JPH11144674A - Plasma ion source mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily make high-reliability spectrometry even in an extremely low- concentration region by obtaining concentration based on the relation between the ion signal intensity of a target element and the ion storage time and the relation between the concentration of the aimed element and the storage time. SOLUTION: The relation between the ion storage time of a standard solution with certain concentration of an target element and signal intensity is obtained, the relation between the storage time and the concentration of the target element is obtained with the ion signal intensity fixed, and they are stored in an operation computer 8. For the quantitative spectrometry of an unknown sample 1, the sample 1 is introduced into a plasma ion source mass spectrometer 7, the storage time is measured until 10,000 counts are obtained, and the storage time is substituted into a relational expression obtained in advance to obtain concentration. When the sensitivity at the time of initial setting and the sensitivity at the time of quantification differ, the ion signal intensity of a sample with the same concentration as the concentration measured in advance at certain storage time is compared, or the storage time is compared until certain ion signal intensity is obtained. When they differ, the correction coefficient is obtained by a prescribed system, and the concentration is multiplied by this correction coefficient to obtain accurate concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plasma ion source mass spectrometer.

[0002]

2. Description of the Related Art In a conventional quantitative analysis method using a plasma ion source mass spectrometer, a calibration solution is prepared by preparing a standard solution in which the concentration of a target element is changed, measuring the ion signal intensity obtained from the device, and preparing an unknown sample. Measure the ion signal strength of
The quantitative value was obtained by reading the concentration indicated by the intensity. However, when analyzing a trace amount of elements at the ng / l or pg / l level, phenomena such as hydrolysis of the elements or adsorption to the vessel wall occur. Creation is difficult.

[0003] Further, in order to suppress these phenomena, an acid is generally added. However, the addition of the acid may cause contamination of a target element. Therefore, it is very difficult to analyze an element having an extremely low concentration using the calibration curve method. As a method to solve this, it is possible to perform highly reliable analysis if the target element in the sample can be concentrated without contamination to a concentration range where the calibration curve can be reliably created. Become.

According to the present invention, a target element is stored in a mass spectrometer of an ion trap type, and a relational expression between the ion signal intensity of the target element and the storage time of the ion obtained beforehand, and the concentration and storage time of the target element are obtained. Is obtained from the relational expression, and it is not necessary to prepare a calibration curve in a trace amount region, and highly reliable analysis is possible.

[0005]

SUMMARY OF THE INVENTION The above prior art is based on the μg
Although the reliability of the analysis value is ensured for the analysis of the concentration at the / l level, no consideration is given to the reliability of the analysis value at the analysis of the concentration at the ng / l and pg / l levels. In order to perform quantitative analysis, a calibration curve was prepared in advance, the ion signal intensity of the target element was measured, and the analytical value was obtained from this value.

However, in the extremely low concentration region,
Hydrolysis of the target element and adsorption to the vessel wall occur, making the calibration curve itself difficult. In order to ensure the reliability of the analytical values, the chemical properties of the element to be measured must also be considered.

An object of the present invention is to accumulate a target element in an ion trap type mass spectrometer, obtain a relational expression between the ion signal intensity of the target element obtained previously and the ion accumulation time, and obtain the concentration of the target element. The concentration is calculated from the relational expression of the accumulation time, and there is no need to create a calibration curve for a trace amount area.
An object of the present invention is to provide a plasma ion source mass spectrometer capable of performing highly reliable analysis.

[0008]

As a means for solving the above-mentioned problems, the present invention provides a method for ionizing a target element present in a sample with an ion source, taking it into an ion trap type mass spectrometer, The relationship between the accumulation time of the ion and the signal intensity of the ions is determined, and the relationship between the accumulation time and the concentration of the target element at a certain ion signal intensity is determined first,
In quantitative analysis, a method is used in which the time required to reach a preset ion signal intensity value is measured, and means for knowing the concentration of the target element from the relationship between the accumulation time and the concentration is adopted. It is not necessary to create a calibration curve.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a block diagram of a plasma ion source mass spectrometer. FIG. 2 shows an example of preparing a calibration curve by a conventional method. FIG. 3 is a diagram in which a solution of a certain concentration is introduced into a plasma ion source mass spectrometer in a plasma ion source mass spectrometer in a plasma ion source mass spectrometer, and a relationship between an ion accumulation time and an ion signal intensity is obtained. It is. As long as the capacity of the ion trap permits, ions can be accumulated, and the relationship between the ion accumulation time and the signal intensity of ions shows good linearity.

FIG. 4 shows the relationship between the concentration of the target element in the measurement solution and the accumulation time when the ion signal intensity indicates a certain count number. The concentration of the target element in the sample solution and the accumulation time of the ions are inversely correlated. At the time of quantitative analysis, a correction coefficient is obtained by comparing the sensitivity of the target element when the above relationships are created with the sensitivity at the time of actual measurement. FIG. 5 shows how to determine the correction coefficient. Also,
The flow sheet for the example is shown briefly in FIG.

In the apparatus to which the present invention is applied, as shown in FIG. 1, a sample 1 is introduced into a plasma 3 in a plasma ion source generating section to ionize a target element, and ions are introduced into a vacuum system via an interface 4. I do. The ions are converged by the ion lens 6 and incident on the ion trap type mass spectrometer 7. Here, high-sensitivity measurement is performed by accumulating ions of the target element and discharging them at once to a detector.

At present, there is a sample in which the concentration of the target element is very low at the ng / l and pg / l levels. In the case of the quantitative analysis using the calibration curve of the conventional method, as shown in FIG. 2A, when the concentration of the target element is low, hydrolysis occurs or the linearity is improved due to adsorption to the vessel wall. A calibration curve cannot be obtained and reliable analysis cannot be performed.

In order to suppress such a phenomenon, an acid is added. However, contamination of a target element is caused, and a reproducible calibration curve cannot be obtained as shown in FIG. 2B. There are cases. Therefore, in order to analyze a sample having an extremely low concentration, it is necessary to perform pretreatment such as concentrating the sample to a range having a linearity of the calibration curve, or to perform the analysis without using the calibration curve.

Therefore, in the present invention, first, as shown in FIG.
0 μg / l), and the relationship between the ion accumulation time and the signal intensity of the ions is determined. In this case, good linearity is exhibited to the extent permitted by the capacity of the ion trap type mass spectrometer.

Next, the ion signal intensity is fixed (here, 1
0000 counts), and the relationship between the ion accumulation time and the concentration of the target element is determined as shown in FIG. In this case, the obtained relational expression is an inverse correlation function. The operations up to this point and the relational expressions obtained by the operations are stored in the operation computer 8 of FIG. 1 prior to the quantitative analysis.

At the time of quantitative analysis of an unknown sample, the sample is introduced into a plasma ion source mass spectrometer comprising an ion trap type mass spectrometer, and the count of the target element is reduced to 10,
Measure the accumulation time until 000 counts are obtained. The obtained accumulation time is substituted into the relational expression shown in FIG. 4 to obtain the density.

Whether the sensitivity at the initial setting and the sensitivity at the time of quantification are different depending on the state of the plasma and the setting state of the ion optical system is determined by introducing a sample having the same concentration as that obtained when the relational expression of FIG. Then, the ion signal intensity at a certain accumulation time may be compared, or the accumulation time until a certain ion signal intensity is obtained may be compared. If different, a correction coefficient is obtained, and the obtained density is multiplied by this to obtain an accurate density.

A method for obtaining the correction coefficient will be described with reference to FIG. A straight line hc indicates a relational expression of a certain element stored in the apparatus as an initial value, and a straight line hd indicates an ion signal intensity i of the standard solution obtained when a correction coefficient is obtained at a certain ion accumulation time j and the origin h. Shows a straight line that passes through. Since the fact that a straight line relationship has been obtained has already been confirmed at the time of creating the straight line hc, it is sufficient to measure only one point and connect it to the origin h.

From this, the sensitivity correction coefficient to be obtained is fi when the ion signal intensity at a certain accumulation time is compared.
/ Gi. Gi / ei is obtained when comparing the accumulation time until a certain ion signal intensity is obtained. The determination of the correction coefficient may be performed before or after the quantitative analysis.

In addition, in order to confirm whether or not the obtained concentration is accurate, the accumulation time was calculated as 10,000 counts in FIG. 3, but in the case of 20,000 counts,
The quantitative value may be obtained by performing measurement at 40,000 counts and at a plurality of points to determine the quantitative value, and determining the quantitative value by the arithmetic average.

With respect to the semi-quantitative analysis, focusing on the signal intensity of a certain ion (here, 10,000 counts) in the relational expression of FIG. The sensitivity ratio is obtained, and this is stored in the apparatus as an initial setting value.

The sensitivity ratio is determined by setting the ion signal intensity to 10,000.
The count is set, and the time until the ion signal intensity is obtained is compared between the respective elements. It is obtained by dividing the accumulation time of the ions of the other elements by the accumulation time of the ions of the representative element. An element having a larger slope than the representative element has a sensitivity ratio smaller than 1, and an element having a smaller slope than the representative element has a sensitivity ratio larger than 1.

To determine the concentration of the representative element, the accumulation time until 10,000 counts are obtained as described above is measured, and the obtained accumulation time is substituted into the relational expression shown in FIG. Then, the concentration of the representative element is corrected and calculated from the separately obtained correction coefficient.

For other elements, the accumulation time for obtaining 10,000 counts is measured, the concentration is obtained using the relational expression of FIG. 4 for the representative element, the concentration is converted from the sensitivity ratio between the elements, and the correction coefficient is calculated. A semi-quantitative value is obtained by riding. That is, the semi-quantitative value of the other element is determined using the sensitivity ratio of the representative element to the other element and the correction coefficient of the representative element.

By using the above-mentioned method, a very small amount of sample can be analyzed without using a calibration curve which is troublesome to prepare, and a highly reliable analytical value can be obtained.

[0026]

Since the present invention is configured as described above, it has the following effects. That is, the present invention relates to a method for analyzing a metal element in an extremely low concentration region, using the relationship between the accumulation time of ions and the signal intensity of ions and the relationship between the accumulation time and the concentration of the target element determined in advance, It calculates the concentration of an unknown sample, and can analyze the concentration of a target element in an extremely low concentration region with high reliability without using a calibration curve.

[Brief description of the drawings]

FIG. 1 is a block diagram of a plasma ion source mass spectrometer according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an example of creating a calibration curve according to a conventional method.

FIG. 3 is a characteristic diagram showing a relationship between an accumulation time of a target element and an ion signal intensity in the ion trap type mass spectrometer in FIG.

FIG. 4 is a characteristic diagram showing the relationship between the accumulation time and the concentration of a target element in the ion trap type mass spectrometer of the present invention.

FIG. 5 is a characteristic diagram showing a method for obtaining a correction coefficient according to the present invention.

FIG. 6 is a flow sheet diagram showing an example of the present invention.

[Explanation of symbols]

1 ... sample, 2,3 ... plasma, 4 ... interface,
5 ... Ion orbit, 6 ... Ion lens, 7 ... Ion trap type mass spectrometer, 8 ... Operation computer.

Claims (4)

[Claims] An ICP or MIP is used as an ion source.
In a plasma ion source mass spectrometer using an ion trap type mass spectrometer in the mass spectrometry section, target elements present in the sample are ionized by the ion source and taken into the ion trap type mass spectrometer to accumulate ions. The relationship between the time and the signal intensity of the ions is determined, and the relationship between the accumulation time and the concentration of the target element at a certain ion signal intensity is determined in advance, and reaches a preset ion signal intensity value during quantitative analysis. A plasma ion source mass spectrometer characterized by comprising means for measuring an ion accumulation time until completion and determining a concentration of a target element from a relationship between the accumulation time and the concentration. 2. The apparatus according to claim 1, further comprising means for providing a plurality of preset ion signal intensity values, obtaining an average value and a relative standard deviation value of the calculated concentrations, and improving the reliability of the measured values. Characteristic plasma ion mass reduction analyzer. 3. The method according to claim 1, wherein the relationship between the accumulation time of the ions and the signal intensity of the ions is determined, and the relationship between the accumulation time and the concentration of the target element at a certain ion signal intensity is determined first. When performing quantitative analysis on
When the sensitivity of the element and the sensitivity at the time of quantitative analysis in the relational expression obtained earlier are different, by comparing the ion signal intensity at a certain accumulation time or by comparing the accumulation time until obtaining a certain ion signal intensity, A plasma ion source mass spectrometer comprising means for calculating a correction coefficient. 4. A relational expression between the ion accumulation time and the ion signal intensity obtained for each element, focusing on a certain ion signal intensity, obtaining a sensitivity ratio between the elements with reference to a representative element, In the measurement of the concentration of the representative element, the ion accumulation time when a certain count is obtained is measured, and the obtained ion accumulation time is substituted into the relational expression between the ion accumulation time and the concentration of the representative element to obtain the concentration. Calculate the concentration of the representative element from the obtained correction coefficient, measure the accumulation time of ions that can obtain a certain count for other elements, and calculate the concentration from the sensitivity ratio with the representative element and the correction coefficient. Characteristic plasma ion source mass spectrometer.