CN109060763B - Seawater COD detection method - Google Patents

Seawater COD detection method Download PDF

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CN109060763B
CN109060763B CN201810952974.8A CN201810952974A CN109060763B CN 109060763 B CN109060763 B CN 109060763B CN 201810952974 A CN201810952974 A CN 201810952974A CN 109060763 B CN109060763 B CN 109060763B
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seawater
cod
concentration
raman spectrum
detection method
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CN109060763A (en
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吴国庆
王碧霖
张宏扬
韩明宏
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Yanshan University
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    • G01—MEASURING; TESTING
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering

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Abstract

The invention provides a seawater COD detection method, and belongs to the field of seawater detection. The method does not need to carry out complex pretreatment and chemical analysis on the actual seawater sample, greatly simplifies the operation steps and shortens the detection time; the Raman spectrum has different absorption characteristics on different substances, so that the influence of water molecules on the absorption of light in a visible-near infrared band is reduced to the maximum extent, and the interference of fluorescence on a detection result is reduced by using the Raman spectrum, so that the detection result is more accurate; the detection method provided by the invention is environment-friendly, and does not consume a large amount of chemical reagents like the traditional detection, so that adverse effects on the environment are avoided.

Description

Seawater COD detection method
Technical Field
The invention relates to the technical field of seawater detection, in particular to a seawater COD detection method.
Background
Water resources are an important resource for our survival and development. And the industrial wastewater, the domestic sewage and other wastes enter water bodies such as rivers, lakes and seas, and the generated pollution is greater than the purification capacity of the water bodies. This will result in many properties of the water being changed, and therefore the value of the water will also be affected, endangering human health, causing damage to the ecological environment and a constant deterioration of the water quality. Therefore, it is extremely important to detect and monitor the quality of ocean water.
The sum of all reducing substances to be oxidized in water, called chemical Oxygen demand, can indicate the pollution of effluent sample, and is often indicated by the symbol COD (chemical Oxygen demand). At present, the domestic standard methods for determining COD comprise a potassium permanganate method and a potassium dichromate method, wherein a strong oxidant is added into a solution to be measured, the content of the consumed oxidant is measured through an oxidation-reduction reaction, and then the content of a reducing substance is calculated to represent the value of COD. In addition to the above oxidation method, other methods for measuring COD include coulometry, spectrophotometry, and the like. However, the methods have the problems of complicated detection process, long detection time, easy secondary pollution of water samples and the like, and in order to avoid the problems, the spectral absorption method becomes a COD detection method which is researched more in recent years. At present, the fluorescence interference is large during ultraviolet-visible light wave band detection, and the interference of the infrared absorption peak of water molecules also influences the detection effect during near infrared light wave band detection.
Disclosure of Invention
The invention aims to provide a seawater COD detection method, which has small fluorescence interference and water molecule infrared absorption peak interference and can realize rapid and efficient detection of the seawater COD value.
The invention provides a seawater COD detection method, which comprises the following steps:
mixing the COD standard solution, seawater crystal and distilled water to obtain simulated seawater samples with different concentrations;
performing Raman spectrum measurement on the simulated seawater sample to obtain a standard curve, wherein the standard curve takes the COD concentration of the simulated seawater sample as a dependent variable and takes the Raman spectrum at 981cm-1The relative intensity of the characteristic peak is an independent variable;
performing Raman spectrum measurement on actual seawater to obtain Raman spectrum of 981cm-1The relative intensity of characteristic peak is 981cm according to the actual seawater Raman spectrum-1And obtaining the concentration of COD in the seawater by using the relative intensity of the characteristic peak and the standard curve.
Preferably, the concentration of COD in the simulated seawater sample is 0.5-100 mg/L, and the simulated seawater sample comprises 35 groups.
Preferably, the low concentration range in the simulated seawater sample is 0.5-10 mg/L, the concentration gradient is 0.5mg/L, the high concentration range is 10-100 mg/L, and the concentration gradient is 5 mg/L.
Preferably, the salt concentration of the simulated seawater sample is 30 per mill.
Preferably, the raman spectroscopy measurement parameters include: excitation wavelength of 785nm and resolution of 4.5cm-1The laser intensity was 270mW, the integration time was 10s, and the average number of times was 3.
Preferably, the wavelength range of the Raman spectrum measurement is 175-3200 cm-1。
Preferably, the standard curve is a linear curve, and the linear curve has a linear correlation coefficient of 0.9270.
Preferably, the linear range of the standard curve is 0.5-100 mg/L.
The invention provides a seawater COD detection method, which comprises the following steps: mixing the COD standard solution, seawater crystal and distilled water to obtain simulated seawater samples with different concentrations; performing Raman spectrum measurement on the simulated seawater sample to obtain a standard curve, wherein the standard curve takes COD concentration of the simulated seawater sample asDependent variable in Raman spectrum at 981cm-1The relative intensity of the characteristic peak is an independent variable; performing Raman spectrum measurement on actual seawater to obtain Raman spectrum of 981cm-1The relative intensity of characteristic peak is 981cm according to the actual seawater Raman spectrum-1And obtaining the concentration of COD in the seawater by using the relative intensity of the characteristic peak and the standard curve. The method does not need to carry out complex pretreatment and chemical analysis on the actual seawater sample, greatly simplifies the operation steps and shortens the detection time; the Raman spectrum has different absorption characteristics on different substances, so that the influence of water molecules on the absorption of light in a visible-near infrared band is reduced to the maximum extent, and the interference of fluorescence on a detection result is reduced by using the Raman spectrum, so that the detection result is more accurate; the detection method provided by the invention is environment-friendly, and does not consume a large amount of chemical reagents like the traditional detection, so that adverse effects on the environment are avoided.
Drawings
FIG. 1 is a schematic view of a sample stage for Raman spectroscopy according to the present invention;
FIG. 2 is a raw Raman spectrum of a simulated seawater sample with a COD concentration of 0.5mg/L according to the present invention;
FIG. 3 is a characteristic wavelength Raman spectrum of a partially simulated seawater sample according to the present invention;
FIG. 4 is a plot of a standard equation according to the present invention;
FIG. 5 is a standard equation curve obtained by artificially preparing seawater according to the present invention.
Detailed Description
The invention provides a seawater COD detection method, which comprises the following steps:
mixing the COD standard solution, seawater crystal and distilled water to obtain simulated seawater samples with different concentrations;
performing Raman spectrum measurement on the simulated seawater sample to obtain a standard curve, wherein the standard curve takes the COD concentration of the simulated seawater sample as a dependent variable and takes the Raman spectrum at 981cm-1The relative intensity of the characteristic peak is an independent variable;
performing Raman spectrum measurement on actual seawater to obtain actual seawater Raman spectrumAt 981cm-1The relative intensity of characteristic peak is 981cm according to the actual seawater Raman spectrum-1And obtaining the concentration of COD in the seawater by using the relative intensity of the characteristic peak and the standard curve.
The COD standard solution, the seawater crystal and the distilled water are mixed to obtain simulated seawater samples with different concentrations. In the invention, the concentration of COD in the simulated seawater sample is preferably 0.5-100 mg/L, and the simulated seawater sample preferably comprises 35 groups.
In the invention, the low concentration range of the simulated seawater sample is preferably 0.5-10 mg/L, the concentration gradient is preferably 0.5mg/L, the high concentration range is preferably 10-100 mg/L, and the concentration gradient is preferably 5 mg/L.
In the present invention, the salt concentration of the simulated seawater sample is preferably 30 ‰.
The source of the COD standard solution is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used. In the invention, the mass concentration of the potassium hydrogen phthalate in the COD standard solution is preferably 20-1000 mg/L.
The mixing method of the present invention is not particularly limited, and a mixing method known to those skilled in the art may be used.
After obtaining the simulated seawater sample, the Raman spectrum measurement is carried out on the simulated seawater sample to obtain a standard curve, the COD concentration of the simulated seawater sample is used as a dependent variable, and the Raman spectrum is used at 981cm-1The relative intensity of the characteristic peak at (a) is an independent variable.
In the present invention, the raman spectrometry parameters preferably include: excitation wavelength of 785nm and resolution of 4.5cm-1The laser intensity was 270mW, the integration time was 10s, and the average number of times was 3.
In the invention, the preferable wavelength range of the Raman spectrum measurement is 175-3200 cm-1More preferably 932-1082 cm-1。
In the present invention, the Raman spectroscopy is preferably performed in a Bidtatch Portable Raman System (i-Raman Plus-785S). In the invention, the schematic structural diagram of the sample stage during Raman spectrum measurement is shown in FIG. 1, wherein 1 in FIG. 1 is a shading cover, 2 is a cuvette, 3 is a support adjusting knob, 4 is a Raman laser probe hole, 5 is a Raman laser probe support, a Raman probe can extend into the cuvette support through the Raman laser probe hole on the cuvette support, and a completely closed dark environment can be formed after the shading cover is covered.
In the present invention, partial least squares are preferably used to align the characteristic Raman shift to 981cm-1And (4) performing regression analysis to obtain a standard curve.
In the present invention, the standard curve is-5.8 x + 8475.0.
In the present invention, the standard curve is a linear curve, and the linear correlation coefficient of the linear curve is preferably 0.9270.
In the invention, the linear range of the standard curve is preferably 0.5-100 mg/L.
The invention carries out Raman spectrum measurement on actual seawater to obtain the Raman spectrum of the actual seawater at 981cm-1The relative intensity of characteristic peak is 981cm according to the actual seawater Raman spectrum-1And obtaining the concentration of COD in the seawater by using the relative intensity of the characteristic peak and the standard curve.
In order to further illustrate the present invention, the method for detecting seawater COD provided by the present invention is described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.
Example 1
Adding different volumes of 1000mg/L COD standard solutions into every 10mL of actual seawater samples to obtain 35 groups of actual seawater samples with COD concentration of 0.5-100 mg/L, wherein the concentration gradient of 0.5-10 mg/L in the low concentration range is 0.5mg/L, and the concentration gradient of 10-100 mg/L in the high concentration range is 5 mg/L. Preparing seawater crystals and distilled water in a mass ratio of 1:25 into simulated seawater samples with salinity of 30, adding different volumes of COD standard solutions with concentration of 1000mg/L into each 10mL of samples to obtain 35 groups of simulated seawater samples with COD concentration of 0.5-100 mg/L, wherein the concentration gradient of 0.5-10 mg/L in a low concentration range is 0.5mg/L, and the concentration gradient of 10-100 mg/L in a high concentration range is 5 mg/L.
A simulated seawater sample was placed in the sample cell described in figure 1. Using a Portable Raman System of Bidtatch (i-Raman Plus-785S), excitation wavelength 785 nm; the detection range of the Raman spectrum is 175-3200 cm-1(ii) a Resolution was 4.5cm-1. Setting the laser intensity to be 270mW, the integration time to be 10s, the average times to be 3 times, and setting the characteristic Raman shift range of the detected sample to be 932-1082 cm-1。
FIG. 2 is a raw Raman spectrum of a simulated seawater sample with a COD concentration of 0.5mg/L, and FIG. 3 is a Raman spectrum at a characteristic wavelength of a part of the simulated seawater sample. The resulting 35 sample spectra were subjected to a division of the training set and prediction set at a ratio of about 6:1 for the 35 samples. Characteristic Raman shift of 981cm by using partial least square method-1The regression analysis is carried out, the experimental result is shown in figure 4, and the correlation coefficient of the training set and the prediction set reaches 0.9270. The standard equation between relative intensity and COD concentration was found to be-5.8 x + 8475.0.
Performing Raman spectrum measurement on actual seawater to obtain Raman spectrum of 981cm-1Has a characteristic peak relative intensity of 8468.1, and is 981cm according to the actual seawater Raman spectrum-1The relative intensity of the characteristic peak and the standard curve obtain that the concentration of COD in the seawater is 1.2 mg/L.
Theoretical verification
The original Raman spectrum of the artificially prepared seawater is similar to that of an actual seawater preparation sample. The raw raman spectral samples of 35 manually configured seawater were partitioned into a training set and a prediction set at a ratio of about 6: 1. Characteristic Raman shift of 981cm by using partial least square method-1The regression analysis was performed, and the experimental results are shown in fig. 5, where the correlation coefficient between the predicted COD concentration and the true COD concentration reached 0.914, and the linear equation was-0.149 x + 1.271. The detection results of the two samples are combined, and the good correlation between the spectral relative intensity and the COD value of the water sample in the characteristic Raman shift range is shown. A regression model of actual seawater may be used for detection.
The method does not need to carry out complex pretreatment and chemical analysis on the actual seawater sample, greatly simplifies the operation steps and shortens the detection time; the Raman spectrum has different absorption characteristics on different substances, so that the influence of water molecules on the absorption of light in a visible-near infrared band is reduced to the maximum extent, and the interference of fluorescence on a detection result is reduced by using the Raman spectrum, so that the detection result is more accurate; the detection method provided by the invention is environment-friendly, and does not consume a large amount of chemical reagents like the traditional detection, so that adverse effects on the environment are avoided.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims (8)

1. A method for detecting COD in seawater comprises the following steps:
mixing the COD standard solution, seawater crystal and distilled water to obtain simulated seawater samples with different concentrations;
performing Raman spectrum measurement on the simulated seawater sample to obtain a standard curve, wherein the standard curve takes the COD concentration of the simulated seawater sample as a dependent variable and takes the Raman spectrum at 981cm-1The relative intensity of the characteristic peak is an independent variable;
performing Raman spectrum measurement on actual seawater to obtain Raman spectrum of actual seawater with excitation wavelength of 981cm-1The relative intensity of characteristic peak is 981cm according to the actual seawater Raman spectrum-1And obtaining the concentration of COD in the seawater by using the relative intensity of the characteristic peak and the standard curve.
2. The detection method according to claim 1, wherein the concentration of COD in the simulated seawater sample is 0.5-100 mg/L, and the simulated seawater sample comprises 35 groups.
3. The detection method according to claim 2, wherein the concentration range of the low concentration in the simulated seawater sample is 0.5-10 mg/L, and the concentration gradient is 0.5 mg/L; the high concentration range is 10-100 mg/L, and the concentration gradient is 5 mg/L.
4. The detection method according to claim 1 or 2, wherein the salt concentration of the simulated seawater sample is 30% o.
5. The detection method of claim 1, wherein the raman spectroscopy measurement parameters comprise: excitation wavelength of 785nm and resolution of 4.5cm-1The laser intensity was 270mW, the integration time was 10s, and the average number of times was 3.
6. The detection method according to claim 5, wherein the Raman spectroscopy has a wavelength ranging from 175 to 3200cm-1。
7. The detection method according to claim 1, wherein the standard curve is a linear curve, and a linear correlation coefficient of the linear curve is 0.9270.
8. The detection method according to claim 1, wherein the linear range of the standard curve is 0.5-100 mg/L.
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