JP4343015B2 - Atomic absorption photometer - Google Patents

Description

  The present invention relates to an atomic absorption spectrophotometer, and in particular, an atomic absorption spectrophotometer suitable for analyzing metal hydride in a flame atomic absorption photometer that quantifies the metal concentration in a sample by heating and atomizing the sample with the heat of a chemical flame. Regarding the total.

  As a method for correcting background absorption in an atomic absorption photometer, a Zeeman atomic absorption photometer that utilizes a Zeeman effect by applying a magnetic field to a sample is known. On the other hand, as a method for atomizing a sample, a method using a heating furnace and a method using a chemical flame (frame) are known. As an application technique of the flame atomic absorption photometer, hydride generation atomic absorption spectrometry is known. This is mainly applied to the determination of elements such as arsenic, selenium and antimony whose hydrides decompose at a relatively low temperature. To perform this analysis, a hydride generator prepared separately is used to generate a hydride of the target element by mixing a sample such as sodium borohydride and hydrochloric acid with a sample. The hydride is pyrolyzed and atomized, and its absorbance is measured.

  Conventionally, a method of directly introducing a hydride into a frame of argon-hydrogen or the like has been used. However, in recent years, a method of introducing a hydride into a quartz tube and heating the hydride in an atomization unit is highly sensitive. Because it is used exclusively.

  In the hydride generation atomic absorption spectrometer, the background correction is performed by the Zeeman method. For example, as described in JP-A-10-221250, the first quartz heated in a heating furnace is used. There is known a tube composed of a tube and a second quartz tube connected to the first quartz tube and disposed between magnets. The hydride introduced into the first quartz tube is heated and atomized, and then introduced into the second quartz tube, where atomic absorption analysis is performed.

JP-A-10-221250

  As a result of various experiments using the atomic absorption photometer having the configuration described in Japanese Patent Application Laid-Open No. 10-221250, the present inventors have found that there is a problem that the sensitivity during atomic absorption analysis is low. . When the reason was examined, it was found that the sample atomized in the first quartz tube is cooled while moving to the second quartz tube, so that almost no atomic absorption can be obtained. .

  An object of the present invention is to provide a high-sensitivity atomic absorption photometer using a hydride generation analysis method while performing background correction by the Zeeman method.

(1) In order to achieve the above object, the present invention provides a magnetic field having a burner portion for burning a gas to generate a frame, and a pair of pole pieces provided with the frame formed by the burner portion interposed therebetween. And a quartz tube disposed in a gap between a pair of pole pieces of the magnetic field generating unit, into which a hydride is introduced, and a metal for analysis in which light emitted from a light source is generated inside the quartz tube. And a photodetector for detecting the amount absorbed by the atomic vapor.
With this configuration, it is possible to perform background correction by the Zeeman method and perform highly sensitive atomic absorption analysis by the hydride generation analysis method.

  (2) In the above (1), preferably, the length of the gap formed between the pair of pole pieces and the quartz tube is 2.5 mm or more.

  (3) In the above (1), preferably, the magnetic field generation means has a pair of magnets fixed to the pair of pole pieces, and is between a frame formed by the burner portion and the magnets. And a heat shielding means for shielding heat generated from the frame from being transmitted to the magnet.

  (4) In the above (3), preferably, the heat shielding means includes a cooling medium flow path for flowing a cooling medium therein.

  (5) In the above (4), preferably, the heat shielding means includes a gutter structure for discharging water droplets attached to the surface due to condensation.

  (6) In the above (3), preferably, the heat shielding means is fixed to the pole piece.

  (7) In the above (1), preferably, the magnetic field generating means has a pair of magnets fixed to the pair of pole pieces, and is a cooling means fixed to the magnets and cooling the magnets. Is provided.

  (8) In the above (7), preferably, the cooling means is provided with a gutter structure for discharging water droplets adhering to the surface due to condensation.

  According to the present invention, it is possible to perform background correction by the Zeeman method and to perform highly sensitive atomic absorption analysis by a hydride generation analysis method.

Hereinafter, the configuration of an atomic absorption photometer according to an embodiment of the present invention will be described with reference to FIGS.
First, the overall configuration of the atomic absorption photometer according to the present embodiment will be described with reference to FIG.
FIG. 1 is a configuration diagram showing the overall configuration of an atomic absorption photometer according to an embodiment of the present invention.

  The atomic absorption photometer according to the present embodiment includes a light source 10, a burner unit 20, a magnetic field generation means 30, a quartz tube 40, a spectrometer 50, and a photodetector 60. The light source 10 is a hollow cathode lamp, for example, and emits light having a wavelength that is absorbed by atoms to be analyzed. The burner unit 20 mixes and burns a fuel gas such as acetylene and an auxiliary combustion gas such as air to form a flame (frame) F.

  Usually, the solution sample is sprayed in the form of a mist by a sprayer and introduced into the frame F together with the fuel gas and the auxiliary combustion gas from the lower part of the burner and atomized. In this embodiment, the quartz tube 40 heated by the frame F is used. Atomize the sample by Using a hydride generator (not shown), a sample such as sodium borohydride and hydrochloric acid is mixed with a sample to generate a hydride of the target element. This hydride is introduced into the quartz tube 40, and the hydride is heated. Decompose and atomize. Although the temperature of the flame | frame F changes with gases to be used, it normally reaches 2000 to 3000 degreeC. With this heat, the sample (hydride) introduced into the quartz tube 40 becomes atomic vapor and absorbs light passing through the atomic vapor.

  The absorption of the sample atoms at this time absorbs light specific to the element, but since the wavelength of the emission line of the hollow cathode lamp which is the light source 10 coincides with this, the light absorption of a specific element is detected.

  The quartz tube 40 is disposed on an optical axis (indicated by a dotted line in the figure) from the light source 10 to the photodetector 60 and is disposed at a position to which a magnetic field generated by the magnetic field generating means 30 is applied.

  Therefore, absorption by sample atoms atomized in the quartz tube 40 is Zeeman-branched and atomic absorption occurs only for light of a specific polarization plane. Of the light emitted from the hollow cathode lamp, which is a light source, light of the first polarization plane (polarization plane parallel to the magnetic field) is absorbed into the quartz tube 40 by atoms and by the non-target elements in the background. The light of the other second polarization plane (polarization plane perpendicular to the magnetic field) receives only background absorption. The spectroscope 50 selects only light of a specific wavelength. The light having the wavelength selected by the spectroscope 50 is converted into linearly polarized light by the polarizer 70 and split into two light beams. One light beam is light having the same polarization component as that of the first polarization plane described above, and the other light beam is light having the same polarization component as that of the second polarization plane described above. Both light fluxes are chopped by a rotating chopper 80 that alternately passes and blocks the two light fluxes, and the light intensity is measured alternately by the photodetector 60.

  A signal corresponding to the light intensity detected by the photodetector 50 is input to the signal processing circuit 90. The signal processing circuit 90 discriminates the signal corresponding to the first light flux and the signal corresponding to the second light flux in synchronization with the signal from the rotating chopper 80, and obtains the difference between them, thereby obtaining the background absorption. A corrected signal is obtained. Furthermore, it is converted into absorbance and output. Since the absorbance depends on the metal concentration contained in the sample, the relationship between the concentration and the absorbance, that is, a calibration curve is obtained using a standard solution with a known concentration, and the metal concentration in the unknown sample can be obtained from this.

  As described above, the atomic absorption method using the Zeeman method is a double beam photometry that measures the polarization component perpendicular to the magnetic field and the polarization component parallel to the magnetic field, so that even if the lamp energy fluctuates, it is corrected. The baseline fluctuation of the received signal can be reduced.

  In order to perform background correction, a polarizer that branches into two light beams and a rotating chopper are used. However, the optical system for background correction is not limited to this method.

Next, the configuration of the sample atomization unit used in the atomic absorption photometer according to the present embodiment will be described with reference to FIG.
FIG. 2 is a side view showing the configuration of the sample atomization unit used in the atomic absorption photometer according to one embodiment of the present invention. FIG. 2 is a view as seen from the optical axis direction shown in FIG. In FIG. 2, the same reference numerals as those in FIG. 1 denote the same parts.

  The sample atomization unit includes a burner unit 20, a magnetic field generation unit 30, and a quartz tube 40. The magnetic field generating means 30 includes a yoke 32, two permanent magnets 34A and 34B, and two pole pieces 36A and 36B. One end of each of the permanent magnets 34A and 34B is fixed to the yoke 32. Further, pole pieces 36A and 36B are fixed to the other end. The yoke 32, the permanent magnets 34A and 34B, and the pole pieces 36A and 36B constitute a magnetic circuit, and a uniform magnetic field with a predetermined strength is formed in a gap (gap) between the pair of pole pieces 36A and 36B. It is formed. The gap length G of the pole pieces 36A and 36B is, for example, 10 mm. When the gap length G is increased, the magnetic field strength between the gaps is reduced, so that the magnets 34A and 34B may be increased in size. However, this increases the size of the atomic absorption photometer device. Therefore, the gap length G is preferably about 10 mm. Cooling water circulation portions 36A1 and 36B1 are formed at the respective tip portions of the pole pieces 36A and 36B (portions where the pair of pole pieces 36A and 36B are opposed to each other through a gap). Cooling water is circulated from the outside. As will be described later, the pole pieces 36 </ b> A and 36 </ b> B are heated by the frame F of the burner unit 20 to prevent the magnetic field strength of the uniform magnetic field from being lowered.

  The burner unit 20 is disposed inside the magnetic field generation means 30. A flame F is formed at the upper end of the burner portion 20 by the mixed combustion of the fuel gas and the auxiliary combustion gas. The frame F is formed in the gap between the pole pieces 36A and 36B. Furthermore, the quartz tube 40 used for atomization of hydride is an upper portion of the burner portion 20 and is a position heated by the frame F, and is disposed in a gap between the pole pieces 36A and 36B. The quartz tube 40 has a cylindrical shape and is arranged so that the center thereof coincides with the optical axis from the light source 10 to the photodetector 60. The diameter (outer diameter) R1 of the quartz tube 40 is smaller than the gap length G of the pole pieces 36A and 36B. In addition, since the diameter of the quartz tube used for conventional hydride atom absorption is as thick as 10 to 20 mm and cannot be inserted into the gap between the pole pieces 36A and 36B as it is, in this embodiment, the quartz tube 40 having a small diameter is used. ing.

Next, the diameter of the quartz tube used in the atomic absorption photometer according to the present embodiment will be described with reference to FIG.
FIG. 3 is an explanatory diagram showing the diameter of a quartz tube used in the atomic absorption photometer according to one embodiment of the present invention and the measurement results.

  As described above, the diameter R1 of the quartz tube 40 needs to be smaller than the gap length G (here, 10 mm) of the pole pieces 36A and 36B. Therefore, the diameter of the quartz tube 40 was changed variously, and the sensitivity with an atomic absorption photometer at that time was measured by a hydride generation method.

As shown in FIG. 3, hydride of a solution containing 10 μg / L of arsenic was generated from a separately prepared hydride generator and introduced into the quartz tube 40. As a result, the absorbance varied depending on the diameter of the quartz tube 40. . When the diameter R1 of the quartz tube 40 was 6 mm or 7 mm, a sensitivity of 0.06 or higher was obtained. When the diameter R1 of the quartz tube 40 was 5.5 mm and 7.5 mm, the sensitivity was 0.05. When the diameter R1 of the quartz tube 40 was 5 mm and 8 mm, the sensitivity was 0.03. When the diameter R1 of the quartz tube 40 is 9 mm, the absorbance was approximately 0.0. When the quartz tube 40 is not disposed, the frame F is formed straight upward from the upper end of the burner portion 20. When the quartz tube 40 is arranged on the upper part of the portion 20 and the diameter R1 is 8 mm to 9 mm, the gap between the pole pieces 36A and 36B installed at both ends is narrow, so that the frame F has a sufficient clearance between the quartz tube and the pole piece. It was found that the temperature of the quartz tube was insufficient and sufficient sensitivity could not be obtained. That is, since the frame F hits only the bottom of the quartz tube 40 and heats the quartz tube 40 only from the bottom, the temperature inside the quartz tube 40 does not rise sufficiently to the temperature required for atomization of the sample. It depends.

  Here, since the quartz tube 40 having a wall thickness of 1 mm is used, when the outer diameter is 6 mm, the inner diameter is 4 mm. On the other hand, the beam diameter of the light emitted from the light source 10 at the position of the quartz tube 40 is 4 mm. Therefore, when the diameter R1 of the quartz tube 40 is 6 mm or less, a part of the light from the light source 10 is vignetted and does not contribute to atomic absorption, so that the absorbance decreases.

  The sensitivity is required to have an absorbance of 0.05 or more for arsenic 10 μg / L hydride measurement. From this viewpoint, it is preferable to set the diameter R1 of the quartz tube 40 to 5.5 mm to 7.5 mm. As can be understood from the experimental results of FIG. 3, the sensitivity is particularly improved at 6 mm to 7 mm. Note that the lower limit value of the diameter R1 of the quartz tube 40 is also related to the beam diameter. If the beam diameter is reduced, the desired lower limit value of the diameter R1 of the quartz tube 40 can be further reduced.

  In order to sufficiently heat the quartz tube 40, it is necessary that the frame rises from the gap between the quartz tube 40 and the pole pieces 36A and 36B. Therefore, when viewed from the viewpoint of the gap length between the quartz tube 40 and the pole pieces 36A and 36B, the total value of the gap length between the quartz tube 40 and the pole piece 36A and the gap length between the quartz tube 40 and the pole piece 36B is 2. .5 mm or more. With this configuration, even when the hydride is measured, even when the quartz tube 40 is disposed between the pole pieces 36A and 36B and the hydride is introduced into the quartz tube 40, the hydride can be sufficiently atomized and the measurement sensitivity can be improved. It can be improved.

  In FIG. 2 again, in this embodiment, metal heat shielding blocks 38A and 38B for shielding heat from the frame F are further provided between the frame F and the magnets 34A and 34B. The metal heat shield blocks 38A and 38B are made of aluminum or brass so that no attractive force is generated by the magnet. Inside the metal heat shielding blocks 38A and 38B, cooling water flow paths for flowing cooling water are formed. And the cooling water is distribute | circulated from the exterior to the inside of metal heat shielding block 38A, 38B with the cooling water pipe P. As shown in FIG. The metal heat shield blocks 38A and 38B are fixed to the pole pieces 36A and 36B by fixing screws S1 and S2. The metal heat shield blocks 38A and 38B can be fixed to the magnets 34A and 34B, but the pole piece is easier to process, and is fixed to the pole piece.

  As described above, when the quartz tube 40 is disposed on the upper portion of the frame F, the frame F is blocked by the quartz tube 40, and the magnets 34A and 34B are heated to a high temperature by turning around the magnets 34A and 34B. . When the temperature of the magnets 34A and 34B rises, the magnetic force decreases, so the background correction effect by the Zeeman method is reduced.

  Therefore, by providing the metal heat shielding blocks 38A and 38B between the frame F and the magnets 34A and 34B, the frame F is prevented from directly hitting the magnets and raising the temperature. Further, by circulating the cooling water through the metal heat shielding blocks 38A and 38B, the metal heat shielding blocks 38A and 38B themselves are heated to prevent the temperature of the magnets 34A and 34B from rising. .

Here, the structure of the metal heat shielding block used in the atomic absorption photometer according to the present embodiment will be described with reference to FIG.
FIG. 4 is a perspective view showing a structure of a metal heat shielding block used in an atomic absorption photometer according to an embodiment of the present invention.

  A cooling water passage CP for flowing cooling water is formed inside the metal heat shielding block 38. And cooling water is distribute | circulated from the exterior to the inside of the metal heat shielding block 38 by the cooling water pipes P1 and P2. The metal heat shield block 38 is provided with a hole 38X for fixing to the pole piece with a fixing screw.

  Further, the metal block 38 is provided with a ridge structure 38Y for discharging water droplets adhering to the dew at the lower part on the side in contact with the frame. Since water vapor is contained in the frame, condensation occurs on the surface of the metal block 38 being cooled when the frame hits the metal block 38. When the condensed moisture adheres to the inside of the apparatus, rust or the like is generated in the apparatus. Therefore, the eaves structure 38Y collects water droplets generated by condensation and is discharged from the drain hose P3. Soot adheres to the shielding block due to the contact of the flame, but the flame does not contact the magnet.

  In addition, when the frame directly hits the magnet, the magnet is oxidized and corroded, and moisture contained in the flame is condensed, which may cause the magnet to corrode. By using it, such a fear can be avoided.

  Here, if the total length of the metal heat shielding block 38 is L1, the width is W1, and the height is H1, the total length L1 is equal to or longer than the length of the burner portion 20 in the optical axis direction. The width W1 is 10 mm. Further, the height H <b> 1 is set such that the position of the lower portion is lower than the height of the upper surface of the burner portion 20.

  Since the shielding block 38 prevents the frame F from coming into contact with the magnet 34, it does not need to be in close contact with the magnet 34 as shown in FIG. For example, a gap of 1 mm or more is formed between the magnet 34. On the other hand, the shielding block 38 can be brought into close contact with the magnet 34 by shifting the positions of the fixing screws S1 and S2. In this case, the shielding block 38 not only functions as a heat shielding means, but also functions as a magnet cooling means, and the magnet is cooled, so that it is more effective under conditions where the temperature of the magnet rises. .

  As a result of measuring the hydride generated by introducing an arsenic 10 μg / L solution into the hydride generator using the atomic absorption spectrophotometer having the above configuration, an absorbance of 0.06 was obtained. In addition, as a result of measuring the hydride generated by introducing the blank solution into the hydride generator for 30 minutes, it was found that the change in absorbance was within 0.000 ± 0.005, and the signal was stable over a long period of time. It was. From this, it is understood that the hydride introduced into the quartz tube according to the present example is decomposed by the heat of the flame to become atomic vapor and is measured for atomic absorption. In addition, it was confirmed that double beam photometry by the Zeeman method is possible, and long-term signal stability and high data reliability can be obtained.

Next, another structure of the metal heat shielding block used in the atomic absorption photometer according to the present embodiment will be described with reference to FIG.
FIG. 5 is a perspective view showing another structure of the metal heat shielding block used in the atomic absorption photometer according to the embodiment of the present invention. The same reference numerals as those in FIG. 4 indicate the same parts.

  The difference from the shielding block 38 of FIG. 4 is that no cooling water flow path is provided inside the metal heat shielding block 38 ′ and no eaves structure is provided. The total length L1 and the height H1 are the same as those in FIG. 4, but the width W2 can be made as thin as the cooling water flow path is unnecessary, and is 2 mm thinner than that in FIG.

  Further, as shown by dotted lines in FIG. 2, instead of the metal heat shielding blocks 38A and 38B, cooling blocks 39A and 39B are provided outside the magnets 34A and 34B (on the side opposite to the side facing the burner portion 20). May be fixed in close contact with each other. Inside, a cooling water channel is provided, and cooling water is circulated from the outside. Even when the magnets 34A and 34B are cooled by the cooling blocks 39A and 39B, it is possible to prevent the magnets 34A and 34B from being heated by the frame of the burner unit 20 and reducing the magnetic force.

  As described above, according to the present embodiment, the sample introduced into the quartz tube is measured at the same time as being thermally decomposed, and in this case, background correction is performed by the Zeeman effect by the magnets on both sides. Accurate measurement is possible. In addition, since the baseline signal is stabilized due to the double beam photometry, highly reliable data can be obtained over a long period of time.

The present invention is suitable for analyzing samples containing trace amounts of arsenic, selenium, antimony, and the like, and can be applied to the analysis of environmental samples, biological samples, industrial materials, foods, and other various samples.

It is a block diagram which shows the whole structure of the atomic absorption photometer by one Embodiment of this invention. It is a side view which shows the structure of the sample atomization part used for the atomic absorption photometer by one Embodiment of this invention. It is explanatory drawing which shows the diameter of a quartz tube used for the atomic absorption photometer by one Embodiment of this invention, and a measurement result. It is a perspective view which shows the structure of the metal heat shielding block used for the atomic absorption photometer by one Embodiment of this invention. It is a perspective view which shows the other structure of the metal thermal-shielding block used for the atomic absorption photometer by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Light source 20 ... Burner part 30 ... Magnetic field generation | occurrence | production means 34A, 34B ... Magnet 36A, 36B ... Pole piece 38A, 38B ... Shield block 38Y ... Saddle structure 40 ... Quartz tube 50 ... Spectroscope 60 ... Photo detector 70 ... Polarizer 80 ... Rotating chopper 90 ... Signal processing unit CP ... Cooling water flow path F ... Flame (frame)

Claims (8)

A burner section for burning a gas to generate a flame;
A magnetic field generating means having a pair of pole pieces provided across a frame formed by the burner portion;
A quartz tube disposed in the gap between a pair of pole pieces of the magnetic field generating means and into which a hydride is introduced;
An atomic absorptiometer, comprising: a photodetector for detecting an amount of light emitted from a light source absorbed by atomic vapor of a metal for analysis generated in the quartz tube. In the atomic absorption photometer according to claim 1,
An atomic absorption spectrophotometer characterized in that a gap formed between the pair of pole pieces and the quartz tube has a length of 2.5 mm or more. In the atomic absorption photometer according to claim 1,
The magnetic field generating means has a pair of magnets fixed to the pair of pole pieces,
An atomic absorptiometer, comprising: a heat shielding means arranged between a frame formed by the burner portion and the magnet, for shielding heat generated from the frame from being transmitted to the magnet. In the atomic absorption photometer according to claim 3,
The atomic absorption spectrophotometer, wherein the heat shielding means includes a cooling medium flow path for flowing a cooling medium therein. The atomic absorption photometer according to claim 4,
The atomic absorption spectrophotometer characterized in that the heat shielding means has a gutter structure for discharging water droplets adhering to the surface due to condensation. In the atomic absorption photometer according to claim 3,
The atomic absorption photometer, wherein the heat shielding means is fixed to the pole piece. In the atomic absorption photometer according to claim 1,
The magnetic field generating means has a pair of magnets fixed to the pair of pole pieces,
An atomic absorption photometer comprising a cooling means fixed to the magnet for cooling the magnet. The atomic absorption photometer according to claim 7,
The atomic absorption spectrophotometer characterized in that the cooling means includes a gutter structure for discharging water droplets adhering to the surface due to condensation.

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