JP4189821B2 - Filtration membrane and simple determination method of lead ion using the same - Google Patents

Description

The present invention uses a filtration membrane and a lead ion-containing specimen sample solution to selectively separate and concentrate lead ions, and then develop the concentrated lead ions with a developer reagent solution. The present invention relates to a method for colorimetric determination of lead ions in a simple manner from the degree of the density.

Conventionally, as a method for quantifying lead ions, instrumental analysis methods such as flame atomic absorption, ICP-AES, ICP-MS (JIS K0102), and spectrophotometric methods after solvent extraction with dithizone (JIS G1229) are known. Yes.
However, although this instrumental analysis method is highly sensitive, the apparatus is large and expensive, and is not suitable for on-site analysis in the field. In addition, this spectrophotometric determination method requires complicated extraction operation with dithizone. In addition, an extraction reagent, an organic solvent, an acid and the like are required, and it is not a simple one.
As other spectrophotometric methods, other examples using reagents such as azo dyes and porphyrins have been reported, but all of them are greatly disturbed by other metal ions and have limited detection sensitivity. It is difficult to measure the concentration of lead ions at the environmental standard level, and it is unsuitable for analyzing samples such as polluted and colored wastewater because the measurement principle is light transmission through the solution.

  In addition, an optical sensor using a chemical equilibrium reaction between a lead ion and an organic reagent having a long-chain alkyl group in a thin film has been proposed (see Non-Patent Document 1), but this sensor is expensive in organic reagent. It is not simple and versatile.

“Analytical Chemistry”, Vol. 64, p. 1534, 1992

It has become clear that when the human body is exposed to lead for a long time, it will cause fatal damage to the brain and nerves, and WHO recommends strict environmental standards of 10 ppb or less as the regulated amount of lead. In Japan, lead is a hazardous heavy metal that is defined as 0.1 ppm or less as an industrial wastewater standard and 10 ppb or less as an environmental standard and tap water standard. Drinking water contamination due to lead elution from water supply lead pipes is also a serious problem, so monitoring is an important issue, but at present, environmental diagnosis is limited to some contractors with large equipment. It has been.
For this reason, lead ions present in trace amounts in aqueous solutions such as industrial wastewater, river water, and drinking water can be easily quantified on site with sufficient sensitivity to determine whether or not the current water quality standards are met. There is an urgent need to develop a simple and versatile lead ion measurement method.

An object of the present invention, under such circumstances, in a high sensitivity can be determined at the current water quality standard value, easy analysis in the field, using a lead ion Simple determination method and it versatile in simple And providing an effective filtration membrane .

As a result of repeating various studies on the lead ion simple quantification method and filtration membrane having the above-mentioned preferred features, the present inventors have focused on the fact that cerium phosphate produces fibrous crystals and strongly holds lead ions, Pass the sample liquid containing lead ions through a filter membrane using fibrous cerium phosphate crystals, filter to capture the lead ions on the filter membrane, separate and concentrate, and then develop the color with a developer and visually check the degree of color development. In addition, the inventors have found that the method of colorimetric quantification, such as photoelectrically colorimetrically, and the above filtration membrane contribute to solving the problems, and have made the present invention based on this finding.

That is, the present invention is as follows.
(1) Fibrous cerium phosphate having lead ion selective capturing ability alone or a composite of the fibrous cerium phosphate and natural fiber and / or synthetic fiber, or the fibrous cerium phosphate alone or the fiber A filter membrane obtained by applying a slurry in which water-like cerium phosphate and other fibrous materials are dispersed in water onto a filter paper attached to a filter, subjecting the slurry to filtration, and drying.
(2) After selectively capturing and concentrating lead ions through the lead ion-containing specimen sample solution on the filtration membrane described in (1) above, the filtration membrane is brought into contact with the developing reagent solution to develop a color, and the degree of color development A simple method for quantitative determination of lead ions, characterized by colorimetric determination.
(3) The method according to (2) above, wherein the composite is a nonwoven fabric.
(4) The method according to (2) or (3) above, wherein the lead ion-containing specimen sample solution is adjusted to pH 1.5-8.
(5) The method according to any one of (2) to (4) , wherein a masking agent is used to suppress interference with coexisting metal ions in the lead ion-containing sample liquid during the lead ion concentration operation.
(6) The method according to any one of (2) to (5) , wherein the color development degree is colorimetrically determined by comparing the darkness of the developed color with that of a standard.

For the filtration membrane used in the method of the present invention, fibrous cerium phosphate having lead ion selective capturing ability is indispensable, and it is preferable that the fibrous cerium phosphate has a crystal structure. The filtration membrane may be produced by netting only with fibrous cerium phosphate, or natural fiber and / or synthetic fiber cerium phosphate and other fibrous materials. It may be produced by forming a net as a composite combined with fibers, forming a nonwoven fabric, or adding a binder and press forming.
Cellulose fibers are preferred as natural fibers used in the composite, and filterability is improved by the combined use of natural fibers, especially cellulose fibers. The ratio of natural fibers in the composite, particularly the ratio of cellulose fibers, is preferably in the range of 10 to 95% by mass. If this ratio is too small, the filterability will not be good, and if it is too large, the ability to trap lead ions will decrease.
Moreover, as a synthetic fiber, nylon, polyester, polypropylene, polyvinylidene chloride, polytetrafluoroethylene, polyethersulfone, etc. are preferable.

  The filter membrane is preferably a filter paper-like thin film. To produce this, a slurry of fibrous cerium phosphate, preferably its crystal structure dispersed in water, or fibrous cerium phosphate, preferably its crystal structure And a mixed slurry in which other fibrous materials, such as cellulose fibers, are dispersed in water, are provided on a filter paper attached to a filter, and are subjected to filtration treatment, dried, or further After that, it is preferable to use a normal paper cutting method such as peeling from filter paper.

The thickness of the filtration membrane is not particularly limited as long as it has the function, but is usually selected in the range of 10 μm to 5 mm, preferably 20 μm to 2 mm, especially 50 μm to 1 mm.
In the case of the above-mentioned paper-making method, it is observed with an electron microscope that the filtration membrane is in an aggregated form with relatively gaps while long cerium phosphate crystal fibers, for example, the fibers having a length of several tens of μm are entangled with each other.

When the filtration membrane is filtered through a lead ion-containing specimen sample solution, lead ions are selectively captured and concentrated by the fibrous cerium phosphate crystals or the portion constituting the filtration membrane.
The filtration membrane is preferably used by being attached to a separable filter.
It is preferable to adjust the pH of the lead ion-containing specimen sample solution to be passed through the filtration membrane as appropriate. Usually, the pH is selected in the range of 1.5 to 9.0. In order to selectively separate ions, it is desirable that the pH is in the range of 1.5 to 8, particularly 1.5 to 4.0.
Examples of the lead ion-containing specimen sample solution include tap water, drinking water, etc., drinking water, factory water, ground water, river water, mine water, drainage, and the like.

Further, it is preferable to use a masking agent in order to suppress interference of coexisting ions during liquid flow.
Examples of the masking agent include dicarboxylic acid salts such as oxalic acid and succinic acid, and hydroxamic acid that conceals iron ions, chelating agents such as Tyrone, ethylenediaminetetraacetic acid, and nitrilotriacetic acid.
There is no particular limitation on the liquid passing speed, but it is preferably 20 ml / min or less for quantitative adsorption of lead ions.

  A filtration membrane enriched with lead ions develops color when brought into contact with a developer reagent solution. It is possible to obtain the concentration of lead ions by colorimetrically determining the color tone and the degree of the color density, in other words, the shade.

  The developer solution is a solution in which a developer is dissolved in a good solvent. The developer is a reagent that reacts with lead ions to change color, for example, reacts with lead ions, Although it is not particularly limited as long as it produces a stable colored compound and colored precipitate, preferably, since lead ions are firmly bound to cerium phosphate, a reagent or precipitate that can be peeled off with a stronger force is preferably used. It is preferable to select a reagent that can be generated. Examples of such a reagent include chromogenic precipitation reagents such as hydrogen sulfide water, sodium sulfide, potassium sulfide, potassium chromate, potassium iodide, and chelate selectively with lead ions. Chelating agents that form and develop color, such as dithizone and diethyldithiocarbamic acid.

In the coloring operation, the darkness of the developed color can be judged visually by using a color tone comparison table, but it is suitable for quantification to digitize with a measuring instrument such as a densitometer, a TLC scanner, or a color difference meter.
When colorimetrically using lead sulfide as a color developer using sodium sulfide as a developer, dilute hydrochloric acid or dilute to avoid interference due to coloration of other ions co-adsorbed on the filter membrane, such as Fe (III) ions. By exposing to a sulfuric acid solution, for example, having a concentration of about 1 to 2 M for an appropriate time, for example, 0.5 to 1 minute, lead sulfide that is hardly dissolved in dilute acid can be left.

According to the method of the present invention, the lead ion can be easily quantified as high-sensitivity that can be discriminated with the current water quality standard value, easy on-site analysis, simple and versatile , The filtration membrane of the present invention is effective for such a method .

  Next, the best mode for carrying out the present invention will be described by way of examples.

  200 ml of 6M phosphoric acid aqueous solution maintained at 95 ° C. was stirred, and a solution of 4 g (0.05 mol) of cerium sulfate dissolved in 200 ml of 1M sulfuric acid was added dropwise thereto at a rate of 3 ml / min. Generated. After completion of the dropwise addition, the stirring was stopped and the precipitate was aged at 95 ° C. for 7 hours. As a result, fine fibrous crystals of cerium phosphate were precipitated. This was filtered with a filter paper, washed well with water, dried, and peeled off from the filter paper to obtain a filter-like thin film molded body.

Add 3.8 g of cellulose fiber powder (commercially No. 5 filter paper crushed in water) and 200 ml of water to 1.6 g of cerium phosphate fibrous crystals obtained in the same manner as in Example 1, and use a mixer. Mixed. The obtained slurry was centrifuged, the supernatant was discarded and the prepared slurry was attached to a filter. The solution was suction filtered with 5 filter paper (diameter: 15 cm), washed with water, and dried to obtain a filter-like thin film molded body.
An electron micrograph of this thin film molded body is shown in FIG.

The thin film molded body obtained in Example 2 was cut into small pieces having a diameter of about 3 cm, and various kinds of filter materials were produced from above on the filter medium that was sandwiched between separable filters (diameter 0.5 cm, filtration area 0.13 cm ² ). 100 ml of lead ion-containing test water having a concentration (adjusted to pH 3.5 with an acetate buffer solution) was sent to each 10 ml with a peristaltic pump, filtered, washed with water, dried, and lead ions were concentrated. A filter medium was obtained.
When the thin film molded body was taken out from the filter medium and immersed in a 0.5% sodium sulfide aqueous solution, black sulfide was detected as a black spot. The results when the lead ion concentration in the lead ion-containing test water is changed to 5, 10, 50, 100, and 500 ppb are shown in FIG.

The relative reflection absorption of the black spot obtained in Example 3 was measured at a wavelength between 400 nm and 600 nm using a TLC scanner and a color difference meter. FIG. 4 shows the result of plotting the integrated value of the reflection absorption spot diameter against the lead ion concentration in the lead ion-containing test water.

A small piece of a thin-film molded body having a diameter of about 3 cm obtained in Example 2 was sandwiched between a separable filter (filtration area: 0.2 cm ² ) and filtered from above, with lead ions of 100 ppb and iron (III) of 1 ppm. (1.8 × 10 ⁻⁵ M) as well as 50 ml of iron iminodiacetic acid (9 × 10 ⁻⁴ M) and adjusted to pH 3.5, 100 ml of lead ion-containing test water was added to the peristaltic pump. Used and sent at 10 ml / min and filtered. After the lead ion-containing test water was filtered and washed with water, the thin film molded article was taken out, immersed in a 0.5% aqueous sodium sulfide solution, and developed as a black sulfide. The intensity of black was the same as when no Fe (III) ion was contained.

River water was collected at a river site where the basin was located under an abandoned mine in the Tohoku region, the pH was adjusted to 3.5, and lead ion-containing test water was prepared. This test water was applied to a filter medium made by sandwiching a small piece of a thin-film molded body having a diameter of about 3 cm obtained in Production Example 2 with a separable filter (filtration area: 0.2 cm ² ), and from the top with a peristaltic pump. After 10 ml of liquid was fed, filtered and washed with water, the thin film molded article was taken out and immersed in a 0.5% aqueous sodium sulfide solution. As a result, lead sulfide was produced and developed black. When the integrated value of the black relative intensity was applied to the calibration curve of Example 4 , the lead ion concentration was approximately equivalent to 10 ppb. As a result of separate ICP-MS analysis on the same sample, the lead ion concentration was 14 ppb. Since the concentration values of both are approximated, it can be seen that the method of the present invention can be used as a simple method for determining the lead ion concentration.

The present invention analyzes lead ions present in trace amounts in an aqueous solution such as drainage, river water, and drinking water with high sensitivity sufficient to determine whether or not the current water quality standard value is satisfied, and is easily analyzed in the field. since ur, it may be utilized in certain specific Irojo amount versatile in simple.

The electron micrograph of the thin film molded object of Example 2. FIG . The separable filter for filtration of Example 3 . The photograph which shows the result of having developed the lead ion of various density | concentration of Example 3. FIG . The graph which shows the relationship between the integrated value of the relative reflection absorption about the black spot obtained in Example 3 , and the lead ion concentration in test water.

Claims (6)

The fibrous cerium phosphate having a lead ion selective capturing ability alone or a composite of the fibrous cerium phosphate and natural fibers and / or synthetic fibers, or the fibrous cerium phosphate alone or the fibrous phosphate A filter membrane obtained by subjecting slurry, in which cerium and other fibrous materials are dispersed in water, to the entire surface of a filter paper attached to a filter, subjecting to filtration, and drying. The lead ion is selectively captured through the lead ion-containing specimen sample solution and concentrated on the filtration membrane according to claim 1, and then the filter membrane is brought into contact with a developing reagent solution to develop a color, and the degree of color development is determined colorimetrically. A simple method for quantitative determination of lead ions. The method according to claim 2 , wherein the composite is a nonwoven fabric. The method according to claim 2 or 3 , wherein the lead ion-containing specimen sample solution is adjusted to pH 1.5-8. The method according to any one of claims 2 to 4 , wherein a masking agent is used to suppress interference with coexisting metal ions in the lead ion-containing sample liquid during the lead ion concentration operation. 6. The method according to claim 2 , wherein the color development is colorimetrically determined by comparing the density of the developed color with that of a standard.