Degree Name

Master of Science (MS)

Semester of Degree Completion

1990

Thesis Director

Blair E. Miller

Abstract

For many years the determination of common inorganic and organic anions was hindered by the lack of adequately sensitive analytical techniques. The determination of these anions was laborious and time consuming (e.g. titration, precipitaion, gravimetric analysis etc.). Because of the development of high-performance liquid chromatography, the anion exchange separation of simple inorganic and organic anions is now possible. Now, there are a broad and ever-increasing array of chromatographic methods supplanting these older chemical methods. However, detection is still a problem, but indirect detection provides a practical route for the detection of non-chromophoric inorganic and organic anions.

This dissertation describes the technique of Indirect Photometric Chromatography (IPC) for the determination of common inorganic anions and short-chain carboxylic and sulfonic acids. In this study, inverted peaks were observed in an elevated baseline as the transparent sample ions were selectively displaced from the anion exchange column by the UV absorbing mobile phase ion sodium benzoate. A Hamilton PRP-X100 (styrene-divinyl benzene) anion exchange column which possessed a low capacity and a wide working pH range (1-13) was employed. The influence of various mobile phase parameters such as benzoate concentration, pH, and percent organic content was investigated. A 2.0 mM concentration of sodium benzoate provided maximum eluting ability for the separation of common inorganic anions (F-, Cl-, Br-, NO2-, NO3-, and H2PO4- ) within eight minutes with UV detection at 260 nm. At high pH, the competition between hydroxide and benzoate ions in the elution process decreases the detection sensitivity. Multicomponent mixtures of straight-chain alkyl carboxylic and sulfonic acids in the anionic form were also separated upon the addition of acetonitrile to the mobile phase.

Combined anion exchange/reversed phase interactions were found to influence the retention of these organic acids.

The application of the benzoate eluent with UV detection method to the determination of anions was demonstrated via the analysis of chloride, EDTA and sorbate in a commercial saline solution. The limits of detection for injected chloride and EDTA were 1.5 ppm, while sorbate was detected at 0.5 ppm.

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