Applied microfluidic stripline NMR spectroscopy

Contains fulltext : 204549.pdf (publisher's version ) (Open Access)NMR spectroscopy is an established analysis technique in chemistry, physics and medicine, which gives unique insight into molecular structures, but has a relatively low sensitivity. When the sample amount is limited, this low sensitivity can become a problem. Microcoil NMR is one of the strategies to improve mass sensivity. The stripline NMR chip is a microcoil structure that gives a high resolution and sensitivity for liquid samples of approximately 150 nl. Depending on the design, the sample can either flow directly into the microfabricated microchannel on chip, or be contained in a capillary reversibly placed into the NMR chip. In this thesis, the stripline chip is used for NMR analysis of some examples of mass-limited samples. Using the replaceable capillary approach, biological samples are analysed: individual mouse CSF of interest for metabolomics and strigolactones under study for parasitic weed control. In addition, coupling of the stripline NMR chip to a microfluidic environment is possible, enabling e.g. online monitoring, in situ microreaction detection and hyphenation to other techniques. Test compounds were measured successfully in continuous flow in the stripline NMR chip, indicating that our stripline NMR chip can beneficially be used in areas such as fast quantitative analysis or quality control. Furthermore, two fast chemical reactions are studied in the stripline NMR chip coupled to a microreactor, the acetylation of benzyl alcohol with DIPEA and the Paal-Knorr pyrrole synthesis. This way, reactions can be monitored during the reaction progress. In both cases, intermediates were spotted that were not visible in conventional NMR. Also, reaction kinetics could be modelled from the data obtained. The results give insight into reaction mechanisms. Moreover, the stripline NMR was hyphenated to an electrochemical (EC) setup, which facilitates in situ analysis of electrochemically conversed unstable compounds, while improving efficiency and decreasing contamination risk.Radboud University, 13 juni 2019Promotor : Kentgens, A.P.M.vi, 214 p