JP3240507B2 - Automatic measurement method of ultra-trace amount of silicate ion in test water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring silicate ions in ultrapure water used in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art It is standardized that the concentration of silicate ions in ultrapure water used in a semiconductor device manufacturing process is 0.1 ppb or less, and a pure water plant is controlled to be within the standard. ing.

As a method for confirming the silicate ion concentration,
At present, graphite atomizer atomic absorption spectrometry is used exclusively. However, although this method has sufficient analytical sensitivity, it takes a long time for analysis, so if a plant trouble occurs and high concentration silicic acid cannot be detected or dealt with even if it flows into the product manufacturing process. There are many. Therefore, a faster automatic measurement method is needed.

As a method for measuring silicate ions, J.
There are molybdenum (yellow) and molybdenum (blue) absorptiometry in accordance with IS-K0555, but both have a detection limit of 1
There is a disadvantage that the analytical sensitivity is insufficient because it is about 0 ppb.

Recently, there has also been disclosed a method in which silicate ions are concentrated in advance using an ion exchange resin method and then measured by an absorption spectrophotometric method using molybdenum (blue) (Japanese Patent Laid-Open No. Sho 62).
-39768, JP-A-1-267456, JP-A-3-1
5754). However, in this method, it is necessary to periodically exchange the resin in order to prevent a decrease in the concentration due to the deterioration of the ion exchange resin, and when the silicate ion is reacted with ammonium molybdate, the heterosilicate molybdenum (yellow) is used. ) Is formed and molybdenum is polymerized at the same time to produce isopolymolybdic acid as a by-product, and this by-product causes interference in the absorbance at the measurement wavelength, resulting in poor reliability due to an error in simultaneous measurement of isopolymolybdate. There are disadvantages.

[0006] A method of increasing the analytical sensitivity by lengthening the absorption cell without using the concentration method is also conceivable, but the interference of isopolymolybdic acid still remains unavoidable, and there remains a problem in accuracy. As described above, the reaction mechanism of the formation reaction of molybdenum (yellow) in the ultra-low concentration region is not considered so much, so that a problem remains in the measurement accuracy.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned various drawbacks and to provide a method for automatically measuring ultra-trace amounts of silicate ions with improved measurement accuracy. I do.

[0008]

According to the present invention, silicate ions in test water are reacted with ammonium molybdate in the presence of a reaction catalyst to form heterosilicone molybdenum (yellow), and the product is further reduced by the reaction. A flow injection method for producing heterosilicone molybdenum (blue) and a hydrophobic ion pair formed from the heterosilicone molybdenum (blue) and a quaternary ammonium ion are applied to a concentration column filled with a polymer carrier. After adsorption and retention, elution is carried out with a mixed solvent of an organic solvent and water, and the ion pair concentration / elution method for measuring the silicate ion concentration is combined.

The present invention also relates to a method for reacting silicate ions in test water with ammonium molybdate in the presence of a reaction catalyst to produce heterosilicone molybdenum (yellow), and further reducing the product to form heterosilicone molybdenum. (Blue), a hydrophobic ion pair formed from the heterosilicone molybdenum (blue) and the quaternary ammonium ion is adsorbed and held on a concentration column filled with a polymer carrier, and then the organic ion is removed. In the method of eluting with a mixed solvent of water and a solvent and measuring the silicate ion concentration, the generated hydrophobic ion pairs are quantitatively sent to a concentration column by time regulation.

The present invention also relates to a method for reacting silicate ions in test water with ammonium molybdate in the presence of a reaction catalyst to produce heterosilicone molybdenum (yellow). (Blue), a hydrophobic ion pair formed from the heterosilicone molybdenum (blue) and the quaternary ammonium ion is adsorbed and held on a concentration column filled with a polymer carrier, and then the organic ion is removed. In the method of eluting with a mixed solvent of a solvent and water and measuring the silicate ion concentration, a hydrophobic ion pair is previously collected in a measuring tube having a predetermined volume, and then sent to a concentration column by a carrier. .

In the present invention, a low molecular weight water-soluble organic solvent such as methanol, ethanol, acetone or acetonitrile is used as the reaction catalyst.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The concentration of silicate ion is 10 ppb.
The reaction rate of the heterosilicate molybdenum (yellow) formed by the reaction between silicate ions and ammonium molybdate below is extremely slow, and requires a long reaction time even when the reaction temperature is increased. However, to minimize the measurement time,
In addition, considering the safety of the measuring device, the reaction temperature is a maximum of 80 ° C. and the reaction time is a limit of 10 to 20 minutes. For this purpose, a catalyst for accelerating the reaction is effective, and the present inventors have found that a low molecular weight water-soluble organic solvent such as methanol has a large effect as a catalyst.
ol% of methanol is added to the sample to improve the reaction rate.

[0013] Heteroiomolybdenum (yellow) is reduced to heterohymomolybdenum (blue) by the action of L-ascorbic acid. As a quaternary ammonium ion used for forming a hydrophobic ion pair of heterosilomolybdenum (blue) and a quaternary ammonium ion, for example, octyltrimethylammonium bromide salt or the like is used.

As the high molecular weight polymer carrier to be packed in the column for concentrating hydrophobic ion pairs, for example, vinylbenzene copolymer, styrene polymer, acrylate polymer and the like can be used, and the particle size is 50 to 150 μm. The degree is preferred.

The eluate for eluting the hydrophobic ion pair adsorbed and held on the concentration column includes acetonitrile, acetone,
A mixed solvent of water and an organic solvent such as methanol or ethanol is preferable. The amount of the mixed solvent used is preferably as small as possible in view of the degree of concentration. In this case, by optimally setting the operating conditions, heterosilicomolybdenum (blue) and isopolymolybdic acid can be separated and eluted. By this separation, the measurement accuracy of helocymolybdenum (blue) can be improved. The carrier for concentration is regenerated by elution with the eluate and returns to the original state. By repeating this step, the concentration carrier (concentration column) can be used semipermanently.

[0016]

FIG. 1 is a system block diagram of an automatic measuring method according to the present invention. (1) Direct introduction method In FIG. 1, reference numerals 24 and 25 denote six-way automatic switching valves each having 6 ports. Concentration columns 20 are connected to ports 2 and 5 of 25 valves with 5 as an inlet and 2 as an outlet. ing. The concentration column 20 has an inner diameter of 3φ, an outer diameter of 4φ, and a length of 3.
It is a pipe made of a 0-mm tetrafluoroethylene resin and filled with a high-molecular polymer carrier.

Reagents, counter ions, eluents, and the like to be used for the reaction are stored in bottles 31 to 36, are sucked by plunger pumps 39 to 44, exit the bottles, and are degassed through a degasser. The test water is always fed into the system by the plunger pump 38, and plays a role in cleaning the system while the reaction is stopped.

When the system is started, first, the test water and the 0.45M aqueous sulfuric acid solution are mixed, and then the 0.6% ammonium molybdate aqueous solution is mixed. Heterosilicate molybdenum (yellow) by reacting for 20 minutes
Is generated. In this case, a considerable amount of a catalyst solvent is added to the aqueous sulfuric acid solution or the aqueous ammonium molybdate solution in advance. Next, a 4.5 M aqueous solution of sulfuric acid and a 0.1 M aqueous solution of L-ascorbic acid are mixed in this order and guided to the reaction tube 46 to generate heterosilicomolybdenum (blue).

Each of the reaction tubes 45 and 46 is formed by spirally winding a tetrafluoroethylene resin pipe having an inner diameter of 1φ, an outer diameter of 2φ and a length of about 20mm around a magnetic tube with a heater.
It is an apparatus that can be set to any temperature in the range from room temperature to 100 ° C.

Subsequently, after the counter ion is added as a carrier to form an ion pair, the concentration column 2 is passed through the ports 12 and 11 of the valve 24 and the ports 6 and 5 of the valve 25.
0 is introduced directly. At this time, the amount of concentration can be optimally adjusted by appropriately setting the introduction time.

The concentrated ion pairs are eluted by an eluent sent from a non-pulsating pump 44, guided to a detector 21, and measured for absorbance at 810 nm, and then discharged through a capillary tube 22 for adjusting back pressure. Is done. The above is the direct introduction method, but the following measurement method may be used.

(2) Measuring method In this method, a measuring tube 23 (tetrafluoroethylene tube having an inner diameter of 2 mm, capacity of 20 ml) is provided between the ports 11 and 8 of the valve 24 in advance. After forming an ion pair in the same manner as in the direct introduction method described above, the port 12 of the valve 24 is
And 11 are introduced into the measuring tube 23 to fill the inside of the measuring tube, and are discharged through the ports 8 and 7 as they are.

Next, the solenoid valve 47 and the valve 24 are switched, and the carrier flows through the ports 10 and 11 of the valve 24 into the measuring tube, so that the entire amount of the ion-pair solution together with the carrier is passed through the ports 6 and 5 of the valve 25 to the column 20. It is led to and concentrated. Thereafter, the valve 25 is switched, eluted by the eluent sent from the pump 44, sent to the detector 21, and the absorbance at 810 nm is measured. After the measurement, it is discharged in the same manner as in the direct introduction method.

Hereinafter, the working conditions used in this embodiment will be described. Concentration carrier Vinylbenzene copolymer resin (particle size: 100-120 μm) Counter ion Octyltrimethylammonium bromide Catalyst Add 50 wt% methanol in 0.45 M sulfuric acid Reaction time 10 minutes for both reaction tubes 45 and 46 Concentration amount Direct introduction method 10 ml for both measurement methods Flow rate Test water 1.0 ml / min 0.45 M aqueous sulfuric acid 0.1 ml / min 0.6% aqueous ammonium molybdate 0 1 ml / min 4.5 M aqueous sulfuric acid 0.3 ml / min 0.1 M L- Ascorbic acid aqueous solution 0.1 ml / min Counter ion aqueous solution 1.0 ml / min Eluent 1.0 ml / min The signal (chromatogram) measured under the above conditions was processed by Chromatopack C-R6A, a data processing device manufactured by Shimadzu Corporation, and peaked. The silicate concentration was determined from the area. As a result, the detection limit was 0.01 ppb.

Further, as shown in FIG. 2, in the present invention, the peaks of heterosilicomolybdic acid and isopolymolybdic acid could be completely separated. Therefore, it was found that only the target heterosilicomolybdic acid can be selectively measured.

[0026]

As is clear from the examples, the present invention is characterized in that a very small amount of silicate ions can be quickly and automatically measured by combining the flow injection method and the ion pair concentration / elution method. There is. In addition, since heterosilicomolybdic acid and isopolymolybdic acid can be separated, their interference can be eliminated and measurement accuracy can be improved. Further, the resin carrier for concentration can be used for a long time without deterioration.

[Brief description of the drawings]

FIG. 1 is a system block diagram of an automatic measurement method according to the present invention.

FIG. 2 is a chromatogram of an eluate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 20 Concentration column 21 Detector 22 Capillary tube for back pressure adjustment 23 Metering tube 24 Hex valve RV1 25 Hex valve RV2 31 0.45M sulfuric acid aqueous solution 32 0.6% ammonium molybdate aqueous solution 33 4.5M sulfuric acid aqueous solution 34 0.1ML -Ascorbic acid aqueous solution 35 Counter ion aqueous solution 36 Eluent 37 Degasser 38-44 Liquid sending pump 45 Reaction tube Reactor 1 46 Reaction tube Reactor 2 47 Solenoid valve

──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyoshi Sugawara 1 off the coast of Ohira Village, Kurokawa-gun, Miyagi Prefecture Inside Miyagi Oki Electric Co., Ltd. (72) Tadao Ihara 2-3-3 Izumigaoka, Izumi-ku, Sendai City, Miyagi Prefecture No. 10 Examiner Hiroshi Miyazawa (56) References JP-A-6-273324 (JP, A) JP-A-5-223744 (JP, A) JP-A-6-180303 (JP, A) JP-A-7-43306 (JP, A) JP-A-1-267456 (JP, A) JP-A-62-29769 (JP, A) JP-A-3-15754 (JP, A) JP-A-2-288848 (JP, A) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 30/06 G01N 21/77 G01N 30/08 G01N 30/84 G01N 30/88

Claims (4)

(57) [Claims] 1. A silicate ion in test water is reacted with ammonium molybdate under a reaction catalyst to produce heterosilicone molybdenum (yellow), and the product is reduced to form heterosilicone molybdenum (blue). The resulting flow injection method, and after adsorbing and holding a hydrophobic ion pair formed from the heterosilicate molybdenum (blue) and a quaternary ammonium ion on a concentration column filled with a polymer carrier, are combined with an organic solvent. An automatic measurement method for ultra-trace amounts of silicate ions in test water, wherein the method is combined with an ion pair concentration / elution method for eluting with a mixed solvent with water and measuring the silicate ion concentration. 2. The reaction of silicate ions in test water with ammonium molybdate under a reaction catalyst to form heterosilicone molybdenum (yellow), and further reducing the product to form heterosilicone molybdenum (blue). After the formation, a hydrophobic ion pair formed from the heterosilicate molybdenum (blue) and the quaternary ammonium ion is adsorbed and held on a concentration column filled with a polymer carrier, and then the organic solvent and water are mixed. And a method for measuring the silicate ion concentration, characterized in that the generated hydrophobic ion pair is quantitatively sent to a concentration column by time regulation, and the ultra-trace amount of silicate in the test water is characterized in that: Automatic ion measurement method. 3. The reaction of silicate ions in test water with ammonium molybdate under a reaction catalyst to form heterosilicone molybdenum (yellow), and further reducing the product to form heterosilicone molybdenum (blue). After the formation, a hydrophobic ion pair formed from the heterosilicate molybdenum (blue) and the quaternary ammonium ion is adsorbed and held on a concentration column filled with a polymer carrier, and then the organic solvent and water are mixed. In the method for eluting with a mixed solvent and measuring the silicate ion concentration, the sample water is characterized in that after collecting a hydrophobic ion pair in a measuring tube of a predetermined volume in advance, the solution is sent to a concentration column by a carrier. Method for ultra-trace amount of silicate ion. 4. The ultra-trace silicate ion in the test water according to claim 1, wherein the reaction catalyst is a low molecular weight water-soluble organic solvent such as methanol, ethanol, acetone and acetonitrile. Automatic measurement method.