Analytical Methods:BCR Fractionation

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BCR sequential method
The BCR method is a modified three-step sequential extraction procedure proposed by the Standards, Measurement and Testing Programme (formerly BCR) of the European Commission (ref).

This method uses:
 * 1) Acetic acid extraction to recover the fraction that is mobile, soluble in water or weak acids, or adsorbed to soil carbonates.
 * 2) Hydroxylammonium chloride extraction to recover the fraction bound to iron and manganese oxides.
 * 3) Hydrogen peroxide followed by ammonium acetate is used to recover the fraction bound to organic matter and sulphides.

Safety
Some of the chemicals used in the method are toxic or highly corrosive. Always consult chemical safety data sheets and follow appropriate health and safety protocols before handling or using chemicals.

Many chemical safety data sheets are available here from this Oxford University based database.

Equipment (excluding final analysis)

 * Fume cupboard
 * Protective clothing
 * Analytical scales
 * Centrifuge capable of taking 100ml tubes
 * Mechanical sample shakers, preferably end-over-end
 * Heated water bath
 * 100 ml centrifuge tubes with stoppers
 * Polythene sample bottles
 * 1 litre glass volumetric flasks
 * Glass beakers, including 1 litre beakers
 * Glass stirring rods
 * Waterproof marker

Reagents
25ml of glacial acetic acid is added to 0.5 l of distilled water in a 1 l volumetric flask. This is made to volume with more distilled water. Then 250 ml of this solution is diluted to 1 litre with distilled water in a second volumetric flask. Dissolve 34.75 g of hydroxylammonium chloride in 400 ml of distilled water. Transfer to a 1 litre volumetric flask and add 25 ml of 2 molar Nitric acid. Make to volume (1 litre) with distilled water. This solution should be used on the day it is made. Use as supplied by manufacturer. Dissolve 77.08 g of ammonium acetate in 900 ml of distilled water. Adjust to pH 2 with concentrated Nitric Acid and make to 1 litre volume with distilled water.
 * Distilled water
 * Solution A (0.11 Molar acetic acid)
 * Solution B (0.5 Molar hydroxylammonium chloride)
 * Solution C (8.8 Molar hydrogen peroxide)
 * Solution D (1 Molar ammonium acetate)

Methods

 * 1) Oven dry the soil or sediment material at 105oC and sieve to less than 2 mm through a stainless steel or polythene mesh.
 * 2) Weigh out 1 g of soil and record weight to 3 decimal places.
 * 3) Add 40 ml of solution A to 1g of soil in a 100 ml centrifuge tube, stopper, and shake for 16 hours (overnight). You must start the shaking immediately the solution is added.
 * 4) Centrifuge at 3000 g for 20 minutes and carefully decant the liquid (supernatant) into a polythene bottle. Label the bottle with sample name and solution name and store in a refrigerator until analysis.
 * 5) Wash the solid residue in the centrifuge tube in 20 ml distilled water, shake for 15 minutes and centrifuge at 3000 g for 20 minutes. Carefully decant off the liquid and discard.
 * 6) Add 40 ml of solution B to the solid residue in the centrifuge tube, stopper and shake for  16 hours (overnight). Begin shaking immediately the solution is added. Centrifuge as in step 4 and store the liquid in a polythene bottle as before.
 * 7) Repeat the wash process (step 5).
 * 8) Add 10ml of solution C to the solid residue in the centrifuge tube; add only a small amount at a time as there can be a violent reaction that may cause the material to ‘boil’ over. Cover the tube loosely and leave for 1 hour, shaking occasionally.
 * 9) Place centrifuge tube uncovered in a water bath at 85oC and leave until less than 3 ml of liquid remains.
 * 10) Add a further 10 ml of solution C, loosely cover and place back in the 85oC waterbath for a further 1 hour.
 * 11) Remove  the cover and continue to heat at 85oC until only about 1 ml of liquid remains. Do not dry completely.
 * 12) Remove from the waterbath and allow to cool.  Add 50 ml of solution D and shake for 16 hours (overnight).
 * 13) Centrifuge and store the liquid as in step 4.

With each batch include at least one procedural blank which is treated in the same way as all the samples but which contains no actual sample material. Store and analyse the liquids from each step exactly as for your samples. Also store and analyse a sample of Solution A, B, C, and D (reagent blanks).

Reference
Rauret, G., L&oacute;pez-S&aacute;nchez, J.F., Sahuquillo, A., Rubio, R., Davidson, C., Ure A. ann Quevauviller, Ph. (1999) Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials. Journal Environmental Monitoring, 1, 57-61.

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