Citrate-Dithionate-Bicarbonate Extraction

Reagents
Sodium Bicarbonate (NaHCO3), 1M
Sodium Citrate, 0.3M
Sodium hydrosulfite (Na2S2O4)

Procedure
Weigh 4g of soil (1g clay) into a 100-mL centrifuge tube. Add 40mL of 0.3M Na-citrate and 5mL of 1M NaHCO3. Bring temperature to 80ºC in a water bath. Add 1g Na2S2O4, stir constantly for 1 minute and occasionally for 15 minutes. Centrifuge for 5 minutes at 1,600 to 2,200 rpm. Decant clear supernatant into 500 mL volumetric flask and make to volume.

References
Mehra, O.P. and M. L. Jackson. 1960. Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bcarbonate. Proc. 7th Natl. Conf. On Clay and Clay Minerals, pp. 317-327. Permagon Press, New York.