SU1303915A1 - Method of identifying chemical compounds - Google Patents

Abstract

The invention relates to a measurement technique and allows the detection of chemical compounds using nuclear quadrupole resonance (NQR). The essence of the invention is a two-frequency effect on the analyzed solid material. For this, the substance is irradiated with a series of radio frequency pulses. The induction signal that occurs after each pulse is summed multiple times. The accuracy of the detection of a substance is determined by the trapping effect, i.e. by changing the amplitude of the induction signal under two-frequency exposure (the sample is exposed to the main multi-pulse series, which creates a recording NQR signal at a given frequency, and a saturating pulse at another frequency, operating between the first and second pulses of the main series). (L: o o: o; o

Description

The invention relates to nuclear quadrupole resonance and can be used to analyze materials using nuclear quadrupole resonance (NQR).

The goal is to increase the rapidity of the method and the possibility of unambiguously determining the chemical compound in a multi-component sample.

night-time and two-frequency series operate during a period (cycle time) tj, -i T (t, is the time of spin-lattice relaxations). The time between one frequency and two-frequency series t - (3-5) T .. The cycle time t- is determined by the number of pulses n in the series, the time between pulses is 2 € (C T). In the case of a multipulse effect on a multilevel quadrupole SIS-: 10 series, a vector is transferred by the theme of a multicomponent sample of the nuclear magnetic induction induced by a single-frequency multi-pulse series of RF field pulses with a preparatory impulse with a fto phase 90 °

J90

- (ir - t.

relative to other -sH), where t is dlJ5

rotating coordinate system. In this case, a continuous NQR signal arises due to the action of radio-frequency pulses. The action of the saturating impulse on the adjacent transition leads to saturation of the transition, a change in the difference between the populations of the levels, violates the phase coherence of the precessing spins in the rotating coordinate system, thereby reducing the signal intensity.

pulse strength; C is the time interval between the pulse in a series of: T (t, is the spin-spin relaxation time of the system); n is the number of the pulse in the series. When the frequency of filling the series coincides. at the frequency of one of the transitions of the quadrupole system, NQR signals appear (in this case, an echo signal). An increase in the signal-to-noise ratio for such echo signals is produced by accumulating echo signals with noise after each pulse. After fast detection of the NQR signal for an hour

), The presence of two part-belonging to one

Tote, from the NQR databank, information is requested about possible chemical compounds, in the spectrum of which there is a frequency of that NQR, and 2,

The chemical compound allows it to be identified. To refine the value of j, a sample is subjected to a two-frequency series consisting of a main multi-pulse series of identical pulses with a preparatory pulse, with an impressed phase b at 90 ° relative to others at a frequency of -5

-t))

relationship (t; and the one who has it,

pulse at a frequency -Jg on an adjacent transition, acting after the first preparatory impulse (the duration of this penetrating impulse is f). When the frequency coincides with the NQR frequency of the chemical compound, the NQR signal at the frequency varies in intensity, i.e. a capture effect is observed.

14

in the case of NQR spin of nitrogen N under the action of the frequency and (where and are high-frequency and low-frequency quadrupole transitions), the signals are attenuated. Od

night-time and two-frequency series operate during a period (cycle time) tj, -i T (t, is the time of spin-lattice relaxations). The time between the single-frequency and two-frequency series t is (3-5) T .. The cycle time t is determined by the number of pulses n in the series, the time between pulses is 2 € (C T). In the case of the action of a multipulse series, the transfer of the magnetization vector of the nuclear induction occurs.

rotating coordinate system. In this case, a continuous NQR signal arises due to the action of radio-frequency pulses. The action of the saturating pulse on the adjacent transition leads to saturation of the transition, a change in the difference of the level populations, violates the phase coherence of the precessing spins in the rotating coordinate system, thereby reducing the signal intensity.

Example. In the study of a mixture of nitrogen-containing substances, NQR signals were observed at frequencies of 4.929 MHz, 3.757 MHz, 2.913 MHz, :) 2.347 MHz at 77 K. The frequency range of the NQR frequencies of nitrogen-containing compounds is 5-5-5 MHz. The total search time for signals t npHuf is 5 kHz and the time the series is turned on after 2 minutes is 30 hours (uf is the NQR line width).

These frequencies belong to sodium nitrite NaNO and urea CO (NH). To search for a specific substance, such as NaNO, we expose the sample to the frequency, 4.929 MHz. Upon detection of the NQR signal, we turn to the data bank. This NQR frequency can enter into the spectrum of two compounds NaNO and С, Н „N0. Frequencies of NaNOj at 77 K 4. 4., 929 MHz, n1 3.757 MHz. AT . N0. 4.930 MHz, 2.6072. The frequencies of these compounds fall into the passband of the NQR spectrometer. The width of the NQR line reaches several kilohertz. To accurately determine the substance, it is necessary to go through the whole spectrum. This is due to the fact that, in the case of a mixture of compounds, their frequencies in the spectrum form a complex picture and some frequencies of the spectra of other compounds can fall on the NaNO frequency. Therefore, single-frequency detection of a signal at a frequency. 3.757 MHz is not an indication of NaNO- detection. The impact of the two-frequency series described by Bbmie at) +, 5 drives

3f

It leads to a sharp weakening of the NQR signal at a frequency (capture effect). This allows us to confidently assert that these two frequencies belong to the same connection.

The use of a dvz frequency method for the identification of chemical compounds makes it possible to produce a quick unambiguous; determination of a specific chemical compound using two NQR frequencies. In this case, there is no need to obtain an NQR spectrum in the entire range of possible frequencies and subsequent analysis of the spectrum. This shortens the time for searching for a specific chemical compound that has two frequencies in the NQR spectrum. This method can find application in chemistry, chemical industry, in geology in the analysis of multicomponent mixtures.

Claims (1)

Invention Formula A method for the identification of chemical compounds, including the search for one Editor A.Dolinich Order 1302/44 Compiled by S. Varlamov Tehred A. Kravchuk Proofreader. Cherni Circulation 777 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 . Production and printing company, Uzhgorod, Projecto st., 4. 14 of the -5 lines, the NQR spectrum of the sample under study by acting on it with a multipulse single-frequency series of radio pulses with a preparatory pulse shifted in phase by 90 relative to the subsequent ones, characterized in that, in order to increase the rapidity of the method and the possibility of unambiguously determining the chemical whom compounds in a multicomponent sample, in the NQR databank choose chemical compounds whose spectra contain a component on the frequency v, for each of the selected compounds in the databank find the second frequency -J associated with a common energy level of -5, affect the sample with a high-frequency field at a frequency as a series of radio pulses and a pinching pulse at a frequency in the interval between the first and second pulses of the specified series, and by the change of the NQR signal at the frequency, are judged on the presence in the sample of a chemical compound with resonant frequencies NQR -5, and j.