Welcome to the Uhrín group at the School of Chemistry, University of Edinburgh. Our work focuses on developing new liquid-state NMR methods and their application to studies of carbohydrates, carbohydrate-protein interactions and complex mixtures like dissolved organic matter, soil and more pleasurable commodities such as Scotch whisky..
We are part of the Scottish NMR Users Group (SNUG) which brings together NMR research and facilities across Scotland. Visit the SNUG webpage to find out more.
Edinburgh University is once again hosting an NMR course for postgraduate students, a great opportunity to expand your knowledge of the technique. Speakers this year can be found in the following programme. Click Here!
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SNUG annual meeting
Quantification of whisky congeners by
1H NMR spectroscopy
Whisky is a complex mixture made up of thousands of compounds originating in different stages of its production. Analysis of whisky congeners is critical to our understanding of the manufacturing process, quality control, and the detection of counterfeit products. The current chromatographic methods have a long analysis time, can require milliliters of sample and may not detect all required compounds in a single analysis. We have demonstrated that the majority of the whisky congeners of interest can be analyzed using 1H NMR spectroscopy in a single session using 500 μL of sample with the addition of 100 μL of buffer. We addressed two issues with this application of NMR: sensitivity and complexity of spectra. The sensitivity issues were solved by using a highly sensitive 600 MHz instrument equipped with a cryoprobe. To achieve consistent quantitative analysis of overlapping signals, Chenomx software was used. This allowed successful determination of the absolute concentration of 13 of the 21 studied whisky congeners with an average relative difference from nominal concentration of 6.4% and a standard deviation of 5.0%. Some compounds such as iso‐amyl acetate and n‐butanol were not accurately quantifiable due to their low concentration and overlapping peaks with those of more concentrated compounds. Scopoletin, lactose, sucrose, and maltose were not detectable in whisky samples, but they were accurately quantified in model mixtures. At higher concentrations, these compounds could be accurately quantified in whisky samples. Overlap of glucose and fructose signals led to >10% deviations from nominal concentration values. The limits of quantification (LOQ) and limits of detection (LOD) for each analyte were determined, with the LOD varying between 10 and 20 μM for the major volatile congeners, 1 to 5 μM for maturation related congeners, and 10 to 30 μM for carbohydrates.
Alan J. R. Smith, Graeme Moore, Andrea J. C. Semiao and Dušan Uhrín
Environ. Sci. Water Res. Technol., 6, 1495-1504, (2020)
Molecular level characterisation of ion-exchange water treatment coupled to ceramic membrane filtration
FT-ICR MS, NMR and ATR-FTIR were used to gain insight into the dissolved organic matter (DOM) removal process throughout a pilot water treatment system. The pilot plant under study utilises suspended ion exchange (SIX) followed by in-line coagulation with (ILCA) polyaluminium chloride and ceramic membrane filtration (CMF). MS results indicate that the SIX treatment is removing DOM irrespective of the compound type (>90% formulae similarity between SIX treated and raw water). However, the ILCA–CMF treatment substantially altered the chemical composition of the DOM by removing a high proportion of the aromatic and phenolic compounds. This was also confirmed by NMR and ATR-FTIR. An adjoining WTW plant which uses the same coagulant as the pilot plant, flocculation mixers for inline flocculation and filtration via MEMCOR® hydrophilic membranes did not show any selectivity when processing the same inlet water. Removal of aromatics/polyphenols in the pilot plant can therefore be attributed to the CMF step. Removal of aromatic/phenolic compounds is important, as these are known to react more readily with chlorine, potentially producing trihalomethanes – substances regulated in potable water.