JPH04338B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mass spectrometer that can obtain stable high-resolution mass spectra even in high magnetic field regions.

A mass spectrometer ionizes a sample and guides it into an analysis field consisting of a homogeneous magnetic field.The analysis field spatially separates the sample ions according to their mass-to-charge ratio, and the ions arriving at that specific position are detected by a detector. It is detected as an electrical signal and a mass spectrum is obtained by sweeping the intensity of the analysis field. Figure 1 is an optical diagram of a conventionally used double-focus mass spectrometer, in which 1 is an ion source, 2 is an electric field for energy dispersion, 3 is an analytical magnetic field for mass dispersion, and 4
indicates an ion detector. An α slit 5 is installed in front of the electric field 2, and a β slit 6 is installed after the electric field, which limits the opening angle of the ion flow toward the electric field and reduces the energy of the ion flow from the electric field toward the analytical magnetic field 3. Spread is limited. If the widths of both slits are made smaller, the resolution will be increased, but if the slit widths are made too small, the sensitivity will be lowered, so the slit width is determined by taking both of these into consideration. Ions from the ion source pass through a slit 5 and are separated according to their energy (velocity) by an electric field 2, and those that pass through a slit 6 enter an analysis magnetic field 3 and are separated according to their mass-to-charge ratio. , only those ions that take that specific trajectory are detected by the detector 4. Therefore, by sweeping the strength of the analysis magnetic field 3, the spatially separated ions will enter the detector one after another, and by displaying or recording the output of the detector, the mass spectrum can be obtained. In other words, we can obtain .

In such an apparatus, the most important parameter in ion optics that determines the convergence conditions of the ion beam on the detector 4 is the magnetic field distribution on the optical axis in the analytical magnetic field 3 including the edge field. The magnetic field distribution function indicating this distribution is usually treated as a constant value, partly because conventional devices are not used at very high magnetic field strengths.

However, as analysis of up to a high mass number has recently become required, the strength of the analytical magnetic field has inevitably increased, and the material of the pole piece of the magnet that forms the analytical magnetic field is in the quasi-saturation region or in a magnetic field higher than that. Now used under strength. The magnetic field distribution in this high field is inevitably worse than in the low field region,
The double convergence condition is no longer satisfied, resulting in a decrease in resolution and sensitivity.

In this way, when the magnetic field strength changes significantly,
Analyzing magnetic field 3 in the plane indicated by X and Y in Figure 1
A method has been used in the laboratory to mechanically adjust the position of the ion beam to satisfy the ion focusing conditions, but the operability is extremely poor and it is impossible to obtain a high-quality mass spectrum over the entire region. Yes, it is not put into practical use.

In view of the above points, it is an object of the present invention to provide an apparatus that can always guarantee high resolution and sensitivity even when the analytical magnetic field is greatly changed from the low magnetic field region to the saturated region.

A mass spectrometer based on the present invention includes an ion source for ionizing a sample, an analysis magnetic field for separating the sample ions according to their mass-to-charge ratio, and a magnetic field intensity sweep for sweeping the magnetic field strength of the analysis magnetic field. and an ion detector for detecting the analyzed ions as an electrical signal,
A quadrupole lens for directional focusing of the ion flow is disposed between the ion source and the analytical magnetic field or between the analytical magnetic field and the ion detector, and the strength of the quadrupole lens is adjusted according to a predetermined function. and a comparison means for detecting that the magnetic field strength swept by the magnetic field strength sweeping means is equal to or higher than a reference value, and the lens strength is determined based on the output signal of the comparison means. By controlling the sweeping means, when the magnetic field strength swept by the magnetic field strength sweeping means is equal to or higher than a reference value, the strength of the quadrupole lens is changed according to a predetermined function according to the magnetic field strength. It is characterized by this.

The present invention will be explained in detail below based on the drawings.

Figure 2 shows the magnetic field distribution of analysis magnetic field 3.
In the figure, 3a and 3b indicate pole pieces, and 3c indicates an effective end face. Also, the horizontal axis is the X-axis, and the vertical axis is the magnetic field strength at each part relative to the magnetic field strength Bo at the center of the analysis magnetic field.
Shows the ratio of Bx. Curve a is the distribution of low magnetic field,
b is the distribution in the pure saturation region, and c is the distribution in the saturation region.The distribution does not change in a low magnetic field, but in the pure saturation region b, it changes rapidly and greatly. Therefore, if we detect this quasi-saturation region and change the ion beam convergence conditions by some means when the magnetic field strength exceeds this region, we should be able to secure sufficiently high resolution and sensitivity even in this high magnetic field region. It is. The present invention focuses on this point, and uses a quadrupole lens, and when the strength of the analysis magnetic field exceeds a certain value, a correction voltage is applied to the quadrupole lens according to the strength of the magnetic field. This is what I did.

3 to 5 are diagrams for explaining one embodiment of the present invention, in which FIG. 3 is an ion optical diagram, FIG. 4 is a block diagram of an electric circuit, and FIG. 5 is an operation explanatory diagram. In FIG. 3, the same reference numerals as in FIG. 1 indicate the same components. Two quadrupole lenses 7 and 8 are used in this example. The quadrupole lens 7 is located before the electric field 2, that is, between the ion source 1 and the α-slit 5, and is used for directional focusing. Also, a quadrupole lens 8 is placed between the electric field 2 and the analytical magnetic field 3 and is used for energy focusing. Among the quadrupole lenses, the energy focusing lens 8 is not necessarily necessary, and may be used when extremely high resolution is required.
A correction signal is supplied to the quadrupole lenses 7 and 8 from a circuit shown in FIG. In FIG. 4, 3a,
3b is a pole piece of a magnet that creates an analysis magnetic field, and is excited by electromagnetic coils 9a and 9b. 10 is a magnetic field detector such as a Hall element inserted between the pole pieces, and its output is introduced into a comparator 12 via an amplifier 11. A reference voltage is supplied to the comparator from a reference power supply 13,
When the output of the Hall element exceeds the reference signal, a detection signal is sent to the correction function generators 14a and 14b. The function generator converts the signal from the comparator into a preset function. The converted signals are sent to adders 15a, 15b, and DC power supplies 16a, 1
6b and applied to each of the quadrupole lenses 7 and 8. the function generator 14a,
14b are set to generate different functions, respectively, so that correction of the convergence conditions by the lenses 7 and 8 is appropriate.

FIG. 5 is a diagram for explaining the operation of FIG. 4, and FIG.
The voltage VQ applied to is shown on the time axis.
In figure a, V ₁ is a reference voltage, which is the voltage at which the quasi-saturation region is reached. Then, the magnetic field is swept, and when the output of the Hall element reaches V ₁ (time t ₁ ), the comparator 1
2 converts the output signal from the Hall element into a function generator 1
4a and 14b, and as shown from _t1 to _t2 of _VQ1 and _VQ2 in Fig. b, a voltage is generated that changes depending on the output of the Hall element (therefore, the strength of the analytical magnetic field). The signals are sent to adders 15a, 15b,
It is added to the constant voltage from the power supplies 16a and 16b. As a result, the lens strengths of the quadrupole lenses 7 and 8 are corrected, and the ion beam is always focused on the detector 4, regardless of changes in the magnetic field distribution at the end face of the pole piece as shown in FIG. It becomes like this.

Although the curve of the signal passed through the function generators 14a and 14b differs depending on the device, it is often approximately a squared curve or approximated thereto, and an error of about 10% can be tolerated in the correction. Therefore, when applied to an actual device, it is advantageous to use a circuit that performs polygonal line approximation using several to ten points, since the configuration is simple and economically advantageous.

With the configuration detailed above, the convergence conditions of the ion beam on the detector hardly change even if the analysis magnetic field is strongly excited to the region where the pole piece is quasi-saturated or saturated, resulting in high resolution. , it becomes possible to analyze high-mass samples while maintaining high sensitivity.

Note that the above is an example of the present invention, and various changes are possible when implementing the present invention. For example, even if a quadrupole lens is placed between the analysis magnetic field and the ion detector, the same correction can be made. Further, although the above description has been made using a double convergence mass spectrometer as an example, the present invention can be similarly applied to a single convergence mass spectrometer that does not have an electric field. in this case,
It is sufficient to use only the quadrupole lens 7 for directional focusing. Also, for correction of directional convergence by lens 7,
Since the energy convergence correction by the lens 8 is one order of magnitude or more smaller, it is not necessary to use the quadrupole lens for energy convergence even in a double convergence mass spectrometer depending on the performance of the apparatus. Further, the magnetic field strength detector, function generator, etc. are not limited to those shown in the drawings, and may be of any type as long as they are suitable for the purpose.

[Brief explanation of drawings]

FIG. 1 is an ion optical diagram of a conventional double focus mass spectrometer, FIG. 2 is a diagram for explaining the principle of the present invention, and FIG. 3 is an ion optical diagram of an embodiment of the present invention.
FIG. 4 is a block circuit diagram showing the main part of an embodiment of the present invention, and FIG. 5 is an explanatory diagram of the operation of FIG. 4. 1: ion source, 2: electric field for energy dispersion,
3: Analysis magnetic field, 4: Ion detector, 7: Quadrupole lens for direction focusing, 8: Quadrupole lens for energy focusing, 10: Magnetic field strength detector, 12: Comparator, 1
3: Reference power supply, 14a, 14b: Function generation circuit,
15a, 15b: Adder, 16a, 16b: DC power supply.

Claims (1)

[Scope of Claims] 1. An ion source for ionizing a sample, an analysis magnetic field for separating the sample ions according to their mass-to-charge ratio, and a magnetic field intensity sweeping means for sweeping the magnetic field strength of the analysis magnetic field. , an ion detector for detecting the analyzed ions as electrical signals, the ion flow direction focusing between the ion source and the analytical magnetic field or between the analytical magnetic field and the ion detector. a lens strength sweeping means for sweeping the strength of the quadrupole lens according to a predetermined function; and a magnetic field strength swept by the magnetic field strength sweeping means is equal to or higher than a reference value. By controlling the lens strength sweeping means based on the output signal of the comparing means, the magnetic field strength swept by the magnetic field strength sweeping means is greater than or equal to the reference value. A mass spectrometer characterized in that the intensity of the quadrupole lens is changed according to a predetermined function in accordance with the magnetic field intensity. 2. The mass spectrometer according to claim 1, wherein when an electric field for ion energy dispersion is provided before the analysis magnetic field, the quadrupole lens is placed between the electric field and the ion source. 3. An ion source for ionizing a sample, an analytical magnetic field for separating the sample ions according to their mass-to-charge ratio, an electric field for energy dispersion placed between the analytical magnetic field and the ion source, and An apparatus comprising an ion detector for detecting ions analyzed in a magnetic field as electrical signals, wherein a quadrupole lens for directional focusing of the ion flow is disposed between the ion source and the electric field, and the A lens intensity sweeping means that disposes a quadrupole lens for energy focusing between the electric field and the analysis magnetic field, and sweeps the intensity of each quadrupole lens according to a predetermined function;
Comparing means for detecting that the magnetic field strength swept by the magnetic field strength sweeping means is equal to or higher than a reference value, and controlling the lens strength sweeping means based on an output signal of the comparing means. Mass spectrometry characterized in that, when the magnetic field strength swept by the magnetic field strength sweeping means is equal to or higher than a reference value, the strength of both quadrupole lenses is changed according to a predetermined function in accordance with the magnetic field strength. Device.