Solid-Phase Extraction for Enrichment and Separation of Herbicides

Abstract

Herbicides are widely used for of broad-leaved weeds and other vegetation. They are relatively inexpensive and very potent even at low concentrations. The majority of herbicides are directly applied to soil or sprayed over crop fields and as consequence of large production and high stability, they are released directly into environment. For that, herbicides can enter as contaminants into streams, rivers or lakes directly from drainage of agricultural areas. The need for herbicide monitoring in natural water is essential for achieving good water quality objectives, because in most countries groundwater is the major source of drinking water. Moreover, the monitoring of herbicides in soil and crops is important in order to control their impact on the environment. Recent studies have focused more on herbicide degradation/transformation products (from hydrolysis, oxidation, biodegradation or photolysis) because they can be present at greater levels in the environment than the parent herbicide and can sometimes be as toxic or even more toxic. New compounds have also come on the market (such as glyphosate, organophosphorus herbicides) and studies are being conducted to understand their fate and transport in the environment (Richardson, 2009). Thus, it is important to develop a reliable and sensitive method for the simultaneous determination of such compounds in different kinds of samples. High-performance liquid chromatography with mass spectrometry or array diode detection are good options for herbicides monitoring (Cheng et al., 2010; Maloschik et al., 2010). Tandem mass spectrometry is usually used to confirm identification of selected herbicides. While LCMS/MS methods are now predominantly used for pesticides and their degradation products, GC-MS methods are still occasionally used. For example, GC-MS was used by Hildebrandt et al. (2007) to measure 30 priority pesticides and their transformation products in agricultural soils and an underlying aquifer in the Ebro River Basin in Spain. The sensitivity of detection, however, is still not high enough in many cases for direct determination of herbicides at the level required by different regulations. Therefore, a preconcentration procedure for the analytes and clean-up steps must be applied for complex samples. Solid-phase extraction (SPE) is the most popular sample preparation technique of environmental, food and biological samples and it already replaced the classic liquid-liquid extraction as the reduction or complete elimination of solvent consumption in analytical procedures, which is very important according to the rules of green chemistry (Camel, 2003;