Sequential fractionation procedures are discredited in so far as attribution to chemical species/phases in soils/sediments.

This could be helpful:

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216881

Do you mean sequential chemical extraction technique? If so, many conditions affect the result (e.g., solids to solution ratio, with or without washing).

Hello Jalali,

Kindly look at this paper

https://edepot.wur.nl/205452