The presence of microplastic debris in the marine environment has been documented during the past 40 years. With the implementation of the Marine Strategy Framework Directive (MSFD) in 2012 the need for reliable data obtained by standardized methods has been growing in order to realize monitoring programs and subsequent mitigation strategies. In this context a reproducible method for the detection of microplastics in marine sediments was developed in this thesis. For the analysis of sediments the extraction method is crucial. In this thesis a density separation approach was adapted that involved the recently invented Munich Plastic Sediment Separator (MPSS) built by Hydro-Bios and a highly dense ZnCl2 solution (density about 1.7 g cm-3). The resulting extracted samples from North and Baltic Sea sediments were purified through enzymatic digestion using technical enzymes, i.e., Protease, Cellulase, Chitinase and additionally H2O2. This enzymatic digestion protocol proved to be efficient and biologically specific since the biogenic organic matter and not the synthetic polymers were affected. A successful purification was necessary to enable the subsequent analysis. In this context, another essential step is the identification of microplastics in order to quantify them. Since this is especially difficult for small microplastic particles (<500 μm), the highly promising μFT-IR mapping technique was applied. Therefore the pre-treated samples were concentrated on Anodisc filters in a 64 mm² area that was completely analyzed using Infrared spectroscopy in transmission mode. Applying this newly developed methodological setup, five North Sea sediment samples could be investigated for their microplastic contamination. The number of microplastic particles per sample detected ranged from 63 to 105. Taking the determined sediment weight of each sample into account the relative abundances of microplastic particles in North Sea sediments ranged from 34 (Sylt, beach) to 74 (German Bight, sublittoral) particles kg-1 dry weight sediment. Furthermore, ten different types of plastic polymers could be detected with a high prevalence of polypropylene (PP) in all the samples. Another omnipresent polymer type although not that frequent was polystyrene (PS). Next to low density polymers like polyethylene (PE) also more dense polymers like polyvinyl chloride (PVC) and polyvinyl acetate (PVA) were identified proving the efficiency of the extraction method. The efficacy of the enzymatic digestion was proven by the relatively clean spectra obtained during the μFT-IR measurement. This approach was applied for the first time for marine sediments and presents a first insight into microplastic pollution of German coastal sediments.