Automated analysis of polar pesticides in water by on‐line solid phase extraction and gas chromatography using the co‐solvent effect

Abstract

In order to meet the requirements of analyzing very low concentrations of pesticides in water (typically at 0.1 pg/l or less), samples have to be concentrated prior to GC-analysis. Sample pre-concentration by off-line methods based on solid phase extraction (SPE) or liquid-liquid extraction are very time consuming and cumbersome. Moreover, the quantitative performance of the analytical method as a whole in terms of accuracy and reliability is seriously hindered by elaborate, manually performed sample pre-treatment steps. This paper describes an automated method based on solid phase extraction and capillary gas chromatography. The technique was applied for the analysis of 31 polar organophosphorus and organonitrogen pesticides. A commercially available HPLC/GC instrument i s modified, using the LC-part for solid phase extraction. The sample, of which only a few ml's is required to obtain sufficiently low detection limits, is delivered by a robotic large volume autosampler. After solid phase extraction and elution, the eluate is transferred into the GC via a so called "loop type interface". In this paper the instrumentation and analytical methodology is described, as well as the main validation results. The quantitative performance (ie. recovery and repeatability) of the most polar solutes like metamitron and dimethoate appears to be better than obtained with off-line SPE as a result of the more beneficial ratio between the amount of sorbent and the sample volume. As the loop-type interface causes losses of the most volatile compounds, a co-solvent is added. This co-solvent provides sufficient trapping capacity in the capillary pre-columns to allow quantitative analysis of even the most volatile pesticides. Moreover a better separation of early eluting compounds is also established.

On-line determination of bipyridylium herbicides in water by HPLC

“…Backflush desorption from SPE cartridges packed with GCB has been reported previously as [22] the only way to desorb those compounds which are strongly retained by GCB [21]. Backflush desorption from SPE cartridges packed with GCB has been reported previously as [22] the only way to desorb those compounds which are strongly retained by GCB [21].…”

“…The exact mechanism involved in the chromatographic process is not well defined. GCB has been shown [16][17][18] to be more effective for trapping polar compounds than adsorbents such as C18 [19] and PLRP-S [20][21]. The proposed technique is particularly attractive as it lends itself to the coupling of extraction and determination for on-line applications [10].…”

Approaches for on-line coupling of extraction and chromatography

“…Methods based on both SPE-GC and LLE-GC have been developed for a variety of environmental determinations, and SPE-GC has also been used for the analysis of drugs in biological fluids [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,53,54,55,56,57,58,59,60,61,62,…”

Method for the Analysis of Triadimefon and Ethofumesate from Dislodgeable Foliar Residues on Turfgrass by Solid-Phase Extraction and In-Vial Elution

“…SPE methods are gaining popularity because they are rapid, easily automated, and use less solvent than liquid-liquid extraction techniques. Solid-phase extraction cartridges containing C 8 and C 18 phases have been used to isolate a number of pesticides from water in an in-line or off-line mode (Noij and van der Kooi, 1995;.…”