Determination of ‘labile’ phosphate in lake sediments using anion exchange resins: a critical evaluation
1992
Waller, Pamela A. | Pickering, William F.
Transfer of phosphate ions from sediment particles to an anion exchanger (Amberlite IR-4B or Duolit A378) has been used to determine the ‘labile’ (or ‘available reactive’) phosphorus content of several salt-water lake sediments. An evaluation of the procedure identified several sources of error, e.g. (i) incomplete transfer of P to the exchanger [due to competition for sites by other anions present in the dried sediments]; (ii) slow intermediate processes such as dissolution of inorganic phosphate compounds; (iii) sorbed P not fully retrieved from the exchanger resins [due to the limited efficiency (∼90%) of the displacement process]; and (iv) absorbance readings in the colorimetric procedure used to determine phosphate can be enhanced by light scattered from fine particles. Accordingly, for the determination of the amount of ‘labile’ phosphate present in sediments it is recommended that one (a) stirs the exchanger/suspension system for at least 24 hours; (b) analyses both the aqueous phase and the resin phase; (c) extracts the resin phases at least twice with 1M NaCI; and (d) repeats the “transfer to resin” step after isolating the partly-washed sediment and re-suspending it in water. The contributions from steps (d) and the non-sorbed P in the aqueous phase segment of (b) changed slightly with changes in the ratio of exchanger to sediment mass.
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