JPH0961401A - Mass analyzing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the mass analysis of an ultramicro-amt. of a sample to be analyzed. SOLUTION: Ions for ionizing a sample (reagent 102) are caught by a three- dimensional mass analyser 101 and a sample 103 to be analyzed is introduced thereinto in a pulse like manner and ionized by the charge transfer accompanied by collision. The capture condition of ions 104 is relaxed to discharge the ions from the capture region and the ions are detected by a detection meter 105 to obtain a mass spectrum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mass-analyzing an extremely small amount of a sample to be analyzed with a three-dimensional mass spectrometer.

[0002]

2. Description of the Related Art Conventionally, a method using a quadrupole mass spectrometer has been the mainstream as a mass spectrometry method. In this method, a neutral sample was ionized mainly by electron impact (or light irradiation), the quadrupole electric field was swept, and the ions that passed under certain conditions were detected. Since it is a transmission type, in this method, the history of initial ionization is directly reflected in the fragment pattern, signal intensity, etc., which makes accurate analysis difficult, and it is necessary to continue introducing a large amount of sample to be analyzed until the analysis is completed. Yes, it is practically impossible to analyze a very small amount of sample.

In recent years, a mass spectrometry method using a three-dimensional mass spectrometer (ion trap mass spectrometer) has been in the limelight. This method uses DC and RF voltages (U and Vcosω
t) is applied to the three-dimensional electrode to simultaneously trap ions within the total specific charge mass range of interest in the electric field created by the electrode. These ions are generated in the quadrupole field or introduced in this region by any of various known techniques, such as electron bombardment. After a certain accumulation time, the DC voltage U, the RF voltage V, and the RF frequency ω are changed in combination or independently to continuously destabilize the trapped ions of continuous specific charge mass. When the trapping of each ion becomes unstable, these ions have a trajectory that crosses the boundary of the electric field. These ions are ejected through holes provided in the electrodes and strike a detector such as an electron multiplier. The detected ion current signal strength as a function of time corresponds to the mass spectrum of the trapped ions.

On the other hand, chemical ionization (CI) mass spectrometry [J. Amer. Chem. Soc.] 88,2621 (19)
66)], the sample, that is, the sample to be analyzed is ionized not by electron collision, photon collision, electric field ionization, etc., but by gas phase ion-molecule reaction.

A chemical ionization (CI) mass spectrometry method using a three-dimensional mass spectrometer is described in JP-A-64-86438. In this method, an electrically neutral reagent sample and a sample to be analyzed are simultaneously introduced into the analyzer, and the reagent sample is ionized by electron impact or the like and captured. Then, the ions of the sample to be analyzed generated by the chemical ionization due to the collision with the reagent sample are also captured at the same time. After capturing and reacting for a desired time, a mass spectrum is obtained and analyzed by the same method as the above method.

A method for obtaining a chemical ionization mass spectrum by using the ion cyclotron resonance (ICR) method has been demonstrated [Analytical Chemistry (Anal. Che.
m. 53, 428 (1981)]. Since the sample exists at a concentration of 1% of the ionizing ions, the sample is also considerably ionized by electron impact, which is an obstacle to mass spectrometry.

[0007]

When operating a three-dimensional mass spectrometer with various chromatographies, the concentration of sample introduced into the capture region for ionization and analysis is variable. Further, generally, the reaction rate of the sample compound also varies. Therefore, in the case of an extremely small amount or / and a slow chemical reaction, it is often difficult to detect the product ions because the product ions are not sufficiently generated.

An object of the present invention is to provide a method for improving the sensitivity of a three-dimensional mass spectrometer.

[0009]

[Means for Solving the Problems] The above object is to capture the ionizing ions of the sample to be analyzed in a three-dimensional mass spectrometer, and to collect a very small amount of electrically neutral sample to be analyzed in a pulsed manner. The sample is ionized by charge transfer due to introduction and collision, and the optimal number of sample ions is generated by adjusting the ion trapping time. The trapping conditions for this ion are relaxed and ejected from the trapping site to detect the above ion. This is solved by obtaining a mass spectrum by

[0010]

The operation of the present invention will be described with reference to FIG. here,
Ions used for ionization of the sample to be analyzed will be referred to as reagent ions. First, the reagent gas is ionized in a sufficient amount using a method such as electron impact or light impact. This reagent ion generation may be performed in a three-dimensional mass spectrometer,
It may be performed outside and then introduced inside. And
As described in the prior art, the electric field is appropriately adjusted to select and capture the reagent ions necessary for chemical ionization (FIG. 1a). The reactivity of the reagent ion greatly differs depending on the partner molecule, and it may not react with a certain sample molecule at all or may react very strongly. Therefore, by selecting an appropriate reagent gas, high specificity for detecting a specific component can be obtained.

Next, while the supply of new reagent ions is stopped and the sample is stably captured, an electrically neutral sample to be analyzed is introduced into the capture region in a pulsed manner (FIG. 1b). The reason why the supply of new reagent ions is stopped and the sample is introduced in a pulsed manner is to reduce unnecessary scattering given to the collision region, reduce the number of ions, and do not affect the reaction path. , Is a feature of the present invention.

Since the kinetic energy of the trapped ions is about 20 eV at most, fragmentation of the sample is suppressed by chemical ionization as compared with electron impact ionization. The number of sample ions generated is determined by parameters such as the number of trapped reagent ions, the number of sample molecules, and the reaction time. In the present invention, in order to efficiently ionize an extremely small amount of sample, reagent ions are trapped in advance and the number of collisions is increased. Moreover, since the generated sample ions are also trapped (FIG. 1c), the point where the number of sample molecules is small can be covered, and the signal-to-noise ratio can be improved. Therefore, in this case, it is desirable that the condition that ions having a relatively wide range of specific charge mass can be trapped.

After sufficient sample ions are generated, the DC voltage U, the RF voltage V, and the RF frequency ω are changed in combination or independently to make the trapped ions of continuous specific charge mass continuously unstable. When the trapping of each ion becomes unstable, these ions have a trajectory that crosses the boundary of the electric field.

These ions are ejected through holes provided in the electrodes (FIG. 1d) and strike a detector such as an electron multiplier. The detected ion current signal strength as a function of time corresponds to the mass spectrum of the trapped ions.
When the sample has a sufficient amount, the signal-to-noise ratio can be improved by performing the above process a plurality of times.

The biggest difference between the method disclosed in JP-A-64-86438, which is a known example, and the present invention lies in the method of supplying reagent molecules (ions) and sample molecules. In a known example, the reagent molecule and the sample molecule are simultaneously introduced into the mass spectrometer and simultaneously exposed to electron impact, so that a large number of fragment ions are generated during the ionization of the sample molecule, and the reaction itself becomes complicated. Becomes complicated. In the present invention, since the reagent ions are selectively captured in advance, the reaction system is simplified, and since the sample is introduced in a pulsed manner after the reagent ions are captured, there is no disturbance due to electron impact. These ideas are not easily inferred from conventional examples.

[0016]

EXAMPLE An example of the present invention will be described with reference to FIG. H + is used as a reagent ion and p-benzoquinone is used as a sample molecule. The electrode of the three-dimensional mass spectrometer 201 has a hole for introducing a reagent, and a water vapor molecular beam is introduced through the molecular beam valve 202. Here, it is ionized in the analyzer by the electron impact of 50 eV emitted from the electron gun 203. At this time, H +, O +, OH +, H 2 O + and H ₃ is O + is produced to selectively capture only H + 206. The introduction of the molecular beam and the electron impact are stopped, and the vacuum degree is improved while H + is trapped for a while.

Next, the trapping conditions are gradually loosened so that ions having a mass number of about 130 can be trapped at the same time. Here, p-benzoquinone (molecular weight 1
08) is introduced as a pulsed molecular beam through the molecular beam valve 204. At this time, the buffer gas may be diluted with He. After this, the sample is sufficiently chemically ionized during a capture time of about 30 minutes, the generated ions 207 are sequentially ejected as described in the conventional technique, and detected by the secondary electron multiplier 205. At this time, as ions, ions of molecular weight 109 and 110 in which protons were added to H + and p-benzoquinone were detected.

Incidentally, when chemical bombardment is not used and electron bombardment is performed, various fragment ions are detected, and it is difficult to know that the original sample is p-benzoquinone.

On the contrary, even if it is not known what is contained in the sample, it can be inferred that p-benzoquinone is contained if the ion of mass number 109 is detected by this ionization. As for the sensitivity, about 100 molecules can be sufficiently detected.

[0020]

According to the present invention, mass analysis of an extremely small amount of sample to be analyzed can be achieved with high sensitivity, and it can greatly contribute to the development of the measurement field.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a mass spectrometry method of the present invention.

FIG. 2 is an explanatory diagram of an experimental device according to an embodiment of the present invention.

[Explanation of symbols]

101 ... Three-dimensional mass spectrometer, 102 ... Reagent ion, 10
3 ... Sample, 104 ... Product ion, 105 ... Detector, 20
1 ... Electrodes of three-dimensional mass spectrometer, 202 ... Molecular beam valve,
203 ... Electron gun, 204 ... Molecular beam valve, 205 ... Secondary electron multiplier, 206 ... Hydrogen ion, 207 ... Product ion.

Claims (2)

[Claims] 1. A step of capturing ions for ionization of a sample to be analyzed in a three-dimensional mass spectrometer, a step of introducing a trace amount of an electrically neutral sample to be analyzed in a pulsed manner,
The step of ionizing the sample by chemical ionization such as charge transfer due to collision, the step of generating an optimum number of sample ions by adjusting the ion trapping time, loosening the trapping condition of this ion, and ejecting it from the trapping site, A mass spectrometric method comprising the step of obtaining a mass spectrum by detection. 2. A mass spectrometric method for increasing the signal-to-noise ratio by repeating the analysis method of claim 1 a plurality of times to integrate signal intensities.