This method is identical to Method 20F1, apart from the analytical finish, which is based on ion chromatography. Because the IC can be made specific for SO42– in solution (rather than for total S in solution), results by this method will almost always be lower than corresponding results by Method 20F1. Clients of laboratories with the option of using both instruments (ICPAES or IC) would be best served by specifying this method when working with highly organic soil samples.
The method described is based on chemically suppressed IC, although single-column IC with electronic suppression of eluent conductivity is equally suitable. See Methods 5A3a and 5A3b for further details on both IC technologies.
As for Method 20F1 for soil extractions and guidance on the preparation of standard solutions, accepting that dilutions down to around 20 mg S/L will be necessary to harmonise with optimal instrument performance in the presence of a strong background of Cl–. For all other solutions, refer to Method 5A3a and to Method 10B4.
Weigh, extract and prepare for analysis as for Method 20F1, then analyse for SO4-S by IC, guided by Method 5A3a and Method 10B4, and adapting calculations to account for the 1:40 soil/solution ratio and for additional dilutions.
Other than dilution, the only preparation required after soil extraction is the removal of particulate matter >0.20 μm by filtration or centrifugation. Analysis can be completed sequentially within ≈30 min or less, using a few mL of extract.
Report SHCl (IC) on an oven-dry (85°C) basis.