ABSTRACT
The LC-NMR system is comprised of an NMR spectrometer console, a superconducting magnet, a workstation, and a flow probe, all under the operation of specialized LC-NMR software. The HPLC portion is comprised of an HPLC pump, HPLC column(s), variable-wavelength UV detector and/or photo diode array detector, and an LC workstation that may be set up for stopped-flow or continuous-flow operation. Timing for movement of a peak between the different positions in the hyphenated system must be carefully calibrated. The time required for a peak to reach the NMR probe or a designated collection unit depends upon the void volume between the LC unit and the collection unit or probe flow cell. This will depend upon flow rate. In order to allow selection of desired peaks, the separation is monitored by an LC detector, usually a UV detector, which displays a chromatogram of the separation. The chromatography software allows certain positions in the chromatogram to be manually or automatically selected for further measurement. The NMR probe or storage compartment is located downstream of the UV detector and is estimated to be reached about 10 to 40 s after the first peak appears in the LC detector [1]. The software calculates the appropriate delays to capture the peak at its desired position, where the necessary actions for storage or measurement are initiated. Software is commercially available from instrument vendors that allow automated or interactive selection of the peaks from the chromatogram and automatic calculation of the time delays. A typical LC-NMR system configuration is shown schematically in Figure 4.1.
