Micro-columns packed with Chlorella vulgaris immobilised on silica gel for mercury speciation

A method has been developed for mercury speciation in water by using columns packed with Chlorella vulgaris immobilised on silica gel. The method involves the retention of CH₃Hg⁺ and Hg²⁺ in micro-columns prepared by packing immobilised algae in polypropylene tubes, followed by selective and sequential elution with 0.03 and 1.5 M HCl for CH₃Hg⁺ and Hg²⁺, respectively. The adsorption capacity of the micro-algae for Hg²⁺ and CH₃Hg⁺ has been evaluated using free and immobilised C. vulgaris. The efficiency uptake for both species at pH 3 was higher than 97%. Studies were carried out on the effect of retention and elution conditions for both species. Furthermore, the stability of mercury species retained on algae-silica gel micro-columns and lifetime of the columns were also investigated. Hg²⁺ showed a higher stability than CH₃Hg⁺ at 0 °C (21 and 3 days, respectively) and a better lifetime than for the organic species.

The developed method was applied to the analysis of spiked tap, sea and wastewater samples. Recovery studies on tap and filtered seawater provided results between 96 ± 3 and 106 ± 2 for Hg²⁺ and from 98 ± 5 to 107 ± 5 for CH₃Hg⁺, for samples spiked with single species. For samples spiked with both CH₃Hg⁺ and Hg²⁺, the average recoveries varied from 96 ± 5 to 99 ± 3 and from 103 ± 6 to 115 ± 5 for Hg²⁺ and CH₃Hg⁺, respectively. However, the percentages of retention and elution on wastewater and unfiltered seawater were only adequate for the inorganic species.