Determination of Biuret Content in Fertilizers by High Performance Liquid Chromatography: Single-Laboratory Validation and Collaborative Ring Test Study

Urea or urea-based fertilizers has become the leading form of nitrogen fertilizers around the world. Biuret, as one of major by-products formed during the manufacturing of urea, was proved to be harmful to plant growth. A Single-Laboratory Validation (SLV) study for a newly proposed High Performance Liquid Chromatography (HPLC) method was conducted. A total of six samples were tested in the SLV study: two urea samples, and four compound fertilizers with various compositions from different sources. In addition, one biuret standard from Aldrich® and one biuret reference from Alfa Aesar® were used as standard materials. The system was linear over a concentration range of 0~200 ppm biuret, with a correlation coefficient≥0.999. Recoveries were determined by spiking three of the validation samples with known amounts of biuret standard solutions and measuring the biuret level according to the method. The recovery rates lies between 98.14% and 107.24%. Method precision was determined by analyzing of six validation samples under five replicate analyses, the RSDs ranged from 0.69% to 1.85%. Further study by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) has revealed that the biuret was well-separated from urea and other N-containing compounds in the system by this method. Moreover, the proposed method is verified in the international Collaborative Ring Test (CRT) study organized by ISO/TC 134 “Fertilizers and Soil Conditioners”. Systematically statistical analysis on the data obtained has proven that this method is capable of effectively monitoring biuret content in a wide range of fertilizers.