Even though the approval of small molecules is still of great importance, the expansion towards newer modalities requires the development of druggable large biomolecules with inherent challenges in their delivery due to their toxicity, poor bioavailability, or lack of cell specificity. The result is that drugs are being formulated in complex drug-excipient conjugates to address the emerging challenges in drug delivery. Polymers are popular excipients due to their synthetic versatility, allowing for achieving the desired pharmacological and physicochemical characteristics of the final product. The use of poly(ethylene) glycols or cyclodextrins as excipients in some formulations enables the production of robust formulations. Poly(ethylene) glycols are safe materials that improve drug delivery by drug encapsulation or binding. Cyclodextrins host drug molecules in their cavity to improve their solubility.The polymeric nature of the materials requires control of their quality from the early stages of drug development. The synthetic approaches of poly(ethylene) glycols as the raw material and the possible degradation pathways lead to the formation of undesired subproducts. The synthesis of (2-hydroxypropyl) cyclodextrin produces a complex mixture that is difficult to characterise. The resulting heterogeneity can lead to sub-potency, so the dose is not administered as required, compromising the treatment reaching the patient. These findings showed the need for further characterisation of the excipients used.This research proposes the combination of ultra-high-performance supercritical fluid chromatography and mass spectrometry to characterise and quantify polymeric excipients, specifically poly(ethylene) glycols and (2-hydroxypropyl) cyclodextrin. The aim was to facilitate the characterisation and quantitation of the materials.