The main objective of environmental analysis is the qualitative and quantitative determination of environmentally important parameters for a variety of samples. Regarding the compliance of limit values, the results of analytical characterisations have a strong impact, because they are often used as basis of decision-making. The potential errors that may occur during a certain analytical method, can be described by specifying the measurement uncertainty. The measurement uncertainty can be estimated by using standard solutions and determination of any influencing factors that occur during the process. If more steps of sample preparation are added to the process (for example drying, shredding, aqua regia digestion), the uncertainty of the test results increases. With the aim of estimating the influence of the sample preparation on the uncertainty, two real samples (residual waste, substitute fuel) were prepared for a detailed analysis in the course of this master thesis. A particular scheme has been elaborated to generate 20 samples per material. The following parameters were examined: anions, ash content, loss of ignition, caloric value, total organic carbon (TOC), total carbon (TC) and (heavy) metals. Furthermore, the obtained results were statistically and graphically evaluated. Finally, the measurement uncertainty was estimated for the parameters magnesium and chromium measured by inductively coupled plasma mass spectrometry (ICP-MS).