Hemicelluloses, the second most abundant polysaccharides right after cellulose, represent complex biopolymers whose structural features are not yet fully understood. Hence, the applicability of functionalized hemicellulose derivatives is still limited. Thus, the development of practical methods to reveal their structure is essential. Anionic, carboxylated GGM was prepared as the substrate, and their corresponding oligomers have been isolated and fully characterized for the first time in the present work. In order to accomplish this, each step has been optimized sequentially. Oxidized GGM was enzymatically digested, and the corresponding oligomers were isolated by preparative GPC. A toolset of wet chemistry and instrumental methods was used to characterize the isolated compounds in detail. Moreover, quantitative 13C-NMR combined with MALDI was demonstrated to deliver accurate analytical data compared to standard but time-consuming wet chemistry methods. The developed toolset is expected to be applicable to other plant polysaccharides and their derivatives as well.