Organic Carbon Determination

Analysis of Soil Organic Matter by Wet Combustion

By Jared L. DeForest

Reagents

In 1 L volumetric flask

• 49.04 g Potassium Dichromate (K₂Cr₂O₇)

Bring to volume with DI water.

• 36 N Sulfuric Acid (H₂SO₄)

Standard (H3)

In 1 L volumetric flask

• 9.5 g Sucrose

Bring to volume with DI water.

• Add 1, 2, 4, 6, and 8 ml of the 4 mg C ml^-1 sucrose standard solution into five 250 ml Erlenmeyer flasks.
• Add 10 mL Potassium Dichromate, swirl.
• Add 20 mL Sulfuric Acid.
• Add 100, 99, 98, 96, 94, and 92 ml of H₂O to the 0, 4, 8, 16, 24, and 32 mg C standards.

Standards: 0, 4, 8, 16, 24, and 32 mg C

Procedure

Add the following to 250 mL Erlenmeyer flask

• 1.0 g Soil (0.5 g if samples is dark)
• 10 mL Potassium Dichromate

Swirl. (Make sure soil is completely covered.)

• 20 mL Concentrated H₂SO₄

Swirl & let sit for 10 minutes.

• 100 mL DI water

Centrifuge for 5 minutes at 2000 rpm.

Using a pipette, transfer supernatant 200 µl into each well in one column on a clear well plate.

Measure absorbance at 620 nm.

Created: 6/25/07