60 MHz Proton NMR

Introduction -- The 60 MHz Proton nuclear magnetic resonance (NMR) spectrometer consists of a Varian EM-360 permanent magnet and a recent upgrade of the electronics and software by Anaszi Instruments. This instrument provides a way to introduce modern FT-NMR spectrometry. The Acorn software called "Nuts" permits advanced NMR data processing. The instrument provides excellent low-field proton spectra of organic compounds. Relaxation time measurements and two-dimensional COSY (COrrelated SpectroscopY) experiments can also be performed. The instrument is located in building 95 room W187, between two organic teaching laboratories.

There are several layers of software. First Windows95 over a DOS environment, second the Anasazi PNMR software to produce a FID, and third the Acorn program "Nuts" which transforms the FID and allows the 1-D spectrum to be labeled and integrated. The commands for each software level vary.

Continuous Wave (CW) versus Pulsed NMR Spectrometers -- There are two "classes" of NMR spectrometers, continuous wave spectrometers and pulse spectrometers. Using a CW spectrometer, the sample is placed in the magnetic field and subjected to a slowly swept frequency. The CW NMR spectrum consists of frequency peaks at which there is absorption of energy as well as the intensities of these absorptions. Using a pulsed spectrometer, the sample is placed in the magnetic field and is pulsed with high power radio frequency (RF) waves sufficient to simultaneously excite all nuclei in the sample. After the pulse, the nuclei, over time, return to the ground state and radiate the absorbed energy. The pulsed spectrometer collects this energy and produces the Free Induction Decay (FID) signal which is the sum of all nuclei radiating over time. The FID does not lend itself to direct interpretation. However, Fourier transformation (FT) converts the time data of the FID into frequency data which is interpreted just like the original CW spectra.

Background -- Developed in the 1960's, NMR is an invaluable tool for organic and analytical chemists. It is used to identify fairly pure unknown substances. The Anazasi EM360 NMR spectrometer is a practical machine. Continuous wave NMR spectrometers have the sample irradiated by a continuous radio frequency (RF) signal while in a strong magnetic field. The spectrum is generated by sweeping a small change in magnetic field over the sample.

Anasazi Instruments -- Model EFT converts existing permanent magnet CW NMR instruments into FT NMR spectrometers. The EFT is an easy to use Windows^TM based PC system that is available for the many CW NMR instruments, e. g. the Varian EM300. The FT NMR configurations available for the EFT upgrade are ¹H and is capable of covering the range ¹H -¹⁹F and ³¹P -²⁹Si. Complete ¹H spectra can be obtained in less than ten minutes.

Model EFT -- It includes an operating console with fixed frequency or synthesizer based RF system of heterodyne design with all frequencies phase locked to a 1.0 MHz oscillator, a state of the art PC computer, CRT, pulse programmer (100 nanosecond time resolution), quadrature phase detection and a HP Deskjet^TM printer. Standard NMR routines are available for 1D survey spectrum with peak pick and integration, T1 measurements, COSY, Kinetics, DEPT, and HETCOR. Other NMR routines are available via the programmable pulse programmer. The library of EFT experiments is designed for users with little or no prior NMR operating experience. This is one tutorial for the Anasazi EFT-60.

Operation

Nuclear Magnetic Resonance (NMR) Spectrometer Anasazi Spectrometer -- The Anasazi EFT-60 Spectrometer uses the magnet from a Varian EM360 CW spectrometer and all new electronics and software operating in a Windows environment to obtain proton NMR spectra. Upon placing the sample in the magnetic field, Anasazi's PNMR software controls the data acquisition parameters and obtains the FID. Acorn's NUTS software converts the FID into the frequency spectrum. The NUTS software can be used to process data from a wide variety of NMR spectrometers. A free, tutorial version of NUTS is available on the web and free software.

The following describe various parts of the procedure:

1.  How To Prepare a Sample for NMR,

2.  Inserting the Sample,

3.  Instrument Start Up Protocol,

4.  Basic Explanations of PNMR commands,

5.  About Windows 95 to run PNMR or Nuts, and

6.  Working with Accorn's Nuts Software.