JPH11237373A - Method and apparatus for quantitatively determining phosphide or the like in solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a target compound such as phosphide or the like in a sample solution with high sensitivity in a short time without being interfered by a suspended matter and a colored matter in water. SOLUTION: A molybdate solution is supplied at a fixed flow rate from a first reagent passage 2, and a sample solution is injected from an injector 6 to the passage 2 and mixed by a mixing coil 8. A thiamine solution is supplied from a second reagent passage 10. The mixed solution from the mixing coil 8 and the thiamine solution from the passage 10 are supplied to a fluorescent detector 14. The supplied solutions are mixed and excited, thereby detecting generated fluorescence. A target compound such as phosphide compound or the like is determined from an intensity of the fluorescence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for determining a target compound in a solution, for example, a phosphorus compound or silica (silicon dioxide). This quantification method can be used as a monitor of a sewage or purified water treatment process, or a water quality monitor of rivers, lakes, seawater, or wastewater.

[0002]

2. Description of the Related Art As a method for determining a phosphorus compound in a sample solution, a molybdate blue colorimetric method is generally employed. In order to perform the total phosphorus quantitative measurement by the molybdate blue colorimetric method, a sulfuric acid-potassium peroxodisulfate solution is added to a sample solution, and the phosphorus compound is converted into phosphate ions by heat decomposition in an autoclave. Then, in order to develop a color, sulfuric acid was added, a mixed solution of ammonium molybdate and ammonium potassium tartrate was added, and then a mixed solution of L-ascorbic acid solution was added, and then colorimetry was performed at a wavelength of 880 nm. Perform quantification.

[0003]

The molybdate blue colorimetric method is difficult to accurately determine the amount of a phosphorus compound in dirty environmental water because of the interference of suspended or colored substances in water. In addition, since the concentration of phosphorus compounds in lake water or seawater is low, it is difficult to determine by this method. In the molybdate blue colorimetric method, since the absorbance is measured after sequentially adding a plurality of types of color formers in order to form a color, there is also a problem that the time required for the measurement becomes longer. The present invention provides a method and apparatus for quantifying a target compound such as a phosphorus compound in a sample solution without interference from suspensions or coloring matters in water, and enabling high-sensitivity and short-time measurement. The purpose is to provide.

[0004]

According to the quantification method of the present invention, a sample solution containing a target compound which reacts with molybdic acid and a molybdic acid solution are mixed to form a sample mixture, and the sample mixture and thiamine are mixed. Irradiating the mixed solution with excitation light to excite the mixture, and detecting the generated fluorescence with a fluorescent detector (FL detector). The concentration of the target compound in the sample solution is determined based on.

[0005] The target compounds suitable for determination in the present invention are phosphorus compounds and silica. The molybdic acid solution is used to include both a solution containing molybdic acid itself and a solution in which a water-soluble molybdate is dissolved. As such a water-soluble molybdate, potassium molybdate, sodium molybdate, ammonium molybdate and the like can be used.

The measurement of the phosphorus compound will be described. Even if the phosphorus compound and molybdic acid each independently react with thiamine, almost no fluorescence is generated. However, phosphomolybdic acid generated by the reaction between the phosphorus compound and molybdic acid is excited by excitation light to emit fluorescence when mixed with thiamine. The reason that phosphomolybdic acid and thiamine act to emit fluorescence is considered to be because phosphomolybdic acid is in a highly oxidized state, but the mechanism of emitting fluorescence has not been confirmed yet. This fluorescence emission intensity corresponds to the phosphomolybdic acid concentration, that is, the phosphorus compound concentration. Therefore, the phosphorus compound in the sample solution can be quantified by measuring the fluorescence emission intensity.

The phosphorus compound measured here is a phosphorus compound which reacts with molybdic acid to produce phosphomolybdic acid, and specifically, condensates inorganic orthophosphoric acid, diphosphoric acid, triphosphoric acid and the like. Phosphoric acid, and organic orthophosphoric acid and condensed phosphoric acid, and salts of these phosphoric acids are included. The entire amount of inorganic orthophosphoric acid reacts with molybdic acid to produce phosphomolybdic acid, while other phosphorus compounds partially hydrolyze to orthophosphoric acid, and the orthophosphoric acid reacts with molybdic acid to react with molybdic acid. Produces molybdic acid.

When a phosphorus compound contained in the sample solution contains a phosphorus compound in an oxidized state other than the phosphorus compound which forms phosphorus molybdic acid by reacting with molybdic acid, it is necessary to perform a quantitative measurement of total phosphorus. May be added with a pretreatment step in which all the phosphorus compounds are reacted with molybdic acid to form phosphomolybdic acid. As such a pretreatment step, in addition to a method using perchloric acid and a method using nitric acid as shown in JIS K0102,
An autoclave decomposition method in which a sulfuric acid-potassium peroxodisulfate solution is added and heat treatment is performed in an autoclave, a method using ultraviolet irradiation, an ozonolysis method, and the like can be employed.

[0009] Silica can be similarly determined. That is, even if silica alone reacts with thiamine, fluorescence hardly occurs. However, when silica is mixed with molybdic acid and then mixed with thiamine, the silica is excited by excitation light to emit fluorescence. In this case as well, the mechanism by which thiamine acts on the reaction product of silica and molybdic acid to emit fluorescence is thought to be because the reaction product of silica and molybdic acid is in a highly oxidized state. , Not yet confirmed. The reaction between the phosphorus compound or silica and molybdic acid occurs under acidic conditions, and the reaction product and thiamine act to emit fluorescence under alkaline conditions.

If the sample solution contains both a phosphorus compound and silica, and if an attempt is made to selectively quantify the phosphorus compound, the molybdic acid solution or the sample solution must contain It is necessary to add a reagent (referred to as an inhibitor) that inhibits complex formation with silica. As such an inhibitor for measuring a phosphorus compound, for example, a water-soluble vanadate such as ammonium vanadate or vanadate itself can be used. By adding such an inhibitor, the generation of a fluorescent silica compound is suppressed.

Further, by adding this inhibitor,
The fluorescence emission intensity at the time of measuring the phosphorus compound is enhanced. FIG.
2 shows the results of measuring the effect of vanadate on the fluorescence intensity from a mixed solution of phosphomolybdic acid and thiamine. The horizontal axis represents the concentration of ammonium vanadate, and the vertical axis represents the fluorescence intensity. The fluorescence intensity was measured using a mixture of phosphomolybdic acid and thiamine (phosphoric acid concentration: 5 × 10 ⁻⁵ M) (M = mol
/ L) is the ratio of the fluorescence intensity S generated by irradiating the excitation light to water and the fluorescence intensity B generated by irradiating the excitation light to water (S / B).
It is represented as According to this result, the fluorescence intensity from a mixture of phosphomolybdic acid and thiamine when vanadate was not added was S / B = 8, whereas when 1 mM ammonium vanadate was added, the fluorescence intensity was increased. Has been enhanced to S / B = 72. That is,
This shows that the addition of 1 mM of ammonium vanadate enhances the fluorescence sensitivity from the phosphorus compound by 9 times.

If the sample solution contains both a phosphorus compound and silica, and if an attempt is made to selectively quantify silica, the molybdic acid solution or the molybdenum solution should be added to the molybdenum solution or the sample solution in order to eliminate interference by the phosphorus compound. It is necessary to add an inhibitor that inhibits the complex formation between the acid and the phosphorus compound. As such an inhibitor for silica measurement, for example, an organic acid such as oxalic acid, tartaric acid or citric acid can be used.

When the sample solution contains both the phosphorus compound and silica, and if none of the above inhibitors is added, the phosphorus compound and silica can be simultaneously determined. If it is clear that the sample solution contains only one of the phosphorus compound and silica, the above-mentioned inhibitor may not be added. However, even when the sample solution contains only a phosphorus compound, it is preferable to add vanadate or vanadate itself for the purpose of enhancing the fluorescence intensity.

A first aspect of the quantitative measurement apparatus of the present invention is a first reagent flow path for supplying a molybdic acid solution at a constant flow rate,
A sample supply means for supplying a sample solution to the first reagent flow path, a mixer provided downstream of the first reagent flow path for mixing the molybdic acid solution and the sample solution, and a second supply means for supplying the thiamine solution at a constant flow rate. It has a two-reagent flow path, and a fluorescent detector for detecting fluorescence emission from a mixed liquid of the mixed liquid passed through the mixer and the thiamine solution from the second reagent flow path.

According to a second aspect of the quantitative measurement apparatus of the present invention, in the first aspect, a sample solution is supplied to a flow path for supplying a molybdic acid solution at a constant flow rate and mixed by a mixer. Is supplied at a constant flow rate, and the molybdic acid solution is supplied to and mixed with the sample supply channel.
According to a third aspect of the quantitative measurement apparatus of the present invention, both the molybdic acid solution and the sample solution are supplied at a constant flow rate and mixed by a mixer.

[0016]

FIG. 2 schematically shows a measuring apparatus according to a first embodiment. The first reagent channel 2 is a channel to which the molybdate solution is supplied, and the molybdate solution is supplied at a constant flow rate by the liquid sending pump 4. The flow path 2 is provided with an injector 6 for supplying a sample solution. The injector 6 is provided with a sample loop 6b in a six-way valve 6a. After a fixed amount of sample solution is collected in the sample loop 6b, the sample solution is introduced into the flow path 2 by switching the valve 6a. Reference numeral 8 denotes a mixing coil of the mixer, which mixes the molybdate solution supplied from the flow path 2 with the sample solution introduced from the injector 6.

The second reagent flow path 10 is a flow path for supplying a thiamine solution, and supplies a thiamine solution at a constant flow rate by a pump 12. The mixed solution from the mixing coil 8 and the thiamine solution from the flow path 10 are supplied to the fluorescent detector 14, and the two supplied solutions are mixed by the fluorescent detector 14, and are mixed in the fluorescent detector 14. Through the flow cell.
The mixed solution flowing through the flow cell is irradiated with excitation light by the fluorescent detector 14, and the mixed solution emits fluorescence. Fluorescence generated from the mixture is detected by a photomultiplier tube of the fluorescence detector 14. The solution after the fluorescence is detected by the fluorescence detector 14 is discarded. Reference numeral 16 denotes a recorder that records the fluorescence emitted from the fluorescence detector 14. As the fluorescence detector 14, a spectrofluorometer (product S33 of Soma Optical Co., Ltd.)
50 type), the excitation wavelength was 375 nm, and the fluorescence reception wavelength was 440 nm. Channels 2 and 1 in this embodiment
Teflon (trade name of polytetrafluoroethylene manufactured by DuPont) was used as a material for the mixing coil 8 and the mixing coil 8.

An ammonium molybdate solution as the molybdate solution supplied from the flow path 2 is used, and a 0.18 M sulfuric acid solution having an ammonium molybdate concentration of 1 mM is used. 7.5 μM 0.1 M borate buffer solution (pH 9.
5) was used. The flow rate of the molybdate solution supplied from the flow path 2 was 0.5 ml / min, and the flow rate of the thiamine solution supplied from the flow path 10 was 1.0 ml / min. The amount of the sample solution introduced from the injector 6 per one time is 100
μl. The mixture obtained by mixing the molybdate solution supplied from the flow path 2 and the thiamine solution supplied from the flow path 10 with the fluorescent detector 14 is alkaline.

FIG. 3 shows an example of the fluorescence emission peak measured by the measuring apparatus of FIG. 2 for the sample solutions having different phosphorus compound concentrations. The same concentration of ammonium vanadate was co-present in the ammonium molybdate solution in order to eliminate the interference by silica and increase the fluorescence intensity. As a sample solution, 310P-ppb (P-ppb =
μg P / l) (E), 155P-ppb (D), 62P
-Ppb (C), and 31P-ppb (B);
This is a result of measurement by introducing 0P-ppb (distilled water) (A) four times each. The time from the introduction of the sample solution by the injector 6 to the peak detection was 60 seconds.
The peak of sample 0P-ppb (A) due to distilled water means a blank measurement, and the value obtained by subtracting the peak height due to this distilled water from the peak height of each sample solution was used as the peak height of each sample for quantification. .

The sample solution has a phosphoric acid concentration of 15P-ppb
FIG. 4 shows an example in which the peak height of the fluorescence emission peak was measured for sample solutions having various concentrations in the range of Ｐ to 310 P-ppb.
Shown in From the results in FIG. 4, there is a correlation between the phosphoric acid concentration in this range and the peak height. By using the result of FIG. 4 as a calibration curve, the concentration of the phosphorus compound in the sample solution can be determined.

Similarly, the target compound in the sample solution is
FIG. 5 shows the relationship between the silica concentration measured by changing the phosphorus compound to silica and the fluorescence emission peak height. In this case, since a sample solution containing only silica and not containing a phosphorus compound was used, an inhibitor for inhibiting the complex formation between molybdic acid and the phosphorus compound was not added.

FIG. 5 shows that the silica concentration was 0.28Si-
ppm (Si-ppm = mgSi / l) to 15Si-
It shows that there is a correlation between the silica concentration and the fluorescence emission intensity between ppm. By using the result of FIG. 5 as a calibration curve, the silica concentration in the sample solution can be quantified.

In the apparatus shown in FIG. 2, the sample solution is introduced into the flow of the molybdate solution by the injector. Conversely, the sample solution is continuously supplied from the flow path 2 and the molybdate solution is introduced by the injector 6. You may make it.

FIG. 6 shows an example of another measuring apparatus. In the embodiment of FIG. 2, the sample solution is intermittently introduced by the injector 6. In the embodiment of FIG. 6, the sample solution is also continuously supplied by the pump 22 through the sample solution supply channel 20. I have. A mixing coil 8 is provided downstream of the flow paths 2 and 20, and after the molybdate solution supplied from the flow path 2 and the sample solution supplied from the flow path 20 are mixed in the mixing coil 8, a fluorescent light emission type The light is guided to the detector 14, mixed with the thiamine solution supplied from the channel 10, and excited by the fluorescent detector 14 to emit fluorescence. As shown in FIG. 6, if the sample solution is continuously supplied, the sample solution can be continuously measured as a monitor of a sewage or water purification process or as a water quality monitor of wastewater, There is no need for the operator to always operate.

[0025]

According to the present invention, a sample solution is reacted with a molybdate solution, then reacted with a thiamine solution, and the reaction product is excited with excitation light to measure the fluorescence intensity generated. The phosphorus compound and silica in the solution can be stably quantified in a short time. By repeating the measurement for obtaining the results of FIG. 4 and setting the S / N (signal / noise ratio) = 3 as the lower limit of quantification based on the measurement results of the variation, the phosphorus compound in the sample solution can be determined by the method of the present invention. It was found that quantification was possible down to a low concentration of 1P-ppb. Similar effects can be obtained when measuring silica in the sample solution.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of vanadate on the fluorescence intensity from the reaction product of phosphomolybdic acid and thiamine.

FIG. 2 is a schematic flow chart showing a first embodiment.

FIG. 3 is a diagram showing an example of a light emission peak in the example.

FIG. 4 is a diagram showing a relationship between a phosphor compound concentration and a fluorescence emission intensity.

FIG. 5 is a diagram showing the relationship between silica concentration and fluorescence emission intensity.

FIG. 6 is a schematic flow chart showing another embodiment.

[Explanation of symbols]

 2 Flow path of molybdate solution 4, 12, 22 Liquid feed pump 6 Injector 8 Mixing coil 10 Thiamine solution supply flow path 14 Fluorescent detector 16 Recorder 20 Sample supply flow path

Claims (9)

[Claims] A step of mixing a sample solution containing a target compound that reacts with molybdic acid and a molybdic acid solution to form a sample mixture; and mixing the sample mixture and a thiamine solution, and then mixing the mixture. Detecting the fluorescence generated by irradiating the excitation light with a fluorescence detector with a fluorescence detector, and determining the concentration of the target compound in the sample solution based on the fluorescence emission intensity of the fluorescence detector. Method. 2. The method according to claim 1, wherein the target compound is a phosphorus compound, and an inhibitor that inhibits the formation of a reaction product between molybdic acid and silica is added to the molybdic acid solution or the sample solution. 3. The method according to claim 2, wherein the inhibitor is vanadate or vanadate. 4. A method for quantifying all the phosphorus compounds contained in the sample solution, the method including an oxidation step of reacting all the phosphorus compounds contained in the sample solution with molybdic acid to produce phosphomolybdic acid, and quantifying all the phosphorus compounds contained in the sample solution. Claim 2 which is a measuring method
Or the quantification method according to 3. 5. The method according to claim 1, wherein the target compound is silica, and an inhibitor that inhibits the formation of a reaction product between the molybdic acid and the phosphorus compound is added to the molybdic acid solution or the sample solution. 6. The method according to claim 1, wherein the target compound is both a phosphorus compound and silica. 7. A first reagent flow path for supplying a molybdic acid solution at a constant flow rate, a sample supply means for supplying a sample solution to the first reagent flow path, provided downstream of the first reagent flow path, A mixer for mixing the molybdic acid solution and the sample solution; a second reagent flow path for supplying a thiamine solution at a constant flow rate; and a mixing of the mixed solution passing through the mixer and the thiamine solution from the second reagent flow path A quantitative measurement device comprising: a fluorescence detector that detects fluorescence from a liquid. 8. A sample supply channel for supplying a sample solution at a constant flow rate, first reagent supply means for supplying a molybdic acid solution to the sample supply channel, and molybdenum provided downstream of the sample supply channel. A mixer for mixing the acid solution and the sample solution, a second reagent flow path for supplying a thiamine solution at a constant flow rate, and a mixed liquid of the mixed liquid passing through the mixer and the thiamine solution from the second reagent flow path And a fluorescence detector for detecting fluorescence from the subject. 9. A first reagent flow path for supplying a molybdic acid solution at a constant flow rate, a sample supply flow path for supplying a sample solution at a constant flow rate, provided downstream of the first reagent flow path and the sample supply flow path. A mixer for mixing the molybdic acid solution and the sample solution supplied from both flow paths, a second reagent flow path for supplying a thiamine solution at a constant flow rate, a mixed solution passing through the mixer and the second reagent A fluorescence detector for detecting fluorescence from a mixed solution with the thiamine solution from the flow path.