Simple Large Volume Injection Method for Trace-Level Glyphosate in Bottled Drinking Water

• Analyze glyphosate without derivatization or ion pairing.
• Unique Raptor Polar X column provides good retention and efficient elution, resulting in better peak shape.
• Direct large volume injection makes it easy to increase sensitivity at ppt levels.

The analysis of glyphosate in water is challenging primarily because it is not retained on reversed-phase columns and its response is often poor due to chelation with metal surfaces along the sample path through the LC-MS/MS system. Derivatization and ion-pairing reagents are often used to improve performance, but they can be unfriendly to the instrument and require additional sample preparation time. Using a Raptor Polar X column is a better alternative because the novel stationary phase has an affinity for polar anionic compounds, such as glyphosate, and it provides both effective retention and efficient elution.

In the method for glyphosate in water shown here, an ion-exchange mechanism in the column provides enough retention under the initial mobile phase conditions to allow large volumes (500 µL) of bottled water to be injected, which is a very simple way to improve low-level sensitivity. To achieve the best retention/elution characteristics, the mobile phase additive and pH were carefully chosen to provide a charge state that leads to adequate retention and optimal sensitivity. In addition, a one-time passivation of the LC system (without an analytical or guard column in the flow path) helped prevent undesirable chelation and a good response was observed at 100 ppt (S:N > 50).