Determination and Monitoring of Polar Compounds and Acidic Herbicides Using a Modified Samos System

Abstract

A system for the automated monitoring of organic pollutants in surface waters (SAMOS) has been developed over the last 5 years to monitor for the presence of organic contaminants in surface water. It uses a solid-phase extraction (SPE) trace enrichment step followed by on-line elution and separation by HPLC. Detection and provisional identification is obtained with diode array detection. For pesticide and herbicide analysis, mainly medium volatile, neutral compounds such as carbamates, triazines and phenyl ureas have been reported. Ionic species such as phenoxy acid herbicides are poorly preconcentrated at normal river pH. These ionic/polar compounds frequently show breakthrough from the SPE cartridge prior to complete loading of the sample. Any retained polar analytes are also often obscured by the presence of co-extracted humic substances in river water samples. The paper presents the required changes to the original SAMOS system to allow ionised and polar pollutants to be successfully analysed. These changes involve allowing the ionic/polar compounds to break through from the loading onto the primary cartridge (PLRP-S), allowing all but the last few ml of sample to go to waste. When breakthrough of the relevant analytes is achieved, the remaining sample is switched automatically on-line to a secondary cartridge (again PLRP-S) with acid being added just prior to this to neutralise the compounds This secondary cartridge effectively preconcentrates the ionic/polar compounds. The two cartridges are desorbed in two subsequent gradient elution LC-DAD runs. Analysis of several major classes of compounds is achieved, notably members of the triazine, phenyl urea, phenol and acid herbicide groups. The system has been designed and tested in the laboratory and applied at an installation remote from the laboratory on a river site as part of an intake protection programme. Details of the method performance, experiences of operation and access of the system via telemetry are discussed.