography. Ion exchange remains the primary separation mode used in ion chromatography today, although the apparatus used for the separation of the... 

In non-suppressed ion chromatography, mixtures of ethylenediamine and aliphatic carboxylic acids (such as tartaric acid or oxalic acid) are typically employed. In suppressed ion chromatography, the required reduction of background conductivity would only be possible by using high-capacity membrane-based suppressor systems. 

In September 1975 ion chromatography was publicly presented at a meeting of the American Chemical Society where the Dionex Corporation exhibited the first commercially available instrument for performing ion chromatography. Several years later, Gjerde et al. developed a variety of ion chromatography, a non-suppressed ion chromatography techniques. 

In non-suppressed ion chromatography systems, mixtures of ethylenediamine and aliphatic dicarboxylic adds such as tartaric add or oxalic add are typically employed as an eluant for the separation of alkaltne-earth metals. Those mixtures have a relatively high intrinsic conductance, so that chromatographic signals are registered as negative peaks. 

Fladdad, P. R. and M. Y. Croft. 1986. The determination of lactate, acetate, chloride and phosphate in an intravenous solution by non-suppressed ion chromatography. Chromatographia 21 648-650. 

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