This method adds value to Method 13B1 by extracting Fe- and Al-bound organic complexes.
As for Methods 6B1, 6B2 or 6B3 and 13B1.
Prepare pyrophosphate soil extracts as described in Method 13B1, then pipette 10.0 mL of extract into 30 mL teflon beakers and evaporate to a low volume on a sand bath or equivalent. Transfer the concentrated pyrophosphate extract for the determination of total C by Method 6B1 or 6B2b, using a minimum amount of water to ensure this step is quantitative.
If using a method based on Dumas high-temperature combustion, add 1 scoop of silica sand and 1 scoop of Fe chips to a LECO crucible and place on the sandbath at least 10 min before they are needed. Next transfer carefully and in stages the concentrated pyrophosphate extract to the contents of the LECO crucible, taking care that the liquid does not soak through the crucible. When dry, add ½ scoop of Sn metal and 2 scoops of Fe chips and determine total C content. Alternatively, use combustion conditions and catalysts as recommended by the instrument’s manufacturer.
Calculate pyrophosphate-extractable C and correct to an oven-dry basis after allowing for the 1:100 ratio of the initial pyrophosphate extract and the 10 mL aliquot taken.
Report as pyrophosphate-extractable C (% C) on an oven-dry basis, using relevant air-dry moisture to oven-dry moisture ratios. Refer to Method 2A1 for guidance with regard to this soil moisture calculation.