JP2008224237A - Wavelength correction method of atomic absorption spectrophotometer and atomic absorption spectrophotometry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength correction method of an atomic absorption spectrophotometer that can correct a wavelength in conditions similar to actual measurement conditions without the use of a correction lamp, and an atomic absorption spectrophotometry using this wavelength correction method. <P>SOLUTION: The method comprises: a step for supplying a gas mixing part 26 with combustion gas and supporting gas in a constant flow that are the same with those used at the analysis and measuring an emission spectrum of a flame combustion part 22 that is generated by this gas mixing part 26; a step for comparing the emission spectrum with a set wavelength of a spectrometer 23; and a step for correcting the set wavelength of the spectrometer 23 by using a wavelength shift obtained from this comparison and a correction expression specific to the spectrometer 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an atomic absorption spectrophotometer, and in particular, correction of the wavelength of a flame atomic absorption spectrophotometer that atomizes a sample by atomizing a liquid sample, a combustion gas, and an auxiliary combustion gas, and combusts to perform spectroscopic analysis. The present invention relates to a method and an atomic absorption analysis method using a wavelength correction method of the flame atomic absorption spectrophotometer.

  A monochromator is used as a spectroscope of the atomic absorption spectrophotometer to obtain monochromatic light having a specific wavelength. In general, a monochromator includes a wavelength dispersion element such as a diffraction grating or a prism, and a rotation driving mechanism for changing the angle of the wavelength dispersion element with respect to incident light. The element is rotated, and monochromatic light having a desired wavelength is extracted through a fixed exit slit.

  As a rotation driving mechanism of the diffraction grating in the monochromator, a mechanism by conversion from linear motion to rotational motion by a sine bar mechanism, a mechanism by open loop control combining a stepping motor and a reduction gear mechanism, or a DC servo motor is used. The thing by the closed loop control used is put into practical use.

  For example, in a configuration having a rotational drive mechanism in which a stepping motor and a reduction gear mechanism are combined, an optical theoretical formula indicating the relationship between the angle of the diffraction grating and the wavelength of the emitted light, the rotation angle of the motor shaft of the stepping motor, and the gear Based on the design relationship with the rotation angle that is the output of the speed reduction mechanism, an ideal correspondence between the number of drive pulses that is the control instruction amount of the motor and the wavelength of the extracted monochromatic light can be obtained by calculation.

  However, the accuracy of the extracted wavelength may be impaired due to various factors such as the mechanical accuracy error of the rotary drive mechanism, the grating constant of the diffraction grating, the refractive index error of the prism, and the installation error of the optical components. As a countermeasure, using a spectrum having a known wavelength such as a zero-order light and emission line spectrum of a deuterium lamp or several emission line spectra of a mercury lamp, a control instruction value (for example, a drive stepping motor) is transmitted to the rotation drive mechanism system. In general, a method of correcting the wavelength from the amount of deviation actually obtained corresponding to the number of driving pulse signals) is performed.

  In recent years, the atomic absorption spectrophotometer has been miniaturized. Along with that, the distance between the heat source such as the combustion section, motor, and light source lamp and the spectroscope is inevitably close, and the spectroscope and optical parts are affected by their heat generation, causing thermal expansion and thermal distortion, The wavelength accuracy is easily deteriorated.

  In order to prevent the spectroscope from being affected by heat, there are a method of reducing the thermal effect by using a heat insulating material and a method of adjusting the temperature of the spectroscope to a constant temperature. It has a problem that it takes.

  Therefore, it is conceivable to perform wavelength correction including thermal effects by performing wavelength correction using a deuterium lamp or mercury lamp in the combustion state, but in this case, absorption of the emission line spectrum by the flame of the burning part As a result, the accuracy of the wavelength correction itself deteriorates.

  On the other hand, deuterium lamps and mercury lamps that have been used for wavelength correction in the past are designated by the European Parliament and Council Directive (RoHS Directive) on waste disposal laws and restrictions on the use of specific hazardous substances contained in electrical and electronic equipment. If possible, refrain from using the substances that are subject to environmental regulations.

  In view of the above problems, the present invention provides a wavelength correction method for an atomic absorption spectrophotometer capable of performing wavelength correction without using a correction lamp and in a state close to an actual measurement state, and the wavelength. It is an object of the present invention to provide an atomic absorption spectrometry method using a correction method without changing the hardware configuration of a conventional atomic absorption spectrophotometer.

  In order to achieve the above object, according to the first aspect of the present invention, (a) a combustion gas and an auxiliary combustion gas, which are the same gases as the gas at the time of analysis, are supplied to the gas mixing section at a constant flow rate. Measuring the emission spectrum of the generated flame burning part, (b) comparing the emission spectrum with the set wavelength of the spectrometer, and (c) the amount of wavelength deviation obtained by this comparison, The gist of the present invention is a method for correcting the wavelength of an atomic absorption spectrophotometer including a step of correcting a set wavelength of a spectrometer using a specific correction formula.

  According to a second aspect of the present invention, (a) supplying a combustion gas and an auxiliary combustion gas at a constant flow rate to a gas mixing unit and measuring an emission spectrum of a flame combustion unit generated by the gas mixing unit; (1) Comparing the emission spectrum and the set wavelength of the spectrometer, (c) Correcting the set wavelength of the spectrometer using the wavelength deviation obtained by this comparison and the correction formula specific to the spectrometer. And (d) a step of atomizing the measurement sample and supplying it to the flame combustion unit in a state where the combustion gas and the auxiliary combustion gas are supplied to the gas mixing unit and the flame combustion unit is formed, and (e) And a step of irradiating the flame burning part with light having a wavelength specific to the target element and measuring the amount of light absorbed. .

  According to the present invention, a wavelength correction method for an atomic absorption spectrophotometer capable of performing wavelength correction without using a correction lamp and in a state close to an actual measurement state, and this wavelength correction method are used. The conventional atomic absorption spectrometry can be provided without changing the hardware configuration of the conventional atomic absorption spectrophotometer.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The following embodiments of the present invention exemplify apparatuses and methods for embodying the technical idea of the present invention. The technical idea of the present invention is based on the material and shape of component parts. The structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the technical scope described in the claims.

(Hardware configuration of atomic absorption spectrophotometer)
As shown in FIG. 1, an atomic absorption spectrophotometer according to an embodiment of the present invention includes a light source lamp 27 that emits light having an emission line spectrum including a resonance line of a target element, and light from the light source lamp 27 passes therethrough. Flame burning unit 22, gas mixing unit (burner) 26 forming flame burning unit 22, spectrometer 23 for obtaining a bright line spectrum from flame burning unit 22, and detector for detecting light from spectrometer 23 24, a control unit (CPU / POWER) 29 for controlling the entire apparatus, and a display unit 13 for displaying the analysis result. As the light source lamp 27, a hollow cathode lamp or an electrodeless discharge tube is generally used. Although not shown, it is a matter of course that a light source power source is connected to the light source lamp 27.

The control unit (CPU / POWER) 29 includes a signal processing unit that amplifies the signal obtained by the detector 24. Although not shown, the control unit (CPU / POWER) 29 is connected to an operation unit for controlling the spectroscope 23 via the control unit (CPU / POWER) 29. A gas control unit 25 that controls the gas supplied to the gas mixing unit (burner) 26 is connected to the gas mixing unit (burner) 26, and fuel gas and auxiliary gas are supplied to the gas control unit 25. As the fuel gas, for example, acetylene gas (C ₂ H ₂ ), for example, air is used as the first auxiliary combustion gas, and for example, dinitrogen monoxide gas (N ₂ O) is used as the second auxiliary combustion gas. An ignition unit 28 is disposed in the vicinity of the flame combustion unit 22, acetylene and air having a predetermined mixing ratio are supplied to a gas mixing unit (burner) 26, and ignition is performed by the ignition unit 28.

  Although not shown, a sample supply device for supplying a measurement sample to the flame combustion unit 22 is provided in the vicinity of the gas mixing unit (burner) 26. The measurement sample is atomized by the sample supply device, mixed with the combustion gas and the auxiliary combustion gas, and combusted in the gas mixing unit (burner) 26. Since the temperature is different in one flame, there are places that are easy to analyze depending on the element. For this reason, the height of the gas mixing part (burner) 26 can be adjusted.

  The light having a wavelength specific to the target element emitted from the light source lamp 27 passes through the sample atomized by the flame burning unit 22 and absorbs an amount corresponding to the amount of the sample at a wavelength corresponding to the type of the sample. Receive. The signal processing unit built in the control unit (CPU / POWER) 29 calculates the absorbance with respect to the specific wavelength light based on this detection signal, and further performs a predetermined analysis process to perform quantitative analysis. The user gives an instruction to the control unit (CPU / POWER) 29 through the input device, and the analysis result or the like is viewed on the display unit 13.

(Wavelength correction method of atomic absorption spectrophotometer)
Next, the wavelength correction method of the atomic absorption spectrophotometer according to the embodiment of the present invention will be described:
(A) The light source lamp 27 is turned off, the acetylene gas used as the combustion gas in the gas control unit 25 and the flow rate of the air used as the auxiliary combustion gas are set to predetermined values, and these gases are supplied to the gas mixing unit 26. Supply. Acetylene gas and air are examples, and combinations with other gases may be used. However, the combustion gas and auxiliary combustion gas are preferably the same as the combustion gas and auxiliary combustion gas at the time of analysis. Thereafter, the ignition unit 28 ignites the gas mixing unit 26, starts combustion, and forms the flame combustion unit 22.

  (B) After a predetermined time (time when the thermal effect is stabilized), the output light of the spectroscope 23 is detected by the detector 24, and the emission spectrum of the flame in the flame combustion unit 22 is measured.

  (C) Thereafter, the control unit (CPU / POWER) 29 compares the preset wavelength of the spectroscope 23 input in advance with the actually measured wavelength of the emission spectrum of the flame.

  (D) A step of correcting the set wavelength of the spectroscope 23 using the wavelength shift amount obtained by this comparison and a correction formula unique to the spectroscope 23. A correction formula unique to the spectroscope 23 is input to the control unit (CPU / POWER) 29 in advance.

  FIG. 2 shows the emission spectrum of the flame in the flame combustion section 22 when acetylene is supplied at 1.8 L / min as the combustion gas and air is supplied at 15 L / min as the auxiliary combustion gas. In FIG. 2, the black square is the case with a burner height of 2 mm, and the black diamond is the case with a burner height of 7 mm. An OH band spectrum is observed at a wavelength of 310 nm, a CN band spectrum at a wavelength of 390 nm, a C2 band spectrum at a wavelength of 470 nm, a C2 band spectrum at a wavelength of 510 nm, and a C2 band spectrum at a wavelength of 550 nm. Accordingly, the amount of deviation between the preset wavelength of the spectroscope 23 input in advance and the wavelength of the emission spectrum of the flame actually measured as shown in FIG. 2 is compared, and the set wavelength of the spectroscope 23 according to the correction formula input in advance. Can be corrected.

  In FIG. 2, five main peak wavelengths are shown, but when correcting the set wavelength, all of these five main peak wavelengths may be used, or a part of the main peak wavelengths may be used. Since the measurement wavelength for each element is determined in a simple manner, the set wavelength may be corrected by selecting the main peak wavelength closest to the measurement wavelength of the target element to be analyzed.

For example, when measuring the silver (Ag) or a measurement wavelength of λ _MES = 328.1nm, copper (Cu) of the measuring wavelength λ _MES = 324.8nm uses the nearest OH band spectrum in this wavelength (around 310 nm) Then, the set wavelength of the spectrometer may be corrected. Similarly, when measuring strontium (Sr) at the measurement wavelength λ _MES = 460.7 nm, the C2 band spectrum (near 470 nm) closest to this wavelength is used to correct the spectrometer, and the measurement wavelength λ _MES = 589 When measuring 0.0 nm of sodium (Na), the set wavelength of the spectrometer may be corrected with the C2 band spectrum (near 550 nm) closest to this wavelength.

In addition, when measuring chromium (Cr) having a measurement wavelength λ _MES = 357.9 nm, it is spectroscopic using either or both of an OH band spectrum (near 310 nm) and a CN band spectrum (near 390 nm) near this wavelength. If the measurement wavelength λ _MES = 422.7 nm of calcium (Ca) is measured, the CN band spectrum (near 390 nm) or the C2 band spectrum (near 470 nm) is close to this wavelength. The spectroscope may be corrected using either or both. In other words, depending on the model of atomic absorption spectrophotometer, there are about 60 specific elements that can be measured by atomic absorption analysis, but the measurement wavelength for each element is fixed, so the flame closest to these wavelengths can be measured. The spectroscope may be corrected using the emission spectrum. At this time, if the combustion conditions such as the gas flow rate are set under the same conditions as the measurement conditions of the target element to be analyzed, wavelength correction with higher reliability becomes possible.

  However, it can be seen from FIG. 2 that the emission energy is larger when the burner height is 2 mm than when the burner height is 7 mm. For this reason, it is preferable to measure the burner height at the time of wavelength correction at a height lower than the burner height generally defined as a measurement condition for each element.

  Although not shown, the control unit (CPU / POWER) 29 includes a storage device. In this storage device, the measurement conditions (combustion conditions) of each element and the combustion conditions at the time of wavelength correction are stored, and by the control unit (CPU / POWER) 29, the gas mixing unit (burner) 26, the gas control unit 25, May be automatically controlled.

In the flame atomic absorption spectrophotometer, acetylene and hydrogen are used as the combustion gas and air or nitrous oxide as the combustion gas as a result of consideration of analytical sensitivity, safety, ease of use, and cost. It has become common to use. When these mixed gases of combustion gas and auxiliary combustion gas are burned, as shown in FIG. 2, various molecules such as N ₂ , CO, and H ₂ O are generated. Of these, OH, CN, O ₂ is a molecule that emits strong light in the ultraviolet to visible wavelength range using an atomic absorption spectrophotometer. If the combustion gas and the auxiliary combustion gas are burned at a constant gas mixture ratio, the emission spectrum is plural. At a specific wavelength. Therefore, the wavelength correction of the spectroscope can be performed by using the emission spectrum of the flame in the flame burning unit 22 instead of the emission line spectrum of the deuterium lamp or mercury lamp.

  In FIG. 2, the combustion gas and the auxiliary combustion gas are specified as acetylene gas and air. However, when a plurality of combustion gases and auxiliary combustion gases are sometimes used in the apparatus, the combination thereof, the mixing ratio, and at that time By obtaining the emission spectrum obtained in advance, it becomes possible to select and correct the combustion gas and auxiliary combustion gas actually used in the measurement.

  In particular, since the temperature of the combustion section changes depending on the type of gas, and the thermal effect also changes, more accurate correction is possible by using the gas actually used in the measurement.

  As described above, according to the wavelength correction method of the atomic absorption spectrophotometer according to the embodiment of the present invention, the actual measurement conditions and Since it is possible to perform wavelength correction in an equivalent situation, correction of the set wavelength of the spectroscope 23 including the influence of heat generation from the flame burning unit 22 and each component is performed at low cost using a lamp containing a substance subject to environmental regulations. It becomes possible to carry out without doing.

(Atomic absorption spectrometry)
Next, an atomic absorption analysis method using the wavelength correction method of the atomic absorption spectrophotometer according to the embodiment of the present invention will be described:
(A) First, the light source lamp 27 is turned off, and the gas control unit 25 is used to supply the combustion gas and the auxiliary combustion gas to the gas mixing unit 26 at a constant flow rate, and the flame combustion unit 22 generated by the gas mixing unit 26. Is measured by the detector 24 via the spectroscope 23.

  (B) Next, the emission spectrum and the set wavelength of the spectroscope 23 are compared.

  (C) Further, the set wavelength of the spectroscope 23 is corrected using the wavelength shift amount obtained by this comparison and the correction formula specific to the spectroscope 23.

  (D) When adjustment of the height and angle of the flame combustion unit 22 is necessary, the flame combustion unit 22 is temporarily extinguished as necessary, and necessary adjustment is performed. Thereafter, the combustion gas and the auxiliary combustion gas are supplied again to the gas mixing unit 26 at a constant flow rate using the gas control unit 25, re-ignited, and burned in the gas mixing unit 26 to re-form the flame combustion unit 22. Further, the measurement sample is atomized by a sample supply device (not shown) and supplied to the frame combustion unit 22 (in addition, if adjustment of the height and angle of the frame combustion unit 22 is not necessary, the frame is corrected even after the set wavelength is corrected. The combustion state of the combustion unit 22 may be maintained, and the measurement sample may be immediately atomized and supplied to the flame combustion unit 22).

  (E) Then, the light source lamp 27 is turned on, light having a wavelength specific to the target element is applied to the flame burning unit 22, the amount of light absorbed is measured by the detector 24 via the spectroscope 23, and the amount of light absorbed. The concentration of the measurement sample is quantified by a signal processing unit built in the control unit (CPU / POWER) 29.

  As described above, according to the atomic absorption spectroscopic method according to the embodiment of the present invention, the wavelength that is equivalent to the actual measurement conditions is used as it is by using the hardware that is normally installed in the flame atomic absorption spectrophotometer. Correction is performed, and the atomic absorption analysis can be performed using the wavelength-corrected spectroscope. Therefore, the set wavelength of the spectroscope 23 including the influence of heat generation from the flame burning unit 22 and each component is corrected by the actual atom. Since it can be performed in the same state as the state of absorption spectrometry, highly reliable atomic absorption analysis can be realized.

(Other embodiments)
As mentioned above, although this invention was described by embodiment of this invention, it should not be understood that the statement and drawing which make a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a typical block diagram explaining the outline of the structure of the atomic absorption spectrophotometer which concerns on embodiment of this invention. It is the emission spectrum of the flame in the flame | frame combustion part at the time of using acetylene as combustion gas and air as auxiliary combustion gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 ... Display part 22 ... Frame combustion part 23 ... Spectrometer 24 ... Detector 25 ... Gas control part 26 ... Gas mixing part 27 ... Light source lamp 28 ... Ignition part 29 ... Control part (CPU / POWER)

Claims (4)

Supplying a combustion gas and an auxiliary combustion gas, which are the same gases as the gas at the time of analysis, to the gas mixing unit at a constant flow rate, and measuring an emission spectrum of the flame combustion unit generated by the gas mixing unit;
Comparing the emission spectrum with a set wavelength of the spectrometer;
Correcting the set wavelength of the spectroscope using a wavelength shift amount obtained by the comparison and a correction formula specific to the spectroscope. Correction method.   The measurement of the emission spectrum is performed while supplying the combustion gas and the auxiliary combustion gas to the gas mixing unit at the same flow rate as that of the combustion gas and the auxiliary combustion gas used during the analysis. The correction method of the wavelength of the atomic absorption spectrophotometer as described. The emission spectrum compared with the set wavelength of the spectrometer is
The method for correcting the wavelength of an atomic absorption spectrophotometer according to claim 1 or 2, wherein the peak wavelength closest to the natural wavelength of the target element to be analyzed is used. Supplying combustion gas and auxiliary combustion gas to the gas mixing unit at a constant flow rate, and measuring an emission spectrum of the flame combustion unit generated by the gas mixing unit;
Comparing the emission spectrum with a set wavelength of the spectrometer;
A step of correcting the set wavelength of the spectroscope using a wavelength shift amount obtained by the comparison and a correction formula specific to the spectroscope;
In a state where the combustion gas and the auxiliary combustion gas are supplied to the gas mixing unit and the flame combustion unit is formed, atomizing a measurement sample and supplying the measurement sample to the flame combustion unit;
An atomic absorption analysis comprising: irradiating light of a wavelength specific to a target element to the flame burning part and measuring the amount of light absorbed; and quantifying the concentration of the measurement sample from the amount of light absorbed Law.

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