General Strategy for Multiresidue Analysis of Polar Pesticides in Ground Water Using Coupled-Column Reversed-Phase LC and Step-Gradient Elution

We describe a strategy for the development of coupled-column liquid chromatographic methods for groups of polar pesticides in environmental water samples. This method is needed in flexible pesticide monitoring programs. The strategy is based on the use of retention data introduced into a computer program; the program calculates conditions for column switching and step-gradient elution. As an example for the validation of this approach, we developed a multiresidue method that is capable of assaying nine polar pesticides: bentazone, DNOC, dinoseb, dinoterb, metamitron, monuron, metribuzin, diuron, and linuron. Using computer simulation, we found proper conditions for the on-line cleanup of extracts by means of column switching and subsequent step-gradient elution for efficient separation of the analytes. The pesticides can be assayed in ground water samples down to a concentration of 0.1 ppb. Recoveries, made at concentrations between 0.2 and 2.8 ppb (n = 10 for each pesticide), ranged from 67 to 114% with relative standard deviations (RSD) of 4.5–8.5%.