Glycosylation is a highly specific and delicately regulated posttranslational process of covalent bonding of complex glycan structures and proteins or lipids. Glycoproteins are invovlved in most intercellular and intracellular biological processes. The topic of this master thesis are N-linked plasma glycoproteins with a focus on immunoglobulin G as an important and widely investigated glycoprotein. In the last few years huge population studies, genome wide association studies and cohort studies have been conducted with the goal of identifying genetic foundation of glycosylation, discovering new diagnostic glycobiomarkers and deepening the understanding of glycosylation in general.All these above mentioned studies encompass the repeated analysis of a large number of samples collected from multiple countries, and variable transport and storage conditions. It is of great importance to determine how repeated freeze-thaw cycles and variable transport conditions as well as the reuse of samples affect the stability of plasma glycan structures and the results of N-glycosylation analysis. In this experiment, N-glycans have been removed from the plasma proteins and the previously isolated IgG both of which have undergone different freeze-thaw cycles. Purified N-glycans have been labeled with a flourescent marker and separated with Hydrophilic interaction ultra performance liquid chromatography (HILIC-UPLC). The result of the experiment points to the conclusion that the repeated freeze-thaw cycles and a longer thawing period may have an impact on the glycan structure analysis of immunoglubulin G and other plasma proteins. The effect was not very large so a much larger study should be conducted in order to determine its real statistical significance.