JP3979769B2 - Atmospheric pressure chemical ionization ion source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an atmospheric pressure chemical ionization ion source used in mass spectrometry, and more particularly to an atmospheric pressure chemical ionization ion source that can efficiently dry (desolvate) atomized sample droplets.
[0002]
[Prior art]
In a chromatograph / mass spectrometer in which a chromatograph and a mass spectrometer are combined, an interface that ionizes components separated in the chromatograph and supplies the components to the mass analyzer is required. As an interface, an atmospheric pressure ionization ion source such as an electrospray ion source or an atmospheric pressure chemical ionization ion source is used in a liquid chromatograph / mass spectrometer.
[0003]
In an electrospray ion source, a liquid sample is sent to the tip of a thin nozzle, and a high voltage is applied to the tip of the nozzle. Thereby, a strong unequal electric field is formed at the tip of the nozzle, and the liquid sample is sprayed as a charged droplet by this strong electric field, and further, the droplet breaks up due to the coulomb repulsion of ions in the droplet, Ionization is performed. On the other hand, in an atmospheric pressure chemical ionization ion source, a liquid sample is forcibly sprayed by a gas flow in a nebulizer (atomizer), and the droplets are dried (desolvation) by heating, followed by corona discharge. The sample is ionized (chemical ionization) by colliding with the generated buffer ions.
[0004]
The electrospray ion source is a suitable interface for high polarity ions, while the atmospheric pressure chemical ionization ion source is a suitable interface for medium to low polarity ions, so that they are in a complementary relationship. The compounds targeted by liquid chromatographs / mass spectrometers are so diverse that one uses an electrospray ion source and the other uses an atmospheric pressure chemical ionization ion source. It is necessary to use both properly.
[0005]
[Problems to be solved by the invention]
By the way, when using an atmospheric pressure chemical ionization ion source, it is important to disperse a liquid sample sent from a liquid chromatograph device or the like as droplets in the atmosphere, and then remove the solvent molecules contained in the droplets. How to remove efficiently to achieve ionization of the sample.
[0006]
FIG. 1 shows a conventional atmospheric pressure chemical ionization ion source. In the figure, 1 is a cylindrical heater that also serves as an atomizing chamber. An atomizing nozzle 2 in which the cylindrical heater 1 is preheated to 400 to 500 ° C., and a mobile phase including a sample from a liquid chromatograph apparatus (not shown) is disposed substantially concentrically and coaxially with respect to the heater hole. From the tip of the mist, it is sent out vigorously with atomizing gas such as nitrogen gas and atomized. As the atomized sample droplet (mobile phase) passes through the heated heater hole, it receives radiant heat from the inner wall of the cylindrical heater 1 and is gradually dried (desolvated). Then, it rides on the flow of the atomized gas and is pushed downstream, and is carried to the vicinity of the mass spectrometer without directly colliding with the inner wall surface of the cylindrical heater 1.
[0007]
The axis of the cylindrical heater 1 and the axis connecting the needle electrode 3 and the sampling orifice 5 provided on the counter electrode 4 of the mass spectrometer are orthogonal to each other by 90 °. A potential difference of about 5 kV is provided between the needle electrode 3 and the counter electrode 4, and corona discharge is generated between the two electrodes. The gas molecules excited by the corona discharge act as buffer ions, and the sample is ionized (chemical ionization) when colliding with the sample droplet dried (desolventized) by the cylindrical heater 1. The generated sample ions are mass analyzed from the sampling orifice 5 by the action of an electric field generated between the needle electrode 3 and the counter electrode 4 and the vacuum differential pressure between the vacuum chamber of the mass spectrometer and the outside. It is sucked into the vacuum chamber of the meter.
[0008]
In such a configuration, the problem of the conventional atmospheric pressure chemical ionization ion source is that the radiant heat from the cylindrical heater 1 is used in order to dry (desolvate) the sample droplet ejected from the atomizing nozzle 2 well. A sufficiently long pass is necessary to receive, and in the short pass the atomized droplets could not be completely dried (desolventization). As a result, there has been a problem that the sample droplet is introduced into the mass spectrometer with insufficient drying (desolvation) of the droplet, and the ion beam is difficult to stabilize in the mass spectrometer.
[0009]
Moreover, if the path | pass for drying (desolvation) is taken long, the length of the cylindrical heater 1 will become long, and there existed a problem that an atmospheric pressure chemical ionization ion source will enlarge. In addition, when the path is long, there is a problem that the sample component diffuses and the sensitivity is lowered, and the possibility of thermal decomposition of the sample component is increased.
[0010]
Furthermore, a steady flow of gas can be made inside the heater hole in the direction of the outlet of the heater hole, and background components of the outside world are drawn into the heater hole from the gap between the cylindrical heater 1 and the atomizing nozzle 2. There is also a problem that background peaks are likely to appear on the mass spectrum.
[0011]
In view of the above-described points, an object of the present invention is an atmospheric pressure chemical ionization ion source that can efficiently dry (desolvate) atomized sample droplets without taking a long path of the cylindrical heater 1. Is to provide.
[0012]
[Means for Solving the Problems]
In order to achieve this object, an atmospheric pressure chemical ionization ion source according to the present invention includes an atomization nozzle for atomizing a liquid sample in a cylindrical heater having a uniform inner diameter , and the atomization. against fog droplets of the liquid sample to be ejected from the tip of the nozzle, spraying the outlet of the drying gas which opens to one side of the atomizing nozzle tip near the drying gas in the vertical direction, and fog droplets dry gas The feature is that they collided violently at a speed close to the speed of sound .
[0015]
The dry gas is preheated by a heating means.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of an atmospheric pressure chemical ionization ion source according to the present invention. In the figure, 1 is a cylindrical heater that also serves as an atomizing chamber. An atomizing nozzle 2 in which the cylindrical heater 1 is preheated to 400 to 500 ° C., and a mobile phase including a sample from a liquid chromatograph apparatus (not shown) is disposed substantially concentrically and coaxially with respect to the heater hole. From the tip of the mist, it is sent out vigorously with atomizing gas such as nitrogen gas and atomized. As the atomized sample droplet (mobile phase) passes through the heated heater hole, it receives radiant heat from the inner wall of the cylindrical heater 1 and is gradually dried (desolvated). Then, it rides on the flow of the atomized gas and is pushed downstream, and is carried to the vicinity of the mass spectrometer without directly colliding with the inner wall surface of the cylindrical heater 1.
[0017]
A dry gas nozzle 6 for supplying a dry gas such as nitrogen gas to the heater hole is opened on the inner wall of the cylindrical heater 1 in the vicinity of the atomizing nozzle 2. Then, a dry gas heated in advance by a heating means such as a heater is sprayed onto the atomized sample droplets from a direction substantially perpendicular to the ejection direction of the atomizing nozzle 2. As a result, the atomized gas near the speed of sound containing the sample droplet and the heated drying gas blown from the perpendicular direction collide with each other inside the heater hole, and the sample droplet is dried (desolventization). ) Goes on at once. In addition, since the inside of the heater hole is somewhat pressurized due to the introduction of the dry gas, the background component of the outside world is drawn into the heater hole from the gap between the cylindrical heater 1 and the atomizing nozzle 2, and the mass is The problem that a background peak appears on the spectrum hardly occurs.
[0018]
The axis of the cylindrical heater 1 and the axis connecting the needle electrode 3 and the sampling orifice 5 provided on the counter electrode 4 of the mass spectrometer are orthogonal to each other by 90 °. A potential difference of about 5 kV is provided between the needle electrode 3 and the counter electrode 4, and corona discharge is generated between the two electrodes. The gas molecules excited by the corona discharge act as buffer ions, and the sample is ionized (chemical ionization) when colliding with the sample droplet dried (desolventized) by the cylindrical heater 1. The generated sample ions are mass analyzed from the sampling orifice 5 by the action of an electric field generated between the needle electrode 3 and the counter electrode 4 and the vacuum differential pressure between the vacuum chamber of the mass spectrometer and the outside. It is sucked into the vacuum chamber of the meter.
[0019]
In the above-described embodiment, the blowing direction of the dry gas is set so as to be substantially perpendicular to the jetting direction of the atomizing nozzle 2, but this is not necessarily limited to the vertical direction. Moreover, in the said Example, although the position of the atomization nozzle 2 was being fixed with respect to the position of the dry gas nozzle 6, the position of the atomization nozzle 2 can be finely adjusted with respect to the position of the dry gas nozzle 6. There may be. Further, the dry gas nozzle 6 is not necessarily thin. Further, the direction of the atomizing nozzle 2 is not necessarily perpendicular to the sampling orifice 5. Moreover, the insertion port of the atomization nozzle 2 in the cylindrical heater 1 does not necessarily need to be in an open state as shown in FIG. 2, and may be closed as shown in FIG. Moreover, the inner surface shape of the cylindrical heater 1 does not necessarily need to be circular, for example, a polyhedron may be used, and further, a part may be cut off and opened.
[0020]
【The invention's effect】
As described above, in the atmospheric pressure chemical ionization ion source according to the present invention, the atomizing nozzle 2 for atomizing a liquid sample is disposed inside the cylindrical heater 1 which also serves as an atomization chamber, and the fog Since the heated dry gas is strongly blown from the dry gas nozzle 6 against the mist droplets of the liquid sample ejected from the tip of the atomizing nozzle 2, the atomized gas and the dry gas collide violently in the heater hole. Well, the efficiency of drying (desolvation) of the sample droplets is greatly improved, and even if the path of the cylindrical heater 1 is shortened to 1/3 or less of the conventional method, the sample droplets are uniformly dried (desolvation) ). In addition, since the drying (desolvation) efficiency is high, the temperature of the cylindrical heater can be set low, and the possibility of thermal decomposition of sample ions can be minimized. Further, since the path is shortened, the diffusion of the sample can be kept low, and the sample ions can be drawn into the mass spectrometer efficiently and with high sensitivity.
[Brief description of the drawings]
FIG. 1 shows a conventional atmospheric pressure chemical ionization ion source.
FIG. 2 is a diagram showing an embodiment of an atmospheric pressure chemical ionization ion source according to the present invention.
FIG. 3 is a diagram showing another embodiment of an atmospheric pressure chemical ionization ion source according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cylindrical heater, 2 ... Atomization nozzle, 3 ... Needle electrode, 4 ... Counter electrode, 5 ... Sampling orifice, 6 ... Dry gas nozzle.

Claims (2)

An atomizing nozzle for atomizing a liquid sample is disposed in a cylindrical heater having a uniform inner diameter , and atomization is performed on the droplets of the liquid sample ejected from the tip of the atomizing nozzle. Atmospheric pressure chemistry characterized by spraying dry gas vertically from a dry gas outlet opening on one side near the nozzle tip so that the mist drops violently collide with the dry gas at a speed close to the speed of sound. Ionized ion source. 2. The atmospheric pressure chemical ionization ion source according to claim 1, wherein the dry gas is preheated by a heating means.

Images