Shortening measurement time by multiple acquisition experiments

  • Summary

NM200008E

Multiple acquisition measurements have been attracting a lot of attention as a method for shortening measurement time in recent years.
These sophisticated experiments allows us to acquire multiple 1D or 2D NMR data in one measurement on an instrument equipped with a single receiver or multiple receivers. Multiple acquisition experiments can significantly shorten the total experimental time compared to acquiring data conventionally.
In addition, multiple acquisition experiments can also benefit from Non Uniform Sampling (NUS), therefore additional shortening of measurement time is possible. However, if there is a significant difference in sensitivity between the experiments combined in the multiple acquisition experiment, it is necessary to set the number of scans according to the least sensitive experiment.

① NOAH method

NOAH (NMR by Ordered Acquisition using 1H-detection) is a useful method which can acquire multiple 2D spectra at once even without using multiple receivers. Fig. 1 shows a NOAH pulse sequence which acquires 2D 1H-13C HSQC, 1H-13C HMBC and 1H-1H COSY spectra altogether.
All the 2D spectra are generated simultaneously after the experiment has finished. Fig. 2 shows results of NOAH-3 of 10% cinnamic acid cis-3-hexen-1-yl ester in CDCl3. These spectra can be obtained within 5 minutes by using NUS.
A dedicated automation was made for NOAH to improve its usability (Fig. 3). User sets the spectrum width, number of Y points, number of scans, and selects/unselects the NUS option. As individual filenames and process lists are automatically set for each data file after the measurement has completed, these data can be analyzed in the same way as traditionally acquired data.

Pulse sequence of NOAH-3

Fig. 1: Pulse sequence of NOAH-3

 NOAH-3: a) HSQC, b) HMBC, c) COSY

Fig. 2: NOAH-3: a) HSQC, b) HMBC, c) COSY

Number of scans: 1, Y points: 256, NUS density: 25%, exp. time: 5 min

Setting screen of NOAH automation

Fig. 3: Setting screen of NOAH automation

Instrument

Reference

② Interleaved method

Interleaved experiments also have multiple acquisition blocks during one experiment. However, when compared to NOAH experiments, interleaved experiments detect different nuclei by means of multiple receivers.
Fig. 4 shows a pulse sequence of interleaved COSY. One receiver observes 1H-1H COSY and the second receiver observes 19F-19F COSY. Therefore, 1H-1H COSY and 19F-19F COSY spectra are recorded at the same time.
Fig. 5 shows results of interleaved COSY collected on 10 mg voriconazole in DMSO-d6. These spectra can be obtained within 3 minutes with NUS.

Pulse sequence of Interleaved COSY

Fig. 4: Pulse sequence of Interleaved COSY

Interleaved COSYの測定結果 a) 1H-1H COSY, 19F-19F COSY

Fig. 5: Interleaved COSY: a) 1H-1H COSY, b) 19F-19F COSY

Number of scans: 1, Y points: 256, NUS density: 25%, exp. time: 3 min

Instrument

③ PANSY method

PANSY (Parallel Acquisition Nmr SpectroscopY) experiments usually acquire two FID data in parallel. These techniques also observe signal of different nuclei using multiple receivers as in the Interleaved method. On the other hand, acquisition blocks are executed at the same time, i.e. in parallel, in PANSY. Fig. 6 shows a pulse sequence of PANSY COSY which acquires 1H-1H COSY and 19F-1H HETCOR spectra.
Fig. 7 shows the results of PANSY COSY on 15 mg 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene in CDCl3.
Fig. 8 shows a pulse sequence of PANSY HMBC which collects 1H-13C HMBC and 19F-13C HMBC spectra.
Fig. 9 shows the results of PANSY HMBC of the same sample. These measurements time were reduced by NUS.

Pulse sequence of PANSY COSY

Fig. 6: Pulse sequence of PANSY COSY

PANSY COSY

Fig. 7: PANSY COSY: a) 1H-1H COSY, b) 19F-1H HETCOR

Number of scans: 1, Y points: 256, NUS density: 25%, exp. time: 3 min

PPANSY COSY
Pulse sequence of PANSY HMBC

Fig. 8: Pulse sequence of PANSY HMBC

PANSY HMBC: a) 1H-13C HMBC, b) 19F-13C HMBC

Fig. 9: PANSY HMBC: a) 1H-13C HMBC, b) 19F-13C HMBC

Number of scans: 4, Y points: 256, NUS density: 25%, exp. time: 8 min

Instrument

Reference of Interleaved and PANSY:

  • Helena Kovacs and Eriks Kupce, Magn. Reson. Chem. 2016, 54, 544-560.
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