Advantages of Eft NMR Spectrometer in Teaching Laboratories

Anasazi Instruments have offer the robust, high quality and convenient 60 MHz and 90 MHz NMR spectrometers, as well as upgrades to industrial and educational markets.

These instruments are being used successfully at several institutions spanning from top-tier universities and large companies to several community colleges.

The Speed Advantage

The key benefit provided by the Eft NMR spectrometer is speed. 50% of methyl linoleate solution dissolved in CDCl₃ solvent provided the ¹H and ¹³C NMR spectra shown in Figure 1. In just 2 minutes, both the spectra were obtained and processed.

It is possible for users to obtain and process the ¹³C and ¹H NMR spectra rapidly and conveniently, and students can also obtain single-dimension and two-dimensional spectra for their respective 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 are two distinct features of the Eft NMR instrument, which make it suitable for teaching laboratories. For considerably large molecules, high resolution is obtained because of the 60 MHz field strength. A high signal to noise ratio and a large sample volume are attained because of the industry proven tube sample measuring 5mm in size.

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

Based on the magnetic resonance laws, in case the sample volume is reduced it will lead to lower levels of signal in a linear manner. It can be seen that with larger sample volume of 0.2 mL compared to the sample volume of a capillary NMR of 0.0001 mL, the 60 MHz instrument can provide 2,000 times the signal to noise ratio for equal magnetic field strengths.

Moreover, in case there is a reduction in field strength, it will cause lower levels of signal and would also cause more 2nd order effects and more crowding of spectra. Spectral interpretation is made more complex by all these aspects. Figure 2 illustrates how the perfect triplet-quartet pattern declines to less than 60 MHz.

Instrument Stability

A key aspect for performing high-resolution NMR experiments easily and effectively is magnetic field stability. In case adequate thermal stability or proper protection is not provided for a permanent magnet, the magnetic field will vary throughout the measurement and eventually affect the result quality.

In contrast, tabletop NMR instruments are highly compact and extremely sensitive. One major test is to determine the chemical shift as a virtue of time.

Figure 3 shows the stability of the Eft-60 instrument over a period of 2.5 hour, which is rather long given that standard and ¹³C spectra need several minutes to achieve the stability while ¹H spectra needs 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 completely-featured Fourier transform-NMR system that can be deployed in complicated experiments such as 2D spectroscopy, T1 and T2 relaxation, and DEPT. The major 2D experiments comprise {¹H}- ¹³C correlation spectroscopy HETCOR and {¹H}- ¹H correlation spectroscopy COSY.

COSY spectra can be obtained by means of gradient improved methods. Therefore, a low resolution COSY can be acquired within a matter of 3 minutes.

In Figure 4, comparison is made 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 HETCOR and DEPT measurements are highly useful and enable students to find the identity of an unknown solution. The spectrum shown on the lower right is an ibuprofen spectrum and the spectrum given on the lower left is a DEPT spectrum of menthol (Figures 5 and 6). These spectra were recorded within a matter of few minutes.

Conclusion

Anasazi’s Eft spectrometer is a 60MHz pulsed Fourier transform NMR instrument that enables rapid collection of 1D and 2D carbon-13 spectra. In the field of education, the Eft offers several undergraduates practical opportunities to obtain and study FT-NMR data.

Furthermore, the broad appeal of the Eft spectrometer is because of the ease of obtaining high-quality NMR spectra on an instrument which does not need cryogens and has minimal maintenance requirements.

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

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