Soil P Hedley Fractionation

By Jared L. DeForest

Reagents - enough for 40 samples

0.5M NaHCO₃

1liter volumetric flask

• 42 g Sodium Bicarbonate
• Bring to volume with DI water.
• Adjust to pH 8.5.

0.1 M NaOH

1 liter volumetric flask

• 4 g Sodium Hydroxide
• Bring to volume with DI water.

1.0 M HCl

1liter volumetric flask

• 83.3 ml Hydrochloric Acid (12 M)
• Bring to volume with DI water.

0.5 M HCl

1liter volumetric flask

• 41.7 ml Hydrochloric Acid (12 M)
• Bring to volume with DI water.

Sequential Extraction Procedure

In a 50 ml centrifuge tube

• 10 g Field fresh, sieved soil

Resin P

• 1 Bicarb charged resin strip (2 x 6 cm; Charging: shake strips 10 min in 100 ml 0.5 M NaHCO₃, rinse 3 times with DI water, shake dry.)
• 25 ml DI water

Shake for 4 hours, centrifuge, and discard supernatant.

In a 250 ml flask

Extract resin with 25 ml of 0.5 M HCl for 1 hour on a shaker.

NaHCO₃ P

• 25 ml 0.5M NaHCO₃

Vortex briefly to break up soil plug.

Shake for 18 hours, centrifuge, and store supernatant at 4°C.

NaOH P

• 25 ml 0.1M NaOH

Vortex briefly to break up soil plug.

Shake for 18 hours, centrifuge, and store supernatant at 4°C.

Sonicate NaOH P

• 25 ml 0.1M NaOH

Vortex briefly to break up soil plug and Sonicate for 2 minutes.

Shake for 18 hours, centrifuge, and store supernatant at 4°C.

HCl P

• 25 ml 1.0M HCl

Vortex briefly to break up soil plug.

Shake for 18 hours, centrifuge, and store supernatant at 4°C

P Residue

In a 60 ml heat treated test tube

• Add soil from HCl P fraction with a minimal amount of DI water.
• 5 ml Sulfuric acid

Heat slowly to evaporate water (block digester) & allow cooling to hand-warm.

• 0.5 ml 30% H₂O₂ (Careful, it may overflow.) Reheat for 30 minutes.

Repeat H₂O₂ additions until liquid is clear (usually 10 times).

Cool, make to volume (i.e., 25 ml) and analyze on the ICP.

Standards

Dilution	Working Standard (ml)	Matrix (ml)
0%	0.0	5.0
1%	0.1	9.9
10%	1.0	9.0
25%	2.5	7.5
50%	3.0	3.0
100%	6.0	0.0

In a 50 ml volumetric flask

• 5 ml of a 1000 ppm certified stand P solution
• Bring to volume with DI water to make a 100 ppm standard.

Mix standards with the extracting solution (matrix).

Resin (5 to 10 ppm)

In a 15 ml disposable centrifuge tube

• 1.5 ml 100 ppm solution
• 13.5 ml 0.5 M HCl (matrix)

Will make a 10 ppm working solution

Follow dilution table.

NaHC0₃ (5 to 20 ppm)

In a 15 ml disposable centrifuge tube

• 3 ml 100 ppm solution
• 12 ml 0.5M NaHCO₃ (matrix)

Will make a 20 ppm working solution

Follow dilution table.

NaOH (50 ppm)

In a 15 ml disposable centrifuge tube

• 7.5 ml 100 ppm solution
• 7.5 ml 0.1M NaOH (matrix)

Will make a 50 ppm working solution

Follow dilution table.

HCl P (10 to 20 ppm)

In a 15 ml disposable centrifuge tube

• 3 ml 100 ppm solution
• 12 ml 1.0M HCl (matrix)

Will make a 50 ppm working solution

Follow dilution table.

P Residue (50 to 100 ppm)

Follow dilution table with DI water.

Revised: 06/30/09 Revised: 10/10/11