This method is almost identical to Method 9I2a, apart from its analytical finish. This is undertaken by ICPAES. The method also permits the analysis of higher solution P concentrations (10 x), relative to the Murphy and Riley colorimetric finish.
0.01 M CaCl2 solution, the Phosphate Equilibrating Solution, and the P Primary Standard (1 L contains 100 mg P) are identical to those for Method 9I2a.
Add appropriate aliquots of the P Primary Standard to 0.01 M CaCl2 to achieve final working standards ranging from 0 to 100 mg P/L in 0.01 M CaCl2.
Weigh 7.0 g air-dry soil (<2 mm) into 100 mL bottle or centrifuge tube and add 70 mL of P equilibrating solution and 3 drops of chloroform (CHCl3) and proceed with soil equilibration as for Method 9I2a.
For ICPAES, aspirate clear soil extracts (as per Method 9I2a) and Working Standards (0 to 100 mg P/L), selecting an appropriate spectral line with due consideration for interferences and the type of instrument. For example, use 213.618 nm for radial mode ICPAES or 178.221 nm for axial mode ICPAES. This ‘finish’ measures all the P in solution regardless of the chemical species present.
Proceed as for Method 9I2a (and Note 1 for that method).
Report PBI+ColP on an air-dry (40°C) basis.