Neutralization of ﬂuctuations in resonance conditions during
registration of NMR spectra in the Earth's magnetic ﬁeld
Pavel Kupriyanov, Vladimir Chizhik
St. Petersburg State University, Russia

Silicates
9Nucleus
19F
29Si
31P
13C

Abundance,%
100
4.7
100
1.1

Spin
1/2
1/2
1/2
1/2

CH3

reduced by 25 time

CH3

CH3- Si - O - Si - O - Si - O 6

CH3

CH3- O - Si - O -4

CH3JH,Si

4,3 HzCH32

3JH,Si8,2 Hz01872

1873

1874

1875

1876

1877

1878

1879

1880

1881

1882

1883

Frequency, HzFig. 6. The spectra of Polimethilsiloxan, 36 time averaging
0.03

Amplitude, a.u.

NMR-spectra in weak ﬁelds are not split due to chemical shifts and theywould seem uninformative for analysis of substances. Nevertheless, NMR in
the Earth magnetic ﬁeld allows ones to register the record resolution ofspectra which are split due to heteronuclear interactions (J-coupling). Thus,
the NMR in Earth magnetic ﬁeld provides an opportunity to measure Jcoupling constant with the highest accuracy. The proton spectrum has asymmetrical structure and a distance between lines determines the degree ofspin interactions. As examples, several J-coupling NMR-spectra which wereobtained with the home-built equipment [1] are represented.There are someactual nuclear isotopes which interact with protons in liquid compounds (it isimpossible to detect NMR in the Earth magnetic ﬁeld in solids). The mainsuch isotopes are presented in Table 1.
There are some actual nuclear isotopes which interact with protons in liquidcompounds (it is impossible to detect NMR in the Earth magnetic ﬁeld insolids). The main such isotopes are presented in Table 1.

Amplitude, a.u.

p.kupriyanov@spbu.ru

CH3

JH,Si=7,4 Hz

0.02

JH,Si=7 Hz
0.010

reduced by 25 time
−0.01
1876

Table 1. The actual isotopes which interact with protons and form theindirect spin-spin J-coupling observed on in the Earth ﬁeld NMR-spectra.

1877

1878

1879

1880

1881

1882

1883

1884

1885

Frequensy, Hz

Fig. 7. The spectra of Hexamethilsiloxan (red) and Hexamethilsilozan (blue),
4 time everaging.

J-coupling spectra which recieved with small averaging
Fluorine-containing liquids

0.05
reduced by 25 time

Amplitude, a.u.

0.04

Amplitude, a.u.

1H-C-C-O-Si-O-C-C-H

1,4 Гц

0.02

0.75
0.01

0.5

1875.4

1875.6

1875.8

1876

1876.2

1876.4

1876.6

1876.81877

1877.2

1877.4

1877.6

1877.81878

1878.2Frequency, HzFig. 8. The spectra of Tetraetoxysilan (red), 4 time everaging.
0ю25

Fig. 2. The spectrum of 2,2,2Triﬂuoroacetic acid. The sensorof the NMR-spectrometer istuned to the proton frequency.

01765

1770

1875

Frequency, Hz

1880

1885

8

6

Amplitutue, a.u.

0.03

JH,F⁓6Hz

3

F4201650

1660

1670

1680

1690

1700

1710

1720

1730

1740

1750

1760

1770

1780

1790

1800

1810Frequency, HzFig. 3. The spectrum of ﬂuorobenzene. The sensor of the NMR-spectrometeris tuned to the ﬂuorine frequency. Averaging is 200 shots. The relation ofsignal-to-noce is not enougth.

Problems in the case of small natural abundanceof interacting nuclei
It is very important to analyze organic liquids but the isotope 13C has naturalabundance of 1.1 % and satellites in proton spectra are very weak. In thiscase it would be eﬀective the signal accumulation. Unfortunately, the Earthmagnetic ﬁeld is not stable enough, especially in laboratory conditions. To
neutralize the ﬂuctuations of the Earth magnetic ﬁeld we developed andpatented the method of the stabilization of resonance conditions [2].
The principle is based on two-sensors scheme [3]. The ﬁrst sensor contains
an investigated sample. A sample in the second sensor is a proton liquid
which possesses a single intensive line in the NMR-spectrum. The signal fromthe second sensor carries an The main feature is detection method of test
probe signal (1). As signal (9) for quadrature detection (10), the synthesizedsin with frequency (8)from second sensor probe(2).
Тhedeviceispatented (RU175 974U1).

12Amplitude, a.u.

10

86CH2

4
20−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −50510 15 20 25 30 35 40 45 50 55 60 65

Frequency, HzFig. 4. The spectra of 2,2,2-triﬂuoroethanol. The sensor of the NMRspectrometer is tuned to the ﬂuorine frequency (red) or to the proton
frequency (blue).
Phosphates
1.5

43JH,PAmplitude, a.u.

Amplitude, a.u.

610,9Hz

13JH,P3,9Hz

JH,P

3,5Hz

50.5

3JH,H

22,6Hz01780

1785

1790

1795

Frequency, Hz

1800

1805

1876

1877

1878

1879

1880

1881

1882

1883

1884

1885

1886

Frequency, Hz

Fig. 5. The spectra of Trimethilphosphate (left) and Triethilphosphate (right).

Fig. 1. The device schemefor
NMR-frequency
stabilization: sensor for aninvestigatedsample (1),reference
sensor(2),
shimmsystems(3),
commutation blocks (4),microcontroller (5), prepolarization power siply (6),preampliﬁer (7), frequency
counter (8), sine generator(9), quadrature detector(10), spectrum visualizer(11).
References
1. P. A. Kupriyanov, K. A. Dmitriev, A. V. Chizhik. On some improvements ofnuclear magnetic resonance in the earth’s magnetic ﬁeld registration.
Vestnik SPSU, Т. 3. № 1. pp. 59-69. 2016.
2. V. I. Chizhik, P. A. Kupriyanov. Equipment for stabilizing the frequency ofnuclear magnetic resonance in the Earth's magnetic ﬁeld. Patent of RussianFederation № 175974. Bull. № 36. 2017.
3. A. Mohoric, G. Planinsic, M. Kos, A. Duh, J. Stepisnik. Magnetic ResonanceImaging System Based on Earth magnetic ﬁeld". Instrumentation Scienceand Technology, Vol. 32, No. 6, pp. 655-667, 2004.