1. Sample preparation

It should be noted at the outset that the general diagram presented in figure 1 does not include sampling, which is an integral part of the measurement process, but will not be dealt with in this article. Several steps may be required after sampling and before extraction and final determination of the chemical compounds; these include sample preservation, filtration, pH adjustments for aqueous samples, drying and homogenization of solid samples, etc. These steps are generally clearly laid down in the sampling procedure. These steps include sample preservation, filtration, pH adjustments for aqueous samples, drying and homogenization for solid samples, etc. Their implementation is generally clearly established, but if they are not carried out properly, the original composition...