SU817556A1 - Pulse spectrometer of nuclear magnetic resonance - Google Patents

Description

The invention relates to radio spectroscopy and can be used to analyze the content of substances by nuclear magnetic resonance (NMR).

Known pulse NMR spectrometer for analysis of substances, including a magnetic pulse emitter, a receiver of signals emitted by a sample placed in the sensor, a computing device for processing these signals, and the input and output of the signal receiver are grounded using electronic keys [1].

However, this spectrometer has a random resolution of 15, which reduces the accuracy of the NMR measurements.

Closest to the proposed technical essence is an NMR pulse spectrometer containing a radio pulse transmitter connected to a sensor and a delay unit, a receiver whose input is connected to the sensor output and the output to an amplifier, ¹ line-pass block, the .25 inputs of which are connected to the outputs of the amplifier and the control unit, the input of which is connected to the output of the delay unit, the integrating unit AND the computing complex, the <_____ ___ ~~ move is to the amplifier, the line-pass unit, the inputs of which are connected to the outputs odes to the amplifier and control unit whose input is connected. to the output of the delay unit, the integrating link and the computer comp _ ^! Lex, consisting of blocks changes ^e mark, summation, multiplication and division, further provided with a second integrating element and block squaring the second integrating element is connected in series with the 'first, the output of the first link via the multiplication unit and an output of the second link through blrk 'sign changes are connected to the inputs of the summing unit - _ the output of the summing unit is connected. »5 is dined to one of the inputs of the division block, to the second input of which the output of the first integrating link is connected through the squaring block. 20

To eliminate high-frequency interference superimposed on a useful low-frequency signal, integration is carried out using an integrating unit, with J5 the signal amplitudes are reduced in proportion to the frequencies, resulting in an increase in the signal-to-noise ratio.

The spectrometer integrates zve- ^di but integrates the signal exponential form of induction, the output of which becomes dependent on the index eksponanta (po.perechnoy relaxation time), which defines 35 thematic systemic error.

The exclusion of the exponent in the output signal of the first integrating link of the proposed spectrometer is carried out using an additional second integrating t - the delay time when measuring the current amplitude i (t); S is a function describing high-frequency noise and causing random measurement errors. Indeed, after the first integration carried out by the first hi integrating event, we obtain the following expression.

s (£) -Jidt 4 (a _o e ' ^{g / m} + S) dt - Ja _o e' ^{t / T} dt> 0.0 O

Jsdt = q _o T (i - _e -> ^T ) '.

taking into account HTofsdt'O · The integration time is determined by the time interval between pulses, i.e. the repetition period of the pulses generated by the transmitter of the radio pulses. Moreover, 4T, (3) what ensures the establishment of zero magnetization at the time of the subsequent pulse. Therefore, for the integration time T _r satisfies the relation (3), expression (2) takes the form _of a T = (4) _ since ie ^t "1.

After the second sequential: integration implemented .vtorym integiruyuschim element connected in series with the first to obtain the following expression (T) * D * F = {Ga _about t) dt ° ----- O = T aT ₀ and _about t * ( Ь ' ^г ' ^т ) go link connected in series to the first. So the way. double integration using two series-connected integrating links eliminates errors of random and systematic origin, which affects the accuracy of NMR measurements.

Transmitter, radio pulse impulse-W _<? An NMR spectrometer generates successively 90 ° pulses that excite the spin system of the sample waved into the sensor. After excitation, the spin system of the sample induces a decay signal of its: water induction in the sensor coil, the current amplitude of which can be written as follows.

-q _o e ~ ^ ^{| T} (1) where a _o is the initial amplitude of ccn - I la, proportional to the number. the number of magnetic nuclei in ob45

I.

razse;

T is the transverse relaxation time; 65

Taking into account relation (3), expression (5) takes the form

3 ₂ (Ί7) = а ₀ Т-б - а ₀ Т ^а , (6) for е <<1.

Substituting T = - from the expression * B0 (4) into equation (6) we obtain the following formula 'for the initial amplitude of the signal _a = __ 3 / _ o - · Π ₄

The proposed device, equipped with a second (4) integrating unit, allows the measurement of 3 ^ signals. and 3 ₂ and make calculations according to formula (7) of the quantity a _о , proportional to the concentration of the substance with high accuracy. This can be seen from formula (7), in which there are no quantities characterized by errors of random and systematic origin.

Calculations by formula (7) are carried out by a computer complex, which can be an electronic computer of the Mir-2 type.

The drawing shows a schematic diagram of a pulsed nuclear magnetic resonance spectrometer.

The NMR spectrometer contains a transmitter 1 of radio pulses, the output of which is connected to the input of the sensor 2, which is connected to the input of the receiver 3, the last output through the amplifier 4 is connected to the input of the line transmitter unit 5. The input of unit 5 is connected to the output of the control unit 6, which is connected through the delay unit 7 to the output of the transmitter 1. The output of unit 5 is connected to series-connected integrating units 8 and 9. The outputs of integrating unit 8 are connected to the inputs of the multiplication unit 10 and erection unit 11 squared, and the output of the integrating link 9 to the input of the sign-changing unit 12, the output of the latter and the block 10 are connected to the summing unit 13, the output of which is connected to the input of the division unit 14 connected through the block 11 of squaring to the input of the block 10.

A pulsed spectrometer operates as follows.

RF pulse transmitter 1 _ you-ops sequence of 90 ° pulses with a repetition frequency coming to the sensor 2. Every 90 ^th pulse excites the spin system of the sample placed into the sensor. 90 ° - the pulse and the induction signal induced in the sensor coil are fed to the input of the receiver 3 ₍ in which the signals are pre-amplified, detected and fed to the block of the main amplifier 4 signals

The amplified signals are fed to the input of block 5 of the linear transmitter, delaying a 90 ° pulse and passing only the useful signal and noise during the time interval generated by the pulses of control unit b, the duration of which is less than the interval between pulses by an amount formed by the pulse of block 7 of the delay, which ensures that transmission elongated due to transients 90 ° - the radio pulse.

After block 5, the obtained induction signal in the form of a decaying exponent and high-frequency noise are fed to the input of the first integrating amplifier 8, which outputs a signal whose value is determined by expression (4). With integration, the signal-to-noise ratio (S 0) increases. The output signal proportional to the initial amplitude and the decaying exponent with the excluded function S goes to the input of the second integrating link 9, connected in series with the first, the output signal of which is expressed by equation (6), is an integral of 3γ and depends on the initial amplitude of the signal, the decay rate exponential and integration time t equal to the period of work. the transmitter.

A

With the output of the integrating links and 9, the signals 3 ^ and 3g are fed to the input of the computer complex.

From the output of the first integrating link, the output signal through the block 10 of multiplication by the value Τ 'and the output signal 3 ₂ from the output of the second integrating link-9 through the block 12, the sign changes go to the summing block -13, from where the output signal is proportional to 3 ^ -с - 3 _d , is supplied to block 14 for dividing ^{into ET} Y the value of 3 ^ obtained in the squaring block 11, where the 3 ^ signal is received, from the output of the first integrating link 8. From the output of block 14, the signal is proportional to the initial the amplitude of the induction signal a <without interference randomly of a systematic origin gets to the recorder (digital voltmeter or printing device).

The proposed spectrometer improves the accuracy of measurements and "Reduces their cost.

Claims (2)

1 .. Patent of France 2350599 (l. G 01 N 27/7 $, published;) b.01.78. 2. Van Putte K. and Van der Enden Puls NMR; Jnstrum (Jof Phus E.) 1973, No. 6, p. 910-912 (prototype).