Detection method of water free radical cations

Abstract

The invention belongs to the technical field of detection, relates to a free radical detection method, particularly provides a water free radical cation detection method, and aims to realize water free radical cation detection which is efficient, rapid, free of sample pretreatment and convenient to analyze. According to the invention, an LTQ-XL linear ion trap mass spectrometer is used as a detection tool, and a dielectric barrier corona discharge method is adopted to provide a water free radical cation detection method. The method comprises the following steps of: filling argon (Ar) between two discharge electrodes as a working gas, applying a certain voltage to two electrodes of a dielectric barrier discharge ionization source (DBDI), detecting water free radical cations to obtain a corresponding mass spectrum to represent the water free radical cations, and optimizing a target signal to obtain corresponding mass spectrum data. The method can be used for efficiently and quickly detecting the water free radical cations without sample pretreatment and the like, is convenient to analyze and apply, and has remarkable innovativeness and wide application prospects.

Description

Technical Field

[0001] The invention belongs to the field of detection technology and relates to a free radical detection method, in particular to a method for detecting water free radical cations. Background Art

[0002] Water (H2O) is the most ubiquitous solvent on Earth. Its ionization and free radical chemistry have important implications in radiation chemistry, atmospheric science, biomedicine, and energy conversion. Water radical cations are transient, highly reactive species formed when a water molecule loses an electron. They possess an unpaired electron and a positive charge and belong to the family of radical-cations. Their existence was first predicted through theoretical calculations and indirectly observed through gas chromatography-mass spectrometry and radiation chemistry experiments in the mid-to-late 20th century. Due to their extremely short lifetimes (femtosecond to picosecond range), their direct capture and characterization became feasible only with the development of modern ultrafast spectroscopy. Water radical cations are primarily generated through high-energy radiation, photoionization, and impact ionization. As strong oxidants, they can initiate chain reactions and play a key role in radiation chemistry, atmospheric chemistry, and biological systems. Despite their widespread applications in atmospheric chemistry, biomedicine, and radiation chemistry, their short lifetime has presented significant challenges for their detection and study.

[0003] Water radical cations are highly reactive, short-lived, transient species, making their detection extremely challenging. Currently, scientists primarily observe them indirectly or directly through spectroscopy, mass spectrometry, radiochemistry, and theoretical calculations. However, these detection methods all have limitations. Ultraviolet-visible absorption spectroscopy (UV-Vis) exploits the characteristic absorption peak of water radical cations at specific wavelengths (e.g., ~600 nm). By photolyzing or ionizing water molecules in a low-temperature matrix (e.g., argon or neon), UV-Vis spectroscopy is used to capture their transient absorption signal. However, the signal is weak and susceptible to interference from other free radicals (e.g., ·OH). Electron paramagnetic resonance (EPR) utilizes the characteristics of the unpaired electrons of water radicals. Its paramagnetic signal can be detected through EPR, allowing the observation of the characteristic free radical peak at low temperatures. However, this detection method suffers from weak signals, requires high sample concentrations or low temperatures to enhance sensitivity, and is susceptible to confounding by paramagnetic resonance signals. Therefore, there is an urgent need for an efficient, rapid, and analytically amenable method for detecting water radical cations. Summary of the Invention

[0004] The purpose of the present invention is to address the many deficiencies of the above-mentioned prior art and provide a method for detecting water radical cations to achieve efficient, rapid, accurate, sample pretreatment-free and easy-to-analyze water radical cation detection.

[0005] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0006] A method for detecting water radical cations is disclosed. The method uses an LTQ-XL linear ion trap mass spectrometer as a detection tool, constructs a dielectric barrier discharge ion source (DBDI), uses argon as a working gas to introduce water vapor into a dielectric barrier corona discharge device under positive ion mode detection conditions, applies a certain voltage to two electrodes, detects water radical cations, and optimizes the target signal.

[0007] Furthermore, the method for detecting water radical cations specifically comprises the following steps:

[0008] S1: Build a dielectric barrier corona discharge device, in which a single-phase contact voltage regulator provides AC voltage to the electrodes at both ends of the dielectric barrier discharge ionization source;

[0009] S2: Using argon as the working gas, water vapor is introduced into the dielectric barrier corona discharge device. The gas flow rate is adjusted by a flow meter, and voltage is applied to perform mass spectrometry testing to obtain the corresponding spectrum.

[0010] S3: Export the spectra and analyze them to characterize the water radical cations.

[0011] Furthermore, in step S1, the blocking medium includes a quartz tube with a thickness of 1 mm and an inner diameter of 3 mm, a stainless steel rod with a diameter of 40 mm is fixed to the central axis as one end electrode, and a stainless steel mesh is wrapped around the quartz tube as the other end electrode.

[0012] Furthermore, in step S2, the single-phase contact voltage regulator has a range of 0-250V, which is optimized within the range of 35-60V, with the optimal voltage being 50V; the flow meter has a range of 0-200mL / min, which is optimized within the range of 50-200mL / min, and the gas flow has little effect on the target signal.

[0013] Furthermore, in step S3, the mass spectrometry conditions were as follows: the LTQ-MS was operated in positive ion detection mode, with a mass spectrometry scan range of m / z 15-200, a distance of approximately 8 mm between the ion source tip and the mass spectrometer port, an ion transfer tube temperature of 150°C, and a sample flow rate of 150 mL / min. High-purity argon with a purity of 99.999% was used as the working gas, and other experimental parameters were automatically optimized by the system.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention directly uses water samples for detection without the need for sample pretreatment.

[0016] 2. The present invention adopts a dielectric barrier corona discharge device and uses a single-phase contact voltage regulator to provide AC voltage to the electrodes at both ends of the dielectric barrier discharge ionization source; argon gas is used as the working gas to bring the sample into the device. The method is simple to operate and the instrument is inexpensive.

[0017] 3. The present invention is based on the LTQ-XL linear ion trap mass spectrometer, which has high sensitivity and low detection limit;

[0018] In summary, the present invention provides a method for detecting water radical cations, which can detect water radical cations efficiently, quickly, accurately, and without the need for sample pretreatment, and has significant innovation and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above advantages of the present invention will become apparent and easily understood in conjunction with the following drawings, wherein;

[0020] Figure 1 A diagram of the device for online detection of water radical cations according to the present invention, wherein: 1 - water storage device; 2 - air inlet channel; 3 - air outlet channel; 4 - sample channel; 5 - mass barrier discharge ion source; 6 - single-phase contact voltage regulator; 7 - mass spectrometer;

[0021] Figure 2 This is the mass spectrum of the online detection of water radical cations of the present invention;

[0022] Figure 3 This is an online diagram for optimizing the mass spectrometry signal of water radical cations, where a is the TIC diagram of water radical cations obtained under the same flow rate and different voltage conditions; b is the intensity change diagram under different voltage conditions; c is the mass spectrum of water radical cations obtained under the same voltage and different gas flow conditions. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] The instrument used in the following examples of the present invention is an LTQ-XL linear ion trap mass spectrometer equipped with an Xcalibur data processing system from Thermo Scientific, USA, with the following parameter settings:

[0025] The mass spectrometer scan range was m / z 15–200, with the distance between the ion source tip and the mass spectrometer port approximately 8 mm. The ion transfer tube temperature was 150°C, and the sample flow rate was 150 mL / min. High-purity argon with a purity of 99.999% was used as the working gas, and other experimental parameters were automatically optimized by the system.

[0026] The following describes the above-mentioned method for detecting water radical cations with several examples:

[0027] The detection method is based on a detection device that includes a water storage device 1, a sample channel 2, a dielectric barrier corona discharge device 3, a single-phase contact voltage regulator 4 and a mass spectrometer 5 arranged in sequence. The water storage device 1 is provided with an air inlet channel 2 and an air outlet channel 3. The air inlet channel 2 is inserted below the liquid level in the water storage device, the air outlet channel 3 is connected to the sample channel 4, and the air inlet channel 2 is connected to argon gas. The dielectric barrier corona discharge device 3 includes a quartz tube with a thickness of 2 mm and an inner diameter of 16 mm. A stainless steel rod with a diameter of 8 mm is fixed to the central axis as a high-voltage electrode. A stainless steel mesh is wrapped around the quartz tube as a low-voltage electrode. The high-voltage electrode and the low-voltage electrode are connected to the single-phase contact voltage regulator 4.

[0028] Example 1

[0029] This embodiment provides a method for detecting water radical cations, comprising the following steps:

[0030] S1: Build a dielectric barrier corona discharge device, in which a single-phase contact voltage regulator provides AC voltage to the electrodes at both ends of the dielectric barrier discharge ionization source;

[0031] S2: Using argon as the working gas, water vapor is introduced into the dielectric barrier corona discharge device. The gas flow rate is adjusted by a flow meter to 150 mL / min. A voltage of 50 V is applied to perform mass spectrometry and obtain the corresponding spectrum.

[0032] S3: Export the spectra and analyze them to characterize the water radical cations, e.g. Figure 2 Shown is the mass spectrum of online detection of water radical cations.

[0033] S4: As Figure 2 As shown, the signals of water radical cations m / z 36 and m / z 37 can be clearly observed using the dielectric barrier corona discharge device, corresponding to (H2O)2 +· and (H2O)2H + .

[0034] Example 2

[0035] S1: Build a dielectric barrier corona discharge device, in which a single-phase contact voltage regulator provides AC voltage to the electrodes at both ends of the dielectric barrier discharge ionization source;

[0036] S2: Argon is used as the working gas, and water vapor is brought into the dielectric barrier corona discharge device. The gas flow rate is adjusted by a flow meter to 150 mL / min. Different voltages are applied, such as 35 V, 40 V, 45 V, 50 V, and 55 V, to perform mass spectrometry tests and obtain corresponding spectra.

[0037] S3: Export the spectra and analyze them to characterize the water radical cations, e.g. Figure 3 As shown in a, it is the TIC diagram of water radical cations under the same flow rate and different voltage conditions, and Figure 3 Figure b is the voltage change diagram. It can be seen that as the voltage increases, the water radical cation signal first increases and then decreases, and the optimal voltage is 50V.

[0038] Example 3

[0039] S1: Build a dielectric barrier corona discharge device, in which a single-phase contact voltage regulator provides AC voltage to the electrodes at both ends of the dielectric barrier discharge ionization source;

[0040] S2: Using argon as the working gas, water vapor is introduced into the dielectric barrier corona discharge device. The gas flow rate is adjusted by a flow meter. The same voltage of 50 V is applied and different flow rates are adjusted to 50 mL / min, 75 mL / min, 100 mL / min, 125 mL / min, 150 mL / min, etc. for mass spectrometry tests to obtain the corresponding spectra.

[0041] S3: Export the spectra and analyze them to characterize the water radical cations, e.g. Figure 3 Figure c shows the mass spectra of water radical cations obtained under the same voltage and different gas flow rates. The spectra show that changes in the working gas flow rate have little effect on the water radical cation signal.

[0042] In summary, the method for detecting water radical cations proposed in this embodiment achieves efficient, rapid, sample pretreatment-free and easy-to-analyze water radical cation detection.

[0043] The above-described embodiments merely represent several specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for detecting water radical cations, characterized in that: In positive ion mode, water vapor was introduced into a dielectric barrier corona discharge device using argon as the working gas. A certain voltage was applied to the two electrodes. An LTQ-XL linear ion trap mass spectrometer was used to detect water radical cations, and the target signal was optimized.

2. The method for detecting water radical cations according to claim 1, wherein: The following steps are involved: S1: Build a dielectric barrier corona discharge device, in which a single-phase contact voltage regulator provides AC voltage to the electrodes at both ends of the ionization source in the dielectric barrier discharge device; S2: Using argon as the working gas, water vapor is introduced into the dielectric barrier corona discharge device. The gas flow rate is adjusted by a flow meter, and voltage is applied to perform mass spectrometry testing to obtain the corresponding spectrum. S3: Export the spectra and analyze them to characterize the water radical cations.

3. The method for detecting water radical cations according to claim 1, wherein: The dielectric barrier corona discharge device includes a barrier medium, which is a quartz tube with a thickness of 1mm and an inner diameter of 3mm. A stainless steel rod with a diameter of 40mm is fixed on the central axis as one end electrode, and a stainless steel mesh is wrapped around the quartz tube as the other end electrode.

4. The method for detecting water radical cations according to claim 1, wherein: In step S1, the range of the single-phase contact voltage regulator is 0-250V, and the range of the flow meter is 0-200mL / min.

5. The method for detecting water radical cations according to claim 4, wherein: The maximum voltage of the single-phase contact voltage regulator cannot exceed 65V; the minimum voltage is 35V.

6. The method for detecting water radical cations according to claim 1, wherein: In step S2, the specific conditions of the mass spectrometry test are: the LTQ-MS operates in positive ion detection mode, the mass spectrometry scanning range is m / z 15-200, the distance between the ion source tip and the mass spectrometry port is about 8 mm; the ion transfer tube temperature is 150°C; the sample flow rate is 150 mL / min; and high-purity argon with a purity of 99.999% is used as the working gas.

7. The method for detecting water radical cations according to claim 1, wherein: The target signal optimization includes voltage optimization and gas flow optimization. The optimal voltage in voltage optimization is 50V; gas flow optimization shows that the flow rate has little impact.

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