Advanced Chromatographic Separation of Diquat and Paraquat: Longer Retention Times and Enhanced Selectivity

Diquat and paraquat are nonselective quaternary ammonium herbicides widely used in agriculture. While effective for plant control, their permanent cationic charge and high-water solubility contribute to acute toxicity in humans and high environmental mobility. Consequently, the Environmental Protection Agency (EPA) strictly regulates these compounds in drinking water and environmental samples to minimize exposure risks. EPA Methods 539 and 549.2 are critical for ensuring the safety of drinking water, making accurate and reliable analytical methods not only a public health imperative but also a regulatory requirement.
 

Laboratories performing these analyses face the dual challenge of achieving stringent detection limits while maintaining high sample throughput. Traditional high performance liquid chromatography (HPLC) methods for quaternary ammonium compounds often rely on longer columns to achieve adequate chromatographic resolution, particularly with complex sample matrices. While effective, these longer columns inherently lead to extended run times, increased solvent consumption, and higher backpressures, all of which can impact laboratory efficiency and operational costs.
 

The analysis of diquat and paraquat is further complicated by their chemical properties. Reversed phase chromatography can be challenging for these analytes due to the permanently charged, highly polar nature of the analytes leading to poorly retained and poorly resolved peaks. Even when retention is achieved, resolution is frequently insufficient, and the two compounds may partially coelute, especially in complex matrices.
 

To address these analytical challenges, Hamilton Company has developed the PRP-Z2, a new stationary phase specifically engineered for robust and rapid separation of diquat and paraquat. The PRP-Z2 features increased crosslinking, deeper pores, higher surface area, and embedded polar moieties, thus improving retention and selectivity for highly polar, cationic analytes. This application note demonstrates how the Hamilton PRP-Z2 delivers fast, robust, and EPA-compatible separation of diquat and paraquat, utilizing both traditional and short column formats and low flow rates to provide increased throughput and reduced solvent use—without compromising precision, accuracy, or regulatory compliance.