Modified procedure for the determination of exchangeable ammonium ions in lake sediments
1990
Hatton, Denise | Pickering, William F.
The determination of the exchangeable ammonium ion content of marine sediments has been re-evaluated and a modified procedure proposed. Optimum recovery in a single extraction step was achieved by gentle mixing of small weight of sample with 0.2 M KCI (pH 2.5) for half an hour, followed by analysis of the filtered extract using an ammonia ion selective electrode. Errors attributable to re-sorption of released ammonium ion by the particulate matter tended to be large, except when extraction time was kept short and the concentration of released NH4⁺ was kept below 1 mg L⁻¹ through use of solid to extractant ratios of 1:30 or 1:60. With contaminated sediments (>50 μg NH4⁺ g⁻¹, a second extraction may be required to retrieve a residual 5 to 10% of the exchangeable ammonium ion content. Recovery levels when standard additions of NH4Cl were made to fine particle sediment suspensions were <100%, another response attributable to the sorption capacity of the sediments. Sediments of different nature were examined, ranging from predominantly sand to black oozes.
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