In order to identify and quantify microplastics, mainly microscopic techniques are used. The particles are visually sorted by type, shape and colour under the light microscope and then counted. However, particles smaller than one millimetre are often not detected because it is difficult to distinguish visually between plastic and non-plastic at this size.
A more reliable method is infrared spectroscopy using FTIR or Raman spectroscopy. FTIR detects significantly more particles than by eye, but it is much more time-consuming. When the microplastic particles become smaller than 0.02 millimetres, this method also reaches its limits. Using Raman spectroscopy, particles down to a size of 0.001 millimetres can still be measured. For smaller particles, especially nanoplastics, there are only a few instruments available that can analyse the plastic particles. (Source: “Microplastics in the Environment”, Ökotoxzentrum, 2015)
Up to now there have been no standardised methods for the detection of microplastics. Depending on how the particles are collected, prepared and analysed, the results therefore vary over several orders of magnitude.