RU33233U1 - Gas chromatography acoustic detector - Google Patents

Description

ACOUSTIC DETECTOR FOR GAS CHROMATOGRAPHY

The utility model relates to the field of analytical technology, namely to means for measuring the concentrations of components in gas chromatographic analysis.

A well-known acoustic detector for gas chromatography (Farzane N.G., Ilyasov L.V. Automatic gas detectors. M: Energy, 1972, C168), containing a working and comparative chambers in which piezoceramic elements are located (emitter and receiver of acoustic vibrations) connected to input and output of electronic amplifiers. The cameras are included in a differential circuit. The difference in the speed of ultrasound in the working and comparative chambers is proportional to the difference in the frequencies of self-excitation of their amplifiers. This difference is fed to the mixer, where the beat frequency is allocated and amplified. To record a chromatogram, a frequency to voltage converter is provided in the circuit.

The disadvantage of this detector is the design complexity and the need to use an additional frequency-voltage converter for recording the chromatogram using automatic potentiometers, which are usually included in the chromatographs.

The closest in technical essence is an acoustic detector for gas chromatography (Negretov, Yu.B. Acoustothermal detector for gas chromatography. Baku AzNIFTEKHIM, 1989, Abstract of a dissertation for the degree of candidate of technical sciences), containing a flow chamber made in the form of a tube, in one end of which has a source of acoustic vibrations, and the other end is closed by a roof, provided with an outlet fitting, a carrier gas fitting mounted in the chamber wall between its ends, a fitting

2003115562

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IPC: 7 G01N30 / 76

auxiliary gas mounted in the wall of the chamber between the nozzle of the carrier gas and the source of acoustic vibrations, and a thermistor placed inside the chamber on its axis and connected to an unbalanced electric bridge. The detector is based on the excitation of a standing acoustic wave in a tube using a source of acoustic vibrations and the measurement of temperature changes in a thermistor caused by a change in the location of a standing wave in a tube when detectable components from a chromatographic column enter it with a carrier gas.

The signal of this detector is the imbalance of an unbalanced electric bridge, which is a function of the concentration of the component and its molecular weight.

The disadvantage of this detector is the need to use an additional analog digital converter to connect the detector to a modern computer processing system

chromatographic information.

The objective of the proposed utility model is to simplify the connection of acoustic detectors to a computer system for processing chromatographic information.

The technical result is achieved by the fact that an acoustic detector for gas chromatography containing a 51 flow-through chamber made in the form of a tube, in one end which houses a source of acoustic vibrations, and in the other a lid equipped with an outlet fitting, a carrier gas is mounted between the ends of the chamber in its wall , between the nozzle of the carrier gas and the source of acoustic vibrations, an additional gas nozzle is mounted in the chamber wall according to the utility model, further comprises an acoustic oscillation receiver, located located in the hole of the tube located between the nozzles of the auxiliary gas and carrier gas, the acoustic vibration receiver is connected to the microphone input of the sound card of the personal system unit

a computer, wherein the system unit further comprises a second sound card, which, together with the first sound card, is connected to a common bus of a personal computer, while the analog output of the second sound card is connected to an acoustic source through an amplifier.

This design makes it possible to simplify the coordination of acoustic detectors with a computer, as it provides for direct connection of the acoustic detector to standard system unit devices - sound cards, and as a result, provides for the simplicity and completeness of processing the detector signal using a computer.

Compared with the prototype, the claimed design has a distinctive feature in the combination of elements and their relative positioning.

The detector circuit is shown in FIG. 1.

An acoustic detector for gas chromatography contains a flow chamber 1 made in the form of a tube, at the end 2 of which there is an acoustic oscillation source 3, and at the end 4 there is a cover 5 provided with an outlet fitting 6. A fitting is mounted between the ends 2 and 4 in the wall 7 of the chamber 1 8 carrier gas, and between the carrier 8 of the carrier gas and the source 3 of acoustic vibrations, a nozzle 9 of the auxiliary gas is mounted in the wall 7 of the chamber 1. The detector also includes a receiver 10 of acoustic vibrations located in the hole 11 located between the fittings 9 and 8.

The acoustic oscillation receiver 10 is connected to the microphone input 12 of the sound card 13 of the system unit 14 of the personal computer 15. Additionally, it contains a second sound card 16, which, together with the sound card 13, are connected to the common bus 17 of the personal computer 15. The analog output 18 of the sound card 16 through an electronic amplifier 19 is connected to a source of 3 acoustic vibrations. Monitor 20

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personal computer 15 is connected to the system unit 14 through a common bus 17.

The operation of the acoustic detector is as follows.

The gas stream from the chromatographic column and the auxiliary gas stream, respectively, which is usually used as the carrier gas in the chromatographic column (helium, hydrogen, nitrogen), are continuously fed into the chamber 1 of the acoustic detector through the nozzle 8 and 9, respectively. Gas flows leave the chamber 1 through the nozzle 6. From the analog output 18 of the sound card 16 through the electronic amplifier 19 and the source 3 serves electric harmonic vibrations of the selected frequency. As a result, the source 3 creates acoustic vibrations that propagate into the chamber 1 along its axis. These vibrations are reflected from cover 5 and, under certain conditions, add up to acoustic vibrations created by source 3. In this case, a standing acoustic wave appears in chamber 1 (Paul R.V. Mechanics, Acoustics and the Doctrine of Heat, Moscow: Nauka, 1971, p. 250h-253).

In the nodes and antinodes of a standing acoustic wave, complex processes of heat and mass bomp occur, caused by a change in the speed of molecules and absorption of energy by a gas (Bergman L. Ultrasound and its application in science and technology M .: Inostr. Lit., 1956, p. 144 -144 )

When only the carrier gas enters from the chromatographic column through the nozzle 8 into the chamber 1, the intensity of acoustic vibrations perceived by the receiver 10 acquires a certain constant value. These acoustic vibrations are converted using the receiver 10 into electrical vibrations, which are introduced through the microphone input 12 into the sound chamber 13, and then into the common bus 17.

When the next detectable component, which differs from the carrier gas by the physicochemical property, comes from the chromatographic column to the part of the chamber 1 together with the carrier gas, the speed of sound and absorption coefficient change in the interval from the nozzle 8 to the receiver 5

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acoustic vibrations. This leads to some displacement of the standing wave and a change in the intensity of acoustic vibrations perceived by the receiver 10. These changes are determined by the volume concentration of the detected component in the carrier gas and the physicochemical property of this component.

The operability test of the proposed detector was performed on an experimental setup including a mock acoustic detector and a personal computer with two sound cards. The layout of the acoustic detector was a 420 mm long tube with an inner diameter of 3 mm, the carrier gas fitting was located at a distance of 105 mm from the lid, and the window in which the microphone was placed was installed at a distance of 105 mm from the emitter. An electromagnetic capsule of the DEMS type was used as a source of acoustic vibrations, and a miniature electret microphone of the NMO0603A type was used as a receiver. Air was used as the carrier gas and auxiliary gas. The flow rates were set equal to 1 l / h. The oscillation frequency was used at 500 Hz, and the microphone signal coming through the sound card to the computer was processed in MATLAB 6.5. In this case, the power of the acoustic signal was calculated. The following gases were used for analysis: helium, methane, carbon dioxide. It was found that the signal of the acoustic detector is associated with molecular weight, and the sensitivity threshold of the detector is 10% vol.

The proposed acoustic detector can be implemented on the basis of standard sources and receivers of acoustic vibrations and a personal computer.

It can be used to determine the concentration of components in gas chromatography, also as an automatic analyzer, the composition of binary and pseudobinary gaseous media.

The advantage of the proposed technical solution is:

-the ability to directly connect acoustic detectors to a computer.

-low cost.

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Claims (1)

An acoustic detector for gas chromatography, containing a flow chamber made in the form of a tube, in one end of which there is a source of acoustic vibrations, and in the other there is a lid equipped with an outlet fitting, a carrier gas is mounted between the ends of the chamber in the chamber wall, between the gas fitting - of the carrier and the source of acoustic vibrations, an auxiliary gas fitting is mounted in its wall, characterized in that the detector further comprises an acoustic vibration receiver located in the tube opening nom between the auxiliary gas and carrier gas, the acoustic vibration receiver is connected to the microphone input of the sound chamber of the system unit of the personal computer, while the system unit further comprises a second sound card, which together with the first sound card are connected to the common bus of the personal computer, while the analog the output of the second sound card through an amplifier is connected to a source of acoustic vibrations.