Soil Laboratory - Sample Preparation

Soil samples collected in the study area are placed in a plastic bag on site, sealed and labelled with a unique sample label. After sample storage, some pre-treatments have to be carried out before the physico-chemical investigation. Pre-treatment includes sample splitting, drying, sieving (< 2 mm for fine soil, see Soil Laboratory - Particle Size Analysis) and digestion. The sample is divided by a riffle divider or by quartering to the desired quantity. The samples are either dried in air (so-called air-dried samples, duration approx. 2 days) or in a drying oven at 105 °C until the weight is constant. The latter is also taken to determine the water content of the samples by differential weighing before and after drying. To prevent the samples from absorbing water during subsequent cooling, they are left to cool in a desiccator over a desiccant (which binds the moisture).
Poorly soluble substances are converted into soluble compounds. The aqueous solutions obtained are then suitable for further analytical examination, e.g. for elemental determination with ICP-OES. Essentially, two methods are used: The digestion with aqua regia according to SCHLICHTING et al. or microwave digestion (Microwave-assisted pressure digestion can be used to digest almost any sample material faster than conventional methods: biological and plant materials, slurries, soils, sediments, geological materials, etc.)