Noah Menard / Chemistry & Biochemistry / Faculty Mentor: Kevin Schug
“Complex mixtures are known to cause difficulties in structural elucidation in the NMR. While LC provides the ability to separate mixtures, most detectors do not provide the ability to determine information regarding the structure of the analyzed compounds. Previous iterations of LC-NMR systems involved large, high-field NMRs, making the coupling of the two systems both difficult and prohibitively expensive. The advent of more compact benchtop-NMR systems with higher field-strengths has allowed NMR to be more accessible as an LC detector while providing a reasonable level of sensitivity.
While online measurements require only high concentrations of analyte and continuous NMR scans, stop-flow LC minimizes this problem by holding the analyte in the NMR cell. However, this requires the calculation of the delay between the photodiode array detector and the NMR flow cell. Stop-flow allows a lower concentration of analyte to be identified, benefiting from the higher number averaged NMR scans typically performed. Mobile-phase solvents commonly used in LC have the potential to cause NMR analyte peak interferences, which add further complexities to compound identification. Initial findings in both online flow detection for higher concentration samples and stop-flow techniques for lower concentration analytes indicate the viability of this technique.”
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