Hyphenation of high-performance liquid chromatography (HPLC) and other chromatographic techniques (SFC, GPC, GC, CE) with nuclear magnetic resonance (NMR): A review

Abstract

The development of the hyphenation of highperformance liquid chromatography (HPLC) and other chromatographic methods (supercritical fluid chromatography (SFC), gel-permeation chromatography (GPC), gas chromatography (GC) and capillary electrophoresis (CE)) with nuclear magnetic resonance (NMR) is reviewed. The focus is not only on application (e.g. pharmaceutical chemistry, food chemistry, polymer analysis, fuel chemistry), but also on technical improvements (e.g. flow rate, flow cell, probe, solvent suppression). The increasing importance and overwhelming analytical possibilities of on-line coupling of HPLC with NMR is demonstrated. The literature up to March 1995 is considered.

LC–NMR coupling technology: recent advancements and applications in natural products analysis

“…24 The optimum flow rate for continuous-flow NMR is usually chosen as a compromise between the rate required for the best chromatographic resolution and the best NMR sensitivity. 25 The measurement time for each analyte is limited by the short residence time within the rf coil at the flow rates normally used, and this often results in a poor S/N ratio for the NMR spectra. Reduction of the flow rate by a factor of 3-10 increases the residence time and hence the measurement time and S/N for each component, but diffusion at slow flow rates may reduce the chromatographic separation of the individual peaks eluting from the LC column or the NMR flow-cell.…”

Direct Determination of Molecular Weight Distribution by Size Exclusion Chromatography with 750 MHz 1H NMR Detection (On-Line SEC-NMR)

“…Recent review articles describe the development and applications of LC-NMR. 1 - 3 From the point of view of polymer analysis and characterization, size exclusion chromatography (SEC) should be the most useful mode of separation for online detection by NMR. As shown in previous experiments using a 500 MHz 1 H NMR spectrometer as a detector of SEc, 4 -9 on-line SEC-NMR is quite useful for studying the molecular weight dependence of chemical structures such as tacticity 7 and comonomer composition 5 in a polymer sample.…”

NMR Difference Probe: A Dual-Coil Probe for NMR Difference Spectroscopy

“…Other solvent suppression techniques such as WATERGATE (water suppression by gradient-tailored excitation) (16) and Water-PRESS (water-presequence suppression) (17,18) provide large suppression factors for protein samples, but one must choose between observing exchangeable protons (WATERGATE) and observing resonances close to the water frequency (Water-PRESS). For LC-NMR, solvent suppression is further complicated by the use of multiple solvents and flowing samples (1)(2)(3). Multiple solvent peaks can be suppressed with techniques that use multiple-frequencyshifted laminar pulses (SLP) (19) such as Multigate (a modified version of WATERGATE) (20) and WET (water suppression enhanced through T 1 effects) (21,22).…”

“…For 1 H NMR experiments this dynamic range must encompass solvent concentrations that often exceed analyte concentrations by a factor of 10 3 or greater. As such, deuterated solvents are commonly used for liquid chromatography LC-NMR (2,3), while sophisticated pulse sequences are used for water suppression in protein NMR (1).…”