JPH0663969B2 - Flameless atomizer for atomic absorption spectrometry - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a flameless atomizer for atomic absorption spectrometry, and more particularly to a quartz atomizer made of graphite or metal for atomizing a sample by applying a current or voltage to heat the gas with a juule heat. The present invention relates to a flameless atomizer for atomic absorption spectrometry, which is suitable for not disturbing the gas flow.

[Background of the Invention]

In a flameless atomizer for atomic absorption analysis, a heating furnace called a cylinder, which is made of metal or metal, is used in a portion where a sample is injected and heated to generate atomic absorption. Electrodes made of a good electric conductor are mounted on both ends of this cube, and a cord from a power supply is connected to the electrodes. This electrode is usually cooled with cooling water so that the temperature does not rise. When the sample is injected into the cuvette, it is heated to about 100 ° C by energization and the water in the sample is evaporated. Next, although it depends on the element, it is heated to several 100 ° C. to decompose or scatter the organic matter in the sample or scatter the coexisting metal atoms or molecules. Next, it is heated at a very high temperature rising rate, and this also varies depending on the element, but it is heated from 2000 ° C. to 3000 ° C. to atomize the target element, at which time atomic absorption is performed. When the water content of the sample evaporates, the organic matter in the sample scatters, or the coexisting substances scatter, the inert gas (called "Kanoa gas") that flows in the cuvette prevents them from being harmful to atomic absorption. Carry it out of the room. Therefore, a significant amount of carrier gas is usually flushed during this time. Then, in atomization (when performing atomic absorption), the flow rate of the carrier gas is reduced. This is because if the flow rate of the carrier gas is high, the target element is carried out of the cube in a short time, resulting in a decrease in sensitivity. However, it is effective to completely eliminate the carrier gas flow rate from the viewpoint of improving the sensitivity, but in the case of measurement of an actual sample, the target element scatters to the end of the cuvette and is re-exposed to the part where the temperature is not so high. The problem of so-called contamination, in which they coagulate and evaporate again during the next measurement, causing atomic absorption, and the coexisting organic substances and coexisting elements evaporate all at once at the atomization stage (realistically, at the previous stage It is almost impossible to completely remove these), and most of the light from the light source is reflected or absorbed, which causes a problem of deterioration of measurement accuracy. Therefore, it is considered preferable to flow a small amount of carrier gas even in the atomization stage. There are two methods of flowing the carrier gas, one is to flow from the center to the end of the cubet, and the other is to flow from the end to the center of the cuvet. In this regard, as described in Japanese Patent Publication No. 53-2323, in the former method, since the coexisting substance and the target element are carried to the cooling section, the problem of contamination and the coexisting acid are condensed in the cooling section. Therefore, there is a problem of causing rust on the metal part, and the latter method, which has less of these problems, is now the mainstream. In addition, there are various types of cubets, but they are roughly classified into a type in which only the sample injection hole is opened in the center of the cuvet, and in addition to the sample injection hole in the center, another hole is formed on the left and right of the injection hole. There is a certain type. The former type of cuvette has a large effect of carrier gas, and usually has a high-grade control function of carrier gas. In addition, in consideration of the temperature distribution of the cuvet, we have devised the thickness and shape of the cuvet. On the other hand, the latter type of kyubet, as shown in Japanese Utility Model Application Laid-Open No. 49-108489, adjusts the temperature distribution of the kyubet by separate holes on the left and right, and therefore, normally,
The hole is much larger than the sample injection hole in the center. Therefore, the carrier gas flowing through the inside of the cuvette flows out of the cuvette through the holes on the left and right, and the carrier gas hardly flows in the central portion where the atomic absorption occurs, and the above-mentioned role as the carrier gas is hardly performed.

Looking at the recent sample morphology, the number of samples, which have a complicated structure such as biological samples and chemical industrial samples, and give great interference during measurement, is increasing. Therefore, there is an increasing need to sufficiently generate the effect of carrier gas.

On the other hand, considering the accuracy when using a flameless atomizer, this method evaporates all of the injected sample,
Needless to say, the precision of sample injection is very important, because the total amount of the target elements in it will be involved in atomic absorption. In addition, since the temperature distribution during heating of the cuvette is not always uniform in the central part (although the shape of the cuvette has been devised to make it fairly uniform), the reproducibility of the injection position of the sample and the shape of the sample during injection Is also related to accuracy. These have been greatly improved recently by using an autoinjector called an autosampler. However, it has not yet been possible to obtain perfect accuracy. One of the possible causes is the instability of the residence time as an atom in the atomization stage of the target element and the non-uniformity of the atom density. For example, inner diameter 6 mm, outer diameter 8 mm, length 30 mm, sample injection hole diameter
Considering a 2 mm cube, the atomization temperature is set to 2700 ° C and the carrier gas flow rate at atomization is set to 50 ml / min. However, the set carrier gas flow rate is a flow rate when cold (at room temperature). When heating is performed under such conditions, the temperature of the carrier gas is 1200 to 1300.
It can be as high as ℃. As a result, the carrier gas flow velocity increased about 5 times due to volume expansion, and the carrier gas ejection speed from the sample injection hole with a diameter of 2 mm was about 1 cm from 25 cm / sec at room temperature.
It changes to 25 cm / sec. And this changing time is 1
It can be said that it takes about 2 seconds and changes almost instantaneously. That is, since the flow velocity changes greatly due to the thermal expansion of the carrier gas in a very short time, it can be said that the state of the change is very unstable. In the case of a real sample, in many cases, a large amount of residual organic matter and coexisting elements or salts remain at the time when atomization begins. Therefore, when they evaporate instantaneously, they expand and diffuse in the cube.
Of course, the target element also shows the same behavior,
The internal pressure of the cucumber is much higher than that of the cucumber gas alone, and the gas flow inside the cuvette (carrier gas, vapors of residual residues and coexisting substances and vapors of the target element, etc.) becomes faster and becomes unsteady. Be stable. Since the atomic absorption occurring in the cube is determined by the number of atoms on the optical axis from the light source, the vapor state of the target element inside the cube is unstable (the gas inside the cube is unstable). According to the above), the accuracy is naturally lowered. In addition, the number of atoms that stay in the chamber (the time that the target element stays in the atomic state) is also determined by the flow velocity, so if the flow velocity becomes unstable (the flow velocity becomes faster), the sensitivity and accuracy will decrease. Will be invited.

As described above, a flameless atomizer such as a conventional graphite atomizer has no problem in accuracy if the internal state is constant (meaning that the state of change is constant even if it changes), but the original nature of carrier gas It is very difficult to remove the instability factor in the measurement of the actual sample while maintaining the above purpose, and as a result, it becomes a cause of lowering the accuracy in the actual sample.

FIG. 6 is a sectional view of the cuvette shown in Japanese Examined Patent Publication No. 53-23236. Carrier gas flows into the cuvette 30 from both ends of the cuvette 30, and the sample injection hole of the cuvette 30.
Spill out from 31. Therefore, any change in the flow velocity caused by the thermal expansion (internal pressure increases) of the gas in the cuvette 30 (carrier gas and residual vapor of coexisting substances, etc.) due to the rapid temperature rise during atomization is caused by the sample injection hole. It is certain that the flow velocity generated from around the sample injection hole 31 will instantaneously become 5 times or more, and the vicinity of the sample injection hole 31 inside the cube 30 (the part where atomic absorption occurs) is very high. It becomes unstable. This state is not considered to be constant for each sample,
As a result, the residence time of atoms becomes unstable and the number of target elements present on the optical axis becomes nonuniform, which is considered to be one of the causes of deterioration of measurement accuracy.

FIG. 7 is a sectional view of the cuvette shown in Japanese Utility Model Laid-Open No. 49-108489, and ventilation holes 34a and 34b are provided on both sides of the sample injection hole 33 of the cuvette 32. This vent 34a,
34b is clearly larger than the sample injection hole 33, and
Almost all the carrier gas flowing inside the air vent 34a,
It spills from 34b to the outside. Therefore, in the cuvette 32 shown in FIG. 7, it is possible to prevent the internal pressure from rising and the change in the flow rate due to the vaporization of the residue coexisting in the sample 10 due to the rapid heating. It is almost impossible to reduce the background absorption and adjust the sensitivity of the target element. Therefore, when the background is large, it is necessary to dilute the sample itself, which is a problem in the analytical operation.

[Object of the Invention]

The present invention has been made in view of the above, and its object is to provide a flameless atomic absorption spectrophotometer having a cubet that can always stabilize the internal state of the cubet during atomization while maintaining the effect of the carrier gas. To provide an atomizer.

[Outline of Invention]

According to the present invention, one of the causes of the decrease in the accuracy of the flameless atomizer for atomic absorption spectrometry is that the pressure in the cubette rises due to the rapid temperature rise at the time of atomization and the change in the flow velocity of the gas in the cubette accompanying it. Yes, and it was made experimentally to confirm that it is in a different state each time.

The gist of the invention will be described with reference to the reference numerals of FIGS. 1 and 2 used in the description of the embodiment. From the both ends of a cylindrical cuvette 1 which has a sample injection hole 2 in the center and generates heat by controlling energization. Pour an inert carrier gas into the cuvette,
In a flameless atomizer for atomic absorption analysis in which the inflowing carrier gas flows out of the cuvette through the sample injection hole 2, a cylindrical surface of the cuvette 1 is symmetrical with respect to the center of the sample injection hole 2 in the cuvette axial direction. At least a pair of fine holes 24a, 24b for adjusting the internal pressure of the cuvette are provided, and the fine holes 24a, 24b allow the gas inside the cuvette to escape when the internal pressure of the cuvette rises due to high temperature in the atomization stage of the sample. The size and number of the holes are determined so as to regulate the internal pressure, and the total cross-sectional area of the holes of the fine holes 24a, 24b is set to be twice the cross-sectional area of the sample injection hole 2 or less. Characterize.

According to the above configuration, in the heating (heating of the sample at several 100 ° C.) at the stage of drying and ashing the sample (the stage before atomizing the sample), a large amount of carrier gas flows from both ends of the cuvette 1 and flows in the respective flows. Flows out of the cuvette through the sample injection hole 2 toward the center of the cuvette 1, and moisture (evaporation) of the sample and scattering of organic substances and coexisting substances in the sample are carried on the carrier gas and carried out of the cuvette.

Next, even in the atomization stage (atomic absorption stage), as described above, a slight amount of carrier gas is used for sample drying and ashing due to contamination problems and removal of residual organic substances and evaporation of coexisting elements. Shed by a route. The carrier gas thermally expands to more than 1000 ° C due to the temperature rise and high temperature (heating of the sample from 2000 ° C to 3000 ° C) in this atomization stage, and the internal pressure of the cuvette rises due to this expansion and residue of organic matter and vaporization of coexisting elements. , Due to the increase in pressure inside the cuvette,
The gas inside the cuvette escapes via 24b to suppress the increase in the cuvette internal pressure, and the cuvette internal pressure is regulated.

Here, the fine holes 24a, 24b are arranged symmetrically with respect to the center of the sample injection hole 2 in the axial direction of the cuvette, and the fine holes 24a, 24b
If the total cross-sectional area of the holes of 24b is less than twice the cross-sectional area of the sample injection hole 2, the flow of the carrier gas from both ends of the cuvette 1 to the sample injection hole 2 will also substantially affect the effects of the fine holes 24a and 24b. As a result of the experiment, it is confirmed that the original function of the carrier gas is maintained well without receiving it.

Therefore, according to the present invention, prevention of contamination, without impairing the original function of the carrier gas of reducing the background absorption, suppressing the increase of the internal pressure of the cuvette at the atomization stage, thereby stabilizing the flow velocity inside the cuvette, Improves atomic absorption measurement accuracy.

Example of Invention

The present invention will now be described with reference to the embodiments shown in FIGS. 1 and 2 and the third embodiment.
This will be described in detail with reference to FIGS.

FIG. 1 is a sectional view showing an embodiment of a flameless atomizer for atomic absorption analysis of the present invention. In FIG. 1, 1 is a cylindrical cuvette made of a heat-generating material, 2 is a sample injection hole provided in the central part of the cuvette 1, and 3a and 3b are electrodes made of a good electric conductor, which support the cuvette 1 and at the same time. Including the above, it shuts the cuvette 1 from the outside air. Four
Is a pipette injection hole provided in the electrode 3a. 5a, 5b is an electrode block, the electrodes 3a, 3b are press-fitted into the electrode blocks 5a, 5b, respectively, and the electrode blocks 5a, 5b are provided with cooling water passages 6a, 6b for cooling. Cooling water is flowing. At one end of each of the electrode blocks 5a and 5b, there is a light transmission hole in the axial direction of the cuvette 1, and there are quartz pipes 7a and 7b for passing light therethrough, and windows 8a and 8b are arranged in them. I am doing it. The windows 8a and 8b shield the inside of the cuvette 1 from the outside air and allow the carrier gas to flow through the inside of the cuvette 1. Reference numeral 9 is an optical axis, 10 is a sample, and 11a, 11b, 12a, and 12b are inlets and outlets of the inner and outer passages of the carrier gas provided in the electrode blocks 5a and 5b, respectively.

Reference numeral 13 is a gas control unit, which is usually unitized, and each of its parts operates in conjunction with a control unit for controlling the temperature. When the main switch of the control unit is turned on,
The solenoid valve 15 is opened, the inert gas is introduced from the inert gas inlet 14, and enters the gas control unit 13. Then, the pressure switch 16 detects whether or not the pressure of the introduced inert gas is sufficient. If the pressure is not sufficient (including the case where there is no inert gas), an alarm is generated and the heating program is not started. This is because the temperature of the cubet 1 rises up to 3000 ° C. at maximum, so that the oxidization of the cuvet 1 due to lack of inert gas is prevented.

Reference numeral 17 is a pressure regulator, and 18 is a pressure meter, which are adjusted to proper pressure in advance. The inert gas is branched behind the pressure regulator 17, and the flow rate of each is adjusted. Kibetsuto 1
A flow meter (in some cases, an orifice is used) 19 having a flow rate adjusting function is arranged in the flow path system flowing outside the chamber, and then connected to the external flow path inlets 12a and 12b of the heating furnace. On the other hand, the flow path system that flows inside the sample 1 (sample storage part) is further divided into two, and flow meters 20 and 21 with a flow rate adjusting function are arranged in each flow path, after which the solenoid valves are respectively installed. 22,23 are arranged. This is so that independent flow rates can be set for the drying and ashing stage and the atomization stage of the sample 10. Therefore, the solenoid valves 22 and 23 are controlled by a temperature program control unit (not shown) and are turned on and off so that the flow rate is switched at a required temperature program stage. solenoid valve
22 and 23 are connected to the inlet ports 11a and 11b of the cuvette. The sample 10 is dripped into the cuvette 1 from the sample injection hole 2 of the cuvette 1 through the pipet injection hole 4. After that, the sample 10 is dried and incinerated. At this time, the carrier gas flowing in the cuvette 1 is relatively large (0.1 ~
1 / min). This flow rate setting is done with the flow meter 20,
The solenoid valve 22 is opened and the solenoid valve 23 is closed. The carrier gas at this time has a function of carrying out the steam and coexisting substances generated in the drying and ashing stages to the outside of the cuvette 1. Next, in the atomization stage, a small amount of carrier gas is allowed to flow. This flow rate is set by the flow meter 21 and the solenoid valve
23 is opened and the solenoid valve 22 is closed. The carrier gas at this time has the function of allowing the target element to stay in the cuvette 1 for a long time and improving the sensitivity. However, if the sample concentration is high or if a large amount of coexisting substances remain, the contamination and background absorption may be increased, so it is necessary to adjust the flow rate according to the sample. Usually, this flow rate is adjusted to 0 to 200 ml / min, and the most frequently used flow rate is about 50 ml / min.
Next, at the cleaning heating stage, the solenoid valve 22 is opened again, and the solenoid valve 23 is closed to allow a large amount of carrier gas to flow into the cuvette 1 to discharge the residue in the cuvette 1. After that, both solenoid valves 22 and 23 are closed, the cuvette 1 is cooled, and then the sample 10 is injected again, and the same operation is repeated.

In addition, the heating furnace shown here (cubet 1 and electrodes 3a, 3b)
Is a typical example, and various modifications are naturally conceivable for the structure for shutting off the cuvette 1 from the outside air, the shape of the electrodes, and the like.

FIG. 2 is a sectional view showing an embodiment of the cuvette 1 of FIG. The sample 10 injected into the cuvette 1 is first dried and incinerated, and at that time, the residual organic substances and the coexisting elements that have coexisted remain. Then it is rapidly heated and atomized. The purpose of the present invention is to eliminate the cause of instability of the internal state of the cuvette 1 and the increase in the internal pressure caused by the expansion of the carrier gas at this time, the residue and the vaporization of coexisting elements. The fine holes 24a and 24b are provided at appropriate positions. These fine holes 24a, 24b
The diameter of the holes is so that the positions of the micro holes 24a, 24b are relative to the center of the cuvette 1 in order to prevent the prevention of contamination and the background reduction function, which are the original purpose of carrier gas. The positions are symmetrical with respect to the axial direction, and the total cross-sectional area of the fine holes 24a and 24b is not more than twice the cross-sectional area of the sample injection hole 2. This is the result confirmed by the experiment. The number of the micro holes 24a and 24b may be one pair on the left and right, or a plurality of pairs on the left and right. In short, there is no problem as long as the above conditions are satisfied. Second
The figure shows the case of two pairs of left and right. Also, the fine holes 24
The positions of a and 24b are preferably at the high temperature part or at a position slightly deviated from the high temperature part, and at the low temperature part, contamination may occur in a high-concentration sample or the like, which is not preferable. According to the results of examination of several kinds of cuvet having different diameters and lengths, the position of the micropores was found to be effective at a position 1 to 2 times the inner diameter of the cuvet, as compared with the sample injection hole of the cuvet. Figure 2 shows the case where the temperature program is dry. In this case,
Most of the carrier gas flows out from the sample injection hole 2 in the center, and effectively carries out moisture and the like during drying.

FIG. 3 is a diagram showing the state of the cuvette shown in FIG. 2 during atomization. As shown in FIG. 3, increase in internal pressure caused by thermal expansion of carrier gas at high temperature is caused by the fine holes 24a,
It escapes from 24b and suppresses the pressure rise in the central part (the most important part in measurement) inside the cuvette 1 to prevent the central part from being disturbed. As a result, a stable state is always obtained and accuracy can be improved.

FIG. 4 is a diagram showing the relationship between the carrier gas flow rate and the background sensitivity ratio for explaining the effect of the present invention.
The figure is also a diagram showing the relationship between the carrier gas flow rate and the copper sensitivity ratio, and in both FIGS. 4 and 5, the a curve is the second curve according to the present invention.
In the case of the cuvette shown in the drawing, the b curve and the c curve are characteristic curves in the case of the cuvette shown in FIGS. 6 and 7, respectively, which are shown for comparison. It can be seen from FIG. 4 that the effect of carrier gas is not lost according to the cuvette 1 according to FIG. 2, and from FIG. 5, according to the cuvette 1 shown in FIG. It is almost the same as the KYUVET 33 of FIG. 7, and it is understood that it is good.

Using a flameless atomizer equipped with a cubette, which has microholes having a cross-sectional area not exceeding twice the cross-sectional area of the sample injection hole on both sides of the above-mentioned sample injection hole of the cube, copper containing 2% of sodium chloride is used. As a result of examining the measurement accuracy of the sample,
Conventionally, the reproducibility, which was 5 to 7% in relative standard deviation (variation coefficient), has been improved to 3 to 5%.

〔The invention's effect〕

As described above, according to the present invention, the internal pressure rises due to the thermal expansion of the carrier gas at the time of temperature rise and high temperature without impairing the original function of the carrier gas such as prevention of contamination and reduction of background absorption. Further, it is possible to eliminate an instability factor due to the instability of the flow velocity, and it is possible to improve the measurement accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the flameless atomizer for atomic absorption analysis of the present invention, FIG. 2 is a sectional view showing an embodiment of the cuvette of FIG. 1, and FIG. 3 is shown in FIG. FIG. 4 is a diagram showing the state of atomization of the cuvette, FIG. 4 is a diagram showing the relationship between the carrier gas flow rate and the background sensitivity ratio for explaining the effect of the present invention, and FIG. 5 is the same as the carrier gas flow rate and the copper sensitivity. A diagram showing the relationship with the ratio, FIG. 6 and FIG. 7 are cross-sectional views of a conventional cuvette. 1 ... Kivet, 2 ... Sample injection hole, 3a, 3b ... Electrode, 4 ... Pipet injection hole, 5a, 5b ... Electrode block, 6
a, 6b …… cooling water passage, 8a, 8b …… window, 9 …… optical axis, 10 ・ ・ ・
… Samples, 11a, 11b …… Introduction of the inner flow path of the cup, 12a, 12b
...... Cybet external flow path inlet, 13 ...... Gas control unit, 19, 2
0,21 …… Flowmeter with flow path adjustment function, 22,23 …… Solenoid valve, 24a, 24b …… Micropore.

Claims (2)

[Claims] 1. An inert carrier gas is flown into the cuvette from both ends of a cylindrical cuvette (1) which has a sample injection hole (2) in the center and generates heat by controlling energization. In a flameless atomizer for atomic absorption analysis, which flows out of the cuvette through the sample injection hole (2), the sample injection hole (2) is provided on the cylindrical surface of the cuvette (1).
At least a pair of fine holes for adjusting the internal pressure of the cuvette (24
a, 24b), and these micropores (24a, 24b) are of a size that allows the gas inside the cuvette to escape and regulate the cuvette internal pressure when the cuvette internal pressure rises due to high temperature during the atomization stage of the sample. And the number of the micropores (24a, 24b), and the total cross-sectional area of the micropores (24a, 24b) is set to not more than twice the cross-sectional area of the sample injection hole (2). Flameless atomizer for. 2. The distance from the fine holes (24a, 24b) to the sample injection hole (2) is set to 1 of the inner diameter of the cuvette (1).
The flameless atomizer for atomic absorption spectrometry according to claim 1, wherein the distance is set to a distance between two times.