A qualification process for a sample to be examined by means of cryo-electron microscopy. The, sample (12) is applied to a sample carrier (10) provided for cryo-electron microscopy and subsequently the sample (12) arranged on the sample carrier is examined by means of dynamic light scattering. The particle size distribution within the sample (12) is determined by means of the dynamic light scattering. Further, a sample holder designed to carry out the qualification process.