SU913192A1 - Quantitative analysis method - Google Patents

Description

The invention relates to physico-chemical analysis and can be used in all fields of science, engineering and industry, which require the determination of the content of any substances in the original, intermediate final products in physical, chemical, biological or technological processes.

The known method of quantitative analysis of substances, based on the registration of signals with pulsed nuclear magnetic resonance (NMR) PZ.

In this method, the substance is a measure of the amount of free induction cores amplitude signal which excites' ⁵ etsya short radio-frequency pulse at the resonance frequency of the nuclei. These nuclear-resonant methods of quantitative

substances have comparatively little analysis

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high reliability and low accuracy, since receiving devices are used for recording the signal, the transmission coefficient of which can vary during

^ time to depend on the properties of the sample. Replaceable standards with a known amount of substance are used to calibrate the receiver gain. However, the change in the transmission coefficient due to the effect of the sample on the properties of the receiving circuit (primarily, the quality factor) increases.

The closest technical solution to the proposed method is a quantitative analysis of substances based on the excitation of two NMR radio pulses in the reference and test samples, placed simultaneously in NMR, registration of NMR signals from the reference and test samples. The studied and reference samples are samples that differ in the times of spin-lattice (longitudinal) relaxation. By acting on the samples by two (or several) pulses, one can separate the free induction signals from the test and reference samples and,

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thus, determine the amount of substance in the sample. In this method, the transmission coefficient from the signals of free induction of the test and reference samples is the same 12]. five

The disadvantage of this method is the limited scope, since it imposes the requirement of a certain ratio of the relaxation times of the nuclei in the reference and test samples. m

The purpose of the invention is to improve the accuracy and reliability of measurements.

• The delivered chain is achieved by the fact that in a known method of quantitative analysis of substances based on the excitation of radio pulses of nuclear magnetic resonance (NMR) in the reference and test samples placed in one NMR sensor, the registration of NMR signals from the reference and test nuclei 20 samples, the excitation of radio pulses is carried out at the frequencies of resonance of the nuclei in the test and \ in the reference samples, and the reference sample contains nuclei with magnetic moments that are 25 different from the magnetic moments of the nuclei of the test. aztsa and recording the NMR signal is performed after the first radio pulse of 'Cores one sample, and after the second rf pulse - of the nuclei to another sample and compared amplitudes of these NMR signals are judged on the number of substances in the sample.

In the proposed method, the advantages of the simultaneous resolution of ³⁵ reference and test samples in a nuclear magnetic resonance sensor are used, but the restriction on the ratio of ropaxation times of nuclei is removed. The main effect is achieved by reducing errors ⁴⁰ associated with a change in the transmission coefficient of the receiving path of various instabilities or / variations in the properties of the receiving circuit of the sensor when samples are introduced into it. For this purpose, ⁴⁵ almost simultaneously simultaneous registration of nuclear magnetic resonance signals from different _nuders for the reference and test samples is used.

FIG. 1 is a diagram ustroy- ^{50-OPERATION;} in fig. 2 is a diagram of receiving free induction signals.

The gap of the magnet 1 is placed nuclear magnetic resonance sensor 2, which is an 10-circuit ⁵⁵ nastro- enny on resonance frequency of the nuclei. The loop inductance covers samples 3 and 4 with the substance. Software 5 device 5 generates video pulses to control all units of the device, including the generator of radio pulses 6 for exciting a free induction signal, a receiver 7 of nuclear magnetic resonance signals and a recording device 8. After the radio pulses .9 and 10 produced by the generator of radio pulses 6, at the receiver output 7 free induction signals 11 and 12 appear. If the generator of radio pulses 6 generates a radio pulse 9 of duration and the amplitude of this magnetic component, then the vector M rotates. ν = ^ · Η _Λ ΐ; . In this case, a component of the vector CK appears, perpendicular to the field H,. The free induction signal is proportional to the value of μ and, since μ is determined by the magnitude of the vector μ, the signal amplitude is proportional to the number of kernels of a given sort in the sample. Naturally, the optimal is the rotation of the vector μ by the angle V = 90 *, when μ ^ takes the maximum value. Over time, the free induction signal 11 decreases, and the attenuation time constant is 4½ (the time of transverse or spin-spin relaxation) is determined both by the state of matter and by instrumental effects, and usually does not exceed 10—

20 ms, if no special measures are taken in the magnets to improve field uniformity.

The initial amplitude of the signals of the free procession is a measure of the number of investigated nuclei in the sample. After amplification in the receiver 7, this signal enters the recording device 8, one of the functions of which can be its memorization and accumulation.

However, the value of the amplitude of the free induction signal depends on the stability of the transmission coefficient of the receiving and recording parts of the device. The change in the quality of the receiving circuit due to variations in the physicochemical properties of the samples placed in the inductor, the change in the gain of the receiver G / due to variations in the supply voltages and the aging of the circuit elements leads to uncertainty in the measured magnitude, which can only be eliminated by a constant calibration of the transmission coefficient of the device.

In order to increase the reliability and accuracy of the instrument readings, it is proposed to place simultaneously in the sensor of nuclear magnetic resonance 2 signals

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two samples: 3 and 4 (test and reference) and register the resonances of different nuclei in the reference and test samples. At the same time, the programming device, the device, must work out special commands for the restructuring of the generator, sensor and receiver from one operating frequency to another. This can be, for example, done using relays or other electronic tuning techniques.

In rezuytayte after the filing of the first radio pulse 9 (Fig. 2) at a frequency of '

£ 4d a free induction signal 11 from one sample is recorded, and after the second radio pulse 10 is applied, a free induction signal 12 from the second sample is recorded at the frequency. Since both samples are in the coil of the receiving circuit of the sensor, it is ₂₀ mode, the instrument transfer coefficients for both signals are interconnected by a constant ratio for any combination of substances in the samples £ and 4.

Since the time между 'between pulses can be ₂ 5 very small (of the order of milli seconds), the receiver's transmission coefficient for free induction signals 11 and 12 does not change during the measurement time.

The use of the proposed method _{30 for} quantitative analysis is possible, in principle, for any combination of nuclei in the test and reference samples. However, the use of nuclei is most convenient with close gyromagnetic ognoshe- niyami _35, and therefore have similar resonant frequencies in .postoyannom magnetic field. Ego circumstance facilitates the rearrangement unit for alternately recording signals from RAE ₄₀ nuclei. As a result of using the proposed method, the measurement accuracy is increased due to the consideration of the effect of samples on the parameters of the receiving circuit of a nuclear magnetic resonance sensor. If signal accumulation is required to further improve the accuracy of measurements, then recording device 8 can sum up the readings of signals 11 and 12 alternately or first accumulate information after a series of identical radio pulses of type 9, and then similarly after the same number of radio pulses of type 10.

express analysis due to the fact that the excitation of free induction signals ο · * · staged does not disturb the magnetization of the sample to be treated and vice versa.

5 The sequential registration of various resonances can increase the rapidity of analysis, especially for substances with large values of longitudinal relaxation, and expand the range of possible application of NMR for quantitative analysis of substances. In addition, the simultaneous placement in the sensor; magnetic resonance of the standard and the sample under study allows the use of flow-through samples. Poe 5 can be used

for automatic control and management of continuous technological processes.

Claims (1)

Claim A method of quantitative analysis, based on the excitation of nuclear magnetic magnetic resonance (NMR) by radio pulses in the reference and test samples placed in one NMR sensor, recording NMR signals from reference and test samples. In order to improve the accuracy and reliability of measurements, the excitation of radio pulses is carried out at the resonance frequencies of the nuclei in the test and reference samples, and in the reference sample the nuclei with magnetic moments, different magnetic moments of the sample followed, and the NMR signal is recorded after the first radio pulse from the nuclei of one sample, and after the second radio pulse from the nuclei of another sample and by comparing the amplitudes of these NMR signals, the amount of the substance in the sample is measured.