A Sequential Injection Analysis Method for the Determination of Glyphosate and Aminomethylphosphonic Acid in Water Samples

A conventional laboratory method for the determination of glyphosate and its degradation product aminomethylphosphonic acid (AMPA) is high performance liquid chromatography (HPLC) followed by post column derivatization with o-phthaldialdehyde (OPA). However, AMPA is partly decomposed in the process causing a deviation in the AMPA detection or even making a simultaneous detection of glyphosate and AMPA with the described postcolumn procedure impossible. We used a compact sequential injection analysis system and optimized the process conditions for both analytes independently from each other. The process conditions were adjusted to the different chemical characteristics of AMPA (primary amine) and glyphosate (secondary amine), which needs to be oxidized to a primary amine prior to the derivatization. An ion exchange column was included in the system to eliminate amines interfering with the method. Limits of detection of 16 and 9 µg L-1 for glyphosate and AMPA, respectively are similar to those achieved with HPLC methods reported in literature, but compared to conventional HPLC methods only small amounts of reagents are consumed.