This document specifies a method for extraction, separation, and determination of inorganic arsenic (iAs) in plant biostimulants using anion-exchange high performance liquid chromatography (HPLC) or ion chromatography (IC) coupled to ICP-MS. This document is applicable to the fertilizing product blends belonging to PFC 7 where the EU fertilising product plant biostimulant contained in the blend represents the highest % by mass in the blend. In case of equal shares, the user can apply either this or the standard(s) applicable to the other component product(s).