CN114664637B - A normal pressure ion source - Google Patents

Abstract

The invention discloses a normal pressure ion source, which comprises an electrospray needle and a mass spectrometer sample inlet which are horizontally arranged, wherein electrospray is emitted from the front end of the electrospray needle to the mass spectrometer sample inlet, and is characterized in that: the periphery coaxial of electrospray needle is provided with the metal cavity, form air current passageway between metal cavity and the electrospray needle, the carrier gas flows to the front end of electrospray export along air current passageway from the rear end, seal through sealing device between the rear end of metal cavity and the electrospray needle, be provided with temperature control device in the front end of metal cavity, the through sample inlet has been seted up to the downside of metal cavity, the below of sample inlet is provided with ultrasonic atomizing device, sample liquid drop forms sample gas after ultrasonic atomizing device atomizes, and carry out ionization by the carrier gas area to the electrospray export through sample inlet entering air current passageway, the advantage is: the liquid sample does not need to be subjected to sample pretreatment, so that the ionization efficiency is improved, and the power consumption of the ion source device is reduced.

Description

A normal pressure ion source

Technical Field

The invention relates to an ion source for a mass spectrometer, in particular to a normal pressure ion source.

Background Art

A mass spectrometer is an analytical instrument that uses the charge-to-mass ratio to separate and detect substances. It is widely used in food safety, pharmaceuticals, life sciences and other fields. A mass spectrometer is generally composed of an ion source, a mass analyzer, a detector and a vacuum system. The analyzed substance is first ionized into charged ions by the ion source, and then the ions are guided into the mass analyzer in a vacuum environment. The mass analyzer is responsible for separating the ions according to the charge-to-mass ratio and sending them to the detector in sequence. The signal obtained by the detector is amplified, collected and processed, and then drawn into a complete mass spectrum by a computer.

Atmospheric pressure ion source is a new type of ion source, which is characterized by the ionization process occurring under atmospheric pressure and requiring no or only a small amount of sample pretreatment. Typical atmospheric pressure ion sources include Desorption Electrospray Ionization (DESI), Direct Analysis in Real Time (DART), Thermal Desorption Electrospray Ionization (TD-ESI), etc.

The thermal desorption electrospray ion source is a typical atmospheric pressure ion source, which has been widely used in the on-site rapid detection of drugs, pesticide residues in fruits and vegetables, etc. The working principle of the thermal desorption electrospray ion source is shown in Figure 1. After the needle of the sampling probe is dipped into the liquid or solid sample, it is placed in a heated stainless steel cavity. The sample is vaporized and volatilized, and is brought into the electrospray ion source area by the airflow for sample ionization. The formed sample ions enter the mass spectrometer for analysis. The advantage of the thermal desorption electrospray ion source is that it does not require sample pretreatment, and liquid or solid samples can be directly analyzed by mass spectrometry on site.

The current thermal desorption electrospray ion source has the following main problems: First, the sample gas molecules that are heated and desorbed can only become sample ions when they come into contact with charged ions in the electrospray. Since the electrospray ionization area is an open space, only a small number of sample gas molecules can be ionized, and the ionization efficiency is low. Second, it takes a lot of power to vaporize the sample by heating the metal cavity, resulting in high power consumption of the entire ion source.

Summary of the invention

In order to solve the above-mentioned deficiencies in the prior art, the present invention provides a normal-pressure ion source for a mass spectrometer, which has the advantages of no need for sample pretreatment for liquid samples, high ionization efficiency and low device power consumption.

The technical solution adopted by the present invention to solve the above technical problems is: a normal pressure ion source, including an electrospray needle and a mass spectrometer injection port arranged horizontally and directly opposite each other, a metal cavity is coaxially arranged on the outer periphery of the electrospray needle, an air flow channel is formed between the metal cavity and the electrospray needle, a carrier gas flows along the air flow channel from the rear end to the front end where the electrospray outlet is located, the rear end of the metal cavity and the electrospray needle are sealed by a sealing device, a temperature control device is arranged in the front end of the metal cavity, a through injection port is opened on the lower side of the metal cavity, an ultrasonic atomization device is arranged below the injection port, sample droplets are atomized by the ultrasonic atomization device to form sample gas, and enter the air flow channel through the injection port and are carried by the carrier gas to the electrospray outlet for ionization.

In some embodiments, the temperature control device includes a heating rod and a temperature measuring rod, and the heating rod and the temperature measuring rod are respectively located on opposite sides of the electrospray needle, and are used to control the temperature of the ionization region formed between the electrospray outlet and the gas flow channel. In this way, the sample gas can be assisted in heating and ionization, which can further improve the ionization efficiency. The auxiliary heating temperature only needs to be around 100 degrees, which is much lower than the high temperature of around 250 degrees of the conventional thermal desorption electrospray ion source, so the power consumption of the ion source device can be greatly saved.

In some embodiments, the sealing device includes a bolt and a rubber ring, the rear end of the metal cavity is provided with an external thread, the bolt is connected with the external thread, and the rubber ring is provided between the metal cavity and the electrospray needle. Thus, a simple matching structure can be used to ensure the sealing of the rear end of the metal cavity and the airflow channel, and it is convenient for on-site assembly.

In some embodiments, an air pump, a pipeline and a joint are further included, wherein the joint is disposed on the upper side of the metal cavity and at the rear end, the gas outlet end of the joint is connected to the air flow channel, and the other end of the joint is connected to the air pump through the pipeline, and the carrier gas generated by the air pump enters the air flow channel and flows to the front end. The carrier gas generated by the air pump enters the metal cavity and flows toward the front end along the air flow channel, so as to provide a carrier gas coaxial with the electrospray needle, thereby further enhancing the ionization efficiency.

In some embodiments, the metal cavity is made of stainless steel or aluminum.

In some embodiments, the blowing gas flow rate of the air pump is 1 to 2 liters/minute, and the carrier gas is a dry inert gas or dry air.

Compared with the prior art, the core of the atmospheric pressure ion source device of the present invention is that the liquid sample is atomized by an ultrasonic atomization device, and the atomized gas sample can be ionized in a coaxial manner with the electrospray needle. The advantages of the present invention are further: (1) No sample pretreatment is required for the liquid sample, and the ultrasonic atomization device can directly generate sample ions for analysis, and the sample gas is ionized in a coaxial manner with the electrospray, which improves the ionization efficiency of the ion source; (2) The ion source device only needs auxiliary heating, which has lower power consumption and reduces costs compared to the method of vaporizing the sample by heating the metal cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a working principle diagram of a conventional thermal desorption electrospray ion source in the background art;

FIG2 is a schematic structural diagram of an embodiment of a normal pressure ion source of the present invention;

FIG3 is a mass spectrum obtained using a normal pressure ion source of the present invention in one embodiment;

FIG. 4 is a mass spectrum obtained using a conventional thermal desorption electrospray ion source in the same embodiment.

Among them, there are an electrospray needle 1, a mass spectrometer injection port 2, an electrospray 3, a metal cavity 4, an air flow channel 5, an injection port 6, an ultrasonic atomization head 7, sample droplets 8, a heating rod 9, a temperature measuring rod 10, an ionization region 11, a bolt 12, a rubber ring 13, an air pump 14, a pipeline 15, and a connector 16; a mass spectrometer 21, an electrospray needle 22, an electrospray ionization region 23, a metal cavity 24, a sampling probe 25, a probe 26, a heating wire 27, and an air pump 28.

DETAILED DESCRIPTION

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but they are not intended to limit the present invention.

Embodiment 1

The device of the present invention is shown in Figure 2, which is a normal pressure ion source, including an electrospray needle 1 and a mass spectrometer injection port 2 arranged horizontally and facing each other, and the electrospray 3 is ejected from the front end of the electrospray needle 1 facing the mass spectrometer injection port 2. A metal cavity 4 is coaxially arranged on the periphery of the electrospray needle 1, and the electrospray needle 1 is arranged in the metal cavity 4. An air flow channel 5 is formed between the metal cavity 4 and the electrospray needle 1. The carrier gas flows from the rear end to the front end of the electrospray outlet along the air flow channel 5. The rear end of the metal cavity 4 and the electrospray needle 1 are sealed by a sealing device. A temperature control device is arranged in the front end of the metal cavity 4. A through injection port 6 is opened on the lower side of the metal cavity 4, and an ultrasonic atomization device is arranged below the injection port 6. In this embodiment, an ultrasonic atomization head 7 is used. The sample droplets 8 are atomized by the ultrasonic atomization head 7 to form a sample gas, and enter the air flow channel 5 upward through the injection port 6 and are carried to the electrospray 3 outlet by the carrier gas, and are ionized to generate sample ions after mixing with the electrospray.

Embodiment 2

A normal pressure ion source proposed in this embodiment limits the specific structure of the temperature control device on the basis of the first embodiment. In this embodiment, the temperature control device includes a heating rod 9 and a temperature measuring rod 10, which are respectively located on opposite sides of the electrospray needle 1, and are used to control the temperature of the ionization region 11 formed between the outlet of the electrospray 3 and the air flow channel 5. Therefore, the sample gas can be auxiliary heated, and the sample gas can be auxiliary ionized, which can further improve the ionization efficiency. The auxiliary heating temperature only needs to be around 100 degrees, which is much lower than the high temperature of around 250 degrees of the conventional thermal desorption electrospray ion source, so the power consumption of the ion source device can be greatly saved.

Embodiment 3

The present embodiment proposes a normal pressure ion source, which defines the specific structure of the sealing device on the basis of the first or second embodiment. In the present embodiment, the sealing device includes a bolt 12 and a rubber ring 13, the rear end of the metal cavity 4 is provided with an external thread, the bolt 12 is connected with the external thread, the rubber ring 13 is arranged between the metal cavity 4 and the electrospray needle 1, and the sealing device is used to ensure that the rear end of the metal cavity and the airflow channel is sealed.

Embodiment 4

The present embodiment proposes a normal-pressure ion source, which defines the specific structure of the gas access device on the basis of the above-mentioned embodiment. In the present embodiment, the normal-pressure ion source also includes an air pump 14, a pipeline 15 and a connector 16, the connector 16 is arranged on the upper side of the metal cavity 4 and located at the rear end, the gas outlet end of the connector 16 is connected to the gas flow channel 5, and the other end of the connector 16 is connected to the air pump 14 through the pipeline 15, so that the carrier gas generated by the air pump 14 enters the metal cavity 4 and flows toward the front end along the gas flow channel 5, and is used to provide a carrier gas coaxial with the electrospray needle.

Embodiment 5

This embodiment proposes a normal pressure ion source, which further defines the remaining features based on the above embodiment. In this embodiment, the material of the metal cavity 4 is stainless steel or aluminum.

In this embodiment, the blowing gas velocity of the air pump 14 is 1-2 liters/minute, and the carrier gas is an inert gas such as dry nitrogen or dry air.

The working principle of a normal pressure ion source of the present invention is as follows: when working, sample liquid droplets are dropped onto an ultrasonic atomizer head, and the ultrasonic atomizer head generates sample atomization gas after being powered on. The atomization gas is ionized by a carrier gas in a coaxial manner with the electrospray, and the sample ions enter a mass spectrometer for analysis to obtain a mass spectrum.

A comparative test was conducted on a normal pressure ion source of the present invention and a thermal decomposition electrospray ion source of a traditional structure. The test method is as follows: the device of the present invention (Figure 2) is used in the experimental group, and the traditional device (Figure 1) is used in the control group. The portable mass spectrometer developed by the laboratory research group is used. The test sample is an enrofloxacin sample with a concentration of 1 microgram/ml, and the electrospray solvent is methanol and water in a volume ratio of 1:1, and 1‰ volume of formic acid is added. The heating temperature in the experimental group device is set to 100 degrees Celsius, the air flow rate of the air pump is 1 liter/minute, and the gas is air. The ultrasonic atomization head uses a single-head atomizer with a frequency of 2.4 MHz, which can produce a mist volume of up to 500 ml/hour and atomized particles less than 5 microns. The device of the present invention is used in the experimental group, and a drop of the test sample (the volume is estimated to be 10-20 microliters) is dripped on the atomization head. After the atomization head is turned on to work the ion source, the enrofloxacin mass spectrum peak (m/z=360) shown in Figure 3 is obtained, and the signal intensity is nearly 5000. The power consumption of the entire device is 30 watts.

The control group also used an enrofloxacin sample with a concentration of 1 μg/ml as a test sample, and the electrospray solvent was methanol and water in a volume ratio of 1:1, with 1‰ volume of formic acid. The traditional thermal analysis was used to heat to 250 degrees Celsius, the air flow rate of the air pump was 1 liter/minute, and the gas was air. The same experimental method was used to dip a drop of sample with a sampling needle, and the estimated volume was also 10~20 microliters, and the comparative test result diagram of the thermal desorption electrospray ion source in Figure 4 was obtained. In the mass spectrum of Figure 4, the signal intensity of the enrofloxacin mass spectrum peak (m/z=360) is only less than 800. Compared with the signal intensity of nearly 5000 of the device of the present invention, it is proved that the ionization efficiency of the present invention is superior to that of the thermal desorption electrospray ion source. In addition, the power consumption of the thermal desorption electrospray ion source is as high as 120 watts, so the present invention improves the ionization efficiency while effectively reducing the power consumption.

It is worth noting that the above is only a preferred embodiment of the present invention, and does not limit the scope of patent protection of the present invention. The present invention can also improve the materials and structures of the above-mentioned various parts, or replace them with technical equivalents. Therefore, all equivalent structural changes made by using the description and illustrations of the present invention, or directly or indirectly applied to other related technical fields are also included in the scope of the present invention.

Claims (6)

1. A normal pressure ion source, comprising a horizontally arranged electrospray needle and a mass spectrometer inlet, wherein the electrospray is ejected from the front end of the electrospray needle facing the mass spectrometer inlet, characterized in that a metal cavity is coaxially arranged on the periphery of the electrospray needle, an air flow channel is formed between the metal cavity and the electrospray needle, a carrier gas flows along the air flow channel from the rear end to the front end of the electrospray outlet, the rear end of the metal cavity and the electrospray needle are sealed by a sealing device, a temperature control device is arranged in the front end of the metal cavity, a through inlet is opened on the lower side of the metal cavity, an ultrasonic atomization device is arranged below the inlet, sample droplets are atomized by the ultrasonic atomization device to form sample gas, and enter the air flow channel through the inlet and are carried to the electrospray outlet by the carrier gas for ionization. 2. A normal-pressure ion source according to claim 1, characterized in that the temperature control device comprises a heating rod and a temperature measuring rod, and the heating rod and the temperature measuring rod are respectively located on opposite sides of the electrospray needle, and are used to control the temperature of the ionization region formed between the electrospray outlet and the airflow channel. 3. A normal pressure ion source according to claim 1, characterized in that the sealing device includes a bolt and a rubber ring, the rear end of the metal cavity is provided with an external thread, the bolt is cooperatively connected with the external thread, and the rubber ring is arranged between the metal cavity and the electrospray needle for sealing the airflow channel. 4. A normal-pressure ion source according to claim 1, characterized in that it also includes an air pump, a pipeline and a joint, wherein the joint is arranged on the upper side of the metal cavity and is located at the rear end, the air outlet end of the joint is connected to the air flow channel, and the other end of the joint is connected to the air pump through the pipeline, and the carrier gas generated by the air pump enters the air flow channel and flows toward the front end. 5 . The atmospheric pressure ion source according to claim 1 , wherein the metal cavity is made of stainless steel or aluminum. 6. A normal-pressure ion source according to claim 4, characterized in that the blowing gas velocity of the air pump is 1-2 liters/minute, and the carrier gas is a dry inert gas or dry air.