JPH0833346B2 - Atomization furnace for atomic absorption spectrophotometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of a graphite heating element used in an atomization furnace for an atomic absorption spectrophotometer, usually a graphite heater called a cuvette, and particularly, measurement operability. The present invention relates to an atomization furnace for an atomic absorption spectrophotometer, which is suitable for the analysis of trace metal impurities having a significantly improved measurement value and high reliability of measured values.

[Conventional technology]

In recent years, the atomization furnace of an atomic absorption photometer has adopted a flameless heating method of heating a graphite cuvette with a large current, instead of a heating method using a flame of a burner. This flameless atomic absorption spectrophotometer atomization furnace is a graphite cylindrical body that self-heats when the furnace body is energized, and atomizes a measurement sample at a high temperature. The furnace is arranged between a light source section that emits measurement light and a measurement section that measures light passing through the atomization furnace, and the measurement light that exits the light source section and enters the hollow part of the cuvette is absorbed by atomized atoms. The amount of transmitted light is measured in the measuring unit and the amount of absorption is calculated.

The graphite cuvette is integrally formed with a cylindrical so-called atomization portion having a small through-hole for injection of a measurement sample formed in the center, and a cylindrical portion appropriately overhanging on both sides thereof, and energizing electrodes at both ends thereof. Mounted in surface contact.

The unit operation of measurement is performed as follows. That is, at a constant flow rate from both ends of the cuvette to the hollow part, for example,
While continuously introducing an inert gas such as argon gas from the electrode holders on both sides in the direction of the cuvette, inject a liquid sample for measurement by operating the device through the injection hole in the center of the cuvette that has been cooled to about room temperature. Then, the sample is slowly heated to about 200 ° C, dried and ashed at about 600 ° C, and then rapidly heated to about 3000 ° C to vaporize the sample into atomic vapor, and the absorption of measurement light by this is increased. measure.

[Problems to be Solved by the Invention]

In the measurement by the calibration curve method using such a flameless atomic absorption spectrophotometer, a calibration curve is created in advance based on the atomization furnace used, and the measurement and quantification of the sample can be performed under the same operating conditions as the creation of the calibration curve. Done. Usually, this atomization furnace is heated to a high temperature of, for example, about 3000 ° C. by AC electricity, and preferably, an external magnetic field is applied to the atomization part for the purpose of background correction. In such a measurement operation, the nuclear reactor is rapidly heated and cooled between about 3000 ° C. and the vertebral temperature for each measurement, and the cuvette expands and contracts about 1 mm each time. Repeatedly, the consumption of the furnace itself gradually progresses and the measurement accuracy deteriorates.
The calibration curve was appropriately checked, and if the reproducibility fell below the desired limit, the calibration curve had to be recreated. Further, in the repeated measurement operation, the inconvenience that the sample cannot be injected often occurs.
Such deterioration of measurement accuracy and inconvenience in sample injection have been a serious problem particularly in the Zeeman type flameless atomic absorption spectrophotometer which performs background correction by applying an external magnetic field.

Therefore, the object of the present invention is to prepare a calibration curve once,
It is to provide an atomic reactor capable of performing as many highly accurate measurements as possible. Another object is to provide a practically excellent atomization furnace that does not cause inconvenience in the injection operation of the measurement sample.

[Means for solving the problem]

As a result of repeated research on an atomization furnace for an atomic absorption photometer capable of solving the above problems, the present inventors have developed a practically highly desirable atomization furnace.

That is, the present invention is a cylindrical atomization furnace used for an atomic absorption spectrophotometer, in which at least one plane not perpendicular to the axis is formed on the outer peripheral surface of one end of the graphite cuvette so as to match with the electrode corresponding surface. The main point is an atomic absorption photometer atomization furnace with excellent measurement stability.

The cuvette of the flameless atomic absorption spectrophotometer atomization furnace according to the present invention has, for example, an inner diameter of 4 mm to 5 mm and an outer diameter of 7 mm to 8 mm,
A small graphite cylinder having a length of about 30 mm, in which a small through hole having a diameter of 1 to 1.5 mm for injecting a measurement sample is formed in the central portion, and the length of the central portion of the cylindrical body is 7 to 8 mm. Is configured so as to function as an atomization portion, and the cylindrical end edge ridge portions thereof are formed into chamfered conical surfaces. Both ends of such an atomization furnace are held by opposing ring-shaped electrode blocks having contact inner surfaces that match their contours to fit them in a mating fashion.

Such an atomizing furnace of the present invention is particularly characterized in that at least one flat surface that is not perpendicular to the cylinder axis is formed on one outer surface of the cylindrical end portion of the cuvette, and this is inserted. The electrode holding part to hold is formed in the joining concave surface matched with the outer shape. At least one plane that is not perpendicular to the cylinder axis formed at one end of the cuvette is a plane parallel or inclined to the cylinder axis, and such a plane may have only one surface with a cylindrical curved surface left. Although good, a plurality of planes, for example, two or eight planes are usually formed practically and advantageously. Further, the plurality of planes may be asymmetric with respect to the axis, but it is more advantageous to form the planes preferably symmetrically.

According to the present invention, by forming such a flat surface on the outer surface of one end of the cuvette, positioning when attaching the cuvette to the electrode and assembly of the atomic reactor can be performed extremely smoothly and accurately, and excellent operation in repeated measurement is possible. It is based on the fact that the practically highly desirable fact that stable and high measurement accuracy in the measurement of absorptivity and absorptiometry is obtained has been found.

It is important to form such a flat surface only on the outer surface of one end of the cuvette, and if the flat surfaces are formed at both ends, it is difficult to position the cuvette on the left and right with respect to the electrodes, and a slight deviation occurs. It seems that stable measurement cannot be obtained. Further, when considering the assembly and operability of the atomic absorption photometer atomization furnace and the measurement accuracy, the plane formed on the outer surface of one end of the cuvette is inclined, for example, slightly closer to the edge side. All four, five,
It is optimum to form the six or eight surfaces into a slanted flat surface group having a truncated pyramid shape, especially a regular pyramid shape, with no cylindrical surface left and slightly tapered on the end side.

 The present invention will be described more specifically with reference to the accompanying drawings.

FIG. 1 is a schematic diagram for explaining an example of an atomic absorption spectrophotometer including an atomization furnace of the present invention, and FIG. 2 is a front view (FIG. A) and a left side view (of a typical cuvette according to the present invention). Fig. B) and right side view (Fig. C). Further, FIG. 3 is a similar view of a conventional representative cuvette, in which FIG. 3 (a) is a front view, FIG. 3 (b) is a left side view and FIG. 3 (c) is a right side view.

As shown in FIG. 1, the cylindrical atomizer has two end portions of a cylindrical cuvette 1 having a sample injection port 2 directed upward in the central portion and small holes 5, 5 for injecting an inert gas. The cylindrical electrode holders 4 and 4'formed with ′ are assembled by holding the cylindrical electrode blocks 3 and 3 ′ attached to the cylindrical electrode blocks 3 and 3 ′, respectively. The sample liquid introduced from the sample injection port 2 is heated in the cuvette that is electrically heated by the power supply device 6, and the cuvette space containing the atomized metal component is irradiated with light of a specific wavelength emitted from the light source device 7. Then, the transmitted light is measured by the photometric device 8. Meanwhile, small hole 5,
From 5 ', an inert gas, usually argon gas, is fed at a constant speed, and the absorbed light amount, that is, the metal component amount is calculated from the difference between the incident light amount and the transmitted light amount.

In addition to the front view, both side views are shown in FIG. 2 in order to facilitate understanding of the characteristic state of both ends of the cuvette. An outer peripheral surface 9 having a regular hexagonal pyramid shape, which is substantially parallel to the axis but slightly inclined, is formed at the end portion on the left side of the drawing. The shape of the corresponding inner side surface of the cylindrical electrode block 3 that holds this portion in a fitting shape is formed as a regular hexagonal pyramidal hollow concave shape that matches the surface contour of the regular hexagonal column shape.
On the other hand, the right end of the cuvette is formed in a cylindrical shape similar to the conventional one.

FIG. 3 is a similar view of the conventional cuvette in which both end portions are both formed into a chamfered cylindrical shape.

[Work]

The atomization furnace of the present invention is extremely easy to attach to the apparatus and is extremely stably held between the electrodes, and thus far, it was necessary to re-align the cuvette every hour or check the sensitivity. On the other hand, in the nuclear reactor of the present invention, the reproducibility of the measurement is highly maintained even if the measurement operation is repeated nearly 200 times a day, and it is possible to perform a highly reliable measurement all day by creating a calibration curve once in the morning. You can

〔Example〕

Next, the present invention will be described in more detail with reference to specific examples.
The numbers of parts in the examples are by weight unless otherwise specified.

Example 1 Quantification of copper (Cu) in quartz glass Preparation of calibration curve: Standard aqueous solutions with various copper concentrations, that is, 0 ppb, 10 ppb, 20 p
A standard aqueous solution containing pb and 30 ppb copper was prepared, and a calibration curve was prepared for each as follows.

The standard aqueous solution was placed in a sample cup, and an autosampler was used to inject the sample into the cuvette. The heating temperature program is as follows: Drying at a temperature of 80 ° C to 200 ° C for 40 seconds, preheating at 600 ° C for 30 seconds, heating at a temperature of 2700 ° C for 5 seconds to atomize Cu, and light with a wavelength of 324.8 nm in the cuvette And the transmitted light was measured with a spectrophotometer to obtain the absorbance. The absorbance of each of the obtained copper concentration standard aqueous solution was 0.093.
These values were plotted at 2, 0.1864 and 0.2796 to obtain a calibration curve showing the relationship between copper concentration and absorbance as shown in FIG.

Next, accurately measure 3 g of quartz glass as a sample for measurement, put it in a closed container together with 20 ml of 50% hydrofluoric acid, completely dissolve it at a temperature of about 160 ° C., and transfer it to a 50 ml volumetric flask. The volume was adjusted with water to prepare a sample solution.

This sample solution was operated in exactly the same manner as the conditions for preparing the calibration curve, and the absorbance was measured with light having a wavelength of 324.8 nm. The same sample was measured three times, and the copper concentration was determined from the average value of the measurements. The concentrations of copper in the sample solution obtained from the calibration curves of the three measured values were 1.30 ppb, 1.31 ppb and 1.28 pp, respectively.
It was pb. The average concentration of 1.297 ppb was calculated by the following conversion formula, and the copper impurity content concentration in the silica glass was 22 ppb.
Met.

In the formula, C is the copper content in the sample solution (ppb) W is the quartz glass collection amount (g) V is the volume of the volumetric flask (ml) X is the copper content in the glass (ppb) .

Further, this quartz glass was operated and measured in exactly the same manner as the 60th sample of the day, and the copper content in the glass determined from the average value by the above calibration curve was 22 ppb. This measurement value is exactly the same as the measurement value of the first sample, and it can be seen that the measurement accuracy of the atomization furnace of the present invention does not decrease even when many samples are measured and is kept high.

Furthermore, when a standard aqueous solution of 10 ppb of copper was measured for the purpose of sensitivity check, the absorbance was 0.0930, which was a sensitivity change that was negligible compared to the first measurement. Therefore, it will be understood that the sensitivity check of the calibration curve and the re-creation of the calibration curve are completely unnecessary during that period.

The atomic reactor of the present invention can measure the maximum number of samples 60 that can be measured within a predetermined time of day with high accuracy without the need to check and recreate the calibration curve.

Comparative Example 1 When the amount of copper contained in quartz glass is similarly quantified using a conventional atomization furnace, it is necessary to perform a sensitivity check with a 10 ppb standard solution for every 4 samples, and 20 samples. At the time of (60 times) measurements, the disadvantage of recreating the calibration curve is unavoidable, and therefore it is at best possible to measure 40 samples per day.

〔The invention's effect〕

Since the atomization furnace of the present invention does not need to check the calibration curve prepared in the morning of the day throughout the day and does not need to readjust the furnace, for example, the number of measurement samples is 5 compared with the conventional one. It has a high measurement efficiency that can be significantly increased. Further, unlike the conventional method, it is not necessary for the operator to constantly monitor, and unmanned automatic operation can perform measurement with excellent accuracy, so that it has a very high practical value.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an atomic absorption photometer including an atomization furnace of the present invention, and FIGS. 2 (a), 2 (b) and 2 (c).
Are the front view, left side view and right side view of the cuvette of the nuclear reactor, respectively, and (Fig. A), (Fig. B) and (Fig. C) of Fig. 3 are similar to the conventional typical cuvette, respectively. It is a front view, a left side view, and a right side view. Moreover, FIG. 4 is a calibration curve prepared in Example 1. Symbols in the figure: 1 ... Graphite cuvette 2 ... Sample injection hole, 3 ... Electrode block, 4 ... Electrode holder, 5 ... Inert gas introduction hole, 6 ... Power supply device, 7 ... Light source device, 8 ... Photometric device

Claims (3)

[Claims] 1. A cylindrical atomization furnace used in an atomic absorption spectrophotometer, wherein at least one plane not perpendicular to the axis of the cuvette is formed on the outer peripheral surface of one end of the graphite cuvette so as to match with the electrode corresponding surface. Atomic absorption furnace for atomic absorption spectrophotometer with excellent measurement stability. 2. A plurality of flat surfaces formed on the outer peripheral surface of the end portion so as to match with the electrode corresponding surfaces, the flat surfaces being formed symmetrically with respect to the cuvette axis.
Atomic reactor described. 3. The atomic reactor according to claim 2, wherein the plurality of symmetrical planes are formed in a regular quadrangular, regular hexagonal or regular octagonal sectional shape.