CN109827916B - Water quality nitrate detection method based on zinc-cadmium reduction salt-free effect - Google Patents
Water quality nitrate detection method based on zinc-cadmium reduction salt-free effect Download PDFInfo
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Abstract
The invention relates to the field of water quality detection, in particular to a nitrate detection method for water quality based on zinc-cadmium reduction salt-free effect, which is suitable for detecting the nitrate content in tap water, surface water, estuary water and seawater and comprises the steps of S1, adding a proper amount of ammonium chloride solution into a water sample with a certain volume; step S2, the nitrate is quantitatively reduced into nitrite through cadmium zinc plating sheets with certain areas; step S3, determining the total nitrite content in the sample by a diazo-azo method; and step S4, subtracting the nitrite concentration in the sample from the total nitrite content determined in the step S3 to obtain the nitrate content, wherein the ammonium chloride solution is added in the process of reducing the nitrate by the zinc and the cadmium, the experimental conditions are optimized, the influence of the salt effect of the zinc and cadmium reduction method is eliminated, the reduction efficiency of the nitrate is improved, and the sensitivity and the resolution of the zinc and cadmium reduction method are improved.
Description
Technical Field
The invention relates to the field of water quality detection, in particular to a water quality nitrate detection method based on zinc-cadmium reduction salt-free effect, which is suitable for detecting the nitrate content in tap water, surface water, estuary water and seawater.
Background
Nitrate nitrogen as a nutrient salt element is an important evaluation index for measuring the eutrophication degree of the water body and is also an important pollution index monitored by an environmental monitoring department. The analysis method of nitrate in water body includes Flow Injection Analysis (FIA), cadmium column reduction method, ion chromatography, gas phase molecular absorption spectrometry, phenol disulfonic acid spectrophotometry, ultraviolet spectrophotometry, zinc-cadmium reduction method, etc.
The ultraviolet spectrophotometry is suitable for measuring nitrate in surface water and underground water, but is easily interfered by dissolved organic carbon, hexavalent chromium, turbidity, a surfactant, bromide, bicarbonate and carbonate in water, and a sample needs to be properly pretreated.
The phenoldisulfonic acid spectrophotometry is suitable for measuring nitrate in drinking water, underground water and clean surface water, organic matters, carbonate, chloride, nitrite and ammonium salt in the water interfere the measurement, a sample needs to be pretreated, and the defects of complex analysis process, harsh condition control, long analysis time and the like exist.
The ion chromatography adopts a mode of separating a conductivity detector by an anion exchange resin analytical column to measure the nitrate in the water, is easily interfered by a large amount of chloride, is usually suitable for detecting the nitrate in clean surface water and tap water, and has the defects of high price of instruments and equipment, high requirement on operators and the like although the test result is accurate and the stability is good.
Ion chromatography, phenol disulfonic acid photometry and ultraviolet spectrophotometry are all interfered by chloride, so that a cadmium column reduction method is generally adopted for measuring nitrate in ocean seawater and estuary water. The cadmium column reduction method is not influenced by salinity, has high reduction rate and stable result, but is generally suitable for analyzing a small amount of samples or applying to an automatic analyzer (such as a flow injection analyzer) due to long analysis time and complicated steps.
In marine environmental monitoring, the zinc-cadmium reduction method is simple, convenient and quick to operate, and is suitable for offshore field analysis, so that the zinc-cadmium reduction method is widely applied to basic monitoring units. However, the reduction efficiency of the nitrate in the method has certain salt effect, the reduction rate is low, the stability and the precision are poor, and the like, and the salinity of the samples is adjusted by adding sodium chloride into the samples from Shinggang, Zhengrui and the like or the ammonium chloride-ammonia water buffer reagent is added into the samples, so that the influence of the salt effect of the samples is reduced, the reduction rate is improved, and better recovery rate and precision are obtained.
Disclosure of Invention
In order to achieve the purpose, in order to solve the prior technical problems, the invention eliminates the influence of salt effect of the zinc-cadmium reduction method by adding the ammonium chloride solution and optimizing the experimental conditions in the process of reducing the nitrate by the zinc-cadmium, improves the reduction efficiency of the nitrate, and further improves the sensitivity and the resolution of the zinc-cadmium reduction method; establishes a zinc-cadmium reduction spectrophotometric method for nitrate determination, which has convenient operation, good nitrate reduction rate, high accuracy and repeatability and no influence of salt effect. The method of the invention is not only suitable for measuring the nitrate in the high salinity seawater, but also suitable for measuring the nitrate content in the low salinity estuary water, tap water and surface water.
The invention provides the following technical scheme: a detection method of nitrate in water quality based on zinc-cadmium reduction salt-free effect comprises the preparation of sulfanilamide solution, naphthylethylenediamine dihydrochloride solution and cadmium chloride solution, a visible spectrophotometer, an oscillator and a common laboratory glassware;
preparation of a sulfanilamide solution: weighing 1.0g to 10g of sulfanilamide, dissolving in 350ml of hydrochloric acid solution with volume fraction of 5 percent to 20 percent, fixing the volume by using water, and uniformly mixing;
preparation of a solution of naphthylethylenediamine dihydrochloride: dissolving 0.2g to 2.0g of 1-naphthylethylenediamine dihydrochloride in water, and uniformly mixing;
preparation of cadmium chloride solution: weighing 5g to 50g of cadmium chloride, dissolving in water, and uniformly mixing; also included, is a nitrate standard solution: GBW (E)081697,100.0 mg/L; nitrate nitrogen standard use solution: GBW 08634-GBW 08637 series;
the method comprises the following steps:
step S1, adding a proper amount of ammonium chloride solution into a water sample with a certain volume;
step S2, the nitrate is quantitatively reduced into nitrite through cadmium zinc plating sheets with certain areas;
step S3, determining the total nitrite content in the sample by a diazo-azo method;
and step S4, subtracting the nitrite concentration in the sample from the total nitrite content determined in the step S3 to obtain the nitrate content.
Further, in step S1, preparing an ammonium chloride solution: 5g to 500g of ammonium chloride is weighed and dissolved in 500mL to 2000mL of water, and the mixture is uniformly mixed.
As a preferable embodiment of the present invention, the zinc sheet is prepared by the following steps: polishing the surface of the high-purity zinc sheet by using metallographic abrasive paper with more than 200 meshes, wiping the surface by using gauze, cutting the high-purity zinc sheet into a rectangular zinc sheet, and rolling the zinc sheet into a zinc roll.
Taking a set amount of water sample into a glassware, adding 0.2-5.0 mL of ammonium chloride solution, mixing uniformly, adding the zinc roll, adding a proper amount of cadmium chloride solution, quickly placing on an oscillator to oscillate for the first time, quickly rolling out zinc after oscillating, adding sulfanilamide solution, mixing uniformly, placing for the second time, adding a solution of naphthalene-ethylenediamine dihydrochloride which is equal to the sulfanilamide solution, mixing uniformly, and placing for the third time until the color is stable; after the color stabilized, the absorbance was measured with a visible spectrophotometer.
The invention has the beneficial effects that:
(1) the used instruments and equipment are low in price, the medicine reagents are easy to obtain, and a visible spectrophotometer, an oscillator and necessary glassware which are common in a laboratory can meet the requirements, so that the operation cost of the laboratory is effectively reduced;
(2) the operation flow is simple, the requirement on laboratory personnel is not high, and common technical personnel can complete the whole analysis process;
(3) the reduction efficiency and stability of the nitrate reduced by the zinc and the cadmium are improved, the influence of the salt effect of nitrate determination is eliminated, the sensitivity of the method is improved, and the stability of a detection result is improved while the detection limit of the method is reduced;
(4) the method has wide application range and can be used for measuring the content of nitrate in seawater, tap water and surface water.
Drawings
FIG. 1 is a comparison of the operating curves of the present invention;
FIG. 2 is the precision and accuracy results of the method of the present invention;
FIG. 3 is the nitrate reduction rate of a nitrate solution of 0.200mg/L under different salinity conditions;
FIG. 4 shows cadmium zinc flake particles after zinc-cadmium reduction according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a water quality nitrate detection method based on zinc-cadmium reduction salt-free effect, which comprises the preparation of sulfanilamide solution, naphthylethylenediamine dihydrochloride solution and cadmium chloride solution, a visible spectrophotometer, an oscillator and a common laboratory glassware;
preparation of a sulfanilamide solution: weighing 1.0g to 10g of sulfanilamide, dissolving the sulfanilamide in a hydrochloric acid solution with the volume fraction of 5 percent to 20 percent, fixing the volume by using water, for example, fixing the volume to 500mL, adjusting according to actual requirements, and uniformly mixing;
preparation of a solution of naphthylethylenediamine dihydrochloride: dissolving 0.2g to 2.0g of 1-naphthylethylenediamine dihydrochloride in 500mL (which can be adjusted according to actual requirements) of water, and uniformly mixing;
preparation of cadmium chloride solution: weighing 5-50 g of cadmium chloride, dissolving in water, and uniformly mixing; also included, is a nitrate standard solution: GBW (E)081697,100.0 mg/L; nitrate nitrogen standard use solution: GBW 08634-GBW 08637 series;
the method comprises the following steps:
step S1, adding ammonium chloride solution with a set volume into a water sample with a certain volume;
step S2, the nitrate is quantitatively reduced into nitrite through cadmium zinc plating sheets;
step S3, determining the total nitrite content in the sample by a diazo-azo method;
and step S4, subtracting the nitrite concentration in the sample from the total nitrite content determined in the step S3 to obtain the nitrate content.
Further, in step S1, preparing an ammonium chloride solution: 5g to 500g of ammonium chloride is weighed and dissolved in 500mL to 2000mL of water, such as 800mL, 1000mL and the like, and mixed evenly.
As a preferable embodiment of the present invention, the zinc sheet is prepared by the following steps: polishing the surface of the high-purity zinc sheet by using metallographic abrasive paper with a grain size of more than 200 meshes, wiping the surface by using gauze, cutting the high-purity zinc sheet into a rectangular zinc sheet with the size of 5cm multiplied by 6cm, and rolling the zinc sheet into a zinc roll with the inner diameter of 1.0cm and the length of 5 cm. It will be appreciated that the parameters of the zinc sheet and the zinc coil are not limited thereto, and those skilled in the art can adjust them based on the above requirements, for example, the error may be 10%.
As a preferable embodiment of the present invention, a set amount of water sample, for example, 50mL, 60mL, 70mL, is added into a glass ware, 0.2 to 5.0mL of ammonium chloride solution is added, mixed, the above zinc roll is added, 0.5mL to 5.0mL of cadmium chloride solution is added, the mixture is rapidly placed on an oscillator to oscillate for a first time, for example, 10 to 20min, or 15min, etc., after oscillating, the zinc is rapidly wound out, sulfanilamide solution is added, the mixture is left for a second time, for example, 3 to 10min, or 5min, etc., then naphthalene-ethylene diamine dihydrochloride solution equal to the sulfanilamide solution is added, the mixture is left for a third time, for example, 10 to 30min, or 15min, 20min, etc., after the color is stable; after the color stabilized, the absorbance was measured with a visible spectrophotometer.
The experimental result shows that at normal temperature, the experimental conditions of the nitrate standard solution with the concentration of 0.200mg/L prepared by deionized water, such as the size of a zinc sheet, the reduction time, the dosage of the ammonium chloride solution and the like, are optimized, and the optimal conditions of the test are determined by taking the reduction rate of the nitrate as an index: for 50mL of sample, the size of the zinc plate is 5cm multiplied by 6cm, the dosage of the ammonium chloride solution is 1.0mL, the oscillation frequency is 180 times/min, and the reduction time is 15 min.
For a better understanding of the invention, the following three sets of working curves were made in different ways, as shown in fig. 1:
working curve I: the method is characterized in that GBW 08634-GBW 08637 series standard solutions with the salinity of 30.5 serving as matrixes are used, NH4Cl solution is not added in the reduction process, a working curve is made according to ocean survey specifications, the regression equation A is 4.5958C +0.0177, and the correlation coefficient R is 0.9991. Wherein A is absorbance, and C is nitrate nitrogen concentration (mg/L);
and a working curve II: adding 1.0mL of NH4Cl solution in GBW 08634-GBW 08637 series standard solutions with salinity of 30.5 as a matrix in a reduction process to obtain a regression equation A of 5.6621C +0.0031 and a correlation coefficient R of 0.9999;
working curve III: nitrate standard solution (gbw (e)081698) with concentration of 100.mg/L was prepared into a series of working solutions with concentrations of 0.000, 0.020, 0.040, 0.080, 0.100, and 0.200 μ g/L in pure water, and 1.0ml of nh4Cl solution was added during the reduction process to prepare a working curve, and regression equation a was 5.7596C +0.0005 and R was 0.9998 were obtained.
Comparing the working curve II with the working curve III, the goodness of fit of the working curve II and the working curve III is very high, the relative deviation of the slope is only 1.7%, which shows that the influence of the salt effect of nitrate reduction is eliminated after the ammonium chloride solution is added, the slope of the working curve III is improved by nearly 15% compared with that of the working curve I, and the addition of the ammonium chloride is beneficial to improving the reduction rate and the sensitivity of the zinc-cadmium reduction nitrate.
For better understanding of the present invention, the reduction rate and the relative variation coefficient (RSD) were calculated by performing 10 parallel tests according to the optimized experimental method with 0.200mg/L nitrate solution, and the actual measurement value was calculated by the linear regression equation formula of the working curve ii, and the RSD was 2.1% (n-10, 0.200mg/L) as shown in fig. 2.
In order to better understand the influence of salinity on the nitrate reduction rate, in the experiment, artificial seawater with salinity of 35 is diluted to artificial seawater with salinity of 0, 7, 14, 21, 28 and 35 respectively, nitrate solutions with concentration of 0.200mg/L are prepared, 50.0mL samples are taken respectively, 1.0mL ammonium chloride solution is added, and then zinc-cadmium reduction is carried out for three times. The result shows that under the condition of the method, the reduction rate of the nitrate is between 94.7 and 102 percent, the reduction rate is stable and is independent of the salinity of the sample, and the influence of the salt effect of the traditional zinc-cadmium reduction method is eliminated, as shown in figure 3, wherein:
r-nitrate reduction rate.
For better measurement, the surface of the zinc sheet is activated by the invention, and the zinc coil containing 5.0mL of (1+6) HCl and 5.0mL of NH is examined in the experiment4Cl, 5.0mL of NH4Effect of activation treatment in three solutions of AC-HAC on the reduction ratio of NO3-N standard use solution of 0.2mg/L without salinity. The results show that after the surface of the zinc sheet is subjected to activation treatment by three different solutions, the reduction rate of the nitrate is improved to 20-30% of that after treatment from about 10% of the zinc sheet without activation treatment. The method is favorable for removing oxides and basic zinc carbonate on the surface of the zinc sheet under the acidic condition, the surface of the zinc sheet is clean, and the cadmium metal is more easily plated on the surface of the zinc sheet in the reduction reaction to promote the reduction of nitrate.
The influence of the ammonium chloride on cadmium plating of the zinc sheet is tested, and the test result is as follows: observing the surface of the cadmium-plated zinc sheet after the reduction of zinc and cadmium, wherein when no ammonium chloride participates, the cadmium particles 10 on the surface of the zinc sheet are thicker and darker in color; after the ammonium chloride is added, the cadmium particles 10 on the surface of the zinc sheet are fine and uniformly distributed, and the color of the zinc sheet is grey white. The surface of the zinc sheet is further scanned by an electron microscope (magnification is 500 times), the distribution result of cadmium particles shows obvious difference as shown in figure 4, and the distribution of cadmium particles 10 is not uniform and the accumulation phenomenon occurs when no ammonium chloride exists in the reduction process; after the ammonium chloride is added, the cadmium particles 10 are uniformly distributed on the surface of the zinc sheet, and the particles are finer.
In order to better understand the present invention, it is further illustrated by the chemical reaction formula below.
Cd2++Zn＝Zn2++Cd (1)
Cd+NO3 -+H2O＝Cd(OH)2+NO2 - (2)
NH4 ++Zn(OH)2＝NH3·H2O+Zn2+ (5)
NH4 ++Cd(OH)2＝NH3·H2O+Cd2+ (6)
As is clear from the formulae (3) to (6), the pH of the solution decreases due to the hydrolysis of zinc and cadmium ions during the nitrate reduction, while the presence of ammonium ions inhibits insoluble Zn (OH)2、Cd(OH)2Thereby avoiding Zn (OH)2、Cd(OH)2The accumulation on the surface of the zinc sheet is beneficial to the improvement of the nitrate reduction rate. Experiments also show that for the seawater sample with the pH value of 8.26, the pH value is reduced to 7.39 and is reduced by 0.87 pH units when no ammonium chloride participates in zinc-cadmium reduction; after 1.0mL of ammonium chloride solution is added, the pH value of the seawater sample is reduced from 8.26 to 7.29, and the pH value is increased to 7.66 after reduction reaction, which shows that the ammonium chloride can effectively inhibit the hydrolysis of zinc and cadmium ions.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. A detection method of nitrate in water quality based on zinc-cadmium reduction salt-free effect comprises the preparation of sulfanilamide solution, naphthylethylenediamine dihydrochloride solution and cadmium chloride solution, a visible spectrophotometer, an oscillator and a common laboratory glassware;
preparation of a sulfanilamide solution: weighing 1.0g to 10g of sulfanilamide, dissolving in a hydrochloric acid solution with the volume fraction of 5 percent to 20 percent, fixing the volume by using water, and uniformly mixing;
preparation of a solution of naphthylethylenediamine dihydrochloride: dissolving 0.2g to 2.0g of 1-naphthylethylenediamine dihydrochloride in water, and uniformly mixing;
preparation of cadmium chloride solution: weighing 5-50 g of cadmium chloride, dissolving in water, and uniformly mixing; also included, is a nitrate standard solution: GBW (E)081697,100.0 mg/L; nitrate nitrogen standard use solution: GBW 08634-GBW 08637 series;
the method is suitable for detecting the nitrate content in tap water, surface water, estuary water and seawater, and comprises the following steps:
step S1, adding ammonium chloride solution with a set volume into a water sample with a certain volume; preparing the ammonium chloride solution: weighing 5g to 500g of ammonium chloride, dissolving in 500mL to 2000mL of water, and uniformly mixing;
step S2, nitrate is quantitatively reduced into nitrite through cadmium-plated zinc sheets, and the cadmium-plated zinc sheets are prepared from zinc sheets after activation treatment under acidic conditions;
step S3, determining the total nitrite content in the sample by a diazo-azo method;
and step S4, subtracting the nitrite concentration in the sample from the total nitrite content determined in the step S3 to obtain the nitrate content.
2. The method for detecting nitrate in water based on zinc-cadmium reduction salt-free effect according to claim 1, further comprising the following steps: polishing the surface of the high-purity zinc sheet by using metallographic abrasive paper with more than 200 meshes, wiping the surface by using gauze, cutting the high-purity zinc sheet into a rectangular zinc sheet, and rolling the zinc sheet into a zinc roll.
3. The method for detecting nitrate in water based on zinc-cadmium reduction salt-free effect as claimed in claim 2, wherein a set amount of water sample is taken into a glassware, 0.2mL to 5.0mL of ammonium chloride solution is added, mixed uniformly, the zinc roll is added, 0.5mL to 5.0mL of cadmium chloride solution is added, the container is rapidly placed on an oscillator to oscillate for the first time, the zinc is rapidly rolled out after oscillation, sulfanilamide solution is added, the mixture is placed for the second time after mixing uniformly, naphthalene-substituted ethylenediamine dihydrochloride solution with the same amount as the sulfanilamide solution is added, the mixture is placed for the third time after mixing uniformly, and the color is stabilized; after the color stabilized, the absorbance was measured with a visible spectrophotometer.
4. The method for detecting nitrate in water based on zinc-cadmium reduction salt-free effect as claimed in claim 3, wherein the absorbance is measured at 543nm on the visible spectrophotometer using a 2cm cuvette with water as reference.
5. The method for detecting nitrate in water based on zinc-cadmium reduction salt-free effect according to claim 3, wherein the first time is 10-20 min, the second time is 3-10 min, and the third time is 10-30 min.
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| CN111521573A (en) * | 2020-04-29 | 2020-08-11 | 山东省科学院海洋仪器仪表研究所 | Reduction method for reducing nitrate into nitrite in water and application of reduction method in detection of nitrate content in water |
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| CN111521573A (en) * | 2020-04-29 | 2020-08-11 | 山东省科学院海洋仪器仪表研究所 | Reduction method for reducing nitrate into nitrite in water and application of reduction method in detection of nitrate content in water |
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