Using Eft NMR Spectrometer in Laboratories

Anasazi Instruments offer the sturdy, high quality and convenient 60 MHz and 90 MHz NMR spectrometers, in addition to upgrades to industrial and educational markets.

These instruments are being employed effectively at a number of institutions ranging from top-tier universities and large companies to a number of community colleges.

The Speed Advantage

The main advantages offered by the Eft NMR spectrometer is speed. Figure 1 shows the ¹H and ¹³C NMR spectra produced by 50% of methyl linoleate solution dissolved in CDCl₃ solvent. Both the spectra were obtained and processed in only 2 minutes.

Users can attain and process the ¹³C and ¹H NMR spectra quickly and easily, and students can also attain single-dimension and two-dimensional spectra for their projects.

Figure 1. 50 wt. % methyl linoleate in CDCl₃. Lower spectrum is single scan ¹H spectrum and upper scan is 1 minute ¹³C spectrum.

High Quality Spectra

There exist two separate features of the Eft NMR instrument, which makes it appropriate for teaching laboratories. For very large molecules, high resolution is attained due to the 60 MHz field strength. A elevated signal to noise ration and a large sample volume are obtained due to the industry proven tube sample measuring 5 mm in size.

Figure 2. Simulation of ethyl group (-CH₂-CH₃) at different magnetic field strengths

Constructed on the basis of magnetic resonance laws, if the sample volume is minimized it will lead to lower levels of signal in a linear fashion. It can be evident that with larger sample volume of 0.2 mL in comparison to the sample volume of a capillary NMR of 0.0001 mL, the 60 MHz instrument can deliver 2,000 times the signal to noise ratio for the same magnetic field strengths.

Furthermore, if there is a reduction in field strength, it will lead to lower levels of signal and would additionally lead to more second order effects and increased crowding of spectra. Interpretation of spectra is made more difficult by all these aspects. Figure 2 shows how the ideal triplet-quartet pattern declines to below 60 MHz.

Instrument Stability

A central facet for performing high-resolution NMR experiments simply and effectively is stability of the magnetic field. If sufficient thermal stability or adequate protection is not offered for a permanent magnet, the magnetic field will fluctuate throughout the measurement and eventually affect the quality of the result.

In comparison to this, tabletop NMR instruments are highly condensed and very sensitive. One primary test is to decide the chemical shift due to time.

In figure 3, the stability of the Eft-60 instrument over a two and a half hour period is shown, which is relatively long given that conventional and ¹³C spectra need a few minutes to attain the stability while ¹H spectra requires only seconds.

Figure 3. Single scan ¹H spectra of 2M ibuprofen over a 2.5 hour time period to demonstrate field stability.

2D Spectroscopy

Anasazi’s Eft spectrometer is a fully-featured Fourier transform-NMR system that can be used in complex experiments, including 2D spectroscopy, T1 and T2 relaxation, and DEPT. The primary 2D experiments are made up of {¹H}- ¹³C correlation spectroscopy HECTOR and {¹H}- ¹H correlation spectroscopy COSY.

COSY spectra can be acquired via means of gradient improved methods. Thus, a low resolution COSY can be obtained within only 3 minutes.

Figure 4 shows a comparison between a COSY-45 1024 x 256 3 data set (right, < 7 minutes) and a 512 x 128 COSY spectrum (left, < 3 minutes) for a 5% solution of ethyl methacrylate dissolved in CDCl₃ solvent.

Figure 4. Left: Single scan COSY spectrum of ethylmethacrylate. Right: High resolution COSY-45 ethyl methacrylate 5 wt% in CDCl₃

Figure 5. DEPT multiplicity spectrum of 30% menthol. Total experiment time 6 minutes

Figure 6. ¹³C-{¹H} HETCOR spectrum of 2M ibuprofen. Total experiment time 4 minutes

The HECTOR and DEPT measurements are very useful and allow students to discover the identity of an unknown solution. In figures 5 and 6, the spectrum shown on the lower right is an ibuprofen spectrum and the spectrum shown on the lower left is a DEPT spectrum menthol. These spectra were obtained within a few minutes.

Conclusion

Anasazi’s Eft spectrometer is a 60 MHz pulsed Fourier transform NMR instruments that allows fast gathering of 1D and 2D carbon-13 spectra. In the educational field, the Eft presents a number of practical opportunities for undergraduates to obtain and study FT-NMR data.

Moreover, the varied appeal of the Eft spectrometer is due to the ease of acquiring high-quality NMR spectra on an instrument that does not require cryogens and has minimal maintenance needs.

This information has been sourced, reviewed and adapted from materials provided by Anasazi Instruments, Inc.

For more information on this source, please visit Anasazi Instruments, Inc.