CN101178381A - Excited state molecular collision surface desorption ionization ion mobility spectrometry detection method and device - Google Patents

Abstract

The invention discloses an excited state molecule collision surface desorption ionization ion mobility spectrometry detection method and a device thereof. An excited state generator is installed before the ion inlet of the ion mobility spectrometer migration tube. The sample placement area is directly exposed to the atmosphere. The excited state generator includes a discharge chamber. The front end of the discharge chamber is connected to a discharge component. The rear end of the discharge component is sequentially installed with an ion filter door and a repelling electrode. The rear end of the repelling electrode is the outlet of the discharge chamber. , the migration tube of the ion mobility spectrometer is equipped with an ion introduction electrode. The invention can work in an open atmospheric environment, the surface to be tested does not need pretreatment, and can realize the desorption ionization and in-situ rapid detection of trace components on the surface of the article, which can be used for the analysis and detection of pesticide residues on the surface, and is also suitable for the danger of poisoning on the surface of the article product testing. It has the characteristics of fast detection speed, high sensitivity, small device size and simple operation.

Description

Excited state molecular collision surface desorption ionization ion mobility spectrometry detection method and device

technical field

The invention relates to a detection and analysis technology for trace substances on the surface of articles, in particular to a detection method and device for excited state molecule collision surface desorption ionization ion mobility spectrometry, which can work in an open atmospheric environment and can directly detect trace substances on the surface of articles In situ desorption ion mobility spectrometry detection was performed.

Background technique

Ion mobility spectrometry uses the different moving speeds of different ions in an electric field under atmospheric pressure to realize the separation and detection of substances. Ion mobility spectrometry technology was invented in the 1960s, and its application in the field of analysis began in the middle of the 20th century. In the past 10 years, ion mobility spectrometry equipment has been used for component analysis of toxic and dangerous goods. The ion mobility spectrometer is mainly composed of ion source, reaction zone, ion gate and transfer tube. Among them, the role of the ion source is to provide a charge donor to ionize the analyte into charged particles. At present, the ion sources used in commercial ion mobility spectrometry instruments are mainly radioactive ⁶³ Ni ion sources. In order to overcome the disadvantages that ⁶³ Ni ion sources are radioactive and that instrument management, maintenance, and disposal are regulated by radioactive source regulations, in recent years, other non-radioactive ion sources combined with ion mobility spectrometry have been gradually developed, such as vacuum ultraviolet lamps or Laser photoionization ion source, surface ionization ion source, electrospray ionization ion source, etc. These existing ion source technologies have the following difficulties and deficiencies when detecting surface substances of objects:

(1) ⁶³ Ni ion sources, vacuum ultraviolet and other photoionization sources, and surface ionization sources are all inside the ion mobility spectrometry system. When the ion mobility spectrometry equipment equipped with these ion sources detects trace substances on the surface of solid objects, it must be detected by a sampler. The surface of the object is wiped and sampled, and then heated and vaporized, and the sample is injected, and the detected object is introduced into the ion source area inside the ion mobility spectrometer for ionization. Therefore, it is difficult for this type of ion source ion mobility spectrometry technology to realize in-situ detection of surface substances on objects. In addition to the need for sampling procedures such as swabbing, there is also the possibility of loss and contamination of the measured substance.

(2) Electrospray ionization ion source ion mobility spectrometry is usually used for the direct detection of substances in liquids, although desorption electrospray ionization technology has recently been used for the detection and analysis of surface substances, but it requires the use of special electrospray solvents, and The use of solvents may cause contamination of the surrounding environment.

(3) Laser desorption ionization under atmospheric pressure can be used to measure solid samples. The samples usually need to interact with the substrate, porous silicon and other surfaces after absorbing laser energy and then ionize. Surface, laser wavelength and energy all have certain requirements.

Contents of the invention

The purpose of the present invention is to provide a detection method and device for ion mobility spectrometry desorption of excited state molecules colliding with the surface, which can work under atmospheric pressure conditions, has no special requirements for the surface matrix of the article, and can realize in-situ desorption of trace substances on the surface of the article Real-time analysis and detection of ionization ion mobility spectrometry; it can be used for in-situ detection of pesticide residues on the surface, and is also suitable for the detection of toxic and dangerous substances adhered to the surface of objects.

Technical scheme of the present invention is as follows:

Excited state molecular collision surface desorption ionization ion mobility spectrometry detection method is characterized in that: using atmospheric pressure gas discharge, the discharge generates excited state atoms, molecules and other charged particles, by setting the voltage of the ion gate and electrode group, remove the charged particles, Let the energy-carrying excited state atoms and molecules collide with the surface of the measured sample, "evaporate" the measured sample from the surface, and ionize it through ion molecular reactions, the sample ions enter the migration tube of the ion mobility spectrometer, and enter the ion gate At the moment of opening, the sample ions enter the separation area of the transfer tube in the form of pulses. Different ions move at different speeds under the action of the electric field to achieve separation and arrive at the ion detection plate successively. After obtaining the ion current signal, the data acquisition system processes, stores and real-time display.

Excited state molecular collision surface desorption ionization ion mobility spectrometer detection device, including ion mobility spectrometer, is characterized in that an excited state generator is installed before the ion entrance of the migration tube of ion mobility spectrometer, and the distance between the excited state generator and ion mobility spectrometer is The area where the sample to be tested is placed is directly exposed to the atmosphere. The excited state generator includes a discharge chamber. The front end of the discharge chamber is connected to a discharge component. The outlet of the chamber is facing the inlet of the ion transfer tube. The front inlet of the discharge chamber is connected to a gas source, and a flow controller is connected to the pipeline between the gas source and the discharge chamber; the ion introduction electrode is installed in the transfer tube of the ion mobility spectrometer, and the repelling electrode and An electric field with voltage drop or rise is generated between the ion introduction electrodes according to the ion species of the sample, and the transfer tube communicates with the ion separation area.

In the excited state generator, the atmospheric pressure discharge of pure He or _N2 gas produces a gas flow containing electronically excited atomic He ^* or _N2 ^* molecules, as well as other charged particles, which pass through the ion filter gate and the repelling electrode at the end of the excited state generator The role is to remove the charged particles in it, so that the excited state He ^* or N ₂ ^* energy-carrying particles flow out from the excited state generator. By colliding with the surface of the object, the energetic particles He ^* or _N2 ^* "vaporize" the sample from the surface and ionize it by ion reaction. The formed sample ions are introduced into the front entrance of the transfer tube under the action of the electric field of the ion introduction electrode. The sample ions in the transfer tube enter the separation area of the transfer tube in a pulsed manner through the opening of the ion gate. Under the action of the electric field in the transfer tube, different ions are separated. , and successively arrive at the ion detection board at the end of the migration tube, the relationship diagram between ion intensity and ion migration time is obtained by the ion current detection and data acquisition system, and the type and concentration of the sample are obtained according to the time characteristics and intensity of the ion signal peak. At the end of the transfer tube, a drift air flow enters and flows in the opposite direction of ion movement. The function of the drift air flow is to wash the transfer tube and maintain the cleanliness of the transfer tube wall.

In the ion mobility spectrometer detection device for desorption and ion mobility spectrometry on the surface of excited state molecules, the surface of the analyzed object is directly exposed to the atmospheric environment. After the excited state molecules collide with it, the trace substances on the surface of the object are desorbed and ionized. The separation and intensity measurement of ions are carried out, and finally the in-situ rapid detection of trace substances on the surface is realized.

The A/D chip used in the data acquisition system has 16-bit precision and a conversion frequency of 100K. The A/D chip digitizes the analog signal output by the detector and other parameter analog signals; the system controls the voltage through a 12-bit D/A chip . Configured RS232 communication port for data exchange with PC.

The gain of the ion current detection device of the present invention can be adjusted between 10 ⁸ -10 ¹⁰ V/A. In actual measurement, when the concentration of the sample is in the order of ppb-ppm, the ion signal received by the detection plate is usually in the range of pA-nA, and the noise signal is lower than 20pA.

The gas flow controller of the present invention is a flow meter with a maximum flow rate of 1 L/min and a minimum adjustment amount of 0.1 L/min.

The present invention has the following characteristics:

1). Real-time measurement of the composition and concentration of trace substances on the surface of objects can be carried out in an open atmospheric environment.

2). It belongs to in-situ and real-time detection, and the item sample does not need pretreatment.

3). The device is compact in structure, light in weight, easy to carry, and suitable for field use.

Description of drawings

Fig. 1 Schematic diagram of the structure of an ion mobility spectrometry detection device for excited state molecules colliding with a surface.

Fig. 2 Excited state molecular collision surface desorption ionization ion mobility spectrometry detects the spectrum of trimethyl phosphate on the surface of the object.

Fig. 3 Excited state molecular collision surface desorption ionization ion mobility spectrometry detects the spectrum of dimethoate on the surface of the object.

Fig. 4 Spectrum of excited state molecule collision surface desorption ionization ion mobility spectrometry detection of fenthion on the surface of the article.

Detailed ways

The detection method and device of excited state molecule collision surface desorption ion mobility spectrometry are shown in Fig. 1 . The specific structure of the device is that the discharge parts 1 and 2 form an atmospheric pressure discharge area, the discharge part 1 is a stainless steel needle, and the discharge part 2 is a stainless steel plate with holes, and the distance between them can be adjusted between 0 and 20 mm. The voltage on the discharge parts 1 and 2 is provided by the DC power supply 7, and a current-limiting resistor is installed between the output terminal of the DC power supply 7 and the discharge part 1, and the output voltage of the DC power supply 7 is adjustable in the range of 0-5KV. Adjust the output voltage of the DC power supply according to different gas types to form a discharge and obtain a gas flow containing excited components. Typical conditions are: if the flow rate of He or N ₂ gas is 1L/min, the output voltage of DC power supply 7 is between 1KV-3.5KV, and the distance between discharge parts 1 and 2 is 1mm-10mm. After the discharge part 2 is the ion filter gate 3 and the repelling electrode 4, its voltage shares the DC power supply 7 with the discharge part 1 and 2 through the voltage dividing resistor, and passes through the radial electric field between the parallel wires on the ion filter gate 3 and the repulsion electrode 4. The axial electric field removes ions and electrons from the discharge products. After the excited state particle He ^* or N ₂ ^* collides with the surface of the object, the trace sample substance on the surface is desorbed and converted into sample ions through ion reaction. The electric field formed between the repelling electrode 4 and the ion introducing electrode 9 introduces the sample ions into the ion separation detection system 18 . The discharge part 1, the discharge part 2, the ion filter gate 3, and the repelling electrode 4 form an excited state generating device 17, which is installed on a support capable of three-dimensional size adjustment.

Between the excited state generator 17 and the ion separation detection system 18 is the sample desorption ionization region 8, the distance of which can be adjusted in the linear range of 0-50mm, due to the diffusion effect and the existence of ambient gas, the sample desorption ionization region 8 The length will affect the concentration of excited state atoms and molecules acting on the sample 8, and then affect the ionization efficiency of the sample. In actual measurement, the appropriate spacing distance can be determined by monitoring the 24 peaks in Figure 2 according to different environmental conditions 8.

The components installed in the ion separation detection system 18 from front to back are the attracting electrode 9 , the ion gate 10 , the pole plate 11 , the grid 12 and the detection pole plate 13 . The output voltage range of the power supply 16 is -10KV～0 and 0～10KV, which can be set according to whether positive ions or negative ions are detected by excited state desorption ionization ion mobility spectrometry. The ion gate 10 adopts the same structure as the ion filter gate 3 , and the opening and closing times are determined by the pulse signal output by the signal control system 15 in the data acquisition system 19 . Considering the impact of the pulse width on the resolution and intensity of the measured signal, the pulse width of the pulse signal is usually set to 0.2ms, and the signal period can be determined according to the time range of the measured signal.

The signal detected by the detection plate 13 is collected and displayed by the collection and display unit 14 in the data collection system 19 via the ion amplification component 20 . The control unit 15 in the data acquisition system 19 can send a pulse signal to control the opening and closing of the ion gate 10 and synchronize the acquisition and display unit 14 . The data acquisition system can exchange and store data with the computer 23 through the RS232 communication port. The gas container 5 provides the pure gas He or N ₂ gas required for discharge, and the flow controller 6 controls the flow of the gas. The air pump 22 and the flow meter 21 control the flow velocity of the migrating gas in the ion separation detection system 18 .

The data shown in Fig. 2, Fig. 3 and Fig. 4 are all average values after 8 scans, and the opening time of the ion gate 10 in the recording process of Fig. 2, Fig. 3 and Fig. 4 is 0.2ms.

Trimethyl phosphate is a simulant of organophosphorus pesticides. Use a PTFE rod with a diameter of 1mm to dip a small amount of trimethyl phosphate analytically pure solution, and place it at the ionization zone 8 of the sample in Figure 1. When the end of the PTFE tube When located in the gas flow of the excited state generator, three strong ion peaks 25, 26 and 27 appear at 5.17ms, 6.59ms and 8.18ms, and the spectrum is shown in Figure 2.

Using the same method to measure trimethyl phosphate, carry out the measurement of surface trace pesticides dimethoate and fenthion. When measuring dimethoate, ion peaks 28, 29, and 30 were recorded at 5.15ms, 5.46ms, and 5.66ms, as shown in Figure 3. When measuring fenthion, ion peaks 31, 32, 33, and 34 were recorded at 5.48ms, 6.31ms, 6.5ms, and 7.52ms, as shown in Figure 4.

The working principle is: the pure gas He or N ₂ is discharged between the discharge parts 1 and 2 under atmospheric pressure, and particles such as excited state He ^* or N ₂ ^* , positive/negative ions and electrons are generated, and pass through the downstream ion filter gate 3 and the repelling electrode 4 to remove the ions and electrons, so that the ion source gas flow contains a large number of excited state He ^* or N ₂ ^* particles. The surface of the object is placed in the area between the exit of the excited state generator 17 and the entrance of the ion separation detection system 18. After He ^* or N ₂ ^* reacts with the sample M in the ambient air, it undergoes reactions such as penning ionization, proton transfer or electron capture. The process can form sample ions such as M ⁺ , MH ⁺ , or [MH] ^- , and these ions are guided into the ion separation detection system 18 under the action of the electric field between the exit of the excited state generator 17 and the entrance of the ion separation detection system 18, When the ion gate 10 is opened, ions enter the migration area in the form of pulsed ion packets. Different ions move at different speeds under the action of the electric field in the migration area, so they are separated and arrive at the detection plate 13 successively, and are converted into voltage signals by the ion current detection device 20. , the data acquisition system 19 performs data acquisition, storage and display. Obtain the relationship diagram of ionic strength and ion migration time in the tube - ion mobility spectrum, and compare it with the database of standard samples to obtain the composition and content of the sample.

Claims (2)

1. Excited state molecular collision surface desorption ionization ion mobility spectrometry detection method, characterized in that: using atmospheric pressure gas discharge, the discharge generates excited state atoms, molecules and other charged particles, by setting the voltage of the ion gate and electrode group to remove the charged particles Particles, let the energy-carrying excited state atoms and molecules collide with the surface of the measured sample, "evaporate" the measured sample from the surface, and ionize it through ion-molecular reactions, and the sample ions enter the transfer tube of the ion mobility spectrometer. At the moment when the ion gate is opened, the sample ions enter the separation area of the transfer tube in the form of pulses. Different ions move at different speeds under the action of the electric field to achieve separation and arrive at the ion detection plate successively. After the ion current signal is obtained, it is processed by the data acquisition system. storage and real-time display. 2. Excited state molecular collision surface desorption ionization ion mobility spectrometry detection device, including ion mobility spectrometry, is characterized in that an excited state generator is installed before the ion entrance of the migration tube of ion mobility spectrometry, and the excited state generator, ion mobility spectrometry The interval is the area where the sample to be tested is placed, which is directly exposed to the atmosphere. The excited state generator includes a discharge chamber, and the discharge part is connected to the front end of the discharge chamber. It is the outlet of the discharge chamber, facing the entrance of the ion transfer tube. The front inlet of the discharge chamber is connected to a gas source, and a flow controller is connected to the pipeline between the gas source and the discharge chamber; the transfer tube of the ion mobility spectrometer is equipped with an ion introduction electrode to repel An electric field with voltage drop or rise is generated between the electrode and the ion introduction electrode according to the type of sample ions, and the transfer tube communicates with the ion separation area.

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