JPH05256782A - Raman spectrometer for analysis of slight amount of constituent - Google Patents

Abstract

PURPOSE:To obtain a Raman spectrometer which can analyze a slight amount of constituent, by using a high-output laser diode as a light source and by using a photomultiplier tube highly sensitive to a specific wavelength as a detector. CONSTITUTION:An incident light is applied from a light source of a high-output laser diode 11 to a sample 13 through an optical system 12. Part of the incident light is radiated as a Raman light in the direction perpendicular to the optical axis of the incident light. This Raman light is converged by an optical system 14 and enters an optical filter 15 provided at a point of convergence. In the optical filter 15, the Raman light is separated into its spectral components and the light component thus obtained is sent to a photomultiplier tube 16 being a detector. The quantity of light detected by the photomultiplier tube 16 is converted into a current and it is amplified by an amplifier 17 and displayed. In this case, detection sensitivity to the Raman light separated into its spectral components is increased by using the photomultiplier tube being highly sensitive to a light of a wavelength 800 to 1000nm, and by using a non-dispersion type spectroscope more preferably, a sulfuric-acid ion, a carbonic-acid ion, a nitric-acid ion and a phosphoric-acid ion, as well as dissolved oxygen of water, in a solid or a liquid can be analyzed in such a high accuracy as 10 to 100mumol/L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Raman spectrometer for analyzing trace components, and more particularly to a Raman spectrometer for analyzing trace amounts of anions such as sulfate ions and carbonate ions and dissolved oxygen in water.

[0002]

2. Description of the Related Art A Raman spectrometer has recently been used as an analyzer for solid samples such as drugs, biopolymers and organic substances, and liquid samples of high concentration.

The Raman spectrometer has a light source 1 as shown in FIG.
When the light from the optical system 2 is condensed by the optical system 2 and the solid, liquid or gas sample 3 is placed at the condensing point, the light having the same frequency as the incident light is transmitted in the optical axis direction 4 and at the same time, it is perpendicular to the optical axis. This utilizes the Raman effect of emitting Raman light having a frequency different from that of the incident light in the direction 5. Recently, a Raman spectrometer using an ion laser such as Ar or Kr that can obtain monochromatic light as the light source 1 has been developed. This is because light of frequency ν is collected from the light source 1 by the optical system 2, and when the sample 3 is placed at the condensing point, light of frequency (ν + ν ₀ ) is emitted as Raman light. If the frequency of incident light is ν, the frequency of Raman light (ν +
[nu ₀ [nu ₀ of) is determined by the material, the intensity of the Raman light in the frequency is related that is proportional to the concentration of the substance. In general, there is a relationship of ν >> ν ₀ . Therefore, when the optical system 6 is provided in the optical path of the Raman light, the Raman light is condensed, the dispersive spectroscope 7 is placed at the condensing point, and the detector 8 is provided in front of it, the Raman light with respect to a certain frequency is obtained. The intensity of light is obtained, and the substance contained in the sample 3 can be identified and quantified. In this case, the solid sample has a fixed shape by a shaping machine, and the liquid or gas sample is filled in a transparent sample cell for use.

[0004]

However, Ar,
Raman spectrometers that use the visible range such as Kr require high-precision spectroscopy in order to improve wavelength resolution. Therefore, light is dispersed and only a very weak light can be used for measurement. Further, in the Fourier Raman spectrometer in the infrared region, there is no highly sensitive detector. Therefore, in the conventional Raman spectrometer, the quantification limit of anions such as sulfate and carbonate ions and dissolved oxygen in water is 0.1 mol /
It is about L.

On the other hand, there is a strong demand for lowering the limit of quantification in environmental analysis of the atmosphere and water. In addition, it has become necessary to analyze biological samples and the like that can obtain only minute amounts of samples.

The object of the present invention is to limit the quantification to 1/1000.
10-100 μmol / L reduced to ~ 1 / 10,000
Is to provide a Raman spectrometer.

[0007]

SUMMARY OF THE INVENTION The present invention uses a high-power laser diode as a light source and a photomultiplier tube having a high sensitivity at a wavelength of 800 to 1000 nm as a detector. Raman spectroscopy for analysis of trace components. It is total.

Further, the present invention is characterized by using a non-dispersive spectroscope for the Raman light spectroscopy.

The present invention also provides a Michelson interferometer or a wavelength of 800 to 1000 n as the non-dispersive spectroscope.
It is characterized by using a near-infrared optical filter that selects a wavelength in a constant width range in m.

[0010]

According to the present invention, a high-power laser diode is used as the light source of the Raman spectrometer, and the wavelength is 785 nm (frequency 1
The light of 2,739 cm ⁻¹ ) is emitted to the sample to generate Raman light, which is dispersed by an optical filter, and the separated Raman light has a wavelength of 800 to 1000 nm (frequency: 12,500 to 1).
The detection sensitivity is increased by using a photomultiplier tube with high sensitivity to light of 20,000 cm ⁻¹ ), and more preferably, by using a non-dispersion type spectrometer, it is 1000 times higher than that of a conventional dispersion type Raman spectrometer. The above light-collecting area is obtained, and by the action of both, it is possible to accurately analyze the sulfate ion, carbonate ion, nitrate ion and phosphate ion in the solid and the liquid, and the dissolved oxygen of water up to 10 to 100 μmol / L.

A preferred example of the non-dispersive spectroscope includes a Michelson interferometer or a near-infrared optical filter that selects a wavelength within a fixed width range from 800 to 1000 nm.

Further, carbon dioxide gas, nitrogen oxides, sulfur oxides, etc. in the gas can be treated to be converted into carbonate ion, nitrate ion and sulfate ion for analysis.

[0013]

EXAMPLES The Raman spectrometer for analyzing trace components according to the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

FIG. 1 is an overall view of a Raman spectrometer 10 for analyzing trace components according to an embodiment of the present invention. Incident light is 1W
From the light source of the high power laser diode 11 to a wavelength of 785 nm
Then, the sample 13 is irradiated through the optical system 12. Most of the incident light becomes transmitted light, but part of the incident light is emitted as Raman light in a direction perpendicular to the optical axis of the incident light. The Raman light is collected by the optical system 14 and enters the optical filter 15 provided at the light collecting point. The optical filter 15 separates the Raman light and sends the separated light components to the photomultiplier tube 16 which is a detector. The amount of light detected by the photomultiplier tube 16 is converted into an electric current, which is displayed by the amplifier 17 with an increased width.

FIG. 2 is a diagram showing the detection circuit of the photomultiplier tube 16 used above. The light dispersed by the optical filter enters the photomultiplier tube 16 through the light entrance window 21, and the photocathode 2
At 2, the electrons are exchanged by photoelectric conversion. That is, the photocathode 22 converts one photon into one electron. Photocathode 2
Since 2 has a negative high voltage (-HV), it acts as a cathode, and the electrons proceed to the anode 25, but on the way, electrodes 231 and 231 called dynodes created by a voltage dividing circuit.
32 ... 23n. The electrons collected at the anode are
It becomes a current and enters the amplifier, is converted into a voltage and is amplified. By using the photomultiplier tube 16, weak Raman light can also be detected.

There are various methods for the optical filter 15 for separating the Raman light. To measure the intensity by changing the wavelength according to the frequency as a non-dispersive spectroscope, FIG.
The Michelson interferometer 30 shown in is preferred. The Michelson interferometer 30 converts the collected Raman light 31 into a half mirror plate 35.
To irradiate. The half mirror flat plate 35 uses half of the Raman light 31 as transmitted light 32, which is reflected by the first plane mirror 36,
It reaches the semi-mirror flat plate 35 again and is reflected here. On the semi-mirror flat plate 35, the remaining half of the Raman light 31 becomes reflected light 33, which is reflected by the second flat mirror 37, reaches the semi-mirror flat plate 35 again, and is transmitted through this time. First plane mirror 3
The light 32 reflected by 6 and the light 33 reflected by the first plane mirror 37 are combined by the semi-mirror flat plate 35 and become light 34, which travels toward the photomultiplier tube 16. When the half mirror flat plate 35 is provided at an angle of 45 ° with the first flat mirror 36 and the second flat mirror 37, the half mirror flat plate 35 and these flat mirrors 36, 3 are formed.
When the difference in distance from 7 is an integral multiple of 1/2 of the wavelength of the incident light, the amount of light 34 becomes maximum due to interference, so that Raman light can be separated by using this. Therefore, the contained substance can be identified and quantified by finely moving the first plane mirror by the computer 18, determining the wavelength, and determining the light intensity at that time.

In addition to this, an optical filter 1 for Raman light spectroscopy
An optical filter that transmits light in the infrared region, which selects a wavelength in a fixed width range from 800 to 1000 nm, may be used as the optical filter 5.

When the sample is gas, a multiple reflection cell 40 as shown in FIG. 4 is used as the sample cell. Using the elliptical mirrors 42 and 43 on both sides of the sample cell 41,
The incident light is reflected many times inside the ellipsoidal mirrors 42 and 43 to emit the intense Raman light 44. In this case, the Raman light 44 has two focal points 45, 46 of the elliptical mirrors 42, 43.
Will be emitted from.

Using the Raman spectrometer of this Example, 0.1 μmol each of nitrate ion, bicarbonate ion and sulfate ion
A chart obtained by analyzing an aqueous solution of / L is shown in FIG. Peak A represents nitrate ion and is at ν ₀ = 1050 cm ⁻¹ . Peak B represents bicarbonate ion, ν ₀ = 1015c
m- ¹ . Peak C represents sulfate ion, ν ₀ = 98
It is at 0 cm ^-1 . Although not shown in the chart, phosphate ion and dissolved oxygen concentration in water also showed similar peaks. The lower limit of quantification of these is the frequency of the Raman light (ν ₀ ).
Are shown in Table 1.

[0020]

[Table 1]

It should be noted that FIG. 1 used in the description of the embodiment illustrates the principle, and the optical systems 12 and 14 are shown in a simplified manner. In reality, a mirror is used to secure the optical path in order to save space distance. Raman light is weaker than transmitted light, so it is devised so that it is not affected by transmitted light.
In addition, since the light emitted from the high power diode is harmful to the human body, a protective measure is taken to prevent it from leaking to the outside.

[0022]

According to the present invention, a high-power laser diode is used as a light source and a high-sensitivity photomultiplier tube is used as a detector to obtain a Raman spectrometer for the analysis of trace components. , Sulfate ion, nitrate ion, phosphate ion and dissolved oxygen 10 to 100 μmol / L
Can be analyzed up to a low concentration. Trace components in solids and gases can be similarly analyzed.

[Brief description of drawings]

FIG. 1 is an overall view of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of a photomultiplier tube 16 used in the device shown in FIG.

FIG. 3 is a diagram for explaining the principle of a Michelson interferometer 30 used in an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a multiple reflection cell 40 used in an embodiment of the present invention.

5 is a chart when a trace component in water is analyzed using the apparatus shown in FIG.

FIG. 6 is a diagram for explaining the principle of a Raman spectrometer.

[Explanation of symbols]

 10 Raman for trace component analysis 11 High-power laser diode light source 13 Sample 15 Optical filter 16 High-sensitivity photomultiplier tube 17 Amplifier 30 Michelson interferometer

Claims (3)

[Claims] 1. A Raman spectrometer for analysis of trace components, which comprises a high-power laser diode as a light source and a photomultiplier tube with high sensitivity at a wavelength of 800 to 1000 nm as a detector. 2. The Raman spectrometer for analyzing trace components according to claim 1, wherein a non-dispersion type spectroscope is used for Raman spectroscopy. 3. The Michelson interferometer or a near-infrared optical filter for selecting a wavelength within a fixed width range of 800 to 1000 nm is used as the non-dispersive spectroscope. Raman spectrometer for the analysis of trace components.