JP2002303578A - Laser-induced fluorescence analysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser induced fluorescence analyzing method capable of easily determining trace amounts of many elements. SOLUTION: In the laser induced fluorescence analyzing method, concentration of an objective element is determined by applying a resonance excitation pulsed laser having an inherent wavelength resonating with the objective element in a sample on the atomized sample and spectrally analyzing a generated quantity of fluorescence. It is characterized by that a pulse time width of the resonance excitation pulsed laser is >=100 fs and <=500 ps as a full width of half maximum. It is favorable that the sample is atomized by one of laser irradiation, heating inside a graphite reactor, high frequency inductively coupled plasma, spark discharge, arc discharge, or glow discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantifying chemical components using laser induction, and more particularly to a laser-induced fluorescence analysis method used for quantifying the concentration of trace components.

[0002]

2. Description of the Related Art Laser-induced fluorescence analysis is a method for measuring fluorescence emitted from an excited state generated by irradiating an atomized sample with a laser having a wavelength that resonates with a target atom. This analytical method is generally known as a highly sensitive and highly selective analytical method. Because of these features, ppm
Numerous studies have been conducted as so-called trace element analysis techniques at or below the level.

[0003] However, in improving the lower limit of quantification of this analysis method, scattered light of the resonance excitation laser is a major inhibiting factor in addition to the background radiation mentioned above. for that reason,
It was necessary to reduce the laser scattered light entering the detection optical system as much as possible by devising the laser irradiation direction and the fluorescence detection direction. However, the lower the concentration, the more it is necessary to create an atomic gas state in which the sample atoms are present at a higher density, and the resonance pump laser is used to increase the mutual interference volume for these vaporized atoms. , Which, on the other hand, also increases the probability that the laser will be elastically scattered by these atoms.

The problem of scattering of the resonance excitation laser can be solved by using a combination in which the resonance excitation wavelength and the fluorescence wavelength are different from each other beyond the resolution of the spectroscope as disclosed in Japanese Patent Application Laid-Open No. 8-75651. There is a problem that elements that can use such a combination of transition wavelengths are limited to a part and cannot be applied to other elements.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, enables fluorescence measurement at a wavelength that is the same as or close to the excitation wavelength, and enables trace-quantification of many elements. An object of the present invention is to provide a laser-induced fluorescence analysis method that can be easily performed.

[0006]

Means for Solving the Problems The above problems are solved by the following method. (1) Irradiating the atomized sample with a resonance excitation pulse laser having a specific wavelength that resonates with the target element in the sample, and spectrally analyzing the amount of fluorescent light generated thereby to obtain the target element A laser-induced fluorescence analysis method for determining a concentration, wherein a pulse time width of the resonance excitation pulse laser is 100 fs or more and 500 ps or less as a full width at half maximum. (2) Atomization of the sample is performed by laser irradiation, heating in a graphite furnace,
High frequency inductively coupled plasma, spark discharge, arc discharge,
The laser-induced fluorescence analysis method according to (1), wherein the method is performed by any one of glow discharge.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. When a laser having a wavelength that resonates with a transition from a lower level to an upper level of the outer electron energy level of the target element is excited, the laser is excited to an upper level by light absorption. The lifetime of this excited level is given by the reciprocal of the spontaneous emission coefficient to the original lower level. If a transition from the upper level to a level other than the original lower level is allowed, the reciprocal of the sum of the spontaneous emission coefficients for all these transitions is the lifetime of the excited level. Among the natural lifetimes thus obtained, the optimum transition excited state lifetime in the determination of trace components by laser-induced fluorescence analysis is in the range of 0.1 to 100 ns for most elements. In an actual system, the pressure is often atmospheric pressure, and sometimes the pressure is higher than the atmospheric pressure. Non-radiative transition or the like due to collision usually occurs, so that the life of the excited state is further shortened.

Conventionally, the pulse width of a pulse laser used in a laser-induced fluorescence analysis method is 5% as a full width at half maximum (FWHM).
２０20 ns. With such a laser pulse width, in many cases, the scattered light of the resonance excitation laser cannot be temporally separated. However, in recent years, ultra-short pulse width lasers such as picosecond and femtosecond lasers have been developed and can be applied to laser fluorescence analysis.

The present invention has been made by paying attention to the fact that the pulse width of these lasers is three to four orders of magnitude shorter than the lifetime of the above-mentioned excited state of atoms. Also, the present invention
Even if the lifetime of the excited state in an actual system mainly under atmospheric pressure or higher pressure conditions is shorter than about 1 ns, the fluorescence of the same wavelength as the laser or a wavelength close to the laser by a wavelength difference of several nm or less is emitted by the laser. This has been achieved as a result of investigations to reduce interference by scattered light and to enable fluorescence to be measured with high efficiency.

The concept of the present invention will be described with reference to the drawings. Now, when the lifetime of the excited state generated by irradiating a laser having a wavelength that resonates with a certain transition of the target element is 1 ns, the excitation generated until the laser intensity reaches the peak (t = 0). The time change of the number density of the state is ignored along with the pulse waveform of the laser, ignoring the effect of the subsequent laser irradiation.
Shown in Here, when the pulse width of the resonance excitation laser is 1 ns at full width at half maximum, the laser intensity is 1/1 times the peak.
Even if the detector gate is opened at the time of decay to 00, the fluorescence detection rate is only less than 30% of the total fluorescence intensity.

On the other hand, when a laser having a pulse width of 500 ps is used in accordance with the present invention, the result is as shown in FIG. 2. When the gate of the detector is opened when the laser intensity attenuates by two digits with respect to the peak, Approximately 50% of the total fluorescence intensity can be collected, and high-sensitivity fluorescence measurement can be realized while temporally avoiding interference of laser scattered light. Further, according to the present invention, when a laser having a pulse width of 100 ps is used, about 80% of the fluorescence can be collected even when the laser intensity is attenuated by four digits. When the laser pulse width is shorter than 100 fs, the fluorescence yield is reduced as a whole, so that the pulse width is preferably 100 fs or more.

FIG. 3 shows an example of the device configuration of the present invention. In the example of FIG. 3, a part of the sample 12 is atomized by irradiating a beam oscillated from the laser 1. After a certain period of time has elapsed with respect to this atomization pulse, a beam oscillated from the resonance excitation laser 2 is irradiated to induce fluorescence of the target element. This fluorescence is guided to a spectroscopic analyzer, and the amount of fluorescence is measured. A mode-locked Ti-sapphire laser or the like can be used as a resonance excitation laser having a pulse width shorter than 1 ns, which is a point of the present invention.

As an atomization laser, a Q switch pulse is used.
It is sufficient that an Nd: YAG laser or the like can be used, and a peak power density of about 1 GW / cm ² can be given on the sample surface by a focusing means such as a lens as appropriate. FIG. 4 shows another example of the device configuration in the present invention. In the example of FIG. 4, a part of the sample is atomized by the graphite furnace 13. Here, a beam oscillated from the resonance excitation laser (2) is irradiated to induce fluorescence of the target element. This fluorescence is guided to a spectroscopic analyzer, and the amount of fluorescence is measured. As the resonance excitation laser, the same laser as in the above example can be used.

[0014]

EXAMPLES (Example 1) A steel sample was analyzed by the apparatus shown in FIG. 3 to quantify Ti. Irradiate the sample surface with Nd: YAG laser,
After an appropriate time, the wavelength of the Ti sapphire laser having a pulse width (FWHM) of 300 ps is set to 2 which is one of the resonance excitation of Ti atoms.
The light was tuned to 93.3 nm and irradiated, and the fluorescence of the same wavelength was measured. As a result, the detection limit was about 0.1 μg /
g was obtained. The BEC (background equivalent content) of the calibration curve was about 10 μg / g on average. (Comparative Example 1) A steel sample was analyzed and Ti was quantified. A sample surface is irradiated with an Nd: YAG laser, and after an appropriate time, the wavelength of a Ti sapphire laser having a pulse width (FWHM) of 1 ns is tuned to 293.3 nm, which is one of resonance excitations of Ti atoms, and irradiated. Fluorescence of the same wavelength was measured. As a result, the detection limit was about 0.7 μg / g. The BEC (background equivalent content) of the calibration curve was about 100 μg / g on average. (Example 2) A steel sample was analyzed by the apparatus shown in Fig. 4 to determine Mg. An aqueous solution sample obtained by acid-decomposing about 1 g of a steel sample and diluting it to a certain volume was dropped into a graphite furnace in an amount of about 5 μl, and heated to about 3000 K in about 10 s to atomize the sample. This is irradiated with a Ti sapphire laser with a pulse width of 500 fs tuned to 285.2 nm, which is one of the resonance excitations of Mg atoms,
Fluorescence of the same wavelength was measured. As a result, about 0.01 μg / g was obtained as the detection limit. The BEC of the calibration curve was about 0.1 μg / g on average. (Comparative Example 2) A steel sample was analyzed and Mg was quantified. About 5 g of an aqueous solution sample obtained by acid decomposition of about 1 g of a steel sample and diluting it to a certain volume was dropped into a graphite furnace, and heated and heated to about 3000 K in about 10 s to atomize. Here, a pulse width of 0.6 tuned to 285.2 nm which is one of the resonance excitations of Mg atoms
Irradiated with Ti sapphire laser of ns, fluorescence of the same wavelength was measured. As a result, a detection limit of about 1 μg / g was obtained. The BEC of the calibration curve was about 10 μg / g on average.

[0015]

According to the present invention, fluorescence having the same wavelength as the excitation wavelength can be measured without interference by the scattered light of the resonance excitation laser, so that it is not necessary to pay attention to the spatial separation of the laser scattered light. In addition, the number of elements to which the laser-induced fluorescence analysis method with high sensitivity can be applied increases, and the application range of the laser-induced fluorescence analysis method can be expanded.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the time dependence of a laser pulse in the related art (1 ns in the excited state and 1 ns in the laser pulse width).

FIG. 2 is a diagram for explaining the time dependence of a laser pulse in the present invention (lifetime of excited state is 1 ns, laser pulse width is 500 ps).

FIG. 3 is a diagram schematically showing an example of an apparatus to which the present invention can be applied.

FIG. 4 is a diagram schematically showing an example of an apparatus to which the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Atomization laser 2 ... Resonance excitation laser 3 ... Pulse generator 4 ... Spectroscope 5 ... Optical fiber 6 ... Laser mirror 7 ... Laser mirror 8 ... Control computer 9 ... Condenser lens 10 ... Optical filter 11 ... Emission and Fluorescence 12 ... Sample 13 ... Graphite furnace

Claims (2)

[Claims] 1. The method according to claim 1, wherein the atomized sample is irradiated with a resonance excitation pulse laser having a specific wavelength that resonates with a target element in the sample, and the amount of fluorescence generated by the irradiation is spectrally analyzed. A laser-induced fluorescence analysis method for quantifying the concentration of an element, wherein a pulse time width of the resonance excitation pulse laser is 100 fs or more and 500 ps or less as a full width at half maximum. 2. The method according to claim 1, wherein the atomization of the sample is performed by any of laser irradiation, heating in a graphite furnace, high-frequency inductively coupled plasma, spark discharge, arc discharge, and glow discharge. Laser-induced fluorescence analysis method.