Solid-phase extraction followed by high-performance liquid chromatography with diode array detection for screening of dicamba herbicide in water

Abstract

Chlorinated acids are selective agricultural herbicides which are widely employed in agriculture and gardening for control the growth of different unwanted vegetable species in crops. Because of high water solubility and toxicological risk of some acid herbicides and their metabolic products, monitoring of their concentration in surface and groundwater is very important task. The acidic herbicides are manufactured in formulation as free acids, as their alkaline salts or as esters. The unionized free acids vary in water solubility (Table 1), but the acidic herbicides most frequently exist in ionized form at environmental pH values. Acidic herbicides formulated as salts are water soluble, while those formulations prepared as esters are less water soluble. In the environment, acidic herbicides formulated as esters have short hydrolysis half-life time (24-48 h) and therefore they are generally present as ionized acids. For most analytes, especially for the acidic herbicides, solid phase extraction (SPE) is the choice of sample treatment, which is followed by appropriate chromatographic separation and sensitive determination of target components. For the acidic herbicides, combination of physico-chemical parameters influences their extraction from aqueous solution. Ionogenicity (pKa) and hydrophobicity (logkow) are especially important in determining the approach of SPE for efficient sample clean-up for further chromatographic analysis of chlorophenoxy acid herbicide in water samples.