Evaporated extracts of samples for pesticide residue analysis simplifies transport from remote places

The increasing use of pesticides demands a world-wide control of residue levels in food and the environment. However, pesticide residue analysis is challenging and needs both experience and instrumentation. Although much can be done with fairly simple means (Aakerblom and Cox 1996), many countries with limited resources can only perform certain analyses. Also in technologically more advanced countries, different laboratories may specialise in certain kinds of analyses. There is also a need to confirm results with an exchange of samples between laboratories. There are usually several technical difficulties connected with the transport of pesticide samples, in addition to the risk of transmission of pests and diseases and related customs control. Currently, frozen samples are sent in insulated containers with dry ice to keep the samples in intact condition. When possible, there are large costs for the transport of heavy packages, and delay in customs may lead to destruction of the samples. In many areas of the world this procedure is not feasible at all. A way to circumvent these difficulties is presented here. Even if a laboratory lacks the basic requirements to purchase, run and maintain instrumentation to analyse pesticide residues, there are often possibilities to extract the pesticide samples. The extracts are taken to dryness in the presence of a 'keeper' substance, and the residues can then be sent in apparently empty glass vials. The use of keepers is well known in residue analysis: a small amount of the keeper, a high boiling compound which dissolves the pesticides, is added to an extract before evaporation of the solvent to avoid loss of volatile compounds. Thus, Thornburg (1963) suggests the use of ethylene glycol, stearic acid, or white oil as keeper, Baumgarten and Pfrang (1989) have investigated the use of dodecane to reduce loss of organochlorine compounds on evaporation, and Albro et al. (1984) used propylene glycol to reduce losses of dibenzo-p-dioxines and dibenzofurans. The natural waxes of pine needles on growing pine trees retain organochlorine compounds sufficiently to be used as sampling medium (Kylin et al. 1994). We have investigated the use of polyethylene glycol as a keeper at harsh conditions, for up to three weeks at 44 degree C. This was done to find out whether the residues remain in the vials at simulated transport conditions. In all 64 pesticides were tested.