CN111912797B - Method for measuring total phosphorus content in water - Google Patents
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- CN111912797B CN111912797B CN201911304174.6A CN201911304174A CN111912797B CN 111912797 B CN111912797 B CN 111912797B CN 201911304174 A CN201911304174 A CN 201911304174A CN 111912797 B CN111912797 B CN 111912797B
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Abstract
The invention relates to a method for measuring total phosphorus content in water, which belongs to the technical field of environmental protection, and solves the problem that heteropoly acid generated by phosphate and molybdate has two AB isomers, and the absorbance difference of the two isomers is large; the invention provides a method for measuring absorbance by adopting two different wavelengths, so as to construct a linear equation set, and the purpose of accurate measurement is achieved by solving the equation set.
Description
Technical Field
The invention relates to the technical field of environmental protection, in particular to a method for measuring the total phosphorus content in water.
Background
The phosphorus in the water includes: phosphorus element, orthophosphate, condensed phosphate, pyrophosphate, metaphosphate, organic group-bonded phosphate, etc. The main sources of the detergent are domestic sewage, chemical fertilizers, organic phosphorus pesticides, phosphate detergents used by modern detergents and the like. Phosphates can interfere with the coagulation process in waterworks. Phosphorus in water is a key element required by algae growth, and excessive phosphorus is a main reason for causing water pollution and foreign odor, leading to sounding and eutrophication of lakes and red tide in gulf. Therefore, in environmental protection, the measurement of the total phosphorus content in water is important.
In the prior art, the most common method for measuring the total phosphorus content is a molybdate spectrophotometry, but the method specified in GB11893-89 is still not accurate enough in measurement accuracy and the measurement time is too long, so that a measurement method with short measurement time and high accuracy is urgently needed.
Disclosure of Invention
In view of the problems in the prior art, the invention provides the following technical scheme: a method for measuring the total phosphorus content in water is characterized by comprising the following steps: the method comprises the following steps:
step (1): obtaining a sample of an object to be measured;
step (2): digesting the sample by adopting potassium persulfate;
and (3): preparing a plurality of standard solutions by using deionized water;
and (4): developing the sample and the standard solution with molybdate and ascorbic acid;
and (5): measuring the absorbance of the developed standard solution at two different wavelengths by using a spectrophotometer; performing blank correction on the absorbance of the developed standard solution;
and (6): two standard curves are formulated according to the absorbance of the corrected standard solution;
and (7): carrying out absorbance detection and blank correction on the developed sample under the same condition as that in the step (5) and under two different wavelengths, and respectively comparing the corrected data with the two standard curve standard curves to obtain the total phosphorus content omegaaAnd ωb；
And (8): the total phosphorus content omegaaAnd ωbAnd combining the specific absorbance values of two isomers of heteropoly acid AB generated by phosphate and molybdate under two different wavelengths to construct a two-dimensional linear equation set, and solving the equation set to obtain the accurate total phosphorus content.
Preferably, in the step (2), the digesting includes: the pH is also adjusted by adding hydrochloric acid and the reaction is accelerated by adding a small amount of nitrate.
Preferably, the blank correction in step (5) and step (7) is the scatter attenuation for the sample.
Preferably, the scattering attenuation a = (I)i-It)r2/r1(ii) a Wherein IiCorrecting the incident light intensity for said blank, ItFor optical inspectionThe light intensity obtained by the measuring unit is r1The optical distance in the sample vessel in the blank correction process is r1；r2Optical path r in sample vessel in order degree test process2。
Preferably, in step (5) and step (7), the two different wavelengths are 710nm and 690nm, respectively.
Preferably, the equation of a first binary equation is specifically as follows: c (a)1X+b1Y)＝ωa；c(a2X+b2Y)＝ωbWherein X is the amount of the heteropoly acid a and Y is the amount of the heteropoly acid b; the constant c is a conversion constant of the phosphorus content to the heteropoly acid.
Compared with the prior art, the invention at least has the following invention points and corresponding beneficial effects:
(1) The heteropoly acid generated by phosphate and molybdate has the problem of AB two isomers, and the absorbance difference of the two isomers is large; the invention provides a method for measuring absorbance by adopting two different wavelengths, so as to construct a linear equation set, and the purpose of accurate measurement is achieved by solving the equation set.
(2) In the digestion process, the pH value is adjusted by adding trace hydrochloric acid, and the digestion speed is accelerated by adding trace nitrate;
(3) In order to improve the detection precision, blank correction is carried out by adopting the selection of a correction light source.
Drawings
FIG. 1 is an absorption spectrum of two AB isomers of a phosphate and molybdate-derived heteropoly acid;
the present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the appended claims.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
To better illustrate the invention and to facilitate the understanding of the technical solutions thereof, typical but non-limiting examples of the invention are as follows:
example 1
In the prior art, the total phosphorus content in water comprises various forms of phosphate and phosphorus-containing organic matters which are dissolved and undissolved, if the total phosphorus is measured, the phosphorus-containing organic matters are digested firstly to be converted into soluble phosphate, and the metaphosphate and pyrophosphate are converted into orthophosphate by virtue of the school flowers. Then, molybdate and potassium tartrate are used to react with the mixed solution in strong acid solution to generate the phosphomolybdic antimony heteropoly acid, and the phosphomolybdic antimony heteropoly acid can be reduced into a blue compound 'molybdenum blue' by a reducing agent under certain acidity.
In the prior art, the problem that heteropolyacid generated by phosphate and molybdate has two isomers of AB exists in the process of detecting phosphate by adopting a spectrophotometry method, and the difference of absorbance of the two isomers is large, so that the error of finally detecting the total phosphorus content in water is large; therefore, the invention provides that absorbance is detected in two different wave bands, so that a linear equation system is constructed, and the accurate total phosphorus content is obtained by solving the equation system. The specific method comprises the following steps:
step (1): obtaining a sample to be detected and filtering;
step (2): adding 4ml of potassium persulfate (50 g/l) solution into a sample, plugging a test tube with scales with a plug, wrapping the tube opening with a piece of gauze, and fastening with a fine line; placing the test tube in a large beaker, heating in a high-pressure steam sterilizer, keeping the temperature at 120 ℃ for about 20 minutes when the pressure reaches 1-1.1kg/cm < 2 >, stopping heating, and taking out and cooling after the reading of a pressure gauge is reduced to 0;
adding deionized water into a plurality of test tubes, respectively adding 0ml, 0.5ml, 1ml, 3ml, 5ml and 10ml of phosphate standard use solution, adding water to 50ml, and determining a blank value by adopting the same method and steps as the sample;
step (4), molybdate solution: 13g of molybdate was dissolved in 100ml of water, and 0.35g of antimony potassium tartrate was dissolved in 100ml of water. Continuously stirring molybdate solution, slowly pouring the molybdate solution into 300ml sulfuric acid (1+1) solution, adding antimony potassium tartrate solution, uniformly mixing, and storing the solution in a brown reagent bottle;
adding 1ml of ascorbic acid (100 g/l) into the sample test tube and the deionized water test tube, uniformly mixing, and adding 2ml of molybdate solution after 30s, and uniformly mixing;
correcting the absorbance data obtained by the deionization test tube, and drawing a standard curve by taking the phosphorus content as an abscissa and the absorbance as an ordinate; wherein the photometer selects two wavelengths of 710nm and 690nm to respectively detect;
step (7) the absorbance measured by the sample test tube under the same condition as the step (6) is corrected, and the corrected data is compared with the drawn standard curve under the two wavelengths of 710nm and 690nm to obtain the total phosphorus content omegaaAnd ωb；
Step (8) of converting the total phosphorus content into omegaaAnd ωbAnd combining the specific absorbances of two heteropoly acid AB isomers generated by phosphate and molybdate at two wavelengths of 710nm and 690nm to construct a two-dimensional linear equation set, and solving the equation set to obtain the accurate total phosphorus content.
FIG. 1 shows absorption spectra of two AB isomers of heteropoly acid generated from phosphate and molybdate; by contrast with the spectrum, the specific absorbances of the heteropoly-acid a and the heteropoly-acid b at two wavelengths of 710nm and 690nm are respectively found to be a1、a2、b1、b2Establishing a linear equation of two to obtain:
c(a1X+b1Y)＝ωa；c(a2X+b2Y)＝ωb
wherein X is the amount of the heteropolyacid a and Y is the amount of the heteropolyacid b; the constant c is a conversion constant of the phosphorus content to the heteropoly acid. The total phosphorus content in the water can be obtained by solving the equation.
Example 2
In the prior art, the total phosphorus content in water comprises the steps of sampling, digestion, standard solution preparation, display, measurement, correction and the like, potassium persulfate is adopted in the digestion step, about 30 minutes is usually needed, a small amount of hydrochloric acid can be added for adjusting the pH value of the digestion solution, and a small amount of nitrate can be added for increasing the reaction speed. The specific method comprises the following steps:
step (1): obtaining a sample to be detected, filtering, and putting 25ml of the sample into a graduated tube;
step (2): adding 4ml of potassium persulfate (50 g/l) solution into a sample, adding a small amount of hydrochloric acid to adjust the pH value to be about 1, adding 4-5g of nitrate (potassium magnesium nitrate), plugging a test tube with scales with a plug, wrapping a piece of gauze at the tube opening, and fastening by using a fine line; placing the test tube in a large beaker, heating in a high-pressure steam sterilizer, keeping the temperature at 120 ℃ for about 25 minutes when the pressure reaches 1-1.1kg/cm < 2 >, stopping heating, and taking out and cooling after the reading of a pressure gauge is reduced to 0;
adding deionized water into a plurality of test tubes, respectively adding 0ml, 0.5ml, 1ml, 3ml, 5ml and 10ml of phosphate standard use solution, adding water to 50ml, and determining blank values by adopting the same method and steps as the samples;
step (4), molybdate solution: 13g of molybdate was dissolved in 100ml of water, and 0.35g of antimony potassium tartrate was dissolved in 100ml of water. Continuously stirring molybdate solution, slowly pouring the molybdate solution into 300ml sulfuric acid (1+1) solution, adding antimony potassium tartrate solution, uniformly mixing, and storing the solution in a brown reagent bottle;
adding 1ml of ascorbic acid (100 g/l) into the sample test tube and the deionized water test tube, uniformly mixing, and adding 2ml of molybdate solution after 30s, and uniformly mixing;
correcting the absorbance data obtained by the deionization test tube, and drawing a standard curve by using the phosphorus content as a horizontal coordinate and the absorbance as a vertical coordinate of the correction data; wherein the photometer selects two wavelengths of 710nm and 690nm to respectively detect;
step (7) correcting the absorbance measured by the sample test tube under the same condition as the step (6), and comparing the correction data with the drawn standard curve under the two wavelengths of 710nm and 690nm to obtain the total phosphorus content omegaaAnd ωb；
Step (8) of converting the total phosphorus content into omegaaAnd ωbTwo isotypes of heteropoly acid AB generated by combining phosphate and molybdateAnd (3) constructing a linear equation system of two variables by the specific absorbance of the structure body at two wavelengths of 710nm and 690nm, and solving the equation system to obtain the accurate total phosphorus content.
In order to accurately measure the absorbance, the absorbance data needs to be corrected in step (6) and step (7), and specifically, the attenuation of light passing through the liquid sample containing "phosphomolybdenum blue" needs to be measured before the absorbance measurement is performed on the liquid sample containing "phosphomolybdenum blue", that is, the transmittance of light passing through the liquid sample containing "phosphomolybdenum blue". The light attenuation is generally dispersion attenuation a, i.e. the attenuation of light by scattering through a liquid medium;
setting the incident light intensity emitted by the light source to be IiThe light intensity obtained by the light detection unit is ItThe optical path length in the sample vessel is r1(corresponding optical path length r in sample vessel during absorbance test)2) (ii) a To avoid the influence of the measured liquid containing the phosphomolybdic blue on the measurement of the light absorbance;
conversion into the scattering attenuation a = (I) in the course of the absorbance testi-It)r2/r1
The absorbance formula after correction in step (6) and step (7) can be expressed as ω = ω 1- (a + b).
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (5)
1. A method for measuring the total phosphorus content in water is characterized by comprising the following steps: the method comprises the following steps:
step (1): obtaining a sample of an object to be measured;
step (2): digesting the sample by adopting potassium persulfate;
and (3): preparing a plurality of standard solutions by using deionized water;
and (4): developing the sample and the standard solution with molybdate and ascorbic acid;
and (5): measuring the absorbance of the developed standard solution at two different wavelengths by using a spectrophotometer; performing blank correction on the absorbance of the developed standard solution;
and (6): two standard curves are formulated according to the absorbance of the corrected standard solution;
and (7): carrying out absorbance detection and blank correction on the developed sample under the same condition as that in the step (5) and under two different wavelengths, and respectively comparing the corrected data with the two standard curves to obtain the total phosphorus content omegaaAnd ωb；
And (8): the total phosphorus content omegaaAnd omegabCombining specific absorbance values of two isomers of heteropoly acid AB generated by phosphate and molybdate at the two different wavelengths to construct a two-dimensional linear equation set, solving the equation set to obtain accurate total phosphorus content,
the system of equations in a binary first order is specifically as follows:
c(a1X+b1Y)=ωa; c(a2X+b2Y)= ωb
wherein X is the amount of heteropoly acid a and Y is the amount of heteropoly acid b; the constant c is a conversion constant converted from heteropoly acid into phosphorus content, and the specific absorbances of heteropoly acid a and heteropoly acid b at the two different wavelengths are respectively a1、a2、b1、b2。
2. The method of claim 1, wherein: in the step (2), the digesting includes: the pH value is adjusted by adding hydrochloric acid, and the reaction speed is accelerated by adding a small amount of nitrate.
3. The method of claim 1, wherein: the blank correction in step (5) is the scatter attenuation for the sample.
4. The method of claim 3, wherein: the scattering attenuation a = (I)i-It)r2/r1(ii) a In which IiCorrecting the incident light intensity for said blank, ItFor the light intensity obtained by the light detecting unit, r1The optical path length in the sample vessel in the blank correction process is calculated; r is2Is the path length in the sample vessel during the absorbance test.
5. The method of claim 1, wherein: in step (5) and step (7), the two different wavelengths are 710nm and 690nm, respectively.
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