Sampling and analyses

Before ordering analyses of pesticides

When analysing pesticides it is important to place demands on the laboratory so that interpretation of the results is easier. It is of course important to check whether the laboratory is accredited for the right sample matrices and the right measurement area for the substances in question. Similarly, for the purposes of the investigation it is worthwhile knowing the detection limit, limit of determination and accuracy of measurement, in order to ensure that the substances can be traced down to the level needed for the investigation. Some other aspects to consider are:

• Ask the laboratory to state the Swedish names of the substances. This sounds self-evident but is unfortunately not always so.
• Ask the laboratory to clearly state how they define the lowest reported analytical limit. Several different concepts are used by laboratories, e.g. detection limit, limit of determination, quantification limit, reporting limit, and it is not always clear what is meant. Some laboratories also state a 'normal' reporting limit, which does not necessarily relate to the actual analysis. The purity of samples varies and sometimes the reporting limits can be higher than the 'normal'. It is a great help in interpretation of the data to know exactly what the relevant level is for the sample in question.
• If the study in question is a follow-up study, the same substances at least should be included and the detection limit should not be higher than in the previous samples. Otherwise it is difficult to draw any conclusions from the results.

If the sample is to be used for some form of legal case, a high degree of transparency is needed in the entire chain from sampling in the presence of an independent observer from the local authority or police, labelling, documentation (for example  photographs) and transport, to the analyses at the laboratory. The analyses should be performed as so-called documentary analyses by one, or possibly two, accredited laboratories. This means that the sample must be analysed on two independent occasions for the results to be as reliable as possible.