DETERMINATION OF SULFATE IN COASTAL SALT MARSH SEDIMENTS WITH HIGH-CHLORIDE CONCENTRATION BY ION CHROMATOGRAPHY: A REVISED METHOD

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Abstract
In order to elucidate the relationship between sulfate reduction and mineralization of organic matter in coastal sediments, the content of sulfate in sediment samples should be measured. Chloride, sulfate, bromide, nitrate, and phosphate are the standard anions in coastal sediment samples. Ion chromatography (IC) is one of the popularly used techniques for determinations of these anions. However, the peaks of the five anions in the IC system coincide with each other under high chloride conditions when using the normal method. In this article, an improved, highly sensitive method for simultaneous separation and determination of sulfate, bromide, nitrate, and phosphate in the samples with high chloride concentration is established and evaluated by IC. In high concentrations of chloride samples, the effects of eluent concentration on the retention time and separation of other anions are studied. The peaks of these anions can be well separated on an AS11 ion-exchange column by a low concentration of NaOH eluent (10 mM). in one injection. Gradient elution is helpful to shorten retention time, especially for phosphate. The method detection limit of sulfate is 0.091 mg · L−1. The recovery of sulfate ranged from 100.5% to 106.8%, when the concentrations of standard solution are close to those of the samples. This technique was validated by determining the content of sulfate and chloride in coastal salt marsh sediment samples.

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