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

✍ Scribed by Noij, Theo H. M. ;van der Kooi, Margo M. E.

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 505 KB
• Volume: 18
• Category: Article
• ISSN: 0935-6304
• DOI: 10.1002/jhrc.1240180905

✦ Synopsis

Abstract

In order to meet the requirements of analyzing very low concentrations of pesticides in water (typically at 0.1 μg/l or less), samples have to be concentrated prior to GC‐analysis. Samplie 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 is 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 (i.e. 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.