Solid-phase-extraction NMR

Exarchou, V. et al., LC-LTV-solid-phase extraction-NMR-MS combined with a cryogenic flow probe and its application to the identification of compounds present in Greek oregano. Anal. Chem., 75, 6288, 2003. 

N.T. Nyberg, H. Baumaim, and L. Kenne, Solid-phase extraction NMR studies of chromatographic fractions of saponins from Quillaja Saponaria, Anal. Chem. 75 (2003), 268-274. 

Four general classes of NMR experiments are routinely used to analyze metabolites (1) ID NMR experiments (2) 2D NMR experiments (3) Solvent suppression methods and (4) Hyphenated NMR experiments. The ID and 2D NMR experiments are commonly used for metabolite structure determination. The various solvent suppression techniques (Gaggelli and Valensin, 1993 Hwang and Shaka, 1995 Smallcombe and Patt, 1995) are crucial for dilute metabolite samples where the solvent peak is the most intense peak in the NMR spectrum. These solvent suppression techniques can be incorporated as needed in both ID and 2D NMR experiments. Since their introduction in the 1990s, hyphenated NMR methods have become common tools in the identification of metabolites. These methods include LC-NMR (Albert, 1995 Spraul et al., 1993, 1994), LC-NMR-MS (Mass Spectrometry) (Shockcor et al., 1996) and LC/SPE (solid phase extraction)/NMR (Alexander et al., 2006 Bieri et al., 2006 Xu et al., 2005 Wilson et al., 2006). 

Emerging hyphenated techniques have already proved their analytical value and in the near future will certainly become common techniques in food sciences. Commercially available equipment include LC-NMR in both on flow and stop-flow versions, LC-NMR-MS, LC-NMR-UV-MS, and more recently hyphenation with soHd-phase extraction (LC-solid phase extraction-NMR). 

Beretta, G., Caneva, E., Regazzoni, L., Bakhtyari, N. G., and Facino, R. M. (2008). A solid-phase extraction procedure coupled to H-NMR, with chemometric analysis, to seek reliable markers of the botanical origin of honey. Anal. Chim. Acta 620,176-182. 

SPE (1) Solid-phase extraction (2) Single-pulse excitation (NMR)... 

The biological applications of NMR include the study of the structure of macromolecules such as proteins and nucleic acids and the study of membranes, and enzymic reactions. Newer methods and instruments have overcome, to a large extent, the technical difficulties encountered with aqueous samples and the analysis of body fluids is possible, permitting the determination of both the content and concentration of many metabolites in urine and plasma. NMR is not a very sensitive technique and it is often necessary to concentrate the sample either by freeze drying and dissolving in a smaller volume cm- by solid phase extraction methods. 

Since considerable amounts of potential interfering materials can be extracted along with the polyphenolics, an isolation/purification step is often required to eliminate components that may interfere with analysis. The fractionation techniques presented in Basic Protocol 2 and Alternate Protocol 2, using solid-phase extraction to minimize the effects of sample preparation/cleanup on the integrity of the extract, will make possible the identification and quantification of individual polyphenolics by HPLC (unit ii j), MS, and NMR. 

LC-NMR. Separations using reverse-phase (RP) liquid chromatography are potentially more powerful because samples can be studied without derivatization. Numerous attempts have been made to separate NOM and while most studies exhibit some degree of separation, to date the complete separation of a NOM sample has not been accomplished. Even only partial separation is possible, and it is worth to hyphenate a separation method with structure information-oriented analytical applications. Liquid chromatography combined with nuclear magnetic resonance and preliminary studies with solid-phase extraction were conducted on NOM isolated from freshwater and soil (Simpson et al., 2004). 

Kaiser, E., Simpson, A. J., Dria, K. J., Sulzberger, B., and Hatcher, P. G. (2003). Solid-state and multidimensional solution-state NMR of solid phase extracted and ultrafiltered riverine dissolved organic matter. Environ. Sci. Technol. 37,2929-2935. 

Notes LOD, limit of detection MeOH, methanol EtOH, ethanol ACN, acetonitrile EtAC, ethyl acetate SPE, solid phase extraction HLB (hydrophilic lipophilic balanced) TFA, trifluoroacetic acid GC, gas chromatography TMS, trimethylsilyl MS, mass spectrometry HPLC, high-performance liquid chromatography DAD, diode array detector NMR, nuclear magnetic resonance ESI, electrospray ionization APCI, atmospheric pressure chemical ionization CE, capillary electrophoresis ECD, electrochemical detector CD, conductivity detector TLC, thin layer chromatography PDA, photodiode array detector. 

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