CN111948303B - Method for detecting concentration of hydroxyl free radicals by using probe compound - Google Patents

Method for detecting concentration of hydroxyl free radicals by using probe compound Download PDF

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CN111948303B
CN111948303B CN202010680216.2A CN202010680216A CN111948303B CN 111948303 B CN111948303 B CN 111948303B CN 202010680216 A CN202010680216 A CN 202010680216A CN 111948303 B CN111948303 B CN 111948303B
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probe compound
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CN111948303A (en
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杨欣
雷宇
程双双
吴洋
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Sun Yat Sen University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
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Abstract

The invention belongs to the technical field of chemical substance detection, and discloses a method for detecting the concentration of hydroxyl radicals by using a probe compound, which comprises the following steps: step S1: adding probe compounds with different concentrations into a solution to be detected containing OH to form a reaction solution, and detecting the concentration of the probe compounds in the reaction solution by using chromatography to obtain an apparent quasi-first-order attenuation rate of the probe compounds; step S2: drawing a chromatographic standard curve of the probe compound, and quantitatively detecting the concentration of the probe compound in the reaction solution. According to the method, through drawing a standard curve of the probe compound and measuring the apparent quasi-first-order attenuation rate of the probe compound in a reaction liquid formed by the probe compound with different concentrations and a solution to be detected for multiple times, the finally obtained concentration value of OH is not influenced by the probe compound, and the detection accuracy is greatly improved. The method eliminates detection errors caused by the volatilization of probe compounds and/or the photolysis under ultraviolet conditions.

Description

Method for detecting concentration of hydroxyl free radicals by using probe compound
Technical Field
The invention belongs to the technical field of chemical substance detection, and particularly relates to a method for detecting concentration of hydroxyl radicals by using a probe compound.
Background
Advanced Oxidation Process (AOP) can be achieved by generating radicals such as hydroxyl radicals (. OH), sulfate radicals (SO)4·-) And the like, the high-activity oxidation active species effectively remove organic micro-pollutants in the water body and inactivate pathogens. Wherein, the advanced oxidation technology based on hydroxyl free radicals has very wide application in the aspects of polluted water body restoration and water body deep treatment. Therefore, the determination of the concentration of the hydroxyl radicals in the water body is particularly important. However, conventional detection techniques commonly used in laboratory studies are difficult to directly determine due to the short lifetime and low concentration of hydroxyl radicals at steady state. For example, the concentration of hydroxyl radicals in the UV/hydroperoxide AOP system is about 10-15To 10-12M (in the present invention, M represents mol/L) is far lower than the detection range of the conventional chromatographic and spectroscopic methods. Therefore, probe compounds have been used in recent years to indirectly detect the concentration levels of hydroxyl radicals.
In the case where the rate constant of the second-order reaction of the target radical with the probe compound is known, the concentration of the target radical can be calculated by detecting the decay of the probe compound. Ideally, the probe compound should have properties such as stability, ease of detection, and selectivity to react only with the target radical. Nitrobenzene (NB) is very reactive with hydroxyl radicals (secondary reaction rate constant k 3.9 × 10)9M-1s-1) But hardly reacts with other coexisting active free radicals (such as sulfate free radicals, carbonate free radicals, singlet oxygen and the like) in the water environment. NB is stable in nature and can be detected by conventional high performance liquid chromatography techniques. Thus, nitrobenzene was commonly used as a probe compound to quantitatively determine the concentration of hydroxyl radicals in previous studies.
The method for detecting the concentration of the hydroxyl radical by using NB as a probe compound in the prior art has serious defects. On the other hand, NB reacts rapidly with OH, the addition of NB inevitably consumes OH in the system, so that the measured OH concentration is low, and the use of NB with different concentrations tends to obtain different hydroxyl radical concentrations for the same analyte. Therefore, one uses NB at as small a concentration as possible to minimize NB consumption of OH. On the other hand, due to the detection limit of conventional chromatographic techniques, researchers have to use higher NB concentrations to ensure accurate measurement results. For example, it is also possible to measure the OH concentration in the UV/hydroperoxide AOP system and in the UV/chloro AOP system using NB as probe compounds, using NB doses varying from nM to. mu.M, which may lead to large differences in the OH concentration measured in the same reaction system.
The concentration of hydroxyl radical (. OH) is an important factor influencing the conversion efficiency of removing pollutants in the AOP process and the engineering application cost, so that the accurate measurement of the concentration of the hydroxyl radical (. OH) is necessary.
Therefore, it is necessary to provide a method for more accurately measuring the concentration of hydroxyl radicals, which is highly efficient, simple and inexpensive.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art described above. Therefore, the invention provides a method for detecting the concentration of the hydroxyl radical by using a Probe Compound (PC), the method for measuring the concentration of the hydroxyl radical (. OH) is not influenced by the concentration of the Probe compound, and the accuracy of the measured concentration of the hydroxyl radical is obviously improved.
A method for detecting hydroxyl radical concentration using a probe compound, comprising the steps of:
step S1: adding probe compounds with different concentrations into a solution to be detected containing OH to form a reaction solution, and detecting the change of the concentration C of the probe compounds in the reaction solution along with the time t by using chromatography, wherein the initial concentration of the probe compounds is C0C is the concentration of the probe compound at time t, on the abscissa, ln (C/C)0) For ordinate, ln (C/C) is plotted0) The slope of the curve relating to t is denoted as kobs，kobsI.e. the apparent quasi-first order decay rate of the probe compound;
step S2: the method for quantitatively determining the concentration of the probe compound in the reaction solution by chromatography is as follows:
putting the solution containing the probe compound with known concentration into a chromatogram for detection, and drawing a chromatogram standard curve of the probe compound;
detecting the reaction liquid in a chromatogram to obtain the absorption peak area of the probe compound in the reaction liquid, and calculating the concentration of the probe compound according to the chromatographic standard curve of the probe compound; then, the concentration of OH in the solution to be measured is calculated.
The calculation method of the concentration of OH in the solution to be measured is as follows:
kobs＝k·OH (1)
k·OH＝k·OH,PC[·OH]SS (2)
k·OHis the quasi-first order decay rate of the probe compound contributed by the. OH reaction, the probe compound is marked as PC, and is calculated by the formula (1); k is a radical of·OHCan also be expressed by formula (2) wherein k·OH,PCIs the second order rate constant of the reaction of OH and PC, [. OH]SSIs the concentration of. OH in the solution to be tested (or called the steady-state concentration of. OH in the solution to be tested);
[·OH]SScan be expressed by formula (3):
Figure BDA0002585562520000021
wherein r isOHThe rate of formation of the OH is,
Figure BDA0002585562520000031
is the quasi-first order decay rate of OH when the concentration of PC in the solution to be measured is 0, [ PC ]]Substituting formula (3) into formula (2) to obtain formula (4):
Figure BDA0002585562520000032
taking reciprocal of the left side and the right side of the formula (4) to obtain a formula (5):
Figure BDA0002585562520000033
according to formula (5) with [ PC]Is abscissa, 1/k·OHPlotting the ordinate yields an intercept of
Figure BDA0002585562520000034
The slope is 1/rOHThe intercept is represented as I, and 1/I represents k when the PC concentration is 0·OHThe value obtained by further combining the formula (3) is 1/(I k) when the concentration of OH is 0·OH,PC) This value is the concentration of. OH in the test solution unaffected by the probe compound PC.
Preferably, the probe compound is selected from at least one of Nitrobenzene (NB), p-chlorobenzoic acid, acetone or benzoic acid; further preferably, the probe compound is nitrobenzene or acetone.
Preferably, the pH value of the solution to be detected is 2-11, and the temperature is 15-35 ℃.
Preferably, the concentration of the probe compound is 20nM to 2. mu.M.
Preferably, the concentration range of OH in the solution to be detected is 1 x 10-16M to 1X 10-10M (in the present invention, M represents mol/L).
Preferably, the chromatography is high performance liquid chromatography.
Further preferably, the detection conditions of the high performance liquid chromatography are as follows: the mobile phase comprises 55-60% of acetonitrile and 40-45% of water by volume ratio; the flow rate is 0.5-1mL min-1(ii) a The detection wavelength was 250-265nm using an ultraviolet detector.
Preferably, the detection conditions of the high performance liquid chromatography comprise that the mobile phase also contains 0.1 percent of acetic acid by volume ratio.
Preferably, in step S1, if the probe compounds with different concentrations are added to the solution to be tested containing OH to form the reaction solution under the closed condition, the quasi-first order volatilization decay rate k of the probe compoundsvolIs 0.
It is preferable thatIn step S1, if the probe compounds with different concentrations are added to the solution to be tested containing OH to form the reaction solution, the reaction solution is not formed under a closed condition, the quasi-first order volatilization decay rate k of the probe compoundsvolIf not 0, after step S1, the method further includes the steps of: control test with water in the dark: under the condition of keeping out of the sun, replacing the solution to be detected containing OH in the step S1 with water to form a reaction solution, and obtaining the quasi-first-order volatilization attenuation rate k of the probe compound by the same operation process as the step S1vol(ii) a Then k isobs＝kvol+k·OH. This additional step is aimed at eliminating the error caused by the volatilization of nitrobenzene in step S1.
Preferably, the water is ultrapure water.
Preferably, in step S1, if the probe compounds with different concentrations are added to the OH-containing test solution to form the reaction solution under the ultraviolet condition, the method further comprises, after step S1: adding the probe compound with the same concentration as the probe compound in the step S1 into the ultrapure water under the closed condition, adding the ultraviolet radiation with the same dosage, and repeating the operation of the step S1 to obtain the quasi-first-order photolysis attenuation rate k of the probe compound under the ultraviolet radiationUVThen k is corresponding toobs＝kUV+k·OH，k·OH＝kobs-kUV. This additional step is intended to eliminate the error caused by photolysis of the nitro group by ultraviolet in step S1.
Preferably, when the probe compounds with different concentrations are added to the OH-containing solution to be tested in step S1 and the reaction solution is formed under the condition of ultraviolet light and no blocking, k isobs＝kUV+kvol+k·OH，k·OH＝kobs-kUV-kvol. The photolysis and volatilization of nitrobenzene caused by reaction conditions are corrected so that the measured kobsAnd k·OHIs more accurate.
Preferably, the method for detecting the concentration of hydroxyl radicals using the probe compound according to the present invention is used for detecting OH in a concentration range of 1X 10-16M to 1X 10-10M is waitingAnd (5) measuring the solution. If the concentration of OH in the solution to be measured is more than 1 x 10- 10M, diluting the solution to be detected to enable the concentration of OH to be in the range, and multiplying the diluted concentration of OH of the solution to be detected by the dilution times to reduce the concentration of OH in the original solution to be detected.
Preferably, when the Probe Compound (PC) is nitrobenzene NB, then k·OH,PCIs denoted by k·OH,NB，k·OH,NBIs the second order rate constant of the reaction of OH and NB, in the range of 15-35 ℃ k·OH,NB＝3.9×109M-1s-1。
The method disclosed by the invention is applied to the field of sewage treatment.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the invention, through drawing a standard curve of the probe compound and measuring the apparent quasi-first-order attenuation rate of the probe compound in a reaction liquid formed by the probe compound with different concentrations and a solution to be detected for multiple times, the finally obtained OH concentration is 1/(I k)·OH,PC) The value is the concentration of. OH in the solution to be detected which is not affected by the probe compound PC, and particularly, when the probe compound is Nitrobenzene (NB), the consumption of. OH caused by the reaction of the Nitrobenzene (NB) and hydroxyl radicals (. OH) can be completely avoided, so that the concentration of. OH in the solution to be detected which is detected is not affected by the concentration of the Nitrobenzene (NB), and the detection accuracy is greatly improved.
(2) The method simultaneously eliminates detection errors caused by the volatilization of Nitrobenzene (NB) and/or photolysis under the ultraviolet condition.
Drawings
FIG. 1 is a HPLC standard curve of nitrobenzene obtained in example 1 of the present invention;
FIG. 2 is a quasi-first order degradation kinetic curve of nitrobenzene in a solution to be tested in the UV/chlorine advanced oxidation process in example 2 of the present invention;
FIG. 3 shows the 1/k of the solution to be tested in the UV/Cl advanced oxidation process in example 2 of the present invention·OHAnd [ NB ]]The linear relationship of (a);
FIG. 4 is a graph showing the quasi-first order degradation kinetics of nitrobenzene in a solution to be tested in the UV/hydrogen peroxide advanced oxidation process in example 3 of the present invention;
FIG. 5 shows the 1/k of the solution to be measured in the UV/hydrogen peroxide advanced oxidation process in example 3 of the present invention·OHAnd [ NB ]]The linear relationship of (c).
Detailed Description
In order to make the technical solutions of the present invention more apparent to those skilled in the art, the following examples are given for illustration. It should be noted that the following examples are not intended to limit the scope of the claimed invention.
The starting materials, reagents or apparatuses used in the following examples are conventionally commercially available or can be obtained by conventionally known methods, unless otherwise specified.
Example 1: HPLC (high performance liquid chromatography) standard curve drawing of nitrobenzene
The HPLC standard curve of nitrobenzene is specifically plotted as follows:
1. preparing nitrobenzene water solution samples with the concentrations of 8.13nM, 12.26nM, 40.65nM, 81.3nM, 162.6nM, 406.5nM and 813nM respectively, and detecting the nitrobenzene water solution samples by using high performance liquid chromatography;
HPLC operating conditions are as follows: the mobile phase comprises 60% acetonitrile and 39.9% water, 0.1% acetic acid, and the flow rate is 1mL min by volume-1Using an ultraviolet detector, and detecting the wavelength to be 265 nm;
3. the HPLC peak time of nitrobenzene was 6.83min, the peak areas of nitrobenzene at different concentrations were 0.0048(8.13nM), 0.0099(12.26nM), 0.0277(40.65nM), 0.06(81.3nM), 0.1211(162.6nM), 0.2983(406.5nM) and 0.594(813nM), respectively, and the peak areas and nitrobenzene concentrations were plotted as straight lines, as shown in FIG. 1, which is the HPLC standard curve of nitrobenzene (y 0.000726x-0.000557, R ═ 9, X-Y, and Y, are shown in FIG. 120.9999) was used in the subsequent examples 2 to 4 to measure the nitrobenzene concentration in the reaction liquid.
Example 2: determination of OH concentration in solution to be measured in ultraviolet/chlorine advanced oxidation process
The specific implementation process of the determination of the. OH concentration in the solution to be measured in the ultraviolet/chlorine advanced oxidation process is as follows:
the test conditions were: the method comprises the steps of preparing a solution to be detected (preparing the solution to be detected, namely taking 0.1mL of a sodium hypochlorite solution with the effective chlorine mass content of 5%, taking 2.5mg of soluble organic carbon (natural organic matters of Schwannehe in terms of carbon), taking 0.054g of anhydrous sodium dihydrogen phosphate, taking 0.11g of anhydrous disodium hydrogen phosphate, taking 500ng of carbamazepine, adjusting the pH to 7 by using a phosphate buffer solution, adding water to a constant volume of 1L, simulating sewage treated by an ultraviolet/chlorine advanced oxidation process, wherein the chlorine concentration in the solution to be detected is 5mg/L, and the pH is 7; the ultraviolet lamp has emission wavelength of 254nm and ultraviolet radiation intensity of 0.55mW/cm2The concentration of the contaminant carbamazepine to be removed is 500ng/L, and the temperature is 25 +/-3 ℃;
step S1: in a closed state, the ultraviolet radiation intensity is 0.55mW/cm2Under the conditions of (1), 24.4nM, 40.7nM, 48.8nM, 65.0nM and 81.3nM nitrobenzene were added to the test solution, respectively, and the change in nitrobenzene concentration in the reaction time of 20 minutes was measured by HPLC (the nitrobenzene concentration was calculated from the HPLC calibration curve of nitrobenzene obtained in example 1) as ln (C/C)0) And time t, the results are shown in FIG. 2; FIG. 2 is a quasi-first order degradation kinetic curve of nitrobenzene, k of nitrobenzene, in a solution to be tested in the UV/chlorine advanced oxidation process in example 2 of the present inventionobsThe apparent quasi-first order decay rates were 4.59X 10, respectively-4s-1(24.4nM)、4.12×10-4s-1(40.7nM)、3.00×10-4s-1(48.8nM)、2.61×10-4s-1(65.0nM)、2.44×10-4s-1(81.3nM)；
Step S2: the method for quantitatively determining the concentration of the probe compound in the reaction solution by HPLC is as follows:
placing the solution containing nitrobenzene with known concentration into HPLC for detection, and drawing a chromatographic standard curve of the probe compound by taking the concentration of nitrobenzene as an abscissa and the peak area of a corresponding absorption peak as an ordinate (the specific process is as described in example 1);
detecting the reaction liquid in a chromatogram to obtain the absorption peak area of nitrobenzene in the reaction liquid, and calculating the concentration of the probe compound according to the HPLC standard curve of the nitrobenzene;
since the step S1 is performed under a closed condition, the volatilization quasi-first order decay rate k of nitrobenzenevolIs 0; nitrobenzene under the same ultraviolet radiation intensity (0.55 mW/cm)2) Quasi-first order photolysis decay rate kUVIs 1 × 10-5s-1Is much smaller than k of nitrobenzene in step S1obsThe apparent quasi-first order decay rate is negligible, so the measured apparent quasi-first order decay rate of nitrobenzene is equal to the quasi-first order decay rate of nitrobenzene contributed by the OH reaction, i.e., k·OH＝kobs；
The method for calculating the concentration of. OH in the solution to be measured is as follows:
kobs＝k·OH (1)
k·OH＝k·OH,NB[·OH]SS (2)
k·OHis the quasi-first order decay rate of the probe compound contributed by the. OH reaction, calculated from formula (1); k is a radical of formula·OHCan also be expressed by formula (2) wherein k·OH,NBIs the second order rate constant of the reaction of OH and NB, [. OH]SSIs the concentration of OH in the solution to be measured;
[·OH]SScan be expressed by formula (3):
Figure BDA0002585562520000061
wherein r isOHThe rate of formation of the OH is,
Figure BDA0002585562520000071
is the quasi-first order decay rate of OH at an NB concentration of 0 in solution, [ NB]Representing the concentration of NB, substituting formula (3) into formula (2) to obtain formula (4):
Figure BDA0002585562520000072
taking reciprocal of the left side and the right side of the formula (4) to obtain a formula (5):
Figure BDA0002585562520000073
with [ NB ]](indicating the concentration of nitrobenzene) is plotted on the abscissa at 1/k·OHA straight line with an intercept of 1257 is obtained for ordinate plotting, as shown in FIG. 3, FIG. 3 shows 1/k in the solution to be tested in the UV/Cl advanced oxidation process in example 2 of the present invention·OHAnd [ NB ]]Linear relationship (y 1257+36.84x, R)20.89); according to [ NB]At a concentration of 0, the intercept I is 1257 (i.e., labeled in FIG. 3, not subject to [ NB ]]1/k of influence·OHValues) OH concentration of 1/(I k)·OH,NB)，k·OH,NB＝3.9×109M-1s-1(the value is constant) it can be found that the concentration of. OH in the solution to be measured is 2.04X 10-13M。
Example 3: determination of OH concentration in solution to be measured in ultraviolet/hydrogen peroxide advanced oxidation process
The test conditions were: the solution to be tested (preparation of the solution to be tested: 0.2mL of 10M hydrogen peroxide solution, 2.5mg of soluble organic carbon (natural organic matter of Schwannier river), 0.054g of anhydrous sodium dihydrogen phosphate, 0.11g of anhydrous disodium hydrogen phosphate, and phosphate buffer solution to adjust pH to 7, and adding water to a constant volume of 1L, wherein the solution simulates sewage treated by ultraviolet/hydrogen peroxide advanced oxidation process), the hydrogen peroxide concentration is 200 muM, the concentration of the soluble organic carbon is 2.5mg/L (natural organic matter of Schwannier river, calculated by carbon), the pH is 7, the ultraviolet lamp emission wavelength is 254nm, and the ultraviolet radiation intensity is 0.55mW/cm2The temperature is 25 +/-3 ℃;
step S1: in a closed state, the ultraviolet radiation intensity is 0.55mW/cm2Under the conditions of (1), 100nM, 200nM, 300nM, 500nM and 700nM nitrobenzene was added to the test solution, and the change in nitrobenzene concentration in the reaction time of 20 minutes was measured by HPLC (the nitrobenzene concentration was calculated from the HPLC standard curve of nitrobenzene obtained in example 1) as ln (C/C)0) The results are shown in FIG. 4, where FIG. 4 is a quasi-first order degradation kinetic curve of nitrobenzene in the solution to be tested in the UV/hydrogen peroxide advanced oxidation process of this example, and the apparent value of NB is quasi-first orderThe decay rates were 0.00373s, respectively-1(100nM)、0.00301s-1(200nM)、0.00267s-1(300nM)、0.0022s-1(500nM)、0.00178s-1(700nM)；
Step S2: the method for quantitatively determining the concentration of the probe compound in the reaction solution by HPLC is as follows:
placing the solution containing nitrobenzene with known concentration into HPLC for detection, and drawing a chromatographic standard curve of the probe compound by taking the concentration of nitrobenzene as an abscissa and the peak area of a corresponding absorption peak as an ordinate (the specific process is as described in example 1);
detecting the reaction liquid in a chromatogram to obtain the absorption peak area of nitrobenzene in the reaction liquid, and calculating the concentration of the probe compound according to the HPLC standard curve of the nitrobenzene;
since the step S1 is performed under a closed condition, the volatilization quasi-first order decay rate k of nitrobenzenevolIs 0; nitrobenzene under the same ultraviolet radiation intensity (0.55 mW/cm)2) Quasi-first order photolysis decay rate kUVIs 1 x 10-5s-1Is much smaller than k of nitrobenzene in step S1obsThe apparent quasi-first order decay rate is negligible, so the measured apparent quasi-first order decay rate of nitrobenzene is equal to the quasi-first order decay rate of nitrobenzene contributed by the OH reaction, i.e., k·OH＝kobs；
The method for calculating the concentration of. OH in the solution to be measured is as follows:
kobs＝k·OH (1)
k·OH＝k·OH,NB[·OH]SS (2)
k·OHis the quasi-first order decay rate of the probe compound contributed by the. OH reaction, calculated from formula (1); k is a radical of formula·OHCan also be expressed by formula (2) wherein k·OH,NBIs the second order rate constant of the reaction of OH and NB, [. OH]SSIs the concentration of OH in the solution to be measured;
[·OH]SScan be expressed by formula (3):
Figure BDA0002585562520000081
wherein r isOHThe rate of formation of the OH is,
Figure BDA0002585562520000082
is the quasi-first order decay rate of OH at an NB concentration of 0 in solution, [ NB]Representing the concentration of NB, substituting formula (3) into formula (2) to obtain formula (4):
Figure BDA0002585562520000083
taking reciprocal of the left side and the right side of the formula (4) to obtain a formula (5):
Figure BDA0002585562520000084
with [ NB ]](indicating the concentration of nitrobenzene) is plotted on the abscissa at 1/k·OHA straight line with an intercept of 243.8 was plotted for the ordinate, as shown in FIG. 5, where FIG. 5 is a graph of 1/k in the solution to be tested in the UV/hydrogen peroxide advanced oxidation process of example 3 of the present invention·OHAnd [ NB ]]Linear relationship (y-243.8 +0.4x, R)20.98); according to [ NB ]]At a concentration of 0, the intercept I is 243.8 (i.e., marked in FIG. 5, not affected by [ NB]1/k of influence·OHValues) OH concentration of 1/(I k)·OH,NB)，k·OH,NB＝3.9×109M-1s-1(the value is constant) it can be found that the concentration of. OH in the solution to be measured is 1.05X 10-12M。
Example 4
Example 4 differs from example 2 in that step S1 was not reacted under closed conditions, and therefore a control test with water under dark conditions was added: under the condition of keeping out of the sun, the solution to be measured in the step S1 is replaced by ultrapure water to form a reaction liquid b, the rest of the operation process is the same as that of the embodiment 2, and the quasi-first-order volatilization attenuation rate k of the nitrobenzene is obtainedvolThen k isobs＝kvol+k·OHThe rest has been calculatedThe procedure was the same as in example 2. In the embodiment, the actual industrial production environment is considered, and the detection error caused by the volatilization of nitrobenzene is eliminated, so that the concentration of OH in the solution to be detected is more accurate.
Comparative example 1
Compared with the example 2, in the comparative example 1, the OH concentration of the solution to be measured in the ultraviolet/chlorine advanced oxidation process is directly calculated by using the single nitrobenzene concentration, and when the nitrobenzene concentration is 24.4nM, the measured OH concentration is 1.18X 10-13M; when the nitrobenzene concentration was 40.7nM, the OH concentration was measured to be 1.06X 10-13M; when the nitrobenzene concentration was 48.8nM, the OH concentration was found to be 7.70X 10-14M; when the nitrobenzene concentration was 65.0nM, the OH concentration was measured to be 6.70X 10-14M; when the nitrobenzene concentration was 81.3nM, the OH concentration was measured to be 6.26X 10-14And M. It can be seen that the measured OH concentration gradually decreased with increasing nitrobenzene use concentration, indicating a gradually increasing deviation from the true value. When the concentration of nitrobenzene is 81.3nM, the measured OH concentration is nearly 2 times lower than that of nitrobenzene with the concentration of 24.4nM and nearly 3 times lower than that of NB with the concentration of 0, which embodies the important role of the invention in improving the OH concentration measurement accuracy.
Comparative example 2
Compared with the example 3, in the comparative example 2, the OH concentration of the solution to be measured in the ultraviolet/hydrogen peroxide advanced oxidation process is directly calculated by using a single nitrobenzene concentration, and when the nitrobenzene concentration is 100nM, the measured OH concentration is 9.56X 10- 13M; when the nitrobenzene concentration was 200nM, the OH concentration was found to be 7.69X 10-13M; when the nitrobenzene concentration was 300nM, the OH concentration was measured to be 6.84X 10-13M; when the nitrobenzene concentration was 500nM, the OH concentration was measured to be 5.64X 10-13M; when the nitrobenzene concentration was 700nM, the OH concentration was measured to be 4.97X 10-13And M. It can be seen that the measured OH concentration gradually decreased with increasing nitrobenzene use concentration, indicating a gradually increasing deviation from the true value. When the concentration of nitrobenzene is 700nM, the measured OH concentration is nearly 2 times lower than when the concentration of nitrobenzene is 0, which shows that the invention is improving the OH concentrationThe important function in the aspect of measuring precision.

Claims (8)

1. A method for detecting the concentration of hydroxyl radicals using a probe compound, comprising the steps of:
step S1: adding probe compounds with different concentrations into a solution to be detected containing OH to form a reaction solution, and detecting the change of the concentration C of the probe compounds in the reaction solution along with the time t by using chromatography, wherein the initial concentration of the probe compounds is C0C is the concentration of the probe compound at time t, on the abscissa, ln (C/C)0) For ordinate, ln (C/C) is plotted0) The slope of the curve relating to t is denoted as kobs，kobsI.e. the apparent quasi-first order decay rate of the probe compound;
step S2: the method for quantitatively determining the concentration of the probe compound in the reaction solution by chromatography is as follows:
putting the solution containing the probe compound with known concentration into a chromatogram for detection, and drawing a chromatogram standard curve of the probe compound;
detecting the reaction liquid in a chromatogram to obtain the absorption peak area of the probe compound in the reaction liquid, and calculating the concentration of the probe compound according to the chromatographic standard curve of the probe compound; then, calculating to obtain the concentration of OH in the solution to be detected;
the method for calculating the concentration of OH in the solution to be measured is as follows:
kobs＝k·OH (1)
k·OH＝k·OH,PC[·OH]SS (2)
k·OHis the quasi-first order decay rate of the probe compound contributed by the. OH reaction, the probe compound is marked as PC, and is calculated by the formula (1); k is a radical of·OHCan also be expressed by formula (2) wherein k·OH,PCIs the second order rate constant of the reaction of OH and PC, [. OH]SSIs the concentration of OH in the solution to be measured or is called the steady-state concentration of OH in the solution to be measured;
[·OH]SScan be expressed by formula (3):
Figure FDA0003615636970000011
wherein r isOHThe rate of formation of the OH is,
Figure FDA0003615636970000012
is the quasi-first order decay rate of OH when the concentration of PC in the solution to be measured is 0, [ PC ]]Substituting formula (3) into formula (2) to obtain formula (4):
Figure FDA0003615636970000013
taking reciprocal of the left side and the right side of the formula (4) to obtain a formula (5):
Figure FDA0003615636970000014
according to formula (5) with [ PC]Is abscissa, 1/k·OHPlotting the ordinate yields an intercept of
Figure FDA0003615636970000015
Figure FDA0003615636970000021
The slope is 1/rOHThe intercept is represented as I, and 1/I represents k when the PC concentration is 0·OHThe value obtained by further combining the formula (3) is 1/(I k) when the concentration of OH is 0·OH,PC) The value is the concentration of. OH in the solution to be tested which is not affected by the probe compound PC;
the probe compound is nitrobenzene;
the chromatogram is a high performance liquid chromatogram.
2. The method according to claim 1, wherein in step S1, the pH value of the solution to be tested is 2-11.
3. The method according to claim 1, wherein the concentration of the probe compound in step S1 is 20nM-2 μ Μ.
4. The method according to claim 1, wherein the detection conditions of the high performance liquid chromatography are as follows: the mobile phase comprises 55-60% of acetonitrile and 40-45% of water by volume ratio; the flow rate is 0.5-1mL min-1(ii) a The detection wavelength was 250-265nm using an ultraviolet detector.
5. The method of claim 1, wherein in step S1, if the probe compounds with different concentrations are added to the solution to be tested containing. OH to form the reaction solution, the reaction solution is not formed under closed conditions, and after step S1, the method further comprises the steps of: control test with water in the dark: under the condition of keeping out of the sun, replacing the solution to be detected containing OH in the step S1 with water to form a reaction solution, and obtaining the quasi-first-order volatilization attenuation rate k of the probe compound by the same operation process as the step S1vol(ii) a Then k isobs＝kvol+k·OHWherein k is·OHIs the quasi-first order decay rate of the probe compound contributed by the. OH reaction.
6. The method of claim 1, wherein in step S1, if the probe compounds with different concentrations are added to the solution to be tested containing. OH to form the reaction solution under the condition of ultraviolet radiation, after step S1, the method further comprises the steps of: adding the probe compound with the same concentration as that in the step S1 into the ultrapure water under the closed condition, adding the ultraviolet radiation with the same dosage as that in the step S1, and repeating the operation of the step S1 to obtain the quasi-first-order photolysis attenuation rate k of the probe compound under the ultraviolet radiationUVThen k isobs＝kUV+k·OHWherein k is·OHIs the quasi-first order decay rate of the probe compound contributed by the. OH reaction.
7. The method according to claim 1, wherein the concentration of. OH in the test solution is in the range of 1 x 10-16M to 1X 10-10M。
8. Use of the method according to any one of claims 1 to 7 in the field of sewage treatment.
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