This document specifies two methods required for the identification of lignosulfonate by UV-Vis spectrophotometry (method A) and gravimetry (method B) in organo-mineral fertilizers. NOTE Lignosulfonate, as a complexing agent, is a natural polymer produced as a by-product of the sulfite method for manufacturing paper from wood pulp in the paper industry. As a natural polymer, it presents a poorly defined and variable chemical structure. It is an intricate mixture of small- to moderate-sized polymeric compounds with sulfonate groups attached to the molecule, and diverse complexing capacity.