School of Earth and Environment

Extraction techniques

In Cohen we have various extraction techniques available to us. Here we will highlight a few key techniques.

Fe Sequential Extraction Procedure

The sequential extraction procedure of Poulton and Canfield (2005) is designed to quantitatively define seven operationally derived iron pools:

  • (1) Fecarb – carbonate associated Fe (siderite and ankerite);
  • (2) Feox1 – easily reducible oxides (Ferrihydrite and lepidocrocite);
  • (3) Feox2 – reducible oxides (Goethite, hematite and akaganèite);
  • (4) Femag – magnetite;
  • (5) FePRS – poorly reactive sheet silicate Fe;
  • (6) Fepy – Fe pyrite;
  • (7) FeU – unreactive silicate Fe

This is the only calibrated quantitative method so far that exists to identify water column redox conditions. This method allows separate identification of magnetite and the complete evaluation of Fe carbonate species. The scheme may be used to successfully assess Fe partitioning in modern and ancient sediments including shales and carbonates.

Fe Sequential Extraction Procedure

The Cohen laboratory is set up to complete this extraction scheme efficiently, with all the correct reagents and equipment available. A simplified procedure is used for ancient sedimentary rocks, only completing steps 1, 3 and 4. Samples are diluted and analysed using AAS.

For more information please get in touch.

Poulton, S. W. and D. E. Canfield. 2005. Development of a sequential extraction procedure for iron: implications for iron partitioning in continentally derived particulates. Chemical Geology, 214(3-4), pp.209-221

Written by Jenny Thompson (10/04/2015)

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P Sequential Extraction Procedure

The SEDEX sequential extraction method of Ruttenberg (1992) was developed for the quantification of 5 sedimentary phosphorus reservoirs, and has been shown to be a robust separation method for a variety of modern sedimentary settings. The main aim of the method is to chemically separate authigenic P phases from detrital apatite of igneous or metamorphic origin (FAP), and hence this dictates the sequence of the extractions, and the conditions required. The method combines extractions previously used in selective leaching schemes for metals and P, which have then been modified to enhance the recovery of the desired P-bearing phases.

P Sequential Extraction Procedure
P Sequential Extraction Procedure

Following each extraction (apart from step II), solutions are analysed for phosphorus colourimetrically on a spectrophotometer, following the phosphomolybdate blue method of Koroleff (1976). Solutions from step II are analysed by ICP-OES.

The Cohen laboratory is set up to complete this extraction scheme efficiently, with all the correct reagents and equipment available.

For more information please get in touch.

Koroleff, F. 1976. Determination of nutirents. In: K. E. A. GRASSHOFF, ed. Methods of Seawater Analysis. 2nd ed. Verlag-Chimie, pp.117-156.

Ruttenberg, K. C. 1992. Development of a Sequential Extraction Method for Different Forms of Phosphorus in Marine-Sediments. Limnology and Oceanography, 37(7), pp.1460-1482.

Written by Jenny Thompson (10/04/2015)

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HF extractions

We have two fume cupboards specially designed for working with hydrofluoric acid (HF). These are regularly used for digestion of rocks.

We also have a Mars Express microwave which can be used for total rock digestion at high temperature (max. 240°C) and pressure (55 bar).

Detailed procedures are in place to keep our workers safe when using HF including regular maintenance of fume cupboards. 

Written by Andy Connelly (10/04/2015)

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