Plastics has become a more and more important part of our society. But very often it reaches the oceans in the form of litter. Here it does not dissolve but is decomposed into smaller and smaller pieces of plastics. Parts smaller than 5 mm are categorized as microplastics. Its impact on the environment is not fully understood yet. But it is already proven that microplastics is ingested by animals and that it has an effect on their health. For that reason the research of microplastics and its impact has become more and more important lately. However, no standardized analysis methods for microplastics exist as of today. One way of detecting and identifying microplastics in marine samples is the use of μFTIR. But before such samples can be measured correctly, its biomass content needs to be reduced. The enzymatic purification is one way of reducing the biomass. This Thesis presents one methodology of the enzymatic purification, which is foreseen to be used as a standardized procedure in future sample analyses. For this particular enzymatic purification the enzyms Protease, Cellulase and Chitinase are used, in combination with the reagents SDS and H2O2. In order to analyze the enzymatic purification method two experiments were performed using Sea-surface-water from the North Sea. In the first experiment the reagents were tested independently. During the second experiment the quality of the enzymatic purification after each reagent treatment was analyzed and its impact on the sample-material was investigated. For these experiments a FlowCAM instrument was used which provides information about particle count and size of the sample-material. In addition, a μFTIR measurement was conducted in order to determine changes in the spectrum of each sample, which allows determining the reduction of biomass during each enzymatic purification step. As a result of this Thesis it can be said that the methodology of the enzymatic purification works. After purification the sample-material has been reduced by about 97 %. This allows for a good detection of microplastics using the μFTIR. SDS and the enzymes showed a good performance. Even the Chitinase was very efficient even without a pretreatment with H2O2. On the other hand H2O2 was much less effective than expected.