CN118156118A - Gas phase ion reaction device, mass spectrometer and detection method of non-polar compounds - Google Patents

Abstract

The present invention discloses a gas-phase ion reaction device, a mass spectrometer and a method for detecting non-polar compounds, wherein the gas-phase ion reaction device comprises an ion source, a sealed cavity, an ion transmission tube and an ion cracking device connected in sequence; and the sealed cavity is provided with a sample inlet to be tested. The gas-phase ion reaction device provided by the present invention can realize specific ionization of non-polar compounds that are difficult to ionize, and the gas-phase ion reaction device can generate metal ions with strong reactivity through collision cracking, and the metal ions with strong reactivity react with non-polar gaseous compounds in the ion cracking device to generate new composite ions, thereby realizing soft ionization of non-polar gaseous compounds, and the composite ions can be subsequently detected by mass spectrometry.

Description

Gas phase ion reaction device, mass spectrometer and detection method of non-polar compounds

Technical Field

The present invention relates to the technical field of mass spectrometry detection, and in particular to a gas phase ion reaction device, a mass spectrometer and a detection method for non-polar compounds.

Background technique

Mass spectrometry is widely used in various analytical fields due to its high sensitivity, low detection limit, small sample usage, high throughput, and fast detection speed. As an important component of mass spectrometry instruments, the ion source is used to ionize the sample to be analyzed and obtain ions with sample information. With the continuous development of mass spectrometry technology, the types of ion sources have also become diverse. Currently, the more common ones are electron impact ionization (EI) source, electrospray ionization (ESI) source, atmospheric pressure chemical ionization (APCI) source, matrix-assisted laser desorption ionization (MALDI) source, etc. Different ion sources are used for different analytes. As shown in Figure 1, the polarity and molecular weight distribution of compounds suitable for analysis by several common ion sources. As the most widely used ion source in liquid chromatography-mass spectrometry (LC-MS), the ESI source is generally suitable for the analysis of polar substances, and is mainly for liquid samples. If you need to analyze a medium-polar substance, you need to use the APCI source, and for non-polar substances (such as alkanes), you often need to use the EI source equipped in the gas chromatography-mass spectrometry (GC-MS) for ionization. Different ion sources have certain limitations in their scope of application. In addition to expanding the versatility of ion sources, developing specific ionization methods for specific analytes also has very important practical value.

Therefore, the prior art still needs to be improved and developed.

Summary of the invention

In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a gas-phase ion reaction device, a mass spectrometer and a method for detecting non-polar compounds, aiming to develop a specific ionization method for difficult-to-ionize non-polar compounds, thereby realizing their detection.

The technical solution of the present invention is as follows:

A first aspect of the present invention provides a gas phase ion reaction device, wherein the gas phase ion reaction device comprises an ion source, a sealed chamber, an ion transmission tube and an ion fragmentation device connected in sequence;

The sealed cavity is provided with an inlet for a sample to be tested.

Optionally, the ion source is an ESI source, an APCI source, a glow discharge source or a photoionization source.

A second aspect of the present invention provides a mass spectrometer, comprising the gas phase ion reaction device of the present invention as described above, and further comprising:

A mass analyzer connected to the ion fragmentation device;

A detector is connected to the mass analyzer.

A third aspect of the present invention provides a method for detecting non-polar compounds, wherein the mass spectrometer of the present invention as described above is used, and the method for detecting non-polar compounds comprises the steps of:

Providing a metal compound solution and a non-polar compound to be detected, wherein the non-polar compound to be detected is a non-polar first gaseous compound;

Passing the metal compound solution through an ion source to generate complex ions containing metal elements or cluster ions containing metal elements;

Introducing the metal element-containing complex ions or metal element-containing cluster ions into the sealed cavity, and then introducing the non-polar first gaseous compound and the carrier gas into the sealed cavity from the inlet of the sample to be tested to form a mixed gas;

The mixed gas is transmitted to an ion cracking device by an ion transmission tube, and the metal element-containing complex ions or metal element-containing cluster ions in the mixed gas collide and crack with the carrier gas to generate metal ions, and the metal ions react with the non-polar first gaseous compound to obtain composite ions;

The composite ions are detected by a mass analyzer and a detector, and the non-polar compound to be detected is identified by the detection result.

A fourth aspect of the present invention provides a method for detecting non-polar compounds, wherein the mass spectrometer of the present invention as described above is used, and the method for detecting non-polar compounds comprises the steps of:

Providing a metal compound solution and a non-polar compound to be detected, wherein the non-polar compound to be detected is a non-polar volatile liquid compound, and the non-polar volatile liquid compound volatilizes to generate a non-polar second gaseous compound;

Passing the metal compound solution through an ion source to generate complex ions containing metal elements or cluster ions containing metal elements;

The metal element-containing complex ions or metal element-containing cluster ions are introduced into a sealed cavity, and then the non-polar volatile liquid compound is placed at the inlet of the sample to be tested, and the non-polar second gaseous compound and the carrier generated by the volatilization of the non-polar volatile liquid compound enter the sealed cavity from the inlet of the sample to be tested to form a mixed gas;

The mixed gas is transmitted to an ion cracking device by using an ion transmission tube, and the metal element-containing complex ions or metal element-containing cluster ions in the mixed gas collide and crack with the carrier gas to generate metal ions, and the metal ions react with the non-polar second gaseous compound to obtain composite ions;

The composite ions are detected by a mass analyzer and a detector, and the non-polar compound to be detected is identified by the detection result.

Optionally, the gas pressure range of the ion splitting device is set to 10 ^-1 ～10 ³ Pa.

Optionally, the voltage difference between the ion transfer tube and the ion fragmentation device is set to -200 to 200 V, and the voltage difference between the ion transfer tube and the ion fragmentation device is not zero.

Optionally, the carrier is an inert gas.

Optionally, the inert gas includes one of nitrogen and argon.

Optionally, the metal compound solution includes an inorganic metal salt solution or an organic metal compound solution.

Beneficial effects: The gas-phase ion reaction device provided by the present invention can achieve specific ionization of non-polar compounds that are difficult to ionize. The gas-phase ion reaction device can produce metal ions with strong reactivity through collision cracking, and the metal ions with strong reactivity undergo gas-phase ion-molecule reaction with non-polar gaseous compounds in the ion cracking device to generate new composite ions, thereby achieving soft ionization of non-polar gaseous compounds. The composite ions can subsequently be detected by mass spectrometry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 shows the polarity and molecular weight distribution of compounds suitable for analysis by several common ion sources in the prior art.

FIG. 2 is a schematic diagram of the structure of a mass spectrometer in an embodiment of the present invention.

Figure 3 is the mass spectrum of the product after ionizing _PdCl2 solution through the ESI source.

FIG. 4 is a mass spectrum of the product after the PdCl ₂ solution passes through the mass spectrometer in Example 1 of the present invention.

FIG5 is a mass spectrum obtained after an n-heptane sample is introduced into the mass spectrometer of Example 1 of the present invention.

Detailed ways

The present invention provides a gas phase ion reaction device, a mass spectrometer and a method for detecting non-polar compounds. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

An embodiment of the present invention provides a gas-phase ion reaction device, wherein, as shown in FIG2 , the gas-phase ion reaction device comprises an ion source 1, a sealed chamber 2, an ion transfer tube 3 and an ion cracking device 4 connected in sequence; the sealed chamber 2 is provided with a sample inlet 21 to be tested.

Some non-polar gaseous compounds are difficult to ionize directly and thus cannot be detected by mass spectrometry. By using the gas-phase ion reaction device provided in this embodiment, metal ions with strong reactivity can be produced through collision cracking, and the metal ions with strong reactivity can undergo gas-phase ion-molecule reaction with non-polar gaseous compounds in the ion cracking device to generate new composite ions, thereby achieving soft ionization of non-polar gaseous compounds, and the composite ions can subsequently be detected by mass spectrometry.

In this embodiment, the ion source is used to generate complex ions containing metal elements or cluster ions containing metal elements (such as complex ions or charged droplets composed of metal ions and solvent molecules) from a metal compound solution, and the sample inlet is used to introduce a gaseous sample containing the analyte.

The sealed cavity is used to control the composition of substances involved in the reaction, especially to reduce the participation of air. Compared with other open ion sources, the closed ion source cavity can prevent a large amount of air from entering the instrument to participate in the reaction, thereby reducing interference with gas-phase ion-molecule reactions.

The ion transfer tube is one of the components that control ion fragmentation. The ion fragmentation device is another component that controls ion fragmentation. The voltage difference between the ion fragmentation device and the ion transfer tube is used to trigger and control ion fragmentation. At the same time, the ion fragmentation device is also the place where metal ions are generated and gas-phase ion-molecule reactions occur. That is, the ion fragmentation device is used to generate metal ions and is also the place where gas-phase ion-molecule reactions occur. Metal ions are generated by collision fragmentation and can immediately participate in the reaction with the non-polar gaseous compound to be measured. The two processes of metal ion generation and gas-phase ion-molecule reaction are realized in the same device (ion fragmentation device), shortening the intermediate links to reduce interference and ion loss. Metal ions in solution often exist in the form of complexes or clusters. It is difficult to obtain metal ions (i.e., pure metal ions) when ionization is performed using only electrospray and other technologies. Generally, complex ions containing metal elements or cluster ions containing metal elements can be obtained, and the complex ions containing metal elements or cluster ions containing metal elements have low reaction activity and cannot react with the non-polar gaseous compound to be measured. In the ion fragmentation device, complex ions containing metal elements or cluster ions containing metal elements can be broken up by collision fragmentation, thereby generating metal ions with higher reactivity (which can undergo gas-phase ion-molecule reaction with the non-polar gaseous compound to be tested), and then subsequent gas-phase ion-molecule reaction can be carried out.

Specifically, a metal compound solution is passed through an ion source to generate complex ions containing metal elements or cluster ions containing metal elements (such as complex ions formed by metal ions and solvent molecules or charged small droplets, etc.); the complex ions containing metal elements or cluster ions containing metal elements are introduced into a sealed cavity, and then a non-polar gas compound and a carrier gas are introduced into the sealed cavity from an inlet of a sample to be tested to form a mixed gas; the mixed gas is transmitted to an ion cracking device by an ion transmission tube, and the complex ions containing metal elements or cluster ions containing metal elements in the mixed gas collide and crack with the carrier gas to generate metal ions (highly active and easy to identify), and the metal ions react with non-polar compounds to obtain complex ions, thereby realizing soft ionization of non-polar compounds.

In addition, although the EI source can ionize non-polar compounds (such as alkanes), the EI source is ionized by high-energy electron bombardment of the gas molecules to be measured. Due to the high electron energy (generally 70eV), the fragmentation of the gas molecules to be measured is accompanied in this process, so there are many fragment ion peaks on the mass spectrum, which is not conducive to spectrum analysis. The present embodiment uses metal ions to react with the gaseous sample to be measured, mainly based on ion-molecule reaction to ionize the sample, which belongs to the soft ionization process in this process, generally does not cause the fragmentation of ions, and the generated product ions can ensure a complete molecular structure, and the peak composition is also simpler. Although the embodiment of the present invention accelerates the metal element-containing complex ions or the metal element-containing cluster ions to produce metal ions, the energy can also reach about 100eV, but these energies have been lost in large quantities in the process of metal ions produced by the collision of the metal element-containing complex ions or the metal element-containing cluster ions with the carrier gas molecules, so the kinetic energy of the metal ions finally produced is already low, and they will not cause the structural fragmentation of gas molecules when the ion-molecule reaction occurs in the collision with the gas to be measured.

In some embodiments, the ion source is an ESI source, an APCI source, a glow discharge source, or a photoionization source.

The embodiment of the present invention further provides a mass spectrometer, which includes the gas phase ion reaction device as described above in the embodiment of the present invention, and further includes:

A mass analyzer connected to the ion fragmentation device;

A detector is connected to the mass analyzer.

That is, as shown in FIG. 2 , the mass spectrometer includes an ion source 1 , a sealed chamber 2 , an ion transfer tube 3 , an ion fragmentation device 4 , a mass analyzer 5 and a detector 6 which are connected in sequence.

Wherein, the ion source can be an ESI source, an APCI source, a glow discharge source or a photoionization source. The ion fragmentation device includes an ion lens assembly, and the present invention does not limit its specific structure. In this embodiment, components such as the ion source, the ion transfer tube, the ion fragmentation device, the mass analyzer and the detector can be obtained through commercial channels. Wherein, the ion transfer tube, the mass analyzer and the detector can specifically be built-in accessories on the Q-Exactive mass spectrometer of Thermo Fisher Scientific, and the ion fragmentation device can be composed of an ion lens.

The EI source is generally only configured in GC-MS for the analysis of non-polar compounds; the ESI source configured in the conventional LC-MS type mass spectrometer is used for the analysis of highly polar compounds. The mass spectrometer provided in the embodiment of the present invention can not only be used to detect non-polar compounds (by reacting with metal ions in the cracking device to form composite ions, thereby realizing the detection of non-polar compounds), but also can be used to detect polar compounds (the EIS source in the mass spectrometer itself can ionize polar compounds to realize the detection of polar compounds), expanding the application range of the ESI source and avoiding the switching of the ion source and even the mass spectrometer. At the same time, the embodiment of the present invention realizes the two processes of metal ion generation and gas phase ion-molecule reaction in the same device (ion cracking device), shortening the intermediate links to reduce interference and ion loss.

The embodiment of the present invention further provides a method for detecting non-polar compounds, wherein the mass spectrometer as described above in the embodiment of the present invention is used, and the method for detecting non-polar compounds comprises the steps of:

S11, providing a metal compound solution and a non-polar compound to be detected, wherein the non-polar compound to be detected is a first non-polar gaseous compound;

S12, passing the metal compound solution through an ion source to generate complex ions containing metal elements or cluster ions containing metal elements;

S13, introducing the metal element-containing complex ions or metal element-containing cluster ions into the sealed cavity, and then introducing the non-polar first gaseous compound and the carrier gas into the sealed cavity from the inlet of the sample to be tested to form a mixed gas;

S14, using an ion transfer tube (loaded with a DC voltage) to transfer the mixed gas to an ion cracking device (loaded with a DC voltage), the metal element-containing complex ions or metal element-containing cluster ions in the mixed gas collide and crack with the carrier gas to generate metal ions, and the metal ions react with the non-polar first gaseous compound to obtain composite ions;

S15, detecting the composite ions by means of a mass analyzer and a detector, and identifying the non-polar compound to be detected by means of the detection results.

The embodiment of the present invention further provides a method for detecting non-polar compounds, wherein the mass spectrometer as described above in the embodiment of the present invention is used, and the method for detecting non-polar compounds comprises the steps of:

S21, providing a metal compound solution and a non-polar compound to be detected, wherein the non-polar compound to be detected is a non-polar volatile liquid compound, and the non-polar volatile liquid compound volatilizes to generate a non-polar second gaseous compound;

S22, passing the metal compound solution through an ion source to generate complex ions containing metal elements or cluster ions containing metal elements;

S23, introducing the metal element-containing complex ions or metal element-containing cluster ions into the sealed cavity, then placing the non-polar volatile liquid compound at the inlet of the sample to be tested, and allowing the non-polar second gaseous compound and the carrier generated by the volatilization of the non-polar volatile liquid compound to enter the sealed cavity from the inlet of the sample to be tested to form a mixed gas;

S24, using an ion transfer tube (loaded with a DC voltage) to transfer the mixed gas to an ion cracking device (loaded with a DC voltage), the metal element-containing complex ions or metal element-containing cluster ions in the mixed gas collide and crack with the carrier gas to generate metal ions, and the metal ions react with the non-polar second gaseous compound to obtain composite ions;

S25, detecting the composite ions by means of a mass analyzer and a detector, and identifying the non-polar compound to be detected by means of the detection results.

In this embodiment, metal ions are generated by the ion transfer tube and the ion fragmentation device in the mass spectrometer, and the metal ions react with the substance to be tested to generate composite ions (containing metal elements, which facilitates the analysis of the mass spectrum and the understanding of the gas phase reaction), thereby realizing the detection of non-polar compounds (non-polar gaseous compounds and non-polar volatile liquid compounds).

In the embodiment of the present invention, a metal compound solution is used as a raw material, a cracking device is used to generate metal ions, and the metal ions have special reactivity, and can selectively react with some gaseous compounds to generate new composite ions, and some non-polar compounds (such as alkanes) that are difficult to ionize are analyzed in this way. In addition, the formed composite ions contain metal ions, and the special isotopic distribution of metal ions can be used to identify the generated composite ions, reducing the difficulty of spectrum analysis. Further, metal ions are the final products of cracking, and even if the energy is increased, they will not be further cracked, that is, the product ions generated by cracking are mainly metal ions. If other organic molecules are selected as raw materials, the degree of fragmentation during cracking will increase with the increase of cracking energy, and some rearrangement reactions will also occur, etc. It is difficult to produce stable and controllable fragment ions, so as to utilize the control and identification of subsequent ion-molecule reactions.

Since metal ions in the solution often exist in the form of complexes or clusters, it is impossible to directly use a plasma source such as an ESI source to generate pure metal ions. Specifically, a _PdCl2 solution is self-attracted through a spray tube, and a voltage (2 to 5 KV) is applied to the spray tube to ionize the solution. When the mass spectrum at this time is observed (as shown in FIG3 ), no Pd ion peak is seen, indicating that direct ionization of the _PdCl2 solution cannot form high-intensity Pd ions, and mainly generates some impurity interfering ions. This shows that after ESI, the Pd ions are "hidden" in some complexes or ion clusters. Therefore, metal ions need to be generated through cleavage, and the metal ions are released from the complexes or ion clusters through the cleavage process.

In some embodiments, the gas pressure range of the ion cracking device is 10 ^-1 to 10 ³ Pa. In the past, most technologies carried out gas-phase ion-molecule reactions in the atmosphere or high vacuum environment. Active reactant ions are not easy to generate in the atmosphere, and the reaction efficiency is low in the high vacuum environment. It is difficult to balance the generation of reactant ions and the reaction efficiency. In this embodiment, low-pressure reaction conditions are constructed to solve the above problems.

In some embodiments, the voltage difference between the ion transfer tube and the ion fragmentation device is set to -200 to 200V, and the voltage difference between the ion transfer tube and the ion fragmentation device is not 0 (for example, it can be -200V, -150V, -100V, -50V, -30V, -20V, -10V, -5V, 5V, 10V, 20V, 30V, 50V, 100V, 150V, 200V, etc.). This voltage is used for ion fragmentation. Specifically, this voltage difference can be used to accelerate the introduced ions or charged clusters, and collide and fragment with the carrier gas molecules in the ion fragmentation device to produce metal ions; at the same time, it also gives the metal ions finally produced a certain kinetic energy (this energy can be adjusted to regulate the reaction process), which can better induce gas-phase ion-molecule reactions.

In some embodiments, the carrier is an inert gas. The inert gas does not participate in the reaction.

In some embodiments, the inert gas includes one of nitrogen and argon.

In some embodiments, the metal compound solution may be _an inorganic metal salt solution such as _PdCl2 solution, CuCl solution, _AuCl3 solution, _AgNO3 solution, etc. The metal compound solution may also be an organic metal compound solution such as Fe( _C5H5 ) ₂ solution, ( _CH3 ) _2Hg solution, etc., but is not limited thereto.

The following describes it in detail through specific embodiments.

Example 1

The present embodiment provides a mass spectrometer, as shown in FIG2 , comprising an ion source 1 (specifically an ESI source), a sealed chamber 2, an ion transfer tube 3, an ion fragmentation device (composed of an ion lens) 4, a mass analyzer 5 and a detector 6 connected in sequence; the sealed chamber 2 is provided with a sample inlet 21 to be tested.

_PdCl2 solution was introduced into the ESI source, nitrogen was introduced into the sealed cavity from the inlet of the sample to be tested, the voltage difference between the ion transfer tube and the ion fragmentation device was set to 50V, and the gas pressure of the ion fragmentation device was set to 30Pa, to form high-intensity Pd ions (Pd ⁺ ). By observing the mass spectrum at this time (as shown in FIG4), it can be found that the spectrum interference can be greatly reduced by the in-source fragmentation method, and high-intensity Pd ⁺ can be formed;

Next, liquid n-heptane (a non-polar liquid compound that is difficult to ionize and cannot be directly analyzed by conventional ESI source mass spectrometry) was placed open at the inlet of the sample to be tested. The volatilized gaseous n-heptane and nitrogen entered the sealed ion source chamber, and finally the addition ion peak of the metal and heptane - [Pd+C ₇ H ₁₆ ] ⁺ was detected, as shown in Figure 5.

In summary, the present invention provides a gas-phase ion reaction device, a mass spectrometer and a method for detecting non-polar compounds. The gas-phase ion reaction device provided by the present invention can achieve specific ionization of non-polar compounds that are difficult to ionize. The gas-phase ion reaction device can produce metal ions with strong reactivity through collision cracking, and the metal ions with strong reactivity can undergo gas-phase ion-molecule reaction with non-polar gaseous compounds in the ion cracking device to generate new composite ions, thereby achieving soft ionization of non-polar gaseous compounds. The composite ions can subsequently be detected by mass spectrometry.

It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims (10)

1. The gas-phase ion reaction device is characterized by comprising an ion source, a sealed cavity, an ion transmission pipe and an ion cracking device which are connected in sequence;

And a sample inlet to be tested is arranged on the sealing cavity.

2. The gas phase ion reaction apparatus of claim 1, wherein the ion source is an electrospray ion source, an atmospheric pressure chemical ionization source, a glow discharge source, or a photoionization source.

3. A mass spectrometer comprising the gas phase ion reaction device of any one of claims 1-2, further comprising:

The mass analyzer is connected with the ion cracking device;

And the detector is connected with the mass analyzer.

4. A method for detecting a nonpolar compound using the mass spectrometer of claim 3, said method comprising the steps of:

providing a metal compound solution and a nonpolar compound to be detected, wherein the nonpolar compound to be detected is a nonpolar first gaseous compound;

passing the metal compound solution through an ion source to produce complex ions containing metal elements or cluster ions containing metal elements;

Introducing the complex ions containing metal elements or cluster ions containing metal elements into a sealed cavity, and then introducing the nonpolar first gaseous compound and carrier gas into the sealed cavity from a sample inlet to be tested to form a mixed gas;

Transmitting the mixed gas into an ion cracking device by utilizing an ion transmission pipe, wherein compound ions containing metal elements or cluster ions containing metal elements in the mixed gas collide with carrier gas for cracking to generate metal ions, and the metal ions react with nonpolar first gaseous compounds to obtain compound ions;

and detecting the composite ions by a mass analyzer and a detector, and identifying the nonpolar compound to be detected by the detection result.

5. A method for detecting a nonpolar compound using the mass spectrometer of claim 3, said method comprising the steps of:

Providing a metal compound solution and a nonpolar compound to be detected, wherein the nonpolar compound to be detected is a nonpolar volatile liquid compound, and the nonpolar volatile liquid compound volatilizes to generate a nonpolar second gaseous compound;

passing the metal compound solution through an ion source to produce complex ions containing metal elements or cluster ions containing metal elements;

Introducing the complex ions containing metal elements or cluster ions containing metal elements into a sealed cavity, then placing the nonpolar volatile liquid compound at an inlet of a sample to be tested, and enabling nonpolar second gaseous compound generated by volatilization of the nonpolar volatile liquid compound and a carrier to enter the sealed cavity from the inlet of the sample to be tested to form a mixed gas;

Transmitting the mixed gas into an ion cracking device by utilizing an ion transmission pipe, wherein compound ions containing metal elements or cluster ions containing metal elements in the mixed gas collide with carrier gas for cracking to generate metal ions, and the metal ions react with nonpolar second gaseous compounds to obtain compound ions;

and detecting the composite ions by a mass analyzer and a detector, and identifying the nonpolar compound to be detected by the detection result.

6. The method according to claim 4 or 5, wherein the gas pressure of the ion cracker is set to a range of 10 ^-1～10³ Pa.

7. The method according to claim 4 or 5, wherein a voltage difference between the ion transport tube and the ion splitting device is set to-200V to 200V, and a voltage difference between the ion transport tube and the ion splitting device is not set to 0.

8. The method according to claim 4 or 5, wherein the carrier is an inert gas.

9. The method of claim 8, wherein the inert gas comprises one of nitrogen and argon.

10. The method according to claim 4 or 5, wherein the metal compound solution comprises an inorganic metal salt solution or an organic metal compound solution.