JP3206697B2 - Acid gas detection paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acid gas detecting paper for optically measuring an acid gas contained in an atmosphere by utilizing a color reaction.

[0002]

2. Description of the Related Art Strong acids such as hydrogen chloride and nitric acid, and weak acid solutions such as hydrogen fluoride, acetic acid and formic acid are widely used as industrial materials as cleaning agents and etching solutions. Is volatilized into the atmosphere and released to the environment.
Since such an acidic gas is harmful to the human body, the allowable concentration in the environment is limited to, for example, about 5 ppm for hydrogen chloride gas. The concentration of these acidic gases is usually detected by an electrochemical sensor using a galvanic cell method, and the concentration in the environment is monitored. However, in the fields that dislike very little rust and corrosion, such as the precision machine industry and the electronics industry, it is required that the concentration of these acidic gases in the environment can be controlled at a concentration far below the environmental standard.

However, the electrochemical gas sensor using the galvanic cell method used for environmental measurement has a detection limit of the order of ppm, so that the acid gas of the sub-ppm order required for quality control as described above is required. There is a problem that the concentration cannot be monitored. On the other hand, for the detection of acid gas of the order of ppb, a chemical measurement method using a color reaction is also used in part, but it is necessary to handle a fluid such as a reagent, so that the measurement operation is troublesome. In addition, there is a problem that skill is required.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and an object of the present invention is to obviate the need for handling fluids such as reagents, and to reduce ppb
An object of the present invention is to provide an acid gas detection paper capable of reliably detecting an acid gas in a wide concentration range from an extremely low concentration on the order to the ppm order required for monitoring environmental standards.

[0005]

According to the present invention, to solve such a problem, a color indicator having a discoloration range in an acidic region having a hydrogen ion concentration of pH 4 or less per square meter is used in a porous carrier. and 005 to 0.08 g, and is configured with a polyhydric alcohol impregnated with 8 to 35 grams.

[0006]

[Action] polyvalent amount of alcohol is an appropriate range, that is polyvalent
Alcohol is restricted to 8 to 35 grams, acidic
Since gas is Ru are easily incorporated into the porous carrier, which change color in proportion to the sampling time. Therefore, by adjusting the sampling time in accordance with the concentration of the acidic gas to be detected, it is possible to detect an acidic gas on the order of ppb to ppm on the same detection paper .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on embodiments. (Example 1) Metanyluyello having a color change range from yellow to red in a hydrogen ion concentration range of 1.2 to 2.3.
A coloring solution is prepared by dissolving 02 g and 15 ml of a polyhydric alcohol having a water absorbing and retaining property such as glycerin or ethylene glycol in an organic solvent such as methanol so that the total amount becomes 100 ml. After the porous sheet made of cellulose or the like is immersed in the coloring solution and absorbed, the excess coloring solution is squeezed with a rubber roller, and the solvent is evaporated at a temperature of about 40 ° C. As a result, the metanyluiello per square meter of paper is 0.026
It is possible to obtain a detection paper in which 25 g of gram and glycerin are developed.

FIG. 1 shows an example of an apparatus for measuring a gas concentration using a gas detection tape according to the present invention. In FIG. A through hole 3 having a diameter of about 1 cm is formed in a surface facing the detection paper 2 in a gas suction section arranged in a vertical direction, and a negative pressure from a suction pump (not shown) acts through a pipe 4. are doing. Reference numeral 5 denotes a measurement head unit 5 disposed on the other surface of the detection paper 2 facing the through hole 3 of the gas suction unit 1, and a detected gas introduction port 9 is provided at a position facing the through hole 3 of the suction unit 1. It is configured as a formed light-tight container, and has a peak wavelength of 5
A 55 nm light emitting diode 7 and a pin type photodiode 8 having a maximum sensitivity at a wavelength of 560 nm are arranged so as to have an incident / reflective relationship so that a reaction mark formed on the detection paper 2 can be detected. .

When the above-described gas detecting paper is cut into a tape shape and set on the reels 10 and 11, and a suction pressure from a pump (not shown) is applied to the suction section 4, the measurement head section from the inlet 9 is formed. The test gas is sucked into 5. The test gas is discharged from the through hole 6 to the outside through the through hole 3 via the detection paper 2. The gas to be detected is taken into the water held by the glycerin on the detection paper 2 in the process of passing through the detection paper 2 and reacts with the metanyluyello originally present, and is proportional to the hydrogen ion concentration. This causes a color reaction to occur.

Thus, a predetermined sampling time,
For example, when about 60 seconds have elapsed, the suction is stopped and the process proceeds to the step of measuring the optical density of the reaction mark. Light emitting diode 7
Light is absorbed according to the optical density of the reaction marks formed on the surface of the detection paper, so the optical density before the measurement starts, that is, the optical density of the background of the detection paper and the optical density of the reaction marks By calculating the difference between the concentrations, it is possible to know the concentration of the acidic gas that has passed through the detection paper or the integrated amount of the acid gas. When the measurement for one sampling is completed, the take-up reel 10 is driven to move the unused portion of the detection paper to the measurement area.

When the change in the optical density of the reaction trace was measured while changing the concentration of hydrogen chloride gas while setting the detection paper in the above-mentioned measuring apparatus, when the sampling time was set to about 60 seconds, as shown in FIG. A good calibration curve was obtained. From this, it was found that a wide range of concentrations from a very low concentration region of about 300 ppb to a high concentration region of about 2.5 ppm can be measured with high reproducibility.

On the other hand, 0.5 ppm, 0.8 ppm, 1.
Sample gases having different concentrations of hydrogen chloride such as 0 ppm, 2.0 ppm, and 3.0 ppm were prepared, and the relative sensitivity at each sampling time was measured while changing the sampling time for each. As shown in FIG. The result was able to be obtained. From this, the product of the sampling time and the concentration of chlorine gas has a very high correlation with the detection sensitivity.If the concentration of the acid gas to be detected is low, set the sampling time to a longer time. By doing so, it is possible to measure with high sensitivity without impairing the measurement accuracy, and when the concentration of the acidic gas to be detected is high, the sampling time is set short to avoid saturation. It has been found that the acid gas concentration can be measured without deteriorating the measurement accuracy.

When measurement was carried out using a sample gas containing nitric acid having a dissociation degree equivalent to that of hydrogen chloride, the same sensitivity characteristic as that of hydrogen chloride gas was also exhibited for nitric acid gas.

On the other hand, when the same measurement was performed on a standard gas containing hydrogen fluoride, formic acid, sulfuric acid, and nitrogen oxide having a smaller degree of dissociation of hydrogen ions than nitric acid and hydrogen chloride, the sampling time was extended to about 5 minutes. However, there was no sensitivity as shown in Table 1.

[0015]

[Table 1]

From these facts, a detection paper using a color indicator having a discoloration range in an acidic region having a hydrogen ion concentration of 4 or less can be obtained by using a hydrochloric acid gas, a nitric acid gas, and similar hydrogen iodide, hydrogen bromide, etc. Was found to selectively react only with strong acids.

Hydrogen ion concentration In order to investigate the effect of the concentration of the color indicator on the detection sensitivity, a detection paper was prepared in which the concentration of glycerin was kept constant at 25 g on the carrier and only the concentration of metanyluiello was changed. When hydrogen chloride gas of the same concentration was measured, the result was as shown in FIG. From this, when the concentration of metanyluiello is as low as 0.005 gram or less per square meter, not only the detection sensitivity is low, but also the concentration of the color reaction varies and the reliability of the measurement result is low, In addition, when the content of metanyluiello is as high as over 0.08 g per square meter, the color of the coloring indicator affects the optical background of the tape. Even in such a case, the detection sensitivity and the S / N ratio may be lowered, and it is not desirable from the viewpoint of cost to increase the concentration unnecessarily. From this, it was found that the optimum concentration of the hydrogen ion concentration indicator was 0.005 g to 0.08 g per square meter of the carrier.

On the other hand, in order to examine the change in detection sensitivity due to the concentration of polyhydric alcohol, the concentration of metanyluiello was kept constant, and a detection paper having only a different glycerin content was prepared. As a result of the measurement, the result shown in FIG. 5 was obtained. In other words, the highest sensitivity is exhibited when about 25 grams per square meter is included, and when it is more than this, the permeability of the porous carrier is reduced. The sensitivity began to decrease gradually. In addition, when the so-called transmission method is not applied, in which the test gas is passed from one surface to the other surface, the degree of reduction in detection sensitivity is small, but when the amount of polyhydric alcohol increases, the detection paper as a carrier is also reduced. The handling becomes inconvenient due to stickiness. Under these circumstances, polyhydric alcohol is used in an amount of 8 to 3 per square meter of the porous carrier.
Preferably, it is limited to about 5 grams.

Further, in order to investigate the long-term storage property, when the detection paper was stored in a container filled with high-purity air containing about 3% of carbon dioxide gas and reported for 12 hours, the detection paper showed no discoloration. Did not.

The same coloration as the above-mentioned meta-nil-yiello is carried out by using another hydrogen-ion-concentration coloring indicator having a color-change gamut in an acidic region having a color-change hydrogen ion concentration of 4 or less, for example, alizarin yellow, benzyl yellow or methyl yellow. When a detection paper was prepared based on the blending amount and a strong acid gas such as hydrogen chloride or nitric acid was measured, not only the same calibration characteristics as in the case of Metanyluiello, but also the hydrogen ion concentration Approximately the same results were obtained in the sensitivity characteristics with respect to the concentration of the polyhydric alcohol. From these facts, it is possible to detect strong acidic gas per square meter of porous carrier by using Methaniluiero, Alizarinyero, Benziruero,
It was concluded that it is desirable to contain at least one type of methyl yellow from 0.005 g to 0.08 g, and from 8 g to 35 g of a polyhydric alcohol such as glycerin or ethylene glycol.

Example 2 0.02 g of methyl red having a discoloration range from yellow to red at a hydrogen ion concentration of 4.2 to 6.2, 0.025 mol of Na as a buffer
20 ml prepared with ₂ CO ₃ and 0.005 mol of NaHCO ₃ / mol, and a polyhydric alcohol having a water absorbing property such as glycerin or ethylene glycol 15
A coloring solution is prepared by dissolving milliliters in an organic solvent such as methanol so that the total amount becomes 100 milliliters. After immersing a porous paper sheet made of cellulose or the like in the prepared solution and absorbing it, excess rubber solution is squeezed with a rubber roller, and the solvent is evaporated at a temperature of about 40 ° C.

[0022] For each square meter of the gas detecting paper thus constituted, 0.026 g of methyl red, 0.006 g of a buffer component, and 25 g of glycerin were added.
The gram will be expanded.

This gas detection paper was set in the above-described measuring apparatus, and the sampling time was set to 20 seconds to measure the concentration of hydrogen fluoride, which is a weak acid gas, as shown in FIG. 6 (I). Thus, a highly linear calibration curve could be obtained. On the other hand, when chlorine gas, which is the above-mentioned strong acid, was measured, saturation was exhibited at a low concentration stage as shown in FIG. Further, when a sample gas containing ethanol was measured in order to examine the coherence of the organic solvent, the same figure (I
As shown in II), it was confirmed that the measurement of a weak acid gas did not have a sensitivity that particularly affected.

Next, detection paper was prepared by changing only the content of the buffer component, and the detection paper was stored in a container and exposed to carbon dioxide gas for 12 hours to examine the degree of discoloration. Those containing less than 0.002 grams per square meter of the component were significantly discolored to the red side, but no discoloration occurred on the detection paper containing more than 0.006 grams.

That is, since the color indicator used in the second embodiment has a color change range in a region having a hydrogen ion concentration of 4 or more and 6.9 or less, it absorbs carbon dioxide in the air to obtain a color on the acidic side. Discolors to. Therefore, when using a color changing indicator having a color transition range to the extent hydrogen ion concentration pH4 or 6.9 or less, long-term storage and, also contain a buffer component in order to enable long-time sampling Becomes a mandatory requirement.

Various acid gases were measured using this acid gas detecting paper, and the results shown in Table 2 were obtained.

[0027]

[Table 2]

From this, gas detection paper using a color indicator having a discoloration area in a weak acid area has sensitivity not only to strong acids such as hydrochloric acid and nitric acid but also to hydrogen fluoride, sulfur dioxide and formic acid. It was confirmed that. Furthermore, phosphoric acid, sulfurous acid gas, nitrogen dioxide, which have the same degree of hydrogen ion dissociation,
It is clear that it has sensitivity to fluorine and the like.

The discoloring hydrogen ion concentration is 4 to 6.9.
Using other hydrogen ion concentration coloring indicators such as neutral red, lacomoid, etc., which make the area of the range of about the range of color change a detection paper with the same blending amount as methyl red described above, hydrogen chloride or nitric acid When a strong acid gas such as that described above was measured, not only the same calibration curve characteristics were exhibited but also the sensitivity dependence on the concentration of the hydrogen ion concentration color indicator and the concentration of the polyhydric alcohol showed almost the same results.

From these facts, at least one of methyl red, neutral red and lacomoid is used for detecting weakly acidic gas at a concentration of at least one of methyl red, neutral red and lacomoid per square meter of the porous carrier.
005 grams to 0.08 grams, 8 polyhydric alcohols
It can be concluded that it is desirable to contain from about gram to 35 grams and about 0.006 grams of the buffer component. Needless to say, since the buffer component has an auxiliary function, it is desirable to appropriately increase or decrease the buffer component according to the environment in which the buffer is stored.

By the way, the above-mentioned detection paper is placed at a position 30 cm directly below a 20-watt fluorescent lamp, and about 1500
When the background color of the detection paper was examined after 8 hours by irradiating the light with looks, the acid gas detection paper using Metanyluyello and methyl red as color indicator did not show any discoloration. Was.

On the other hand, the detection paper using neutral red as the hydrogen ion concentration color indicator showed discoloration. Then, when the gas concentration was measured using the discolored detection paper, it was confirmed that the detection sensitivity was reduced by 30% or more compared to the detection paper before discoloration due to the increase in the optical density of the background.

From these facts, in ordinary use, when the detection of a strongly acidic gas is intended as a hydrogen ion concentration color indicator, Metanyluyello is used. It is desirable to use not only red but also a buffer component. However, when no exposure is performed during storage, it is possible to realize a sufficiently practical acid gas detection paper even by using the other color indicator described above.

On the other hand, a detection paper constituted by developing a color reagent such as methyl red, neutral red, lacomoid or the like having a discoloration range in a hydrogen ion concentration range of 4 to 6.9 together with a buffer component is a general environmental paper. Since it has no detection sensitivity for carbon dioxide and nitrogen dioxide that are also present in it, and has sufficient sensitivity for weak acid gases such as hydrogen fluoride and formic acid used in factories, This is optimal for detecting acidic gas to be monitored for environmental standards.

(Third Embodiment) Methyl orange having a discoloration range with a hydrogen ion concentration of 3.1 to 4.4 was used as a color indicator, and 0.02 g of the same was used as a color indicator, and water retentivity such as glycerin or ethylene glycol was used. Is dissolved in an organic solvent such as methanol or ethanol to a total volume of 100 ml to prepare a coloring solution. After the porous sheet made of cellulose or the like is immersed in the coloring solution and absorbed, the excess coloring solution is squeezed by a rubber roller, and the solvent is evaporated at a temperature of about 40 ° C. As a result, a detection paper containing 0.026 g of methyl orange and 25 g of glycerin per square meter of the sheet is obtained.

Using this, a concentration of 0.05 to 0.2 pp
When the hydrogen chloride gas of m was measured, a calibration curve as shown by a mark in FIG. 7 could be obtained. For comparison,
When the hydrogen chloride gas having the same concentration as above was measured with the above-mentioned tape using methyl yellow or metanyluyello as a coloring reagent, calibration curves indicated by marks ● and ○ were obtained, respectively.

From this, the tape of this embodiment using methyl orange having a discoloration range in the hydrogen ion concentration of 3.1 to 4.4 is particularly high for an acid gas having a very low concentration of about 0.1 ppm. It was found to show sensitivity.
In addition, benzyl orange having a discoloration range in the acidic region equivalent to methyl orange (the discoloration range has a hydrogen ion concentration of 1.9 to 3.3) and tropeolin (the discoloration range has a hydrogen ion concentration of 1.4 to 3.2) can be used. The density of 0.05 to 0.2 pp was used for a detection paper manufactured using the same method as described above.
When the hydrogen chloride gas of m was measured, the mark in FIG.
As in the case of the calibration curve indicated by, specific high sensitivity could be obtained.

[0038]

As described above, in the present invention,
Hydrogen ion concentration p per square meter on porous carrier
A color indicator having a discoloration range in an acidic region of H4 or less is used in an amount of 0.
005 to 0.08 grams and polyhydric alcohol from 8 to
35 grams and impregnated with
If the amount of alcohol is in the proper range, that is, 8 alcohols
It is regulated to 35 g and easily supplies acid gas.
Can take write Mukoto to the porous carrier, it detects the sampling time
By adjusting to the concentration of acid gas to be released
To detect acid gas in ppm order from ppb order
Can be

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a measuring device to which the acidic gas detection paper of the present invention is applied.

FIG. 2 is a diagram showing a calibration curve of the acidic gas detection paper of the present invention.

FIG. 3 is a diagram showing a relationship among a concentration of a test gas, a sampling time, and a detection sensitivity.

FIG. 4 is a diagram showing the relationship between the concentration of a coloring reaction reagent and the detection sensitivity.

FIG. 5 is a diagram showing the relationship between the concentration of a humectant and the detection sensitivity.

FIG. 6 is a diagram illustrating calibration characteristics of a detection sheet according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating calibration characteristics of a detection sheet according to a third embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 31/22 G01N 21/77 G01N 21/78

Claims (5)

(57) [Claims] 1. A porous carrier comprising 0.005 to 0.08 g of a color indicator having a discoloration range in an acidic region having a hydrogen ion concentration of pH 4 or less per square meter, and 8 to 35 g of a polyhydric alcohol. Acid gas detection paper made by impregnation. 2. The method according to claim 1, wherein the color indicator is metanyluiello,
The acidic gas detection paper according to claim 1, wherein the paper is at least one selected from azaline yellow, benzyl yellow, methyl red, methyl yellow, methyl orange, benzyl orange, and tropeolin. 3. A color indicator having a discoloration range in an acidic range of not less than pH 4.9 and not more than 6.9 per square meter on a porous carrier in an amount of 0.005 to 0.08.
Acid gas detection paper constituted by impregnating a gram, a polyhydric alcohol with 8 to 35 gram, and a buffer component. 4. The acidic gas detection paper according to claim 3, wherein the color indicator is any one of methyl red, neutral red, and lacomoid. 5. The method according to claim 1, wherein the buffer component comprises Na2CO3 and NaH.
The acid gas detection paper according to claim 3, wherein the paper is CO3.