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Determination of inorganic anions at parts per billion levels using single-column ion chromatography without sample preconcentration

journal contribution
posted on 2023-05-26, 16:21 authored by Heckenberg, AL, Paul HaddadPaul Haddad
Single-column ion chromatography using low-capacity ion-exchange columns and dilute eluents contaioning an aromatic acid {ref. 1-9} have proved to be a popular alternative to suppressed ion chromatography {ref. 10} for the determination of inorganic anions. The single-column methods appear to be readily adaptable to conventional high-performance liquid chromatography (HPLC) instrumentation and have been employed with conductivity {ref. 1-8}, indirect refractive index {ref. 9}, or indirect UV absorbance {ref. 8-9} detection methods. Detection limits are comparable for the above detection methods and are typically in the range 0.2-1.0 ppm, depending on the particular ion being determined. Lower detection limits are possible if sample pre-concentration methods are employed {ref. 11}, such as the use of an ion-exchange pre-column onto which a relatively large volume of sample is loaded before elution onto the analytical column. The utility of this sample pre-concentration procedure is strongly dependent on the sample composition, the procedure used to load the concentrator column, and preconditioning of the concentrator column. For example, samples containing a mixture of strongly adsorbed ion (such as sulphate) and a weakly adsorbed ion (such as chloride) must be preconcentrated with care to avoid loss of chloride through displacement by sulphate. One possible alternative to sample preconcentration is the use of large injection volumes (up to 2 ml), and this approach has been reported for the determination of chloride and sulphate using conductivity detection {ref. 2}. In our experience, conductivity detection is not optimal with large injection volumes due to severe baseline instability following injection. We have found that indirect UV absorbance detection {ref. 8,9,12} is superior and in this paper, we report the use of this detection method for the determination of a mixture of inorganic anions at low ppb* levels. *Throughout this article, the American billion (10^9) is meant.


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Journal of Chromatography







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