JP2010271085A - Method and instrument for measuring formaldehyde - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a formaldehyde measuring method which enables the efficient and continuous analysis of a very small amount of formaldehyde present in a sample solution, and a formaldehyde measuring instrument. <P>SOLUTION: The formaldehyde measuring method includes the gasifying step for gasifying the sample solution by bubbling to form sample gas, the collection step for collecting the sample gas by a microgas collector to concentrate the same and the fluorescence analyzing step for subjecting formaldehyde in the sample solution to fluorescence analysis by an acetylacetone method. A mode preliminarily subjecting the sample solution to hypochlorous acid treatment, a mode wherein the detection range of formaldehyde is 0.1-10 mg/L or the like are preferable. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a formaldehyde measurement method and a formaldehyde measurement apparatus capable of efficiently and continuously analyzing formaldehyde present in a trace amount in a sample solution.

Formaldehyde is widely used in various fields because of its excellent bactericidal action and strong reducing action. However, formaldehyde is highly toxic and may cause respiratory distress, dizziness, vomiting, irritation in the oral cavity and stomach when taken by humans, and its concentration must be controlled.
In recent years, there has been a problem of factory wastewater management of formaldehyde generated in the metal treatment process in the factory. In 2004, the standard of formaldehyde concentration in tap water was established at 0.08 mg / L or less, and monitoring of formaldehyde concentration in wastewater has become important.

Conventionally, as a method for analyzing formaldehyde in a solution, for example, the following is known.
(1) Ammonium chloride method: neutralize the sample solution with sodium hydroxide, add ammonium chloride and a certain amount of sodium hydroxide, and the produced ammonia reacts with formaldehyde to form hexamethylenetetramine, so the remaining ammonia Is titrated with acid.
(2) Hydroxylamine hydrochloride method: Since formaldehyde reacts with hydroxylamine hydrochloride to liberate hydrochloric acid, it is titrated with an alkali and determined.
(3) Gas chromatography (GC) method: A sample is analyzed as it is or after 2,4-dinitrophenylhydrazine derivatization.
(4) Laurylamine method: Dissolve a sample solution in an alcohol / benzene mixture, add an ethylene glycol / isopropyl alcohol solution of laurylamine, and perform potentiometric titration with salicylic acid.
(5) Acetylacetone method: Formaldehyde reacts with acetylacetone and ammonia or ammonium salt to produce diacetyldihydrolutidine. This shows yellow, and since there is absorption at 412 nm, the intensity is measured and quantified.

In this case, as an analytical method in which the formaldehyde concentration in the sample solution is 0.5 mg / L or less, there is the gas chromatography (GC) described in (3) above. This GC method takes time to start up the apparatus. Because analysis takes time, feedback to wastewater management is practically difficult.
For example, Patent Document 1 discloses a solid alkaline reagent composition mainly composed of potassium hydroxide, sodium hydroxide or lithium hydroxide, 4-amino-3-hydrazino-5-mercapto-1,2,4. -A formaldehyde measurement kit comprising a solid coloring reagent composition mainly composed of triazole and a solid or liquid oxidizing reagent composition mainly composed of metaperiodate as constituent reagents has been proposed. ing. However, with this proposal, even if a trace amount of formaldehyde in the solution can be measured, it is difficult to perform continuous analysis efficiently and monitor the formaldehyde concentration.

JP 2003-254959 A

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, an object of the present invention is to provide a formaldehyde measurement method and a formaldehyde measurement apparatus capable of efficiently and continuously analyzing formaldehyde present in a trace amount in a sample solution.

Means for solving the problems are as follows. That is,
<1> A vaporization step of generating a sample gas by bubbling the sample solution;
A sampling step of collecting and concentrating the sample gas with a micro gas collector, and
A method for measuring formaldehyde, comprising: a fluorescence analysis step of fluorescence analysis of formaldehyde in a sample by an acetylacetone method.
<2> The method for measuring formaldehyde according to <1>, wherein the sample solution is treated with hypochlorous acid in advance.
<3> The method for measuring formaldehyde according to any one of <1> to <2>, wherein the detection range of formaldehyde is 0.1 mg / L to 10 mg / L.
<4> The method for measuring formaldehyde according to any one of <1> to <3>, wherein continuous monitoring of formaldehyde concentration in factory waste water is possible.
<5> Vaporization means for vaporizing the sample solution by bubbling;
Collection means comprising a micro gas collection device for collecting and concentrating the vaporized sample gas;
And a form aldehyde measuring apparatus comprising: a fluorescence analyzing means for fluorescence analysis of formaldehyde in a sample by an acetylacetone method.

  ADVANTAGE OF THE INVENTION According to this invention, the problem in the past can be solved, and the formaldehyde measuring method and formaldehyde measuring device which can analyze continuously and efficiently the formaldehyde which exists in a trace amount in a sample solution can be provided.

FIG. 1 is a schematic diagram illustrating an example of a micro gas collection device. FIG. 2A is a diagram illustrating another example of the micro gas collection device. FIG. 2B is a partially enlarged view of the honeycomb-shaped microchannel of FIG. 2A. FIG. 2C is a photograph showing another example of the micro gas collection device. FIG. 3 is a schematic view showing an example of a formaldehyde measuring apparatus according to the present invention. FIG. 4 is a diagram showing signal results obtained by measuring formaldehyde using the formaldehyde measuring apparatus shown in FIG. FIG. 5 is a diagram showing the relationship between concentration and output measured using the formaldehyde measuring apparatus shown in FIG. FIG. 6 is a diagram showing a calibration curve in the method for measuring formaldehyde of the present invention. FIG. 7 is a diagram showing the results of examining the effect of salt addition in the method for measuring formaldehyde of the present invention. FIG. 8 is a diagram showing a relationship with formaldehyde concentration in an experiment in which residual hexamine is decomposed into formaldehyde by hypochlorous acid. FIG. 9 is a diagram showing a relationship with time in an experiment in which residual hexamine is decomposed into formaldehyde by hypochlorous acid.

(Formaldehyde measurement method and formaldehyde measurement device)
The method for measuring formaldehyde of the present invention includes a vaporization step, a collection step, and a fluorescence analysis step, and further includes other steps as necessary.
The formaldehyde measuring apparatus of the present invention comprises vaporization means, collection means, and fluorescence analysis means, and further comprises other means as required.
In the present invention, the conventional acetylacetone method is employed for the analysis of formaldehyde. However, in the conventional acetylacetone method, a distillation method is used to eliminate interference with coexisting metals, but in order to greatly shorten the analysis time, the liquid sample is vaporized by bubbling, and the gas sample is collected with a micro gas collector. Collect and concentrate. Thereby, a trace amount of formaldehyde concentration can be continuously measured with high sensitivity in real time.
In the conventional acetylacetone method, spectrophotometric analysis is performed, but in the present invention, sensitivity can be greatly improved by measuring formaldehyde by fluorescence analysis.
Hereinafter, the formaldehyde measurement method and formaldehyde measurement apparatus of the present invention will be described in detail.

<Vaporization process and vaporization means>
The vaporization step is a step of vaporizing the sample solution by bubbling to generate a sample gas, and can be suitably performed by vaporization means.

-Sample solution-
There is no restriction | limiting in particular as said sample solution, According to the objective, it can select suitably, For example, factory drainage, tap water, agricultural water, well water, river water, lakes, seawater etc. are mentioned.

-Bubbling-
The bubbling is a method in which air is passed through the water to be treated to generate formaldehyde gas vapor in the waste water. A sample solution is placed in a 50 mL test tube serving as a bubbler, and air or nitrogen gas is passed through the porous glass sphere. In the case of air, clean and dry in advance with an activated carbon column or silica gel column. The formaldehyde vapor discharged from this bubbler is immediately mixed with clean air or an inert gas such as nitrogen, and the humidity is reduced from saturation to prevent adsorption of formaldehyde, which is highly compatible with water, to the pipe. Can do.

<Collection process and collection means>
The collection step is a step of collecting and concentrating the sample gas with a micro gas collection device, and can be suitably performed by a collection means.

-Micro gas collection device-
For example, as shown in FIG. 1, the micro gas collection device (micro channel scrubber) forms a micro channel 2 having a honeycomb structure on the surface of a substrate 3 made of polydimethylsiloxane (PDMS), and a reaction solution (acetylacetone solution) is formed. A place to store. A gas permeable membrane 1 is fixed on the microchannel 2 of the honeycomb structure. The reaction solution is allowed to flow through the microchannel 2, an air sample is introduced outside the gas permeable membrane 1, and the target component is taken in via the gas permeable membrane 1. In FIG. 1, 4 is a reaction solution inlet, and 5 is a reaction solution outlet.
An ultrathin liquid layer can be obtained with a certain thickness by the microchannel of the honeycomb structure. In addition, the gas absorption area can be increased. Also, the reaction solution spreads uniformly on the absorption surface while repeating the branching and gathering of the reaction solution according to the grooves of the reaction solution honeycomb structure. Since it flows around, it has little effect on the overall characteristics.
The honeycomb structure means a structure in which the flow path of the microchannel spreads in a hexagonal shape and flows to spread over the entire microchannel portion while repeating branching and merging. It is characterized in that a shallow flow path of 10 μm to 200 μm can be achieved over a wide area. The honeycomb structure can be expected to have both a wide collection area and high gas permeability for the purpose of high collection and concentration effects.
Since a substrate made of polydimethylsiloxane (PDMS) is used for the microchannel, a gas permeable film can be fixed in the process of polymerizing and solidifying PDMS. Therefore, it can fix without using an adhesive agent.
The depth of the channel of the microchannel is preferably 10 μm to 200 μm.
The width of the channel of the microchannel is preferably 40 μm to 1,000 μm.
As the gas permeable membrane, for example, a porous Teflon (registered trademark) membrane is preferable.

  By using the micro gas collector, gas can be collected with high efficiency, and extremely low concentration gas can be measured in real time or in a short time. Moreover, it is easy to handle the flow rate of the absorption reaction solution as 10 to 100 μL per minute, and the absorption reaction solution can be easily supplied.

<Fluorescence analysis process and fluorescence analysis means>
The fluorescence analysis step is a step of fluorescence analysis of formaldehyde in the sample by the acetylacetone method, and can be suitably performed by a fluorescence analysis means.

-Fluorescence analysis-
When molecules constituting a substance are irradiated with light (excitation light), the light energy is absorbed and then emitted as light, which is called fluorescence. In the fluorescence analysis, the property and concentration of the sample can be examined by measuring the fluorescence intensity. Since the sensitivity is higher than that of the spectrophotometric method and molecular species that emit fluorescence are relatively limited, it is possible to selectively detect the target component. A substance that does not emit fluorescence can be analyzed by being guided to a fluorescent substance by a chemical reaction. Also in the present invention, the fluorescence analysis was performed by reacting formaldehyde with acetylacetone.

<Other processes and other means>
Examples of the other steps include the control step.
The control step is a step of controlling each of the steps, and can be suitably performed by a control unit.
The control means is not particularly limited as long as the movement of each means can be controlled, and can be appropriately selected according to the purpose. Examples thereof include devices such as a sequencer and a computer.
Also, by providing a concentration calculation system, it is possible to convert the detector signal into a concentration in real time. In addition, by providing an alarm system, for example, when the amount of formaldehyde in water is managed, it is possible to manage the operation within the control value such as prevention of excess emission standards.

  The detection range in the method for measuring formaldehyde of the present invention is preferably 0.1 mg / L to 10.0 mg / L, preferably 0.1 mg / L to 2.0 mg / L, and wastewater management standard 0 Measurement of 5 mg / L formaldehyde is possible. Moreover, the measurement method of formaldehyde of this invention can be continuously analyzed for 1-3 hours, and is suitable for the monitoring of a factory waste liquid.

  Here, FIG. 3 shows an example of the formaldehyde measuring apparatus of the present invention. In FIG. 3, formaldehyde vapor is generated by venting indoor air purified through an activated carbon column to a sample solution placed in a bubbler. Since this generated steam contains a large amount of water vapor and may cause adsorption of formaldehyde on the pipe, it is diluted with dry air of the corresponding flow rate and introduced as it is into the micro gas collector. Here, an acetylacetone solution is introduced into the microchannel portion, and formaldehyde in the gas phase is taken into the reaction solution. This reaction solution is introduced into the fluorescence detector through a reaction coil maintained at 50 ° C. In addition, a three-way solenoid valve and an activated carbon column were installed in front of the micro gas collection device (micro channel scrubber) to introduce zero gas and sample gas alternately. As a result, a response corresponding to the formaldehyde concentration is obtained on the baseline.

The various analysis conditions using the formaldehyde measuring apparatus shown in FIG. 3 are described in Table 1 below.
Micro gas collector: The microchannel scrubber shown in FIGS. 1 and 2A to 2C was used. By adopting a honeycomb structure, this apparatus can achieve both a wide collection area and high gas permeability, and a high collection and concentration effect can be obtained.

Next, when the formaldehyde concentration is actually measured by the formaldehyde measuring apparatus shown in FIG. 3 under the above analysis conditions, a signal corresponding to the concentration is obtained by switching between zero gas and sample gas every 5 minutes as shown in FIG. Could get. In addition, at the same concentration, results with good repeatability could be obtained. When a calibration curve is drawn based on this response data, as shown in FIG. 5, a good straight line of Signal (V) = 0.0951 × HCHO (mg / L) +0.0038 (R ² = 0.999). A relationship was obtained.
Thus, it can be judged that the formaldehyde concentration is sufficiently measurable from 0.1 to 2.0 mg / L. The detection limit obtained from S / N = 3 was 0.03 mg / L.

  In the formaldehyde measuring apparatus of the present invention, nitrogen gas can be used instead of air in the measuring chamber. Thereby, management of the column for purification and the column for drying becomes unnecessary. Also, the blank value can be ignored.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
For factory wastewater samples containing a small amount of formaldehyde, the following vaporization collection AA fluorescence method (the method of the present invention), the following distillation-acetylacetone-absorption photometric method (comparative method 1), and the following PFBOA derivatized GC-MS analysis method (comparative method) Measurement by the three methods with 2) was performed. All the analytical methods are not treated with hypochlorous acid.

-Method of the present invention (vaporization collection AA fluorescence method)-
The measurement was performed under the analytical conditions shown in Table 2 below using the formaldehyde measuring apparatus shown in FIG. The results are shown in Table 3.
Micro gas collector: The microchannel scrubber shown in FIG. 1 and FIGS. 2A to 2C was used. Microchannels are formed in a honeycomb shape, and the absorption reaction solution is passed therethrough. The microchannel is covered with a gas permeable membrane, and a water-soluble gas component is dissolved and collected in the absorption reaction solution through the permeable membrane.
As shown in FIG. 2A, the honeycomb-shaped microchannel is located at the center of the PDMS block having a slide glass size (26 mm × 76 mm). As shown in FIG. 2B, the honeycomb structure is composed of a regular hexagon having a side of 0.6 mm, the solution proceeds by repeating branching, the channel depth is 60 μm, the channel width is 500 μm at the portion A, B The portion was formed to gradually become 400 μm at a portion of 300, 300 μm at a portion of C, and 200 μm at a gas collection portion (GCA). The channel area at the gas collection part is 142.2 mm ² and the volume is 10.9 μL.
As a gas permeable membrane, pPTFE membrane (thickness 30 μm, pore diameter 0.45 μm, Poreflon (registered trademark), HP-045-30, manufactured by Sumitomo Electric Fine Polymer) or pPP membrane (thickness 94 μm, Accurel (registered trademark), PPIE, Membrana) was used.
FIG. 2C is a photograph showing a microchannel scrubber.

-Comparison method 1 (distillation-acetylacetone-absorptiometry)-
First, the sample solution was heated and boiled, and formaldehyde dissolved at this time was vaporized with the evaporation of water. This was cooled and liquefied again and collected. When most of the sample solution evaporates, pure water is added and distillation is repeated to completely vaporize formaldehyde. Distilled water was mixed with acetylacetone and ammonium acetate, and the absorbance of the resulting yellow product was measured. The results are shown in Table 3.

-Comparison method 2 (PFBOA derivatized GC-MS analysis method)-
50 mL of test water was taken in a separatory funnel, and 3 mL of 1 mg / mL pentafluorobenzylhydroxylamine (PFBOA) hydrochloride solution was added and mixed. After standing for 2 hours, 0.8 mL of sulfuric acid (1 + 1), 20 g of sodium chloride, and 5 mL of n-hexane were mixed vigorously for 5 minutes. After the stationary phase separation, the n-hexane phase was separated and dehydrated with an appropriate amount of anhydrous sodium sulfate. Next, 1 mL was collected from the dehydrated n-hexane phase, 1 μL of 100 mg / L 1-chlorodecane was added, and this was analyzed by GC-MS. The results are shown in Table 3.

From the results in Table 3, the value according to Comparative Method 1 (distilled AA absorption method) was remarkably high.
When this cause was examined, it was thought that hexamine remained, and the method of the present invention (vaporization collection AA fluorescence method) and the comparative method 2 (PFBOA-GCMS method) were treated with hypochlorous acid. It was.
The treatment conditions were as follows: 1 mL of 8.5 to 13.5% NaClO diluted 100-fold to 50 mL of sample water and standard solution for calibration curve was added, reacted for 30 minutes, and then added with 1 drop of 10% sodium thiosulfate solution. The procedure was the same as in the previous method. In the same manner, Comparative Method 1 (distilled AA absorption method) showed a high value. In addition, both the method of the present invention (vaporization collection AA fluorescence method) and the comparison method 2 (PFBOA-GCMS method) have a downwardly convex calibration curve and lack reliability in the low concentration region. About this cause, when sodium thiosulfate is used, it is thought that there is a contamination of sulfurous acid. Formaldehyde is known to form complexes with sulfite ions. For this reason, I think that the measurement result by the process by hypochlorous acid was not good.

(Example 2)
The factory wastewater sample containing a trace amount of formaldehyde as in Example 1 was analyzed only by oxidative decomposition treatment without neutralizing excess hypochlorous acid with sodium thiosulfate. The results are shown in Table 4.

From the results in Table 4, the values obtained by the method of the present invention (vaporization collection AA fluorescence method) and the comparison method 1 (distilled AA absorption method) showed very good agreement. The comparative method 2 (PFBOA-GCMS analysis method) was a slightly lower value. Although the cause of this is not well understood, in Comparative Method 2 (PFBOA-GCMS method), since treatment was performed with sodium thiosulfate, there may still be a negative factor as a result of omitting this step. However, it was found that a very good correlation was obtained between the method of the present invention (vaporization collection AA fluorescence method) and the comparative method 1 (distilled AA absorption method), and the method of the present invention gave sufficient analysis results.
FIG. 6 shows a calibration curve obtained by the method of the present invention (vaporization collection AA fluorescence method). The addition of hypochlorous acid has no effect, but the addition of thiosulfuric acid has been found to be inferior in quantitativeness.

  As described above, 0.1 to 2.0 (maximum 10.0) mg / L of HCHO can be measured at 10-minute intervals by the vaporization collection-AA-fluorescence method. In addition, it has been found that hexamine is instantaneously decomposed into HCHO by addition of hypochlorous acid, and in order to obtain total HCHO including hexamine, it is found that sodium hypochlorite should be added immediately before the HCHO vaporization section. It was.

(Example 3)
-Investigation of coexisting metal ions in batch acetylacetone reaction-
The reason why distillation or vaporization collection is necessary in the HCHO measurement using the acetylacetone reaction is that the coexisting metal ions and acetylacetone form a complex and color. For iron III ions, copper II ions, and silver I ions, the effects of both the absorptiometry and the fluorometry were confirmed. The results are shown in Table 5.

The results in Table 5, although interference was observed in three metal ions all tested, particularly large interference Fe ^3+. This is a level that cannot be used at all by the spectrophotometric method. There was some interference with the fluorescence method. Interestingly, the spectrophotometric method showed a large positive error, and the fluorometric method showed a negative error. This is considered to be because a positive error occurred in absorbance due to the color reaction, whereas the self-absorption effect was effective in the fluorescence method.

Example 4
-Salt effect in HCHO vaporization-
NaCl was added to examine the effect of the salt.
FIG. 7 shows the results when the 1,000 mg / L Na ⁺ is not present in the HCHO 2 mg / L solution and when it is present.
From the results of FIG. 7, the average of the five response intensities was 0.104 ± 0.004V and 0.103 ± 0.005V, respectively, and no significant difference was observed. Sodium ion was added as NaCl.

(Example 5)
-Hexamine decomposition experiment (hypochlorous acid)-
Stoichiometric and kinetic investigations were carried out when decomposing residual hexamine into HCHO with hypochlorous acid.
First, 1 mL of a 100-fold diluted sodium hypochlorite solution was added to 50 mL of 0 μM, 10 μM, and 20 μM HCHO solutions and allowed to stand for 30 minutes. One drop of 10% sodium thiosulfate solution was added dropwise thereto, and then fluorescence analysis was performed using acetylacetone reaction. The results are shown in FIGS.
FIG. 8 shows a calibration curve for HCHO, which was measured directly (cross (×)) and treated with hypochlorous acid / thiosulfuric acid (triangle (▲)). Although the slope of the calibration curve was about 2/3 due to the hypochlorous acid / thiosulfuric acid treatment, the linearity was maintained. A similar test was performed for hexamine, and the results of direct measurement (square (■)) and hypochlorous acid / thiosulfuric acid treatment (circle (●)) were obtained. Even in the direct measurement of hexamine, a certain amount of fluorescence signal is obtained due to self-degradation, but the signal is tripled by the degradation treatment. When the horizontal axis of HCHO and hexamine concentration was 1: 6 for this hypochlorous acid / thiosulfuric acid treatment, it was found that the calibration curves of HCHO and hexamine overlapped. That is, it was found that 6 mol of HCHO was produced from 1 mol of hexamine.
Next, FIG. 9 shows the fluorescence signal by changing the reaction time from adding sodium hypochlorite to 1.66 μM and 3.33 μM HMTA solution and adding sodium thiosulfate to stop the decomposition reaction. Was monitored. As a result, it was found that the decomposition was completed within 1 minute. On the contrary, when the degradation time was lengthened, there was also a tendency that the fluorescence signal decreased slightly (10% per 2 hours). It seems that the oxidation reaction of HCHO is proceeding slowly.

  The formaldehyde measurement method and formaldehyde measurement apparatus of the present invention can be suitably used for wastewater management of formaldehyde such as factory wastewater because a trace amount of formaldehyde present in a sample solution can be efficiently and continuously analyzed.

1 Gas-permeable membrane 2 Microchannel 3 Substrate 4 Reaction solution inlet 5 Reaction solution outlet

Claims (5)

A vaporization step of generating a sample gas by vaporizing the sample solution by bubbling;
A sampling step of collecting and concentrating the sample gas with a micro gas collector, and
A method for measuring formaldehyde, comprising a fluorescence analysis step of fluorescence analysis of formaldehyde in a sample by an acetylacetone method.   The method for measuring formaldehyde according to claim 1, wherein the sample solution is treated with hypochlorous acid in advance.   The formaldehyde detection range is 0.1 mg / L to 10 mg / L. The method for measuring formaldehyde according to claim 1.   The method for measuring formaldehyde according to any one of claims 1 to 3, wherein continuous monitoring of formaldehyde concentration in industrial wastewater is possible. Vaporization means for vaporizing the sample solution by bubbling;
Collection means comprising a micro gas collection device for collecting and concentrating the vaporized sample gas;
A measurement apparatus for formaldehyde, comprising: a fluorescence analysis means for fluorescence analysis of formaldehyde in a sample by an acetylacetone method.