JP2005214863A - Method of measuring water and aqueous solution by ultraviolet ray - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discriminate/determine quantitatively micro amounts of various dissolved components in an aqueous solution without using a near infrared spectroscopy. <P>SOLUTION: An analytical curve for indicating a correlation between an absorption intensity in one or more of wavelength in a long wavelength side containing no absorption peak of a dissolved substance itself, in an absorption peak in the vicinity of 160nm of water, and a concentration is preliminarily determined in the first measuring method. Then, an ultraviolet spectroscopic spectrum of the aqueous solution is measured by the one or more of wavelength. The concentration of the micro amount of component in the aqueous solution is determined quantitatively using the analytical curve on the basis of an obtained ultraviolet spectroscopic spectral data. An ultraviolet spectroscopic spectrum as to each of a plurality of standard aqueous solutions is measured preliminarily in a prescribed wavelength range in the absorption peak in the vicinity of 160nm of the water, in the second measuring method. Then, an ultraviolet spectroscopic spectrum of an aqueous sample solution containing the micro amount of component is measured in the prescribed wavelength range, to judge that the ultraviolet spectroscopic spectrum of the aqueous sample solution is consistent with the ultraviolet spectroscopic spectrum in any of the standard aqueous solutions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to identification and quantitative analysis of water or water-soluble components.

  In the discrimination / quantitative analysis of water or water-soluble components, spectroscopic analysis is widely used as a very effective means. The spectroscopic analysis methods are roughly classified into ultraviolet-visible spectroscopy, near-infrared spectroscopy, and infrared spectroscopy depending on the measurement wavelength region.

In particular, in near-infrared spectroscopy, an absorption spectrum reflecting water-specific hydrogen bonds is remarkably observed at 800 nm to 1400 nm. For example, JP-A-3-175341 discloses a method for measuring dissolved components in water using this spectrum. Proposed. Water molecules are hydrogen bonded to each other in the liquid state, but when other dissolved components are mixed in water, the hydrogen bond state changes very sensitively. Then, by examining the state of the change, it becomes possible to quantitatively analyze the mixed components. More specifically, when an inorganic electrolyte is ionized in an aqueous solution, hydrogen bonds are broken or distorted between water molecules in the vicinity of ions and bulk water molecules generated by ion hydration, and water molecules are generated by the electric field of ions. Due to the influence of the polarization of water, the bonding state of water molecules themselves and the bonding state of water-bonded water molecules are affected, and the near-infrared absorption spectrum differs from that of pure water. Therefore, by calibrating the change in advance, the concentration of ionic species having no absorption spectrum in the near infrared can be determined from the change in the absorption spectrum of water.
JP-A-3-175341 JP-A-3-220452

  For example, in today's semiconductor manufacturing process, circuit miniaturization advances and the concentration of the inorganic electrolyte in the chemical solution used tends to decrease accordingly. In addition, from the viewpoint of environmental problems related to waste liquid treatment, component analysis at a very low concentration is required. However, the absorption spectrum of water appearing in the near infrared is inherently forbidden transition and weakly absorbed, and the concentration of trace components cannot be measured. Therefore, it is necessary to measure the concentration of a very small amount of dissolved component for which a significant difference cannot be obtained in the near-infrared spectrum.

  As will be described later, the present invention uses far-ultraviolet spectroscopy, but JP-A-3-220452 describes a method for determining hydrogen peroxide in coexistence with ammonia or sodium hydroxide using the absorbance of ultraviolet light. Has been. What is measured here is a hydrogen peroxide concentration of 0 to 10% by weight, an ammonia concentration of 0 to 15% by weight, and a sodium hydroxide concentration of 0 to 8% by weight. We do not analyze trace components.

  An object of the present invention is to enable identification and quantitative analysis of water containing various trace amounts of dissolved components using the absorption spectrum of water appearing in the far ultraviolet.

  The absorption spectrum due to the n → σ * transition of water having a peak near 160 nm shifts to the longer wavelength side due to the effect of the electric field formed between the water itself and the hydrated ion dissolved in the water, and part of the spectrum is Identification and quantitative analysis of aqueous solutions is performed by using the fact that it appears in a region that can be measured with a regular spectrometer (a spectrometer that does not require vacuum).

  That is, in the first aqueous solution measurement method using ultraviolet light according to the present invention, one or more wavelengths (for example, 180 to 210 nm) not including the absorption peak of the dissolved substance itself on the long wavelength side of the absorption peak near 160 nm of water. A calibration curve between absorption intensity and concentration within the range is determined in advance. Next, the ultraviolet spectrum of the aqueous solution is measured at the one or more wavelengths. And the density | concentration of the trace component in aqueous solution is quantified using a calibration curve from the obtained ultraviolet spectroscopy spectrum data.

  In the second aqueous solution measurement method using ultraviolet light according to the present invention, the wavelength dependence of the ultraviolet spectrum of a plurality of standard aqueous solutions is set to a predetermined wavelength range (for example, 180 to 210 nm) on the long wavelength side of the absorption peak near 160 nm of water. Range) in advance. Next, the ultraviolet spectrum of the aqueous solution sample containing a trace component is measured in a predetermined wavelength range, and it is determined which standard aqueous solution the ultraviolet spectrum of the aqueous solution sample matches.

  Far ultraviolet spectroscopy enables the identification and quantitative analysis of trace components in aqueous solutions. Also, this measurement can be analyzed by a simple method.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
In general, in the spectroscopic analysis using visible / ultraviolet rays, the absorption spectrum extends to the energy level of the electronic transition of the substance to be measured, and therefore involves a much larger energy change than the absorption spectrum of near infrared rays. The history of spectroscopic analysis using this fact is deep, and it has been applied to qualitative and quantitative analysis of various luminescent groups. Today, the spectrum of most chromophores is known. As described above, UV-visible spectroscopy has been widely used, but has been applied only to solutions having an absorption band in the 200 nm to 800 nm region. For example, nitrate ions (NO ₃ ²⁻ ) and nitrite ions (NO ₂ ⁻ ) in precipitation are known to have absorption peaks at 201 nm and 210 nm, respectively, and detection and measurement using these wavelengths are performed. ing.

By the way, the water molecule has an unpaired electron in the oxygen atom in the molecule, and this unpaired electron can participate in the covalent bond with other molecules, and the antibonding property formed at that time An energy change in the ultraviolet region called an n → σ ^* transition is accompanied with the molecular orbital σ ^* . The absorption spectrum of water is known to have a peak at a wavelength of 167.0 nm in a gas state, and shows a peak around 160 nm in a liquid. However, no attempt has been made so far to detect or measure substances dissolved in water using the absorption spectrum of the water itself. This is because when the amount of the component dissolved in the water is very small, it is obvious that the main component is water, and the change in the absorption amount of the spectrum of the water itself due to the mixing of the trace component is so small that it can be ignored. .

The inventor of the present invention pays attention to the fact that the energy required for the n → σ ^* transition of water shows an inherent change in the hydrated ion in a state where the dissolved component is hydrated in water. The state of change of n → σ ^* transition spectrum of water related to ions was systematically investigated. As a result, in the state where the dissolved component is hydrated in water, the electric field of the hydrated ions affects the bottom of the absorption peak near 160 nm caused by the n → σ ^* transition (with a 180 to 210 nm common spectrometer). Ascertaining that the intensity, position, and band width of the absorption band appearing in the measurable region change very sensitively to hydrogen bonding and hydration of water, and use this for the identification and quantitative analysis of aqueous solutions. It was proved that it was possible to measure the concentration of trace components dissolved in water and the change in water quality. That is, the absorption spectrum due to the n → σ ^* transition of water has a very steep slope in the wavelength region of 180 nm to 210 nm as shown in FIG. 1, but the position of this slope changes the state of water. Even if the concentration of the substance dissolved in water is very small, and the magnitude of the absorption peak of water hardly changes, the slight shift of the spectrum shows the state of the change from 10 ³ to It will be magnified 10 ⁵ times and reflected.

Example 1: Temperature change in the ultraviolet spectrum of pure water.
The ultraviolet spectrum of pure water changes with temperature. For example, the ultraviolet spectrum shown in FIG. 2 shows the bottom of the absorption of water having a peak near 160 nm when the temperature of pure water is changed at eight temperatures every 5 ° C. within the range of 20 ° C. to 55 ° C. It is an absorption spectrum of. As the temperature of pure water rises and the hydrogen bond strength of water itself is relaxed, the ultraviolet spectrum shifts to the longer wavelength side, and the water spectrum in this region reflects changes in the bonding state between water molecules. It shows that.

Example 2: Change in the ultraviolet spectrum of water due to a trace amount of dissolved components.
Moreover, the ultraviolet spectrum of water changes with respect to the concentration of a very small amount of components dissolved in water. For example, FIG. 3 shows a measurement example of the change in the far ultraviolet spectrum of water found in an aqueous nitrite ion solution. Here, sodium nitrite is dissolved in pure water at 25 ° C. within a range of 20 μmol / l to 200 μmol / l at a concentration of 20 μmol / l. As the concentration of sodium nitrite increases, the amount of absorption at the absorption peak (wavelength 210 nm) of nitrite ions (NO ₂ ⁻ ) increases, while the absorption in the region of 190 nm to 200 nm is proportional to the increase in nitrite ions. It can be seen that it has increased. This can be understood as a spectrum in which the long-wavelength shift of the absorption spectrum of water due to hydration of sodium nitrite overlaps the original absorption spectrum of nitrite ions (spectrum estimated by the dotted line in the figure). That is, the change in the spectrum from 190 nm to 200 nm is caused by the hydration of sodium nitrite in pure water, so that the binding state of water molecules is relaxed, and the water absorption spectrum is shifted in correlation with the concentration of sodium nitrite. This shows that the concentration of sodium nitrite can be quantified from the change in the amount of absorption in the region of 190 nm to 200 nm due to this shift. In the measurement of Examples 1 and 2, the apparatus shown in FIG. 4 was used.

  As described above, ultraviolet-visible spectroscopy has been widely used, but has been applied only to substances having an absorption band in the 200 nm to 800 nm region. On the other hand, since the present invention analyzes the spectrum of water that varies depending on the substance that dissolves in water, even if the spectrum of the dissolved substance itself does not appear in a region observable by a regular spectrometer of 180 nm or more, it is extremely small. It enables quantitative measurement of water-soluble substances.

  FIG. 4 shows the configuration of an ultraviolet spectroscopic measurement apparatus used for measuring ultraviolet spelling of water. Ultraviolet rays generated from the light source 10 pass through the measurement sample in the optical cell 12. The measurement light transmitted through the optical cell enters the spectroscopic unit 14 and is split into a plurality of wavelengths. (A grating may be used for the spectroscopic method, or an interference filter may be used.) The signal processing unit 16 calculates a concentration by calculating a signal at each measurement wavelength. Further, the data output unit 18 displays or outputs the calculation result. This device configuration is the same as the conventional one. Specifically, as the signal processing unit 16 and the data display unit 18, a conventional spectroscopic device capable of measuring at a wavelength of 190 nm to 280 nm can be used. Here, an ultraviolet / visible spectroscopic analyzer 3100PC manufactured by Shimadzu Corporation was used.

ただし、基準液では、ｃ＝０である。

また、これらの式において、ａ_ｎは、系の測定成分以外の物質吸光度であり、たとえば、セル、フィルターやレンズの材質の吸光度やそれらに付着する汚れの吸光度などがあげられる。また、ｂ_ｎは、それら吸収をもつ物質の厚みである。これらの式では、それらサンプル以外による光の吸収をまとめてｅｘｐ(−ａ_ｎ×ｂ_ｎ)と表わしている。 The concentration calculation formula is obtained as follows. When the amount of light emitted from the light source 10 I, the reference solution the amount of light beam splitting unit sensor after passing through the cell containing the (pure water) is received I _b, the amount of light sensor receives light after passing through the sample liquid and I _s, respectively the relationship between the light intensity _I b, _{I s} and concentration c, expressed from Lambert-Beer law, equation (1), as an expression (2). Here, a represents the substance absorbance of the measurement component, and b represents the thickness (cell length) of the sample. Further, γ is a change in detection intensity, which is a change in sensitivity of the sensor or a change in light quantity.

However, c = 0 in the reference solution.

Also, in these equations, a _n is a substance absorbance other than the measurement component of the system, for example, cells, dirt absorbance adhering to the filter and the lens material absorbance and thereof. B _n is the thickness of the substance having such absorption. In these equations, the absorption of light by other than those samples is collectively expressed as exp (−a _n × b _n ).

Therefore, in such a configuration of the optical path, the transmitted light amount I _s having received the absorption by measurement component, and dividing by the conditions other than the measurement components are all equivalent reference fluid quantity of transmitted light I _b, absorption related to the concentration only And the measured component concentration c can be obtained from the equation (3).

  A two-wavelength method is also used for actual concentration measurement. In the two-wavelength method, the first wavelength is selected as a wavelength having a large absorbance with respect to the sample, the absorbance is different from the first wavelength as the second wavelength, and other factors are changed in the same manner as the first wavelength. Select the wavelength and measure at these two wavelengths to calculate the concentration c.

  In addition, when quantifying the concentration of multiple components, a multi-variate analysis of absorbance at multiple wavelengths obtained from the spectrum is used to create a calibration curve, and the concentration of each component is calculated from the obtained calibration curve. (Multiple regression analysis and principal component analysis) are effective.

  Thus, in the method for measuring trace components in an aqueous solution by ultraviolet light, the absorption intensity at one or more wavelengths (for example, in the range of 180 nm to 210 nm) on the long wavelength side of the absorption peak near 160 nm of water is 1 or A calibration curve with the concentration of two or more trace components is determined in advance. Next, the ultraviolet spectrum of the aqueous solution is measured at the one or more wavelengths. And the density | concentration of the trace component in aqueous solution is quantified using a calibration curve from the obtained ultraviolet spectroscopy spectrum data. This measurement method enables quantitative measurement of a very small amount of water-soluble substance even when the spectrum of the dissolved substance itself does not appear in the far ultraviolet region. In addition, the base of the absorption peak of the dissolved substance may overlap. In this case as well, the calibration curve can be similarly determined to quantify the concentration of the trace component in the aqueous solution. Since this measurement method does not measure the absorption peak of the dissolved substance itself, the measurement wavelength does not need to include the absorption peak of the dissolved substance itself. Good.

  In another measurement method, instead of using a calibration curve, the wavelength dependence of the ultraviolet spectrum for a plurality of standard aqueous solutions is set to a predetermined wavelength range (for example, 180 nm to 210 nm) on the long wavelength side of the absorption peak near 160 nm of water. Measure within the range. Next, the ultraviolet spectrum of the aqueous solution sample containing a trace component is measured in a predetermined wavelength range, and it is determined which standard aqueous solution the ultraviolet spectrum of the aqueous solution sample matches.

  An example of measurement will be described below.

Example 3: Identification of commercial natural water.
Eight types of commercially available natural waters W1 to W8 and distilled water were analyzed. Table 1 shows the ion concentrations and pH values of these eight types of commercially available natural waters W1 to W8. Pure water was prepared by distilling water twice and passing through activated carbon and a reverse osmosis filter. Of the commercially available natural waters, W1 is “Rokuko's delicious water” (trademark) (house food), W2 is “Southern Alps natural water” (trademark) (Suntory), and W3 is “Nature of Tateyama mountain range” "Water" (trademark) (Sapporo Beer), W4 is "News from the Forest" (trademark) (Coca-Cola), W5 is "Evian" (trademark) (Calpis), and W6 is "alkaline ion""Water" (trademark) (Kirin Beverage), W7 is "Echizen no Mizu" (trademark) (High Peace), and W8 is "Yuyu Shusui" (trademark) (Nestlé Japan).

Table 1 shows the cation and anion concentrations (mg / 100 ml) and pH values of eight natural water samples.

  In the measurement using the apparatus shown in FIG. 4, the temperature of water was 25 ° C. A quartz cuvette cell having an optical path length of 10 mm was used as the optical cell 12, and water or an aqueous solution as a measurement sample was placed in the quartz cuvette cell 12. And the ultraviolet spectrum in the wavelength range of 180 nm-310 nm was measured.

FIG. 5 shows the far-ultraviolet spectral patterns of these eight kinds of commercially available natural waters W1 to W8 and pure water (distilled water) in the wavelength range of 190 nm to 250 nm. The wavelength range of 190 nm to 210 nm of these spectra overlaps with the bottom of the absorption band near 160 nm due to the n → σ ^* transition of water.

As can be seen by comparing the spectral pattern of FIG. 5 with Table 1, there is no simple relationship between the spectral pattern and the amount of dissolved component (mineral). This is because the spectral pattern in FIG. 5 is not formed only by the absorption of the dissolved component itself but reflects the difference in hydration of the dissolved component in each sample. That is, the data show that the intensity, peak position, and bandwidth of the n → σ ^* transition change sensitively due to the hydration of the dissolved component.

  As is clear from FIG. 5, these eight kinds of natural waters W1 to W8 can be clearly identified from the difference in their spectral patterns, and no preprocessing of the spectrum is required for identification. Accordingly, the wavelength dependence of the ultraviolet spectral spectrum is measured in advance for the eight standard aqueous solutions of natural water, and the ultraviolet spectral spectrum of a certain aqueous solution sample is measured. By judging whether or not it matches the spectrum, it is possible to identify which natural water the aqueous solution sample is. In contrast, although not shown, the near-infrared spectra of the eight types of water measured by the present inventor appear to be the same with the naked eye, and are completely discernible even when performing sophisticated and complex principal component analysis. could not.

Example 4: Quantitative measurement of trace amounts of 0-20 ppm hydrochloric acid in water.
The hydrochloric acid solution was prepared as follows. First, Mitsubishi Chemical's 36% hydrochloric acid solution was diluted to 1000 ppm with pure water, and further diluted with pure water in 11 ways: 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20 ppm. Diluted to a HCl concentration of

  As in Example 3, the temperature of water was 25 ° C. in the measurement using the apparatus shown in FIG. A quartz cuvette cell having an optical path length of 10 mm was used as the optical cell 12, and water or an aqueous solution as a measurement sample was placed in the quartz cuvette cell 12. In the far ultraviolet spectrum, two wavelengths of 193 nm and 215 nm were used as measurement wavelengths. The latter is a reference wavelength for the two-wavelength method. For the spectral analysis of the one-component system, a calibration curve was obtained by approximation by the least square method with respect to the difference absorbance at the two wavelengths.

  The determination of HCl is important in various fields today. For example, HCl is used as a detergent solution in a semiconductor cleaning process, and the concentration must be accurately controlled for monitoring the process. FIG. 6 shows the far ultraviolet spectrum of an aqueous HCl solution at 11 concentrations (1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20 ppm) in the range of 0-20 ppm. , Shows the correlation of a calibration curve model for predicting the concentration of HCl. The model correlation coefficient R and standard deviation σ were 0.9987 and 0.18 ppm. It can be seen that a trace amount of HCl up to at least 100 ppm can be quantitatively measured with high accuracy. The detection limit of HCl in the aqueous solution in this measurement example was 0.5 ppm. Of course, if a cell having a longer optical path length is used, the detection limit is further improved. Further, when the measurement was performed at a shorter wavelength of 185 nm in a state where the optical system portion of the apparatus was purged with nitrogen and absorption by oxygen in the air was removed, the detection limit was 0.05 ppm.

  On the other hand, at present, there is no known simple method for measuring a trace amount of HCl in an aqueous solution. Near-infrared spectroscopy is used to measure halide ions and is simple but requires multivariate analysis. The detection limit is about 100 ppm. Therefore, it turns out that the measurement using the above-mentioned far ultraviolet spectrum is very effective for the determination of a trace amount of HCl.

  In addition, as an example of measuring the HCl concentration in a more complex aqueous solution, HCl in natural water (South Alps natural water) containing a wide variety of cations and anions in pure water was measured. FIG. 8 shows a spectrum of an aqueous solution in which HCl is added to natural water at a concentration of 0 to 20 ppm. The HCl concentration is 2, 4, 6, 8, 10, 16, 20 ppm. Natural water containing no HCl is used as a spectrum blank. Because of the presence of various dissolved components in aqueous solution, the behavior is different from that of increasing HCl in pure water, but the change in spectrum shows a certain correlation with increasing HCl. The correlation coefficient R and standard deviation σ when the calibration curve was created were 0.9971 and 0.34 ppm, respectively. Therefore, it can be seen that this method allows quantitative measurement of a specific dissolved component even in a state where a fixed amount of the dissolved component exists in pure water.

Example 5: Quantitative measurement of 0 to 100 ppm of a mixed solution of trace ammonia in water and trace hydrogen peroxide.
A mixed solution of ammonia water and hydrogen peroxide solution was prepared by diluting to a solution having a concentration range of 10 ppm to 100 ppm using pure water, and the apparatus shown in FIG. And measured.

  FIG. 9 shows the far ultraviolet spectrum (wavelength range of 190 nm to 330 nm) of a solution containing ammonia and hydrogen peroxide at a concentration of 100 ppm. Thus, the far ultraviolet spectra of ammonia and hydrogen peroxide in an aqueous solution are different, and they have different effects on the spectrum of pure water.

10 and 11 show the correlation of the calibration curve model that predicts the concentrations of ammonia and hydrogen peroxide. Multiple regression analysis was used for the analysis of the binary system. Here, five wavelengths of 195, 200, 205, 230, and 290 nm were used as measurement wavelengths. The correlation coefficient R and standard deviation σ of the model for ammonia and hydrogen peroxide were 0.9998 and 1.44, 0.99999 and 0.50, respectively. It can be seen that both ammonia and hydrogen peroxide can be accurately quantified to a concentration of 100 ppm. The detection limit of ammonia and hydrogen peroxide is 0.2 ppm in this measurement example. Thus, this method is also useful for two-component systems.

Water spectrum Graph showing how the ultraviolet spectrum changes with respect to the temperature change of pure water Graph showing the state of water spectrum change in nitrite aqueous solution Diagram of ultraviolet spectrometer Far ultraviolet spectra of distilled water and 8 aqueous solutions Far-ultraviolet spectrum of HCl aqueous solution with a concentration of 0-20pm Graph showing correlation of calibration curve model for predicting HCl concentration Far ultraviolet speckle of HCl aqueous solution with concentration of 0-20ppm in natural water Far ultraviolet spectrum of a solution of ammonia and hydrogen peroxide at a concentration of 100 ppm Graph showing the correlation of a calibration curve model for predicting ammonia concentration Graph showing the correlation of a calibration curve model that predicts the concentration of hydrogen peroxide

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light source, 12 Optical cell, 14 Spectrometer, 16 Signal processing part, 18 Data output part

Claims (4)

A calibration curve between absorption intensity and concentration at one or more wavelengths not including the absorption peak of the dissolved substance itself on the long wavelength side of the absorption peak near 160 nm of water is determined in advance.
Measure the ultraviolet spectrum of the aqueous solution at one or more of the above wavelengths,
An aqueous solution measurement method using ultraviolet light, wherein the concentration of trace components in an aqueous solution is quantified using a calibration curve from the obtained ultraviolet spectral data. The method for measuring an aqueous solution according to claim 1, wherein the wavelength is in a range of 180 nm to 210 nm. The wavelength dependence of the ultraviolet spectrum for a plurality of standard aqueous solutions was previously measured in a predetermined wavelength range on the long wavelength side of the absorption peak near 160 nm of water,
Measure the ultraviolet spectrum of an aqueous solution sample containing trace components in the specified wavelength range,
An aqueous solution measurement method using ultraviolet light to determine which standard aqueous solution the ultraviolet spectrum of an aqueous solution sample matches. The aqueous solution measurement method according to claim 3, wherein the wavelength region is in a range of 180 nm to 210 nm.

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