DIN EN 16109:2012-01

The European Standard specifies two complementary methods (method A and method B) that allow lignosulfonates to be identified as soluble complexing agents in fertilizers. 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 represents 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. The methods are applicable to EC fertilizers covered by Regulation (EC) No 2003/2003 on fertilizers. The method for the determination of the phenolic hydroxyl content is based on the ultraviolet absorption of phenols in alkaline solution (phenolate). The absorbance of an alkaline solution of the sample is measured directly against an acid solution of the same sample. The phenolic hydroxyl content of the sample is calculated from the molar extinction coefficient maximum of the resulting curve and the molar extinction coefficient of reference compounds determined in the same way. The determination of the absorption at 232,5 nm is normally considered the method for the quantification of lignosulfonates, providing that no other ultraviolet absorbing organic compounds are present. Both methods have been validated on the European level in various inter-laboratory tests. A first inter-laboratory test was carried out in 2008 with eight participating laboratories and three different samples: one non-commercial, Zn lignosulfonate, one commercial, Fe lignosulfonate and one commercial micronutrient complex, not lignosulfonate. The reproducibility results were poor, especially those corresponding to Method B (organic S content). A second inter-laboratory test was performed in 2009 with eight participating laboratories from four countries and three different samples. The samples were the same as the ones of the first ring test except for the Zn lignosulfonate, and a commercial Zn lignosulfonate was chosen. For this test some modifications were included in the method. The results of this inter-laboratory test are summarized in Annex A. The European Standard has been prepared by CEN/TC 260 "Fertilizers and liming materials" (secretariat: DIN). National Mirror Committee is Working Committee NA 057-03-02 AA "Düngemittel" ("Fertilizers") of NAL.