Introduction Metaldehyde is a molluscicide whose use has markedly increased in recent years as a result of changing agricultural practices. This has resulted in a number of exceedences of the 0.1?g/l EU pesticide standard in treated drinking waters. Geosmin and 2-methylisoborneol (MIB) are naturally occurring alicyclic alcohols which possess potent earthy/musty taste and odour tainting properties. They can occur in raw and potable waters as metabolites derived from various micro-organisms including actinomycete fungi and blue-green algae.

Solid Phase Extraction Method Kinesis, in partnership with South West Water, have developed an application note for extraction metaldehyde, geosmin and 2-methylisoborneol from various waters. The SPE method uses TELOS ENV 200mg/6ml SPE Columns.  A summary of the method is as follows: Sample Pre-Treatment The procedure is based upon a one litre sample but smaller volumes may be used if high concentrations of the analytes are likely to be present. No sample preservation is necessary but samples should be stored in the dark at 2-8°C for a period not exceeding 14 days. Column Conditioning On a suitable vacuum manifold, condition the column with ethyl acetate (2 column volumes), methanol (2 column volumes) and ultra-pure water (1 column volume). Do not allow the pre-conditioned column to dry out. Sample Application Extract the analytes by filtering the samples under vacuum through the TELOS ENV SPE columns at a flow rate of approximately 30-35ml/min. Dry the loaded columns under vacuum (typically about one hour). The sorbent becomes a universal light brown colour when thoroughly dry. Analyte Elution Place the dried columns onto a suitable elution rig with collection tubes in place. Add 2ml of ethyl acetate to each column and allow to soak for at least 5 minutes. Drain the solvent to the level of the sorbent, then add a further 2ml of ethyl acetate and allow to elute. Evaporation and Reconstitution Carefully evaporate the eluates to ~100?l using nitrogen and a water bath at 40°C. Add 2ml of iso-octane to each sample, evaporate to ~500?l and add 50?l of a 2ng/?l solution of naphthalene-d8 in iso-octane to act as an internal standard. Centrifuge at 2500rpm for 4 minutes to remove precipitated material and carefully remove the supernatant for analysis.  

Recoveries Typical recoveries of the three analytes from various waters are as follows:  

  Acknowledgement The information presented in this application note was supplied courtesy of Natasha Keitch & Ian Townsend, South West Water Ltd, Bridge Road, Countess Wear, Exeter, Devon, UK, EX2 7AA.

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