Method for measuring trace heavy metal pentavalent antimony in water

Abstract

The invention discloses a green detection method for determining trace heavy metal ion pentavalent antimony-Sb (V) in water based on a rhodamine B-cloud point extraction-atomic furnace graphite absorption method. The rhodamine B is used as a complexing agent of Sb (V), so that the color development is sensitive, and the complexing is stable. According to the method, the nonionic surfactant Triton X-114 is used as the extraction agent, the cloud point temperature is low, a complex can be efficiently extracted, a micelle phase is formed, the extraction agent is easily and effectively separated from a water phase, cloud point extraction is carried out under ultrasonic assistance to enrich and concentrate trace antimony, the enrichment factor is high, matrix interference in a water sample to be detected can be effectively eliminated, and the detection precision of Sb (V) is improved. By adopting a cloud point extraction technology, the use amount of an organic reagent can be effectively reduced, and the waste liquid treatment cost is reduced. According to the method, other oxidation methods can be combined, total antimony can be measured based on complexing color development of Sb (V), valence state distribution of free antimony can also be measured, and the method has wide applicability.

Description

Technical Field

[0001] The invention relates to the technical field of water quality detection, in particular to a method for determining trace amounts of heavy metal pentavalent antimony in water, and in particular to a green detection method for determining trace amounts of heavy metal ions pentavalent antimony-Sb(V) in water based on rhodamine B-cloud point extraction-graphite furnace atomic absorption spectrometry. Background Art

[0002] Antimony (Sb) is a heavy metal with a silver luster. It is a semi-volatile element and exists mainly in the form of the sulfide ore stibnite (SB2S3) in nature. Antimony has high application value in both industrial production and materials. As the value of antimony materials is developed, its demand and usage are gradually increasing, but the environmental pollution problems it brings are also becoming more and more serious. After the discarded antimony materials enter the water environment, due to its difficulty in natural degradation, antimony will gradually enter various organisms through the water cycle. At the same time, the biomagnification of the food chain will cause antimony to be enriched in the human body. The toxicity mechanism of antimony is similar to that of arsenic. After entering the human body, it damages the heart, liver, kidney and nervous system by affecting the activity of biological enzymes, especially cardiac toxicity. The World Health Organization (WHO) stipulates that the antimony content in drinking water should not exceed 5μg / L, the United States stipulates that it should not exceed 6μg / L, and Japan stipulates that the maximum allowable concentration in water is 2μg / L. my country's GB3838-2002 "Surface Water Environmental Quality Standard" stipulates that the antimony content in drinking water sources should not exceed 5μg / L. As the largest antimony reserve and exporter, my country faces a high risk of antimony pollution. Therefore, pollution monitoring and concentration detection of antimony in water bodies are of great practical significance.

[0003] There are many methods for detecting antimony in water, which can be roughly divided into atomic fluorescence spectrometry (AFS), atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), electrochemical analysis and spectrophotometry. Among them, AFS, AAS, ICP-MS and other methods have high detection accuracy and low detection limit, but the instruments used are expensive and require high sample pretreatment. During the use of electrochemical analysis, factors such as the influence of coexisting ions and the state of the electrode surface must be considered. The uncertainty of the electrode state limits the application potential of this method in continuous detection. However, most detection methods are based on the detection of Sb(III). The discharged waste liquid or waste gas contains a large amount of Sb(III), which is much more toxic than Sb(V) and brings certain pressure to the environment. Therefore, it is of great significance to develop a safe, environmentally friendly, economical, efficient and green Sb(V) detection method. Summary of the invention

[0004] The present invention provides a method for determining trace amounts of heavy metal pentavalent antimony in water, which mainly comprises the following steps:

[0005] Step S1: complexation color development: the water sample to be tested is acidified in an environment with a pH value less than 3, and Sb(V) in the water sample to be tested is acidified to form complex anions; after the complexing agent Rhodamine B solution is added dropwise, the complex anions and Rhodamine B cations undergo complexation reaction to form a hydrophobic complex for color development;

[0006] Step S2: turbidity point extraction: after the complexation color development is stable, a quantitative concentration of non-ionic surfactant Triton X-114 is added, and turbidity point extraction is performed under the conditions of ultrasound assistance and constant turbidity point temperature; the constant turbidity point temperature is higher than the turbidity point of the non-ionic surfactant Triton X-114;

[0007] Step S3: Centrifugal separation: After the extraction is stabilized for a certain period of time, the aqueous phase and the antimony-containing micelle phase are separated by centrifugation;

[0008] Step S4: AAS determination: dilute the micellar phase obtained by centrifugation and send it into a graphite furnace atomic absorption sampler to measure its absorbance to obtain the net absorbance value of the water sample to be measured;

[0009] Step S5: Sb(V) detection: Substitute the net absorbance value of the water sample to be tested into the Sb(V) working curve established by measuring a standard solution of known concentration to obtain the Sb(V) concentration value in the water sample to be tested.

[0010] Furthermore, the specific process of step S1 is as follows:

[0011] (a) Take a 15 mL centrifuge tube and add 5.00 mL of the water sample to be tested. The water sample to be tested is preferably acidified with concentrated hydrochloric acid. Use a pipette to accurately pipette 2.00 to 5.00 mL of concentrated hydrochloric acid, preferably 3.33 mL, and then dilute to 10 mL with deionized water and shake well. At this time, the hydrochloric acid concentration in the 10 mL sample is about 3.0 to 5.0 mol / L, preferably 4.0 mol / L.

[0012] (b) Continue to add 0.20 mL of a 100-300 mg / L (preferably 200 mg / L) rhodamine B solution dropwise into the centrifuge tube and shake for 30 seconds.

[0013] Furthermore, the specific process of step S2 is as follows:

[0014] (a) After shaking, quickly add 2.00 mL of a 1% to 3% Triton-114 solution, preferably 2%, and place in an ultrasonicator for ultrasonic treatment for 30 seconds. The mass percentage concentration of the TritonX-114 solution is selected from a concentration between 1% and 3%.

[0015] (b) placing the ultrasonically treated centrifuge tube in a constant temperature water bath at a temperature of 30 to 60° C., preferably 45° C., and heating the tube. After balancing for 10 to 20 minutes, preferably 15 minutes, the tube is taken out; the constant cloud point temperature is selected from a temperature value between 30 and 60° C.

[0016] Furthermore, in step S2, the concentration of the TritonX-114 solution is selected from a concentration between 1% and 3%; and the constant cloud point temperature is selected from a temperature value between 30 and 60°C.

[0017] Furthermore, in step S2, the constant turbidity point equilibrium time is 10 to 20 minutes; in step S3, the centrifugation condition is to centrifuge at a speed of 3500 r / min for 5 minutes until the aqueous phase and the micelle phase are completely separated, and then kept in ice water for 5 minutes after centrifugation.

[0018] Furthermore, the specific process of step S3 is as follows:

[0019] (a) Place the centrifuge tube in a centrifuge and centrifuge until the aqueous phase and the micelle phase are completely separated. Then take it out and keep it in ice water for 5 minutes to increase the viscosity of the micelle phase to facilitate separation. Use the pouring method to discard the upper aqueous phase.

[0020] Furthermore, in step S4, the absorbance is measured using a graphite furnace atomic absorption injector; the graphite tube uses an As-1-2 antimony element lamp, the sensitive line wavelength is 217nm, the lamp current is 13mA, and the injection volume is 20μL.

[0021] Furthermore, in step S4, the net absorbance value is the difference between the absorbance value obtained by detecting the micellar phase and the absorbance value obtained by detecting the blank solution according to steps S1, S2, S3, and S4; the blank solution is deionized water.

[0022] Furthermore, the specific process of step S4 is as follows:

[0023] (a) After adding 100 μL of anhydrous ethanol to the lower surfactant-rich phase, i.e., the micelle phase, to dilute its viscosity, the sample was placed in a graphite furnace atomic absorption injector to measure its absorbance. The graphite tube used was a high-density graphite tube, an As-1-2 antimony element lamp, a sensitive line wavelength of 217 nm, a lamp current of 13 mA, and an injection volume of 20 μL.

[0024] Furthermore, in step S5, the standard solution is a potassium hexahydroxyantimonate standard solution.

[0025] Furthermore, in step S5, the Sb(V) working curve is obtained by linearly fitting the concentration values ​​and net absorbance values ​​of the standard solution Sb(V) according to the net absorbance values ​​obtained in steps S1, S2, S3, and S4 for multiple groups of standard solutions with known gradient concentrations.

[0026] Furthermore, the net absorbance value is an average net absorbance value obtained by averaging more than three net absorbance values.

[0027] Furthermore, in step S1, the water sample to be tested is acidified with concentrated hydrochloric acid. In the acidic solution, Sb(V) can quickly react with Cl- to form a [SbCl6]- complex anion, and the basic dye Rhodamine B reacts with RhB in a strong polar solvent. +- Ions exist, when pH is less than 3, RhB +- The carboxyl anion captures a proton to become RhB + , this ion can react with [SbCl6] - The hydrophobic complex RhB[Sb(Cl)6] is formed. 5+ With Cl - The formed complex ions can be complexed with the basic dye molecules again, while the other valence states of antimony will not have such a reaction. The selective reaction is used to realize the complexation and color development of trace Sb(V). The reaction principle is shown in formulas (1) and (2):

[0028] Sb 5+ +6Cl - =[SbCl6] - (1)

[0029] [SbCl6]-+RhB + =[RhB][SbCl6] (2)

[0030] When the temperature is higher than the cloud point of the nonionic surfactant, the complex [RhB][SbCl6] will be wrapped by a large number of micelles formed, and then separated from the water phase into two phases. After centrifugation, Sb(V) is enriched in the lower micelle-rich phase, thereby achieving selective enrichment and separation of Sb(V). After the separated micelle phase is diluted, it is measured by graphite furnace atomic absorption spectrometry, and the working curve established after the standard solution is measured can be used to obtain the Sb(V) concentration value in the water sample to be tested.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) In the complexation color development, rhodamine B is used as the complexing agent of Sb(V), which has sensitive color development and strong stability of the complex produced; in the turbidity point extraction, the surfactant Triton X-114 is used as the extractant, which has a low turbidity point temperature and can efficiently extract the complex and form a micellar phase (organic phase), which can be effectively separated from the aqueous phase. The two together ensure a high recovery rate of Sb(V);

[0033] (2) The turbidity point extraction method can enrich and concentrate trace heavy metal ions with a high enrichment factor. It can also effectively eliminate matrix interference in the water sample to be tested and improve the detection accuracy of Sb(V);

[0034] (3) Ultrasonic-assisted turbidity point extraction is used to enrich, concentrate and separate complexes in water, which can effectively reduce the amount of organic reagents used, reduce the risks of the extraction process and the cost of waste liquid treatment;

[0035] (4) Based on Sb(V) detection, compared with the highly toxic Sb(III), the complex product of Sb(V) has low toxicity and is safer and more environmentally friendly. In addition, the low-valent Sb can be completely oxidized to the high-valent Sb(V) to determine the total antimony (TSb), and the free antimony valence distribution (Sb(III), Sb(V)) can also be determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the steps of the method of the present invention;

[0037] Figure 2 It is the Sb(V) working curve of the present invention. DETAILED DESCRIPTION

[0038] In order to make the public have a thorough understanding of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments, but it should not be understood as limiting the present invention. The present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention, and those skilled in the art can fully understand the present invention without these detailed descriptions. The reagents, materials, etc. used in the following examples can all be obtained from commercial sources.

[0039] See also Figure 1-Figure 2 The green detection method for determining trace heavy metal ions pentavalent antimony-Sb(V) in water based on rhodamine B-cloud point extraction-graphite furnace atomic absorption spectrometry includes the following steps:

[0040] Reagent preparation:

[0041] 1. Preparation of Rhodamine B solution:

[0042] Weigh 0.1000 g of rhodamine B (RhB) and transfer it to a 50 mL brown volumetric flask, make up to volume and shake well to prepare a RhB stock solution with a concentration of 2000 mg / L.

[0043] The RhB stock solution was diluted stepwise with deionized water to obtain a Rhodamine B working solution with a concentration of 50 mg / L to 1000 mg / L.

[0044] 2. Preparation of Triton X-114 solution:

[0045] Weigh 0.2000g, 0.5000g, 1.0000g, 2.0000g, 3.0000g, 4.0000g and 5.0000g of TritonX-114 in a 150mL glass beaker, add 100mL of deionized water to the beaker respectively, stir evenly on a magnetic stirrer and let stand until clear, and prepare Triton X-114 solutions with gradient concentrations of 0.2%, 0.5%, 1%, 2%, 3%, 4% and 5% respectively. Triton X-114 is a nonionic surfactant, and its chemical name in Chinese is: polyoxyethylene mono-tert-octylphenyl ether / diethylene glycol mono[(1,1,3,3-tetramethylbutyl)phenyl]ether / polyoxyethylene octylphenol ether; chemical identification code CAS number is 9036-19-5; molecular formula: C 18 H 30 O3 can be purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0046] 3. Preparation of Sb(V) solution:

[0047] Weigh 0.1078 g of potassium hexahydroxyantimonate into a beaker, dissolve it with a small amount of deionized water, transfer it to a 50 mL volumetric flask and make up to volume with deionized water to prepare a Sb(V) stock solution with a concentration of 1000 mg / L.

[0048] Pipette 0.10 mL of Sb(V) stock solution into a 100 mL volumetric flask, dilute to the mark with deionized water and shake well to prepare a Sb(V) intermediate solution with a concentration of 1 mg / L.

[0049] Pipette 1.00 mL of Sb(V) intermediate solution into a 50 mL volumetric flask, dilute to the mark with deionized water and shake well to prepare a Sb(V) working solution with a concentration of 20 μg / L.

[0050] 4. Detection method for trace heavy metal ion pentavalent antimony - Sb(V) in water based on rhodamine B-cloud point extraction-graphite furnace atomic absorption spectrometry

[0051] (1) Complexation and color development

[0052] (a) Take a 15mL centrifuge tube, add 5.00mL of blank solution, standard solution (Sb(V) working solution) or water sample to be tested, accurately pipette 3.33mL of concentrated hydrochloric acid, and then dilute to 10mL with deionized water and shake well. At this time, the concentration of hydrochloric acid in the 10mL sample is about 4.0mol / L.

[0053] (b) Continue to add 0.20 mL of 200 mg / L Rhodamine B solution into the centrifuge tube and shake for 30 seconds.

[0054] (2) Cloud point extraction

[0055] (a) After shaking, quickly add 2.00 mL of 2% Triton-114 solution and place in an ultrasonicator for 30 seconds.

[0056] (b) Place the ultrasonically treated centrifuge tube in a constant temperature water bath at 45°C and heat it. Take it out after balancing for 15 minutes.

[0057] (3) Centrifugal separation

[0058] (a) Place the centrifuge tube in a centrifuge and centrifuge at 3500 r / min for 5 min until the aqueous phase and the micelle phase are completely separated. Then take it out and keep it in ice water for 5 min to increase the viscosity of the micelle phase to facilitate separation. Use the pouring method to discard the upper aqueous phase.

[0059] (4) AAS determination

[0060] (a) After adding 100 μL of anhydrous ethanol to the lower surfactant-rich phase, i.e., the micellar phase (about 400 μL), to dilute its viscosity, the phase was placed in a graphite furnace atomic absorption injector to measure its absorbance.

[0061] (b) Graphite tube uses high-density graphite tube, antimony element lamp model As-1-2, sensitive line wavelength 217nm, lamp current 13mA. The graphite furnace heating program and photometer test conditions are set based on the national standard HJ 1047-2019 combined with the instrument preset parameters. The specific heating steps are shown in Table 1.

[0062] Table 1 Graphite furnace heating program for determination of antimony

[0063]

[0064]

[0065] (5) Establish Sb(V) working curve

[0066] The basic principle of the detection of Sb(V) based on rhodamine B-cloud point extraction-atomic absorption spectrophotometry in the present invention is to establish a linear model between the absorbance of the micellar phase solution after extraction and the Sb(V) concentration. A gradient concentration antimony standard solution is prepared, and extraction is performed according to the preferred cloud point extraction process conditions and the absorbance of the micellar phase solution is detected. S At the same time, use deionized water as a blank to replace the sample for a blank experiment, record the blank absorbance Ab, and the difference between the two is the net absorbance Ar.

[0067] Use Sb(V) intermediate solution to prepare Sb(V) standard solutions with concentrations of 1 to 25 μg / L, namely Sb(V) working solutions. Take 5 mL of the above standard solutions in centrifuge tubes for extraction, and calculate the net absorbance A after determination by graphite furnace atomic absorption spectrometry.r , Sb(V) working curve data are shown in Table 2.

[0068]

[0069] Table 2 Sb(V) working curve data

[0070] The working curve drawn according to the data in Table 2 is as follows Figure 2 The working curve equation of the determination of Sb(V) by rhodamine B-turbidity point extraction-graphite furnace atomic absorption spectrometry was obtained by fitting the data in Table 2 in the range of 1-25 μg / L: y=0.0052x+0.0055, (R 2 =0.9978, R 2 is the coefficient of determination. The closer the value is to 1, the better the fit between the model and the data, which means that the model can explain most of the data variability), where x represents the concentration of Sb(V) and y is the net absorbance measured after extraction.

[0071] (6) Rhodamine B-cloud point extraction-graphite furnace atomic absorption spectrometry performance verification of Sb(V)

[0072] The absorbance of the micelle-rich phase measured after the sample was extracted under optimized conditions is A s , the absorbance measured after extraction with deionized water instead of sample is blank A b , the determination was performed in parallel 8 times, and the experimental results are shown in Table 3. According to the content requirements of my country's national standard HJ 168-2020, the detection limit of rhodamine B-turbidity point extraction-graphite furnace atomic absorption spectrometry was calculated to be MDL≈0.5544μg / L.

[0073] Table 3 Blank test results

[0074]

[0075] Sb(V) solutions with concentrations of 4μg / L and 16μg / L were further prepared. The net absorbance was determined and the concentration was calculated according to the optimized rhodamine B-turbidity point extraction-graphite furnace atomic absorption method, and the determination was performed in parallel 6 times. The RSD and average relative error of the 6 results were calculated, and the maximum RSD was used as the precision, and the maximum average relative error was used as the accuracy. The test results are shown in Table 4.

[0076] Table 4 Rhodamine B-cloud point extraction-graphite furnace atomic absorption spectrometry accuracy test

[0077]

[0078]

[0079] According to the results in Table 4, when the concentration of Sb(V) was within the range of 1 to 25 μg / L, the precision of the rhodamine B-turbidity point extraction-graphite furnace atomic absorption spectrometry was 3.33% and the accuracy was 1.73%.

[0080] Although the embodiments are described and explained separately above, they involve some common technologies. For those of ordinary skill in the art, it can be understood that these embodiments can be modified without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the attached claims and their equivalents. The above only describes the preferred embodiments of the present invention, but it cannot be understood as a limitation on the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. In short, all changes made within the scope of protection of the independent claims of the present invention are within the scope of protection of the present invention.

Claims

1. A method for determining trace amounts of heavy metal pentavalent antimony in water, characterized in that: The following steps are involved: Step S1: complexation color development: the water sample to be tested is acidified in an environment with a pH value less than 3, and Sb(V) in the water sample to be tested is acidified to form complex anions; after the complexing agent Rhodamine B solution is added dropwise, the complex anions and Rhodamine B cations undergo complexation reaction to form a hydrophobic complex for color development; Step S2: Cloud point extraction: After the complexation color is stable, a quantitative concentration of non-ionic surfactant Triton X-114 is added, and cloud point extraction is performed under the conditions of ultrasound assistance and constant cloud point temperature; the constant cloud point temperature is required to be higher than the cloud point of the non-ionic surfactant Triton X-114; Step S3: Centrifugal separation: After the extraction is stabilized for a certain period of time, the aqueous phase and the antimony-containing micelle phase are separated by centrifugation; Step S4: AAS determination: dilute the micellar phase obtained by centrifugation and send it into a graphite furnace atomic absorption sampler to measure its absorbance to obtain the net absorbance value of the water sample to be measured; Step S5: Sb(V) detection: Substitute the net absorbance value of the water sample to be tested into the Sb(V) working curve established by measuring a standard solution of known concentration to obtain the Sb(V) concentration value in the water sample to be tested.

2. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S1, the water sample to be tested is acidified with concentrated hydrochloric acid, and the concentration of the hydrochloric acid after acidification is 3.0-5.0 mol / L; the concentration of the rhodamine B solution is 100-300 mg / L.

3. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S2, the mass percentage concentration of the TritonX-114 solution is selected from a concentration between 1% and 3%; and the constant cloud point temperature is selected from a temperature value between 30 and 60°C.

4. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S2, the constant turbidity point equilibrium time is 10 to 20 minutes; in step S3, the centrifugation condition is to centrifuge at a speed of 3500 r / min for 5 minutes until the aqueous phase and the micelle phase are completely separated, and then keep in ice water for 5 minutes after centrifugation.

5. The method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: During dilution, anhydrous ethanol is used to dilute the micelle phase.

6. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S4, the absorbance is measured using a graphite furnace atomic absorption injector; the graphite tube uses an As-1-2 antimony element lamp, the sensitive line wavelength is 217nm, the lamp current is 13mA, and the injection volume is 20μL.

7. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S4, the net absorbance value is the difference between the absorbance value obtained by detecting the micellar phase and the absorbance value obtained by detecting the blank solution according to steps S1, S2, S3, and S4; the blank solution is deionized water.

8. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S5, the standard solution is a potassium hexahydroxyantimonate standard solution.

9. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1, characterized in that: In step S5, the Sb(V) working curve is obtained by linearly fitting the net absorbance values ​​of multiple groups of standard solutions with known gradient concentrations according to steps S1, S2, S3, and S4 using the Sb(V) concentration values ​​and net absorbance values ​​of the standard solutions.

10. A method for determining trace amounts of heavy metal pentavalent antimony in water according to claim 1 or 9, characterized in that: The net absorbance value is an average net absorbance value obtained by averaging more than three net absorbance values.

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