A pulse controlled flow injection method and system for liquid microwave spectroscopy cluster analysis

Abstract

This invention provides a pulse-controlled flow injection method and system for liquid microwave spectroscopy cluster analysis, belonging to the field of microwave spectroscopy analysis technology for liquid samples. The method employs inert carrier gas-assisted injection, decoupling and coordinating the carrier gas back pressure and pulse width to control the single injection volume. Specifically, a constant back pressure is applied to the liquid storage unit with inert carrier gas to determine the instantaneous mass flow rate of the liquid when the pulse valve is fully open. The target injection volume is determined by matching the pulse width. Opening the pulse valve allows the liquid to mix with the high-speed carrier gas, forming a gas-liquid two-phase pulsed jet that is injected into the vacuum expansion and detection chamber. After closing the valve and cutting off the liquid flow, the carrier gas is used to purge the valve port to eliminate injection tailing. The jet undergoes adiabatic expansion to form a cold ultrasonic jet that retains in-situ clusters, triggering spectral acquisition to complete the injection. This invention can retain weakly bonded liquid clusters in situ, suppress spectral broadening, and improve the detection signal-to-noise ratio, making it suitable for high-resolution cluster analysis of complex liquid samples.

Description

Technical Field

[0001] This invention relates to the field of microwave spectroscopy analysis technology for liquid samples, and in particular to a pulsed flow-controlled injection method and system for liquid microwave spectroscopy cluster analysis. Background Technology

[0002] Chirped pulsed Fourier transform microwave (CP-FTMW) spectroscopy is a broadband rotational spectroscopy technique widely used in chemical kinetics, analytical chemistry, and chirality determination studies. For gaseous samples, common injection methods include Laval nozzle flow, static sample cell, buffer gas cooling cell, and differential pumping; for liquid samples, the mainstream injection method is heated reservoir ultrasonic molecular beam technique.

[0003] Applying the aforementioned liquid injection techniques to the cluster structure analysis of complex liquids such as baijiu (Chinese liquor) presents significant problems. First, clusters are prone to thermal and collisional dissociation. Heated storage supersonic beam injection relies on thermal evaporation, and the high temperatures directly disrupt weakly bonded clusters such as ethanol-water-ester compounds in baijiu. If the liquid is directly pulsed into a vacuum, the lack of a carrier gas causes violent flash evaporation rather than adiabatic expansion. The latent heat of phase change leads to a sudden local temperature rise, and the high-density vapor triggers intense intermolecular collisions, further breaking down weakly bonded clusters. Simultaneously, collisional broadening and Doppler broadening severely reduce the resolution of microwave spectral lines. Second, conventional pulse injection valves suffer from flow control blind spots and tailing effects. Existing pulse valves are mostly designed for gas injection, only allowing full opening or full closing, and cannot directly regulate liquid flow. Due to liquid viscosity and surface tension, droplets easily remain at the valve orifice, resulting in severe pulse waveform tailing, essentially degenerating into micro-continuous injection. During pulse intervals, background gas is continuously released, disrupting the vacuum environment and jet cooling effect.

[0004] Furthermore, the aforementioned issues directly limit the improvement of injection efficiency and detection signal-to-noise ratio. In coherent microwave spectroscopy techniques such as CP-FTMW, signal intensity depends on the coherent polarization of molecules. Continuous or tailing injections can cause high background pressure, leading to molecular collision dephasing and significantly reducing the signal-to-noise ratio of the free induction decay (FID) signal. Meanwhile, while multi-nozzle injection can achieve quadratic signal growth, the issues of liquid flow control and tailing in single-nozzle injections remain unresolved, making parallel multi-nozzle injections highly susceptible to instantaneous vacuum system collapse. Currently, the analysis of baijiu components mainly employs gas chromatography-mass spectrometry (GC-MS) or nuclear magnetic resonance (NMR). The former can damage sample cluster structures, while the latter struggles to distinguish specific cluster structures at the molecular level. Due to the lack of effective liquid pulse-controlled flow injection methods, chirped pulse Fourier transform microwave technology has not yet been applied to the direct cluster analysis of complex liquid systems such as baijiu. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a pulsed flow control injection method and system for liquid microwave spectroscopy cluster analysis. By using inert carrier gas to assist pulsed flow control and valve port pneumatic purging, the weakly bonded cluster structure in the liquid can be preserved in situ, eliminating injection tailing, suppressing spectral broadening and improving the detection signal-to-noise ratio, thereby realizing high-resolution microwave spectroscopy analysis of cluster structures in complex liquid systems.

[0006] To achieve the above objectives, the present invention provides the following solution: On one hand, this invention provides a pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis, which employs inert carrier gas-assisted injection and decouples and coordinates the single injection volume through carrier gas back pressure and pulse width, including the following steps: Step 100: Apply a constant back pressure provided by an inert carrier gas to the liquid storage unit containing the liquid sample, so that a stable static pressure is formed at the front end of the normally closed pulse injection valve, and the instantaneous mass flow rate of the liquid when the pulse injection valve is fully open is determined by the constant back pressure. Step 200: Set the opening pulse width of the pulse injection valve, and match the target single injection volume by multiplying the instantaneous mass flow rate and the pulse width. Step 300: Open the pulse injection valve. The liquid enters the valve chamber under the back pressure of the carrier gas and mixes with the high-speed inert carrier gas to form a gas-liquid two-phase pulse jet that is injected into the vacuum expansion and detection chamber. Step 400: Close the pulse injection valve to cut off the liquid flow, and use high-speed inert carrier gas to pneumatically purge the valve port to remove residual liquid droplets and eliminate injection tailing. Step 500: The gas-liquid two-phase pulse jet expands in the vacuum and vaporizes in the detection chamber, and undergoes adiabatic expansion with the participation of inert carrier gas. The system temperature drops sharply to form a cold ultrasonic jet containing in-situ cluster structures, which then triggers microwave spectral signal acquisition to complete the sample pulse injection.

[0007] Preferably, step 100 specifically includes: The inert carrier gas is divided into two paths. The first path is introduced into the gas phase space of the liquid storage unit to apply a constant carrier gas back pressure P to the liquid surface. The second path is introduced into the carrier gas channel of the pulse injection valve to establish a stable carrier gas pressure. When the pulse injection valve is normally closed, the instantaneous mass flow rate Q of the liquid when the pulse injection valve is fully open is uniquely determined by the valve port pressure difference corresponding to the carrier gas back pressure P.

[0008] Preferably, step 200 specifically includes: The target single injection volume V is determined based on the requirements of the vacuum system pumping speed and microwave spectroscopy detection sensitivity; based on the instantaneous mass flow rate Q, the opening pulse width t of the pulse injection valve is adjusted so that the product of the instantaneous mass flow rate Q and the pulse width t matches the target single injection volume V, i.e., V = Q × t.

[0009] Preferably, step 300 specifically includes: The output drive signal is consistent with the set pulse width t, which switches the pulse injection valve to the fully open state; the liquid in the storage unit flows into the valve cavity under the drive of constant carrier gas back pressure P, and meets the high-speed inert carrier gas in the carrier gas channel; the carrier gas entrains, tears and atomizes the liquid through momentum transfer, forming a gas-liquid two-phase pulse jet, which is injected into the vacuum expansion and detection cavity at an instantaneous mass flow rate Q, and completes the delivery of a single injection volume V within the pulse width t time.

[0010] Preferably, step 400 specifically includes: After the drive signal terminates, the valve core of the pulse injection valve resets and closes, cutting off the liquid passage; the high-speed inert carrier gas remaining in the carrier gas channel continues to flow out of the valve port, forming a pneumatic purging effect at the valve port, overcoming the viscosity and surface tension of the liquid, shearing off the residual droplets at the edge of the valve port and blowing them into the vacuum expansion and detection chamber, thus achieving sharp cutoff of the pulse waveform.

[0011] Preferably, step 500 specifically includes: After the gas-liquid two-phase pulse jet enters the vacuum expansion and detection chamber, it vaporizes instantly and undergoes adiabatic expansion with the participation of a large amount of inert carrier gas. The system temperature drops sharply, forming a cold ultrasonic jet containing in-situ cluster structures. This triggers microwave spectral signal acquisition. During the interval between the closing of the pulse injection valve, the residual gas in the chamber is evacuated to maintain a low background vacuum, suppress collision broadening and collision dephase, and complete the pulse injection of the sample.

[0012] Preferably, the method further includes an injection parameter optimization step, which uses a two-dimensional scanning method to determine the optimal injection conditions, specifically: With the pulse width t fixed, the carrier gas back pressure P is gradually increased to increase the instantaneous mass flow rate Q. The linewidth and intensity of the microwave transition signal of the target cluster are monitored, and the back pressure value when the spectral line undergoes obvious collision broadening is taken as the upper limit of the back pressure under the pulse width. With the carrier gas back pressure P fixed, the pulse width t is gradually increased, and the intensity of the microwave transition signal of the target cluster is monitored. The pulse width value at which the signal intensity stops increasing linearly with the pulse width t is taken as the upper limit of the pulse width under the back pressure. The carrier gas back pressure P, which has the highest signal-to-noise ratio and the narrowest spectral linewidth, is selected as the combination with the pulse width t as the injection parameters for formal analysis.

[0013] On the other hand, the present invention also provides a system for implementing the above-mentioned pulsed flow injection method for liquid microwave spectral cluster analysis, comprising: The liquid storage unit is a sealed, pressure-resistant container used to hold liquid samples; The back pressure control unit includes a high-pressure inert gas source and a precision proportional pressure regulating valve. The high-pressure inert gas source is divided into two independent gas supply lines. The first gas supply line is connected to the gas phase port of the liquid storage unit and is used to apply a constant and precise driving gas pressure to the sample liquid surface. The second gas supply line is connected to the carrier gas inlet of the coaxial pulse injection valve and is used to deliver high-speed inert carrier gas into the valve. The pulse injection valve is a coaxial pulse injection valve with a liquid channel and a carrier gas channel. Its liquid inlet is connected to the liquid phase port of the liquid storage unit, and its carrier gas inlet is connected to the second gas supply line of the back pressure control unit. The sample outlet leads to the vacuum expansion and detection chamber. The pulse injection valve only responds to external electrical signals to perform a fully open or fully closed action. The liquid enters the valve chamber through the liquid channel, and the inert carrier gas enters the valve chamber through the carrier gas channel. The two are mixed in the valve chamber. The timing control unit is a pulse signal generator used to output a square wave electrical signal with a precisely adjustable opening time to the pulse injection valve. The vacuum expansion and detection chamber is equipped with a high-vacuum pump set to provide a vacuum environment for the adiabatic expansion of the liquid. The chamber is equipped with a microwave window for microwave spectroscopy detection.

[0014] Compared with the prior art, the present invention discloses at least the following technical effects: (1) The present invention adopts an inert carrier gas-assisted quantitative pulse injection method, which, combined with the adiabatic expansion process under vacuum, can preserve the weakly bonded cluster structure in liquid samples in situ. Unlike the high-temperature damage of traditional heating and evaporation injection and the flash thermal effect of direct injection without carrier gas, the present invention forms a jet by encapsulating liquid with carrier gas, which cools down rapidly during expansion, avoiding thermal dissociation of weakly bonded structures such as ethanol-water hydrogen bond clusters and trace flavor molecule clusters; at the same time, by controlling the single injection volume, collision-induced dissociation caused by excessive molecular density in the cavity is avoided, thus maintaining the original micro-cluster morphology of the sample when it enters the detection area.

[0015] (2) This invention utilizes a pneumatic purging mechanism at the valve port to completely eliminate the tailing effect of liquid pulse injection. When conventional gas pulse valves are applied to liquids, the viscosity and surface tension of the liquid cause droplets to remain at the valve port and continue to evaporate during pulse intervals, resulting in micro-continuous leakage and raising the background pressure of the cavity. In contrast, after the liquid flow is cut off by closing the valve, this invention uses the high-speed airflow remaining in the carrier gas channel to continuously flush the valve port, relying on pneumatic shearing force to cut off and remove residual droplets, achieving sharp cutoff of the pulse waveform and maintaining a low background pressure environment in the cavity. This low-pressure environment can effectively suppress spectral broadening and signal dephasing caused by molecular collisions. Combined with the weakening effect of jet cooling on molecular thermal motion, it simultaneously reduces the influence of Doppler broadening, ultimately obtaining a microwave spectral signal with narrow linewidth and high signal-to-noise ratio.

[0016] (3) This invention addresses the shortcomings of existing liquid component detection technologies in cluster characterization and expands the application scenarios of microwave rotational spectroscopy. Traditional gas chromatography-mass spectrometry requires pretreatment of samples by vaporization and ionization, which directly destroys the original weakly bonded cluster structure in the liquid and makes it impossible to obtain in-situ cluster information; nuclear magnetic resonance technology has resolution limitations and is difficult to capture the dynamic conformation of micro-clusters. However, the pulsed flow-controlled injection method provided by this invention allows chirped pulsed Fourier transform microwave spectroscopy to be directly applied to complex liquid samples such as baijiu, providing a high-resolution spectroscopic characterization method for studying the evolution of hydrogen bond networks, intermolecular interactions, and micro-cluster structures in liquids. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a pulsed flow-controlled sample introduction method for liquid microwave spectroscopy cluster analysis according to the present invention.

[0019] Figure 2 This is a schematic diagram of the coaxial pulse injection valve provided by the present invention.

[0020] Figure 3 A cross-sectional view of the coaxial pulse injection valve provided by the present invention.

[0021] Figure 4 This invention provides a comparison chart of the signal intensities of ethanol-water dimer and ethanol dimer under different neon back pressures.

[0022] Figure 5 This invention provides a comparison of the signal intensities of ethanol-water dimer and ethanol dimer under different molecular beam pulse widths.

[0023] Figure 6 Comparison of rotational transition spectra of various ethanol dimer conformations in wine samples S1-S6 provided by this invention.

[0024] Figure 7 Comparison of rotational transition spectra of the single ethanol dimer conformation of wine samples S1-S6 provided by this invention.

[0025] Figure 8 Comparison of rotational transition spectra of two ethanol dimer conformations in wine samples S1-S6 provided by this invention.

[0026] Figure 9Comparison of spectral transitions of ethanol hydrated clusters and dimer conformations in wine samples S1-S6 provided by this invention.

[0027] Figure 10 Comparison of the spectral transitions of ethanol dimers in wine samples S1-S6 provided by this invention.

[0028] Figure 11 This invention provides a high-resolution spectral comparison of two ethanol dimer conformations in wine samples S1-S6.

[0029] Explanation of reference numerals in the attached figures: 1. Valve body housing; 2. Return spring; 3. Electromagnetic drive valve core assembly; 4. Valve body base; 5. Sample outlet; 6. Valve core sealing cone surface; 7. Upper end of valve body; 8. Lifting valve core; 9. Solid wall; 10. Valve cavity; 11. Central small hole; 12. Stepped surface; 13. Mounting hole. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] like Figure 1 As shown, this invention provides a pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis. It employs an inert carrier gas for assisted injection and decouples and coordinates the carrier gas back pressure and pulse width to control the single injection volume. Specifically, it includes the following steps: Step 100: Apply a constant back pressure provided by an inert carrier gas to the liquid storage unit containing the liquid sample, so that a stable static pressure is formed at the front end of the normally closed pulse injection valve, and the instantaneous mass flow rate of the liquid when the pulse injection valve is fully open is determined by the constant back pressure.

[0033] In this step, the inert carrier gas is divided into two paths. The first path is introduced into the gas phase space of the liquid storage unit to apply a constant carrier gas back pressure P to the liquid surface. The second path is introduced into the carrier gas channel of the pulse injection valve to establish a stable carrier gas pressure. When the pulse injection valve is normally closed, the instantaneous mass flow rate Q of the liquid when the pulse injection valve is fully open is uniquely determined by the valve port pressure difference corresponding to the carrier gas back pressure P.

[0034] Step 200: Set the opening pulse width of the pulse injection valve, and match the target single injection volume by multiplying the instantaneous mass flow rate and the pulse width.

[0035] In this step, the target single injection volume V is determined according to the requirements of the vacuum system pumping speed and microwave spectroscopy detection sensitivity; based on the instantaneous mass flow rate Q, the opening pulse width t of the pulse injection valve is adjusted so that the product of the instantaneous mass flow rate Q and the pulse width t matches the target single injection volume V, i.e., V = Q × t.

[0036] Step 300: Open the pulse injection valve. The liquid enters the valve chamber under the back pressure of the carrier gas and mixes with the high-speed inert carrier gas to form a gas-liquid two-phase pulse jet that is injected into the vacuum expansion and detection chamber.

[0037] In this step, a drive signal consistent with the set pulse width t is output to switch the pulse injection valve to the fully open state; the liquid in the storage unit flows into the valve chamber under the drive of constant carrier gas back pressure P and meets the high-speed inert carrier gas in the carrier gas channel; the carrier gas entrains, tears and atomizes the liquid through momentum transfer to form a gas-liquid two-phase pulse jet, which is injected into the vacuum expansion and detection chamber at an instantaneous mass flow rate Q, and the single injection volume V is delivered within the pulse width t time.

[0038] Step 400: Close the pulse injection valve to cut off the liquid flow, and use high-speed inert carrier gas to pneumatically purge the valve port to remove residual liquid droplets and eliminate injection tailing.

[0039] In this step, after the drive signal is terminated, the valve core of the pulse injection valve is reset and closed, cutting off the liquid passage; the high-speed inert carrier gas remaining in the carrier gas channel continues to flow out to the valve port, forming a pneumatic purging effect at the valve port, overcoming the viscosity and surface tension of the liquid, cutting off the residual droplets at the edge of the valve port and blowing them into the vacuum expansion and detection chamber, thus achieving sharp cutoff of the pulse waveform.

[0040] Step 500: The gas-liquid two-phase pulse jet expands in the vacuum and vaporizes in the detection chamber, and undergoes adiabatic expansion with the participation of inert carrier gas. The system temperature drops sharply to form a cold ultrasonic jet containing in-situ cluster structures, which then triggers microwave spectral signal acquisition to complete the sample pulse injection.

[0041] In this step, the gas-liquid two-phase pulse jet instantly vaporizes after entering the vacuum expansion and detection chamber. With the participation of a large amount of inert carrier gas, it undergoes adiabatic expansion, causing the system temperature to drop sharply and forming a cold ultrasonic jet containing in-situ cluster structures. This triggers microwave spectral signal acquisition. During the interval between the closing of the pulse injection valve, the residual gas in the chamber is evacuated to maintain a low background vacuum, suppress collision broadening and collision dephase, and complete the pulse injection of the sample.

[0042] In addition, the method provided by this invention also includes a sample injection parameter optimization step, which uses a two-dimensional scanning method to determine the optimal sample injection conditions, specifically: With the pulse width t fixed, the carrier gas back pressure P is gradually increased to increase the instantaneous mass flow rate Q. The linewidth and intensity of the microwave transition signal of the target cluster are monitored, and the back pressure value when the spectral line undergoes obvious collision broadening is taken as the upper limit of the back pressure under the pulse width. With the carrier gas back pressure P fixed, the pulse width t is gradually increased, and the intensity of the microwave transition signal of the target cluster is monitored. The pulse width value at which the signal intensity stops increasing linearly with the pulse width t is taken as the upper limit of the pulse width under the back pressure. The carrier gas back pressure P, which has the highest signal-to-noise ratio and the narrowest spectral linewidth, is selected as the combination with the pulse width t as the injection parameters for formal analysis.

[0043] To achieve the above method, the present invention also provides a pulsed flow control injection system for liquid microwave spectroscopy cluster analysis, the system comprising a liquid storage unit, a back pressure control unit, a pulse injection valve, a timing control unit, and a vacuum expansion and detection chamber.

[0044] The liquid storage unit is a sealed, pressure-resistant container used to hold complex liquid samples such as liquor. An external temperature control device can be installed to maintain the consistency of the liquid viscosity.

[0045] The back pressure control unit includes a high-pressure inert gas source and a precision proportional pressure regulating valve. The high-pressure inert gas source branches into two independent gas supply lines. The first gas supply line is connected to the gas phase port of the liquid storage unit and is used to apply a constant and precise driving gas pressure to the sample liquid surface. The second gas supply line is connected to the carrier gas inlet of the coaxial pulse injection valve and is used to deliver high-speed inert carrier gas into the valve. In this embodiment, the high-pressure inert gas source is a neon gas source.

[0046] like Figure 2 and Figure 3 As shown, the pulse injection valve is a coaxial pulse injection valve. Its main mechanical structure is precisely assembled from the upper valve body 7 and the lower valve body base 4, and the whole is firmly fixed through the mounting holes 13 on the outer periphery of the valve body shell 1. The core components inside the valve include the electromagnetic drive valve core assembly 3 and the return spring 2. The return spring 2 abuts against the inner wall of the valve body shell 1 and the electromagnetic drive valve core assembly 3, providing reliable return spring force. The valve body is designed with independent liquid channels and carrier gas channels, which are respectively connected to the external system: the liquid inlet is connected to the liquid phase port of the liquid storage unit, the carrier gas inlet is connected to the second gas supply line of the back pressure control unit, and the sample outlet 5 is directly connected to the vacuum expansion and detection chamber.

[0047] The valve body base 4, serving as the supporting structure at the bottom of the main body, is tightly connected to the solid wall 9, forming a stable foundation for the valve body. The solid wall 9 contains a valve cavity 10, providing space for the mixing and atomization of liquid and carrier gas. The key moving component, the lifting valve core 8, has a high-precision valve core sealing cone surface 6 at its lower end, which can tightly engage with the stepped surface 12 on the inner side of the upper end 7 of the valve body, forming a sealing pair. When an external electrical signal is received, the electromagnetic drive valve core assembly 3 drives the lifting valve core 8 to overcome the elastic force of the return spring 2 and move it upwards, causing the valve core sealing cone surface 6 to disengage from the stepped surface 12, instantly opening the passage. Conversely, when the power is off, the return spring 2 pushes the lifting valve core 8 downwards, causing the valve core sealing cone surface 6 to adhere to the stepped surface 12, achieving a high-pressure seal. In the open state, the liquid sample enters the valve cavity 10 through the liquid channel, while high-speed inert carrier gas is injected into the valve cavity 10 through the central small hole 11 at the upper end 7 of the valve body. The two components undergo vigorous mixing and atomization within the valve cavity 10, ultimately exiting at high speed through the sample outlet 5, ensuring that the sample enters the downstream detection system accurately and controllably.

[0048] The timing control unit is a pulse signal generator used to output a square wave electrical signal with a precisely adjustable opening time to the pulse injection valve.

[0049] The vacuum expansion and detection chamber is equipped with a high-vacuum pump set to provide a vacuum environment for the adiabatic expansion of the liquid, and the chamber is equipped with a microwave window for microwave spectroscopy detection.

[0050] Comparative Example 1 To further demonstrate the technical effects of this invention, a conventional liquid pulse injection scheme is given below as a comparative example. This scheme does not have an independent carrier gas channel and relies solely on back pressure and pulse width decoupling to control the injection volume. Its injection system mainly includes the following units: Liquid storage unit: a sealed and pressure-resistant container used to hold complex liquid samples such as liquor. An external temperature control device can be equipped to maintain the consistency of liquid viscosity.

[0051] Back pressure control unit: includes a high-pressure inert gas source (such as argon or nitrogen) and a precision proportional pressure regulating valve, which is connected to the gas phase port of the liquid storage unit and is used to apply a precise and constant driving gas pressure to the sample liquid surface.

[0052] Pulse injection valve: Internally equipped with a fast-response component driven by either electromagnetic or piezoelectric mechanisms. Its inlet connects to the liquid phase port of the storage unit, and its outlet leads to the vacuum expansion chamber. This valve only responds to external electrical signals to perform a "fully open / fully close" action; it does not have its own flow regulation function and lacks an independent carrier gas channel.

[0053] Timing control unit: Pulse signal generator, used to output a square wave electrical signal with precisely adjustable opening time (pulse width t) to the pulse injection valve.

[0054] Vacuum expansion and detection chamber: Equipped with a high vacuum pump set to provide a vacuum environment for the adiabatic expansion of the liquid, the chamber is equipped with a microwave window for CP-FTMW or chamber FTMW detection.

[0055] This comparative injection control method decouples and coordinates back pressure (which determines the instantaneous flow rate Q) and pulse width (which determines the injection time t), and precisely controls the single injection volume V (V=Q×t) through the product of the two. The specific steps are as follows: A constant pressure P is applied to the liquid storage unit via a back pressure control unit. Since the pulse valve is normally closed, static pressure is established before the valve. This back pressure P determines the pressure difference across the valve port at the instant the pulse valve opens. Because the conductance is constant when the pulse valve is fully open, pressure P uniquely determines the instantaneous mass flow rate Q of the liquid passing through the fully open valve port. By adjusting the back pressure P, effective macroscopic control of the instantaneous flow rate during sample injection is achieved, providing a benchmark for subsequent volume calculations.

[0056] Based on the pumping speed of the vacuum pump set and the sensitivity requirements of microwave spectroscopy detection, the target single injection volume V is set. Based on the instantaneous flow rate Q determined in step S1, the opening time of the pulse valve (i.e., pulse width t) is set through the timing control unit so that V = Q × t meets the optimal injection volume requirement.

[0057] The timing control unit outputs a high-level signal with a width of t, energizing the internal drive component of the pulse injection valve and fully opening the valve. Under constant back pressure P, the liquid in the storage unit is injected into the vacuum expansion chamber at a constant flow rate Q, completing the injection of a trace volume V within an extremely short time t.

[0058] When the electrical pulse signal ends, the drive component demagnetizes, and the armature instantly resets under mechanical force, closing the valve. At this moment, the constant back pressure P plays a crucial role in preventing leakage. That is, at the instant the valve core closes, the stable upstream air pressure prevents droplet siphoning caused by a sudden drop in pressure difference. At the same time, the air pressure pushes the liquid remaining in the tiny dead volume at the valve orifice backflow or maintains force balance, overcoming the viscosity and surface tension of the liquid, eliminating valve orifice residue and sample tailing, and achieving sharp waveform cutoff.

[0059] A single pulse of micro-volume liquid V vaporizes instantaneously and expands adiabatically within the vacuum expansion chamber, causing a rapid drop in system temperature and forming a cold ultrasonic jet containing in-situ cluster structures. This triggers microwave spectral acquisition. During the interval Tclose between pulse valve closures, the vacuum pump assembly removes residual gas from the chamber, maintaining the background vacuum and suppressing collision broadening and collision dephasing.

[0060] In addition, condition optimization is performed before actual sample analysis: With a fixed pulse width t, the back pressure P is gradually increased (Q is increased), and the linewidth and intensity of the target cluster transition signal are monitored. When the linewidth begins to widen significantly due to collision broadening, the upper limit of the back pressure under that pulse width is reached. With a fixed back pressure P, the pulse width t is gradually increased, and the signal strength is monitored. When the signal strength no longer increases linearly with t (indicating that the cooling efficiency decreases due to insufficient expansion of molecules at the jet end), the upper limit of the pulse width under that back pressure is reached. By performing the above dual-dimensional scanning, the optimal combination of back pressure P and pulse width t with the highest signal-to-noise ratio and narrowest linewidth is obtained, thus optimizing the optimal injection volume V for subsequent formal analysis of baijiu samples.

[0061] Compared with the comparative example, the present invention, by adding an independent carrier gas channel and a pneumatic purging mechanism at the valve port, can more thoroughly eliminate the sample tailing caused by residual droplets at the valve port. At the same time, with the help of the carrier gas-assisted adiabatic expansion process, the weakly bonded cluster structure is better preserved, resulting in higher spectral resolution and signal-to-noise ratio.

[0062] The actual effect of the method of the present invention is verified through three sets of examples. All experiments were carried out using the above-mentioned pulsed flow injection system in conjunction with the CP-FTMW microwave spectroscopy device. The detection objects were ethanol-water dimer (transition frequency 12568.3MHz) and ethanol dimer (transition frequency 8342.7MHz).

[0063] Example 1 This embodiment is used to verify the regulation law of carrier gas back pressure on cluster detection signals, determine the optimal back pressure parameters suitable for two target dimers, and correspond to the regulation logic of back pressure determining instantaneous mass flow rate in this method. The experiment fixed the opening pulse width of the pulse injection valve and set 11 gradients of neon back pressure conditions: 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, and 6 atm. The characteristic transition signal intensities of ethanol-water dimer (transition frequency 12568.3 MHz) and ethanol dimer (transition frequency 8342.7 MHz) were detected respectively. The results are as follows: Figure 4 As shown.

[0064] Combining the gas-liquid two-phase jet and adiabatic expansion mechanism of this invention, the signal intensity exhibits a pattern of first increasing and then decreasing with back pressure. That is, in the low-pressure range, as the carrier gas back pressure increases, the valve port pressure difference increases synchronously, the instantaneous mass flow rate Q of the liquid increases linearly, the total number of sample molecules entering the cavity in a single pulse increases, and the number of effective cluster molecules in the cold ultrasonic jet increases accordingly, thus the signal intensity continues to rise. When the back pressure exceeds the peak point, the molecular density in the cavity becomes too high, and the frequency of intermolecular collisions increases significantly. On the one hand, this causes collision broadening and signal dephase; on the other hand, frequent collisions will destroy the stability of weakly bonded structures such as ethanol dimers, leading to a decrease in the effective cluster concentration, and the signal intensity then falls back.

[0065] Furthermore, the peak positions of the two dimers differ because the hydrogen bonding energy of the ethanol-water cluster is relatively higher, which allows it to withstand stronger collision environments, resulting in a higher optimal back pressure; while the intermolecular forces of the ethanol dimer are weaker, allowing it to reach the signal peak at a lower back pressure.

[0066] Considering the signal performance of the two dimers, the cavity vacuum recovery efficiency, and the experimental stability, 2.5 atm was ultimately selected as the carrier gas back pressure condition for subsequent experiments.

[0067] Example 2 This embodiment is used to verify the effect of pulse width on the regulation of single injection volume and detection signal, and to match the optimal injection pulse width, corresponding to the volume quantification logic of "V=Q×t" in this method. The experiment fixed the carrier gas back pressure of 2.5 atm obtained in Example 1, and set six pulse width conditions of 200, 300, 400, 500, 600, and 700 μs, simultaneously detecting the microwave signal intensity of two target dimers. The results are as follows... Figure 5 As shown.

[0068] Experimental results show that when the pulse width is 200 μs, the single injection volume is extremely small, the total number of cluster molecules in the jet is below the detection limit, and no effective signal is detected for either dimer. Within the 300–500 μs range, with increasing pulse width, the single injection volume V increases linearly, the total number of clusters in the cold ultrasonic jet increases synchronously, and the signal intensity shows a stable upward trend. When the pulse width exceeds the optimal value, the jet duration becomes too long, and when the jet tail molecules enter the cavity, the background pressure inside the cavity has already increased, the cooling efficiency of adiabatic expansion decreases, cluster cooling is insufficient, and the probability of molecular collisions increases, causing the signal intensity to no longer increase linearly with the pulse width and gradually decrease. Thanks to the valve port pneumatic purging mechanism of this invention, the pulse waveform maintains sharp cutoff characteristics under all pulse width conditions, with no trailing or leakage interference, and the change in signal intensity is determined only by the injection volume and the expansion cooling effect.

[0069] Considering the detection sensitivity of the two dimers and the gas recovery efficiency during the chamber interval, 400 μs was finally selected as the molecular beam pulse width for formal analysis.

[0070] Example 3 This embodiment is used to verify the in-situ cluster detection capability of the proposed method in actual complex liquid samples, and to verify the practical effect of this scheme in solving the problems of cluster destruction and insufficient resolution in traditional detection methods. The experiment used the optimized injection parameters of 2.5 atm neon back pressure and 400 μs pulse width to detect six types of baijiu samples (S1-S6). Qualitative analysis was performed on the characteristic rotational transition spectra of the six conformations of ethanol dimer: g+g+, g+t, g-g+, gt, tg+, and tt. The detection results are as follows: Figures 6 to 11 As shown.

[0071] Thanks to the inert carrier gas-assisted adiabatic expansion mechanism of this invention, the weakly bonded ethanol dimers in baijiu do not undergo thermal dissociation or collisional dissociation during sample introduction and expansion, and the cluster structure is preserved in situ. At the same time, the low background vacuum environment effectively suppresses collisional broadening, and jet cooling weakens Doppler broadening. The resulting spectral lines have narrow linewidths and high resolution, and can clearly distinguish the characteristic rotational transition peaks of different conformations.

[0072] Experimental results show that the g+g+, tg+, and tt conformations can be stably detected in multiple wine samples, while the g+t and g-g+ conformations are only detected in samples S1 and S2, and the tt conformation is detected in samples S1, S2, and S3. The differences in the types and signal intensities of conformations detected in different wine samples directly reflect the differences in microscopic intermolecular interactions and cluster composition. This demonstrates that this method can be used for in-situ characterization of cluster structures in complex liquid systems such as baijiu, providing a high-resolution spectroscopic tool for studying the microscopic mechanisms of flavor differences in wine samples.

[0073] Therefore, by employing the pulse-controlled flow injection method and system described above for liquid microwave spectroscopy cluster analysis, the weakly bonded cluster structure in the liquid can be preserved in situ through pulse-controlled flow assisted by inert carrier gas and pneumatic purging at the valve port. This eliminates injection tailing, suppresses spectral broadening, and improves the detection signal-to-noise ratio, thereby achieving high-resolution microwave spectroscopy analysis of cluster structures in complex liquid systems.

[0074] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0075] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis, characterized in that, Inert carrier gas-assisted injection is employed, and the single injection volume is controlled through the decoupled and coordinated control of carrier gas back pressure and pulse width. The process includes the following steps: Step 100: Apply a constant back pressure provided by an inert carrier gas to the liquid storage unit containing the liquid sample, so that a stable static pressure is formed at the front end of the normally closed pulse injection valve, and the instantaneous mass flow rate of the liquid when the pulse injection valve is fully open is determined by the constant back pressure. Step 200: Set the opening pulse width of the pulse injection valve, and match the target single injection volume by multiplying the instantaneous mass flow rate and the pulse width. Step 300: Open the pulse injection valve. The liquid enters the valve chamber under the back pressure of the carrier gas and mixes with the high-speed inert carrier gas to form a gas-liquid two-phase pulse jet that is injected into the vacuum expansion and detection chamber. Step 400: Close the pulse injection valve to cut off the liquid flow, and use high-speed inert carrier gas to pneumatically purge the valve port to remove residual liquid droplets and eliminate injection tailing. Step 500: The gas-liquid two-phase pulse jet expands in the vacuum and vaporizes in the detection chamber, and undergoes adiabatic expansion with the participation of inert carrier gas. The system temperature drops sharply to form a cold ultrasonic jet containing in-situ cluster structures, which then triggers microwave spectral signal acquisition to complete the sample pulse injection.

2. The pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis according to claim 1, characterized in that, Step 100 specifically involves: The inert carrier gas is divided into two paths. The first path is introduced into the gas phase space of the liquid storage unit to apply a constant carrier gas back pressure P to the liquid surface. The second path is introduced into the carrier gas channel of the pulse injection valve to establish a stable carrier gas pressure. When the pulse injection valve is normally closed, the instantaneous mass flow rate Q of the liquid when the pulse injection valve is fully open is uniquely determined by the valve port pressure difference corresponding to the carrier gas back pressure P.

3. The pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis according to claim 1, characterized in that, Step 200 specifically involves: The target single injection volume V is determined based on the requirements of the vacuum system pumping speed and microwave spectroscopy detection sensitivity; based on the instantaneous mass flow rate Q, the opening pulse width t of the pulse injection valve is adjusted so that the product of the instantaneous mass flow rate Q and the pulse width t matches the target single injection volume V, i.e., V = Q × t.

4. The pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis according to claim 1, characterized in that, Step 300 specifically involves: The output drive signal is consistent with the set pulse width t, which switches the pulse injection valve to the fully open state; the liquid in the storage unit flows into the valve cavity under the drive of constant carrier gas back pressure P, and meets the high-speed inert carrier gas in the carrier gas channel; the carrier gas entrains, tears and atomizes the liquid through momentum transfer, forming a gas-liquid two-phase pulse jet, which is injected into the vacuum expansion and detection cavity at an instantaneous mass flow rate Q, and completes the delivery of a single injection volume V within the pulse width t time.

5. The pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis according to claim 1, characterized in that, Step 400 specifically involves: After the drive signal terminates, the valve core of the pulse injection valve resets and closes, cutting off the liquid passage; the high-speed inert carrier gas remaining in the carrier gas channel continues to flow out of the valve port, forming a pneumatic purging effect at the valve port, overcoming the viscosity and surface tension of the liquid, shearing off the residual droplets at the edge of the valve port and blowing them into the vacuum expansion and detection chamber, thus achieving sharp cutoff of the pulse waveform.

6. The pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis according to claim 1, characterized in that, Step 500 specifically involves: After the gas-liquid two-phase pulse jet enters the vacuum expansion and detection chamber, it vaporizes instantly and undergoes adiabatic expansion with the participation of a large amount of inert carrier gas. The system temperature drops sharply, forming a cold ultrasonic jet containing in-situ cluster structures. This triggers microwave spectral signal acquisition. During the interval between the closing of the pulse injection valve, the residual gas in the chamber is evacuated to maintain a low background vacuum, suppress collision broadening and collision dephase, and complete the pulse injection of the sample.

7. The pulsed flow-controlled injection method for liquid microwave spectroscopy cluster analysis according to claim 1, characterized in that, It also includes a step for optimizing injection parameters, using a two-dimensional scanning method to determine the optimal injection conditions, specifically: With the pulse width t fixed, the carrier gas back pressure P is gradually increased to increase the instantaneous mass flow rate Q. The linewidth and intensity of the microwave transition signal of the target cluster are monitored, and the back pressure value when the spectral line undergoes obvious collision broadening is taken as the upper limit of the back pressure under the pulse width. With the carrier gas back pressure P fixed, the pulse width t is gradually increased, and the intensity of the microwave transition signal of the target cluster is monitored. The pulse width value at which the signal intensity stops increasing linearly with the pulse width t is taken as the upper limit of the pulse width under the back pressure. The carrier gas back pressure P, which has the highest signal-to-noise ratio and the narrowest spectral linewidth, is selected as the combination with the pulse width t as the injection parameters for formal analysis.

8. A system for implementing the pulsed flow-controlled sample introduction method for liquid microwave spectroscopy cluster analysis as described in any one of claims 1 to 7, characterized in that, include: The liquid storage unit is a sealed, pressure-resistant container used to hold liquid samples; The back pressure control unit includes a high-pressure inert gas source and a precision proportional pressure regulating valve. The high-pressure inert gas source is divided into two independent gas supply lines. The first gas supply line is connected to the gas phase port of the liquid storage unit and is used to apply a constant and precise driving gas pressure to the sample liquid surface. The second gas supply line is connected to the carrier gas inlet of the coaxial pulse injection valve and is used to deliver high-speed inert carrier gas into the valve. The pulse injection valve is a coaxial pulse injection valve with a liquid channel and a carrier gas channel. Its liquid inlet is connected to the liquid phase port of the liquid storage unit, and its carrier gas inlet is connected to the second gas supply line of the back pressure control unit. The sample outlet leads to the vacuum expansion and detection chamber. The pulse injection valve only responds to external electrical signals to perform a fully open or fully closed action. The liquid enters the valve chamber through the liquid channel, and the inert carrier gas enters the valve chamber through the carrier gas channel. The two are mixed in the valve chamber. The timing control unit is a pulse signal generator used to output a square wave electrical signal with a precisely adjustable opening time to the pulse injection valve. The vacuum expansion and detection chamber is equipped with a high-vacuum pump set to provide a vacuum environment for the adiabatic expansion of the liquid. The chamber is equipped with a microwave window for microwave spectroscopy detection.

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