JP2000088840A - Simplified measuring method for cod, and spectrophotometer used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out COD measurement more simply and economically than a JIS method. SOLUTION: One-tenth amounts or less of sample water and reagents compared with a JIS method are put in a test tube to be heated for 30 minutes at 100 deg.C by a block heater, then cooled to stop imediately reaction, filtered with inorganic filter paper having 1.0 μm of holding particle size or less, a concentration of a permanganate ion in a filtrate is measured thereafter using absorbance in the vicinity of 525 nm or 543 nm, and a COD is calculated based on a reduced amount thereof. A spectrophotometer built-in with a program of an operation expression [expresssion (8)] for the COD based on absorbance reduction, and capable of digital-displaying an operation result is used to allow direct reading of a COD value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple method for measuring the COD of a water sample and a spectrophotometer used for the method.

[0002]

BACKGROUND OF THE INVENTION COD (chemical oxygen consumption) using potassium permanganate
Is an index that indicates the total amount of pollutants in water, and is widely used in the management of various water qualities. COD measures the amount of contaminants that consume oxygen in water based on the amount of oxygen consumed during oxidative decomposition by reacting contaminants in water with oxidizing agents under specific conditions. In Japan, permanganic acid is used as an oxidizing agent. Potassium is used. That is, JIS
After reacting the permanganate ion with the contaminant in a boiling water bath for 30 minutes using K01017, an aqueous solution of sodium oxalate as a terminator is added, and the COD in the water is again determined by back titration with a potassium permanganate solution. It has been calculated. However, the measurement uses a large amount of harmful potassium permanganate and expensive and harmful silver nitrate,
The measurement operation is also complicated and requires skill, and the calculation is performed manually, so that there is a problem that the social burden is large. Further, in the COD measurement using potassium permanganate, the oxidative decomposition of organic substances does not completely proceed, so that the measured value has a different meaning if the reaction conditions determined by JIS are changed.
Therefore, in order to obtain the same value as in the JIS method, the method must be the same as the solution composition, the reaction temperature and the time under the oxidation reaction conditions of the JIS method.

On the other hand, there is a method of automating COD measurement using a flow analyzer, which is specified in JIS. However, maintenance and management of equipment is troublesome, and a large amount of expensive and harmful reagents are used. However, there is a problem that a large amount of hazardous waste liquid is generated. In addition to this, there is a device that performs coulometric titration only on a titration portion, but it is not used much because it is not very efficient because it is expensive. Conventional simple methods for measuring COD include a method using UV absorbance instead, and a packed test method in which a reaction is carried out at room temperature using a reagent contained in a tube. Since the principle is completely different, there is a problem that a limited water sample can only be used in correlation with the JIS method.

The present invention has been made in order to solve the above-mentioned problem, and reduces the amount of sample water and the amount of expensive and harmful chemicals to one-tenth.
After the reaction is reduced under the same conditions as in the JIS method and filtered, the amount of permanganate ion reduced is measured by absorbance instead of the titration operation, thereby greatly simplifying the operation and increasing the cost. The aim is to provide an economical and simple method of measuring COD that can reduce the amount of harmful reagents and harmful waste liquids required for processing to less than one-tenth and the power consumption to less than one-tenth. is there. In particular, by displaying the COD value calculated by a spectrophotometer in which the arithmetic expression has been programmed as a program and enabling direct reading,
A simpler measuring method can be provided.

[0005]

Means for Solving the Problems The present invention is based on one of the JIS methods.
Sample water and reagents in a volume of 0/1 or less are placed in a test tube, heated at 100 ° C. for 30 minutes by a block heater, and the reaction is immediately stopped by cooling. Means for filtering COD from the amount of reduction by measuring the concentration of permanganate ion in the filtrate at around 525 nm or 543 nm by absorbance after filtering through an inorganic filter paper of 0.0 μm or less,
The above problem was solved by adopting a means of using a spectrophotometer incorporating a program of an arithmetic expression of COD based on a decrease in absorbance of potassium permanganate.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a special purpose in which one-tenth or one-twentieth sample water used in the conventional measuring method is placed in a test tube in which a reagent is previously placed, and a large number can be heated simultaneously. After heating at 100 ° C. for 30 minutes with a block heater, immediately cooled with water, filtered through a glass fiber filter paper having a retained particle size of 1.0 μm or less, and the permanganate ion concentration of the filtrate was calculated by using an arithmetic expression as a spectrometer. By measuring with a photometer, the C calculated from the decrease
The OD is digitally displayed so that it can be read directly. Then, the present inventors conducted the following experiment to verify the present invention.

In this experiment, all reagents were of special grade or 1 grade.
Grade standard reagents were used. Various solutions used for COD measurement are JIS K0102 17. Was prepared as follows. Pure water: tap water was desalted by passing it through an ion exchange resin, and further purified water was passed through an activated carbon column. Sulfuric acid (1 + 2): 200 ml of pure water was placed in a beaker, and 100 ml of special grade sulfuric acid was gradually added thereto while stirring. 200 g / l silver nitrate solution: 20 g of primary silver nitrate was dissolved in pure water to make 100 ml. 12.5 mmol / l sodium oxalate solution: 1.68 g of special grade sodium oxalate was dissolved in pure water to make 1 liter. 5 mmol / l potassium permanganate solution: 0.8 g of special grade potassium permanganate in pure water at 1050 to 1100 m
l. This was boiled gently for 1 to 2 hours and then left overnight. The supernatant is filtered using a glass filter,
The filtrate was stored in a brown glass bottle at room temperature. This solution is JIS K0102 17. The factor was accurately determined by the method described above before use. In addition, glucose, acetic acid, tartaric acid, citric acid, glutamic acid, glycerin, phenol, p-cresol standard aqueous solution used for evaluating the absorbance method was prepared by dissolving a primary or special grade reagent in pure water and diluting it in several steps. Using.

In this experiment, the operating procedure of the JIS method was JIS K
0102 17. (1993) as follows. (1) An appropriate amount of the sample having a COD of about 10 mg / l and 100 ml of pure water together in a 300 ml Erlenmeyer flask, and 5 ml of a 200 g / l silver nitrate solution while shaking.
And 10 ml of sulfuric acid (1 + 2). (2) 5 mmol / l potassium permanganate solution 10 m
1 and shaken, immediately placed in a boiling water bath and heated for 30 minutes. (3) Removed from the boiling water bath, 10 ml of a 12.5 mmol / l sodium oxalate solution was added, shaken, and reacted well. (4) While maintaining the solution temperature at 60 ° C., titration was performed with a 5 mmol / l potassium permanganate solution until the solution became slightly red. (5) Separately, 100 ml of pure water was placed in a 300 ml Erlenmeyer flask, and operations (1) to (4) were performed. (6) COD (mg / l) was calculated by the following equation.

(Equation 1) Here, COD: oxygen consumption by potassium permanganate at 100 ° C. (mg / l), a: 5 required for titration
mmol / l potassium permanganate solution (ml), b:
5 mmol / l potassium permanganate solution (ml) required for titration in the test using pure water, f: factor of 5 mmol / l potassium permanganate solution, V: sample amount (m
l), 0.2: 5 mmol / l Oxygen consumption of 1 ml of potassium permanganate solution (mg) In the experiment of the present invention, an 11 ml screw-hole test was conducted on the vessel without changing the reaction conditions based on the JIS operation procedure. A simple measuring method with a low environmental load was achieved by changing the volume of the liquid to 1/20 in a tube, changing the boiling water bath to a block heater capable of heating 16 tubes simultaneously, and changing the titration to absorbance measurement. An experiment in which the liquid volume was reduced to 1/10 was also performed for comparison.

[0009] When the titration is changed to absorbance measurement, the sample volume may be about 10 ml, so that many samples can be heated in a small space. Therefore, a sample of 1/20 liquid volume of the JIS method was placed in an 11 ml screw-cap test tube, and it was examined whether or not the block heater could reproduce the same heating state as the boiling water bath by the water bath in the JIS method.

In the boiling water bath according to the JIS method, Toyo Seisakusho's 4
Using a continuous water bath WB-14S, pure water and each reagent were placed in a 300 ml Erlenmeyer flask in the same manner as in the blank measurement by the JIS method, and used as a sample.

In the experiment of the present invention, a 16-block heater made by Hack Co. was used. FIG. 1 schematically shows a block heater. The test tube in which the sample is placed has an outer diameter of 16 (inner diameter of about 11.7) and a length of 10 that can be set in the block heater
Using a screw-threaded test tube with a cap of 0 × 9 mm in inside diameter and a capacity of 11 ml, pure water and each reagent were added to each of them in a 1/20 volume to prepare a sample.

In measuring the temperature of the sample, the thermocouple was inserted so that the tip was located at the center of each sample, and the temperature change was measured from the start of heating to 10 minutes after the heating was completed and the sample was taken out. At this time, in the heating by the block heater, after heating for 30 minutes, instead of adding the sodium oxalate solution according to the JIS method, a screw-hole test tube in which the sample is put in tap water previously stored in a water tank is cooled and reacted. We devised to reduce the speed.

In order to determine the measurement wavelength for obtaining the reduction amount of permanganate ion, the concentration of the potassium permanganate solution was set to 0.4 mmol / l at the time of COD measurement, and 300 nm
The absorption spectrum at ９００900 nm was measured. The absorption spectrum and the absorbance were measured with a 10 mm glass cell using UV-DEC-430A manufactured by JASCO Corporation as a visible ultraviolet spectrophotometer.

[0014] In the measurement of COD, potassium permanganate is added, the suspension is heated in the sample after heating for 30 minutes, and it is necessary to perform filter filtration before measuring the absorbance. Therefore, it was examined whether or not the absorbance of the blank was changed by filtration with a glass fiber filter having a retention particle diameter of 0.4 μm or 1.0 μm or filtration with a membrane filter having a pore diameter of 0.45 μm. At the time of sample filtration, a filter paper holder was connected to the tip of a 10 ml glass syringe, the whole sample after heating was filtered, and the absorbance of the filtrate was measured.

In order to clarify the formation reaction of a suspension generated after heating in COD measurement, an aqueous solution of manganese sulfate containing no organic substance was used as a sample, a potassium permanganate solution was added, and after heating, the retained particle diameter was 0.4 μm or 1.0
The solution was filtered through a glass fiber filter having a thickness of μm, and it was examined how the absorbance of the filtrate was changed and whether or not suspension was caused even with another aqueous solution of metal sulfate. Monovalent potassium, sodium, divalent manganese, zinc, iron, trivalent iron, and aluminum are selected as metal ions, and the concentration after addition is approximately equal to the electric quantity of permanganate ion. 0.
The concentration was set to 4, 0.2, and 0.13 mmol / l, and a 0.5 and 1.5-fold concentration before and after the test was also tested. Further, for manganese ions, an additional test was performed at 0.05 to 0.5 mmol / l in 10 concentrations of 0.05.

In the method of the present invention, if the reagents to be used are put in a screw-mouth test tube in advance, when measuring a large number of samples at once, it is only necessary to add sample water to the screw-mouth test tube. The preparation of the reagents was considered unnecessary, and the storage stability of the reagents was confirmed. That is, sulfuric acid (1+
2) Two or three types of 200 g / l silver nitrate solution and 5 mmol / l potassium permanganate solution were mixed at the same ratio as in the JIS method, and the mixture was put into a screw-mouth test tube. confirmed. In addition, the preservability of a highly reactive 5 mmol / l potassium permanganate solution alone was confirmed. Further, the solution was filled into 50 ml or 100 ml brown screw-neck bottles, respectively, and two bottles each were stored at room temperature and in a refrigerator.

The method of the present invention determined in the above experiment was compared with the JIS method. First, the already mentioned 8
Absorbance method, JIS for standard aqueous solutions of various organic substances
In both cases, the number of measurements was set to n = 4, and the arithmetic average value was used as the measured value. In addition, in this experiment, in order to examine the possibility of reducing silver nitrate, which is a masking agent for chloride ions, measurement was also performed when the silver nitrate solution concentration was changed from 200 g / l to 40 g / l. Next, as actual samples, river water, lake water, university experimental wastewater, treated water, domestic wastewater, sewage, treated water, industrial waste landfill leachate, sludge landfill leachate, automobile factory wastewater, and treated water A total of 60 samples of pond water in the university were used. For each sample, the number of measurements n = 2 to 4 for both the method of the present invention and the JIS method, and the arithmetic average value was calculated for each.
However, in both the method of the present invention and the JIS method, in order to obtain the variation at the time of measuring the same sample, the number of measurements n
= 9. The measurement of these samples was performed by two persons, and the number of each measurement sample was 23,37.

FIG. 2 shows the time change of the temperature of the sample heated by the block heater and the water bath set at 100 ° C. The time to reach 90 ° C. or more was only about 5 minutes and 30 seconds with the block heater and about 5 minutes and 30 seconds with the water bath. In addition, the maximum temperatures reached in both cases were about 95 ° C., which were almost equal. The difference in the heating time was about 1.7% of the total heating time, and it was confirmed that there was almost no difference. In cooling after heating, the test tube could be cooled to a liquid temperature of 35 ° C. or less in just one minute after being immersed in tap water. Normally, when the temperature decreases by about 10 ° C. near normal temperature, the rate of the chemical reaction is reduced by half to one half.
To decline. Therefore, also in this case, the decomposition reaction rate of the pollutants in the water is 1/50 to 1/1000 of that in the water bath.
The reaction after cooling was considered to have no effect on the measurement. As described above, in the method of the present invention, the sample was heated by the block heater for 30 minutes, and immediately thereafter, the sample was cooled with water.

Here, the amount of electricity used and the area occupied by the two heating devices used this time were compared. First, the maximum power consumption is 1.2 kW for the water bath and 0.22 kW for the block heater, and the block heater has a power saving of less than 1/5 or less than that of the water bath and 1/20 or less per sample. became. The occupied area of the device is about 1400 cm ^{2 for the} water bath and about 400 cm for the block heater.
^{In 2} , the space saving of the block heater was less than one-third of that of the water bath and less than one-fifth of the space per sample. Therefore, it was also found that by using the block heater, both the amount of sample water and the amount of harmful waste liquid were reduced to 1/20, and it was possible to further save energy and space.

FIG. 3 shows the absorption spectrum of the potassium permanganate solution. Peak wavelengths are 525 nm and 543
nm, indicating that it is better to measure the absorbance around this wavelength. Next, as a result of measuring the change in absorbance with and without heating and filtration, the decrease in absorbance due to filtration with a glass fiber filter after heating was reduced by about 0.05 regardless of the retained particle diameter.
And the reproducibility was also good. On the other hand, in the case of filtration with an organic polymer membrane filter, adsorption occurred, and the amount decreased by about 0.3. Therefore, it was found that it was necessary to use inorganic filter paper. According to the absorbance method of the present invention, a value smaller than the initial absorbance by 0.05 can be calculated as the absorbance after heating / filtration when there is no contaminant, and the decrease therefrom can be calculated as the COD of the sample.

It was found that a suspension occurred in the sample at the time of heating, and it was found that the absorbance at 525 nm when not filtered was larger than the initial absorbance. The reduction reaction of permanganate ion in the sample at this time is described by the following equations (1) and (2).

Embedded image

As described above, in an acidic solution, permanganate ions are converted into divalent manganese ions by a redox reaction with pollutants, and further react with unreacted permanganate ions.
It has been found to form manganese dioxide. When actually looking on the glass filter after filtration, a black precipitate was collected, and it was found that the precipitate was manganese dioxide. In the JIS method, when an excessive sodium oxalate solution is added as a reaction terminator to a heated sample water, the suspension disappears. The reaction at this time can be expressed as follows.

Embedded image Therefore, according to the JIS method, manganese dioxide does not exist at the time of titration, and only excess oxalate ion in the sample reacts with permanganate ion.

Next, an aqueous solution of seven kinds of metal sulfates having a valence of +1 to +3 was heated in three steps to a concentration of 0.4 μm.
Table 1 shows the measurement results of the amount of decrease in absorbance when filtered through a glass fiber filter paper of m. From these results, for divalent manganese ion and divalent iron ion, the absorbance decreases and the relationship with the concentration is almost proportional, but in other cases, the absorbance decreases regardless of the ion species. No suspension formation reaction such as manganese dioxide was found to occur.

[0024]

[Table 1]

FIG. 4 shows the change in the absorbance decrease ΔA525 depending on the concentration of divalent manganese ions. The relationship between the divalent manganese ion concentration and the decrease in absorbance ΔA525 clearly became a linear relationship. Here, taking the ratio of the reduced permanganate ion calculated from the divalent manganese ion concentration and the absorbance decrease amount A525, it is almost constant regardless of the divalent manganese ion concentration.

Embedded image It became. This relationship was completely the same even when glass fiber filter paper having a retained particle diameter of 1.0 μm was used, as in the case of 0.4 μm. Therefore, the divalent manganese ion reacts with the remaining permanganate ion at a ratio of 3: 2 as in the suspension formation reaction of the formula (2), and the manganese dioxide suspension generated by this reaction is independent of the concentration. It was found that all particles were collected on glass fiber filter paper having a retention particle size of 1.0 μm or less.

Here, the results will be considered for divalent manganese ions as well as divalent iron ions having a change in absorbance in addition to metal ions. In the case of divalent iron ions, an oxidation reaction occurs as shown in equation (4), which can be a COD value.

Embedded image Then, when the reactions of equations (1), (2) and (4) are performed,
Equation (5) is obtained.

Embedded image

As described above, in the divalent iron ion solution, it was considered that the oxidation reaction of the divalent iron ion and the reaction of forming manganese dioxide occurred simultaneously. Here, it was calculated whether or not the measurement result of the absorbance decrease actually coincided with the absorbance decrease in the equation (5). As a result, the theoretical decrease in absorbance was 0.078, 0.15
5, 0.233, the actual decrease in absorbance is 0.09, 0.
19 and 0.27, which were substantially coincident with each other, and it was confirmed that the reaction represented by the formula (5) was occurring. Normally, divalent iron ions are considered as the COD component in this way, and it was confirmed that exactly the same result was obtained here. This allows
The behavior of permanganate ion in the sample water became clear, and it became possible to derive the COD calculation formula in the method of the present invention. It was also found that other metal cations did not interfere with the manganese dioxide formation reaction between divalent manganese ions and permanganate ions.

As described above, in the method of the present invention, three-fifths of the decrease in the absorbance from the initial absorbance is considered as the consumption of potassium permanganate by the organic substance, and
The formula for calculating OD was derived as follows. First, the amount of potassium permanganate in the method of the present invention is 20 as in the JIS method.
It corresponds to a COD of mg / l. Further, as can be seen from the equation (2), the potassium permanganate corresponding to the decrease in the absorbance is about 3% of the potassium permanganate used in the actual redox reaction.
5 times as much. From the above, the equation (6) is satisfied when the dilution rate is taken into consideration, where y is the absorbance decrease rate.

(Equation 2) Here, assuming that the absorbance of the sample is A, y is given by equation (7).

(Equation 3) Therefore, COD can be obtained from equation (8). That is, if a calculation result is digitally displayed by using a spectrophotometer incorporating a program of the calculation formula, the COD value can be directly read.

(Equation 4)

Hereinafter, equation (8) was used in the measurement of the organic standard aqueous solution and the actual sample and the analysis of the results. Next, regarding the storage test results of the reagents, potassium permanganate self-decomposes under acidic conditions and decreases by about 50% after one day. The amount was reduced by about 20%, indicating that it was impossible to mix potassium permanganate and other reagents in advance. However, it has been found that the mixed reagent of sulfuric acid and silver nitrate can be stored at room temperature for more than two months, and the operation steps during measurement can be reduced by putting these two kinds of reagents in a screw-cap test tube in advance.

As a result of confirming the preservability of the 5 mmol / l potassium permanganate solution, the factor of potassium permanganate changed only 1% in about 100 days regardless of the storage temperature and the size of the storage container. No, they were all storable. Therefore, in the method of the present invention, silver nitrate and sulfuric acid are mixed in advance in a large number of test tubes with caps, and only the sample water and a potassium permanganate solution stored in a brown screw cap are added during measurement. And

Based on the above results, an example of the operating procedure in the method of the present invention is shown in FIG. Details will be described below. (1) 0.25 ml of a 200 g / l silver nitrate solution and 0.5 ml of sulfuric acid (1 + 2) are placed in many test tubes with caps. (2) 5 ml of a sample diluted to an appropriate COD value is added thereto. (3) 0.5 ml of a 5 mmol / l potassium permanganate solution is added thereto, shaken, and immediately put into a block heater set at 100 ° C. (4) Remove after 30 minutes and cool in a water bath. After cooling, the sample is placed in a syringe with a filter paper holder at the tip, filtered immediately, and the absorbance of the filtrate at a wavelength of 525 nm is measured using a 10 mm cell. (5) From the results of (4), COD (mg /
1) is calculated. In addition, this equation was input to a spectrophotometer as a program, and the calculated COD value was digitally displayed so that it could be read directly.

(Equation 5) The upper limit of the measurement range in the method of the present invention is such that the absorbance of the sample is 0.
Considering that the absorbance of the sample is twice as low as 0.05, which is assumed to be a blank decrease, that is, when the absorbance is 0.855 or less, the lower limit is substantially the same as that of the JIS method.
It will be in the range of 6 to 10.8 mg / l.

In the operation procedure (1), sulfuric acid (1+
If 2) and an aqueous solution of silver nitrate are added in advance, precipitation of silver sulfate occurs, but the amount of sulfuric acid reduced here is a few percent of the total,
It is considered that the decrease in sulfuric acid concentration does not affect the oxidative degradation of pollutants in water by potassium permanganate. Also, in actual measurement, the block heater can heat 25 test tubes at a time. If the sample heating interval is shifted by 5 minutes and measured by 5 tubes, 25 samples can be obtained in less than 2 hours including the time of absorbance measurement. It becomes measurable. This is about 2.5 times or more of the JIS method.

FIG. 6 shows the results obtained by measuring the concentration of the aqueous solution of sodium oxalate in five steps and calculating the COD value from the decrease in absorbance according to the formula (8). As a result, irrespective of the sodium oxalate concentration, C calculated from equation (8)
The OD value and the theoretical COD value calculated on the assumption that sodium oxalate reacts 100% with potassium permanganate were in good agreement, and the validity of equation (8) could be demonstrated.

Next, FIG. 7 shows the results of the measurement according to the method of the present invention and the JIS method using eight kinds of organic substance aqueous solutions. ● is JIS
○ indicates the measurement result when a 200 g / l solution similar to that of the method was added, and ○ indicates a case where a 40 g / l solution having a ５ concentration was added. Regarding substances other than acetic acid and glutamic acid, the COD values of the JIS method and the method of the present invention were in good agreement regardless of the amount of silver nitrate added, and the difference was about 10% or less of the measured value. However, in the case of acetic acid and glutamic acid, the concentration of the aqueous solution of silver nitrate is 20%.
The COD value at 0 g / l was in good agreement with the JIS method COD value, but the COD value at a concentration of 40 g / l was JIS method COD value.
It was significantly smaller than the D value. It has been reported that silver sulfate and silver nitrate accelerate the oxidative decomposition reaction of organic substances by potassium permanganate, and it was considered that a COD value of a substance which is hardly oxidized such as acetic acid or glutamic acid was reduced by reducing the amount of added silver nitrate. Actual samples such as factory wastewater contain various pollutants with different reactivities, and the concentration of the aqueous silver nitrate solution added by the method of the present invention was determined to be 200 g / l, the same as in the JIS method.

FIG. 8 shows the measurement results of the actual sample. It is considered that the COD values obtained by the method of the present invention and the JIS method are completely identical, and the square of the correlation coefficient is r ² = 0.99, which is a very good result when y = 1.00x. In a very wide concentration range having a COD value of 1 to 100 mg / l or more, it was proved that the values measured by the method of the present invention and the JIS method completely matched. In addition, it was confirmed that there was no difference in the measured values when the liquid volume was reduced to 1/10 of the JIS method. In addition, the samples measured this time are very different in the quality and quantity of contaminants, and it has been demonstrated that the method of the present invention can be applied to various actual samples. In addition, it is considered that there is not much red-purple drainage or environmental water having the same absorbance at about 525 nm or 543 nm as potassium permanganate, but the absorbance method of the present invention cannot be used for such a sample.

FIG. 9 shows the variation between the method of the present invention and the JIS method when one sample is measured two to four times for the 60 samples measured. Here, the variation was defined as the larger value of the difference between the average value, the maximum value, and the minimum value when measuring the same sample. However, in the first 5 samples among the samples measured by the measurer B, the variation in the absorbance method exceeded 15%, which was extremely large compared to the other results, and there was a possibility that the user was not used to the operation or an operation error. Therefore, it was deleted from this analysis. In both methods, 50% of all samples were within 5% variation by the absorbance method and within 3.5% by the JIS method. In both methods, the variation of 95% or more of the samples was within 15%. Although the reproducibility was slightly better in the JIS method, the difference was almost insignificant in actual measurement. Therefore, it was confirmed that the variation of the measured value itself when the same sample was measured was substantially the same in both the absorbance method and the JIS method. There was no difference between the measurers.

Further, when the coefficient of variation by the method of the present invention and the JIS method when three types of samples were measured nine times were examined, the variation of the two types was 2 to 7% for all three types of samples. Turned out to be comparable.

In the actual measurement, in the case of the JIS method, the temperature control of the boiling water bath and the like must be carefully controlled in many points, and skill in operations such as titration is also required. On the other hand, in the case of the absorbance method of the present invention, it is considered that the temperature control is easy and the reproducibility of the measured value is good no matter who performs the method.

As a result of trying to develop the above-mentioned COD absorbance method, the following new findings were obtained. (1) The peak wavelength of the potassium permanganate solution is 525
nm and 543 nm, and the decrease in absorbance in a blank test using glass fiber filter paper was about 0.05. (2) It was found that the reaction was easily performed under the same conditions as in the JIS method by heating the solution with a block heater with the liquid amount being 1/10 or less of the JIS method, and the reaction could be stopped immediately by water cooling. (3) In the sample liquid at the time of the reaction, divalent manganese ion and permanganate ion react as shown in the following formula, and all the generated manganese dioxide can be removed by a glass fiber filter paper having a retained particle diameter of 1.0 μm or less. understood.

Embedded image (4) In consideration of (2), the following equation was obtained as the COD calculation equation in the absorbance method of the present invention.

(Equation 6) (5) When the relationship between the JIS method and the COD value of the method of the present invention for a total of 60 kinds of actual samples is y = 1.00x, the square of the correlation coefficient is very good, r ² = 0.99. Result
It was proved that the measured values by the method of the present invention and the JIS method completely coincided. (6) It was confirmed that the measurable range of the JIS method and the method of the present invention and the variation of the measured values themselves were almost the same, and that there was no difference between the measurers. As described above, CO2 is easier to operate than the JIS method and can greatly reduce the environmental load.
A simple method for measuring D was developed, and its practicality was confirmed.

[0040]

As described above, the present invention can reduce the amount of a sample from one tenth to one twentieth of the conventional JIS method, and can also use expensive and harmful reagents and processing costs. The amount of such hazardous waste liquid is 1/10 to 20
The power consumption can be reduced to about one-twentieth by using a block heater for heating.
This greatly improves the economical efficiency, and the operation is much simpler than the conventional JIS method because it is only necessary to measure the amount of reduction of permanganate ion by absorbance instead of the conventional JIS method for titration. It has an excellent effect of being economical and economical. In particular, by using a spectrophotometer incorporating a program of the formula (8), the calculation result is digitally displayed, and the COD value can be directly read.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an example of a block heater used in the present invention.

FIG. 2 is a diagram showing a time change of the temperature of a sample heated by a block heater and a water bath in the present invention.

FIG. 3 is an absorption spectrum diagram of the potassium permanganate solution in the present invention.

FIG. 4 is a graph showing a change in the amount of decrease in absorbance depending on the concentration of divalent manganese ions in the present invention.

FIG. 5 is a diagram showing an example of an operation procedure of the measuring method according to the present invention.

FIG. 6 is a comparison diagram between measured COD and theoretical COD in an aqueous solution of sodium oxalate according to the present invention.

FIG. 7 is a comparison diagram of the results of measurement by an absorbance method according to the present invention and a JIS method in a standard aqueous solution of an organic compound.

FIG. 8 is a comparison diagram of the measurement result of each actual sample according to the present invention and the measurement result by the JIS method.

FIG. 9 is a comparison diagram of the variation between the measurement result according to the present invention and the measurement result according to the JIS method.

[Procedure amendment]

[Submission date] July 30, 1999 (July 7, 1999)
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[Correction method] Change

[Correction contents]

The present invention has been made in order to solve the above-mentioned problems, and reduces the amount of sample water, which is the sample water to be measured, and the amount of chemicals used as expensive and harmful reagents to one- tenth or less. After reacting and filtering under exactly the same conditions, the amount of permanganate ion depletion is measured by absorbance instead of the titration operation, which greatly simplifies the operation and costs expensive and harmful reagents and processing. It is an object of the present invention to provide an economical and simple method for measuring COD which can reduce the amount of such hazardous waste liquid to 1/10 or less and the power consumption to 1/10 or less. In particular, a simpler measuring method can be provided by digitally displaying a COD value calculated by a spectrophotometer in which an arithmetic expression is input as a program and enabling direct reading.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

Means for Solving the Problems The present invention relates to JIS K0
10217. The method for measuring COD defined in 10217, wherein
Sample water less than 1/10 of JIS method and reagents
Therefore, permanganic acid less than 1/10 of the JIS method
, Silver sulfate less than 1/10 of the JIS method and
And 1/10 or less of sulfuric acid according to the JIS method described above were put into test tubes, respectively , and heated at 100 ° C. for 30 minutes with a block heater. Then, the reaction was immediately stopped by cooling, and the resulting suspension was removed. Filtration with an inorganic filter paper having a retention particle size of 1.0 μm or less,
Then, by measuring the concentration of permanganate ion in the filtrate at around 525 nm or 543 nm by absorbance, the COD is calculated from the decrease, and the COD calculation formula based on the absorbance decrease of potassium permanganate Built-in programs and display the calculation results digitally
The above problem has been solved by employing a means of using a spectrophotometer configured as described above.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

DETAILED DESCRIPTION OF THE INVENTION The present invention employs a conventional measurement method 2 0 min sample water for measurement of 1 1 or 1 0 minutes
(Hereinafter referred to as sample water ) is placed in a test tube containing reagents in advance, heated at 100 ° C. for 30 minutes by a dedicated block heater capable of heating many at the same time, immediately cooled with water, and the retained particle diameter is 1.0 μm. Filtration is performed using the following glass fiber filter paper, and the permanganate ion concentration of the filtrate is measured using a spectrophotometer with a programmed arithmetic expression, and the COD calculated from the decrease is digitally displayed and read directly. It is made possible. Then, the present inventors conducted the following experiment to verify the present invention.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

In this experiment, the operating procedure of the JIS method was JIS K
0102 17. (1993) as follows. (1) COD is a 100ml together a suitable amount of pure water for dilution of the sample such that the longitudinal diluted after 10 mg / l 300 ml
The flask was placed in an Erlenmeyer flask, and 5 ml of a 200 g / l silver nitrate solution and 10 ml of sulfuric acid (1 + 2) were added with shaking. (2) 5 mmol / l potassium permanganate solution 10 m
1 and shaken, immediately placed in a boiling water bath and heated for 30 minutes. (3) Removed from the boiling water bath, 10 ml of a 12.5 mmol / l sodium oxalate solution was added, shaken, and reacted well. (4) While maintaining the solution temperature at 60 ° C., titration was performed with a 5 mmol / l potassium permanganate solution until the solution became slightly red. (5) Separately, 100 ml of pure water was placed in a 300 ml Erlenmeyer flask, and operations (1) to (4) were performed. (6) COD (mg / l) was calculated by the following equation.

Where COD: oxygen consumption by potassium permanganate at 100 ° C. (mg / l), a: 5 mmol / l potassium permanganate solution (m
l), b: 5 mmol required for titration in a test using pure water
/ L potassium permanganate solution (ml), f: 5 mmo
Factor of 1 / l potassium permanganate solution, V: sample amount (ml), 0.2: oxygen consumption of 1 ml of 5 mmol / l potassium permanganate solution (mg) In the experiment of the present invention, the JIS operation procedure was used. Using a 11 ml screw-cap test tube without changing the reaction conditions and changing the liquid volume to all twentieth, changing the boiling water bath to a block heater capable of heating 16 tubes simultaneously, and measuring the absorbance by titration The environmental load was reduced by changing to a simple measurement method. An experiment in which the liquid volume was reduced to 1/10 was also performed for comparison.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Ishii 1234 Karasuyama-cho, Kohoku-ku, Yokohama-shi, Yokohama, Kanagawa Prefecture No. 401 Fuji Kazuki Corp. (72) Inventor Kumiko Hayashi 4-2-13-Aobadai, Meguro-ku, Tokyo 601 F term (reference) 2G054 AA02 AB10 BB02 BB12 CA08 CB02 CB03 CE01 EA04 EB01 FA06 FA19 FA37 GA03 GB01 JA01 JA04 JA20

Claims (2)

[Claims] 1. A sample water and reagents which are 1/10 or less of the method of JIS K01017 are put into a test tube, heated at 100 ° C. for 30 minutes by a block heater, and the reaction is immediately stopped by cooling to produce. The suspension is filtered through an inorganic filter paper having a retention particle size of 1.0 μm or less, and then 525 n
A simple method for measuring COD, comprising measuring the concentration of permanganate ion in a filtrate at around m or around 543 nm by absorbance, and calculating COD from the decrease. 2. A spectrophotometer for use in a simple method for measuring COD, comprising a program for calculating a COD based on a decrease in absorbance of potassium permanganate.