A method for speciation determination of ultra-trace inorganic arsenic in water

Abstract

The present invention relates to the technical field of water environment analysis and monitoring, and specifically to a method for morphological determination of ultra-trace inorganic arsenic in water, the steps of which are: adding porous nano zinc oxide to a water sample to enrich ultra-trace arsenic; removing the aqueous phase and collecting the solid phase; adding the solid phase to a hydrochloric acid solution and dissolving it to a constant volume; using hydride generation atomic fluorescence spectrometry to determine the content of trivalent arsenic ions As(III); repeating the first and second steps, and adding the obtained solid phase to a hydrochloric acid solution to dissolve, adding a reducing agent thiourea, and then using a hydrochloric acid solution to constant volume; using hydride generation atomic fluorescence spectrometry to determine the content of inorganic arsenic ions; subtracting the concentration of trivalent arsenic from the total arsenic concentration to obtain the concentration of pentavalent arsenic ions in the water sample. The method of using porous nano zinc oxide-hydride atomic fluorescence spectrometry to determine ultra-trace arsenic in water is enriched, separated and morphologically determined, without the need to use organic solvents and desorption, and does not interfere with subsequent atomic fluorescence determination.

Description

Technical Field

[0001] The invention relates to the technical field of water environment analysis and monitoring, and in particular to a method for determining the form of ultra-trace inorganic arsenic in water. Background Art

[0002] Arsenic is an element widely distributed in nature. The concentration of arsenic in natural water varies greatly depending on the water source and geographical conditions. The arsenic concentration in fresh water is 0.2-230 g / L, with an average of 0.5 g / L. The arsenic concentration in seawater is 1-8 g / L, with an average of 3.7 g / L. Natural water is dominated by inorganic arsenic, including trivalent arsenic As(III) and pentavalent arsenic As(V). Trivalent arsenic As(III) is composed of As(OH)3, As(OH)4 - 、AsO2OH 2- and AsO3 3- Composition, pentavalent arsenic As(V) is composed of H2AsO4 in water - ,HAsO4 2- 、AsO4 3- Composition. Domestic data surveys show that the cancer rate in patients with chronic arsenic poisoning is as high as 15%. With the research and understanding of the toxicity of arsenic and its compounds, some countries and regions have taken some measures to limit the production and use of arsenic-containing materials. The treatment of arsenic-containing water bodies has also attracted more and more attention. The analysis of arsenic in environmental water bodies has also become an important topic. Since arsenic exists in many forms, only measuring the total arsenic content in the sample cannot accurately describe the arsenic exposure level and the environmental effects of arsenic. Therefore, the morphological analysis of arsenic is very important. Establishing a morphological analysis method for arsenic in water bodies is of great significance for evaluating the environmental and ecological effects of arsenic, studying the migration and transformation of arsenic, and selecting arsenic-containing wastewater treatment solutions.

[0003] The total arsenic content in natural environmental water samples is low, and the content of various forms is even lower. It is difficult to directly determine the arsenic form with general detection methods. Therefore, combining efficient separation and enrichment technology with highly sensitive detection methods is an effective method for ultra-trace arsenic form analysis. The combined technology is not only more selective than a single technology, but also greatly reduces the method detection limit, and can be more effectively used for the form analysis of trace elements in water.

[0004] Liang used the separation method of dispersed liquid-liquid microextraction with graphite furnace atomic absorption (DLLME-GFAAS) to analyze and determine As(III) and As(V) in lake water, river water, and tap water. At pH 3-5, As(III) in the sample can be extracted by tetrachloromethane, but As(V) cannot, so the two can be separated. After the sample is centrifuged, the extract phase is directly measured by graphite furnace atomic absorption to obtain the As(III) content. After the sample is reduced with sodium thiosulfate and potassium iodide, the total arsenic content can be measured. The difference between the two is the As(V) content. The detection limit of As(III) is 0.036g / L, and the water sample recovery rate is between 96% and 103%. Murata uses the co-precipitation method to separate As(III) and As(V). When pH = 5.3, As(III) in the water sample can form a co-precipitation with copper-pyrrolidine (PDC) complex while As(V) cannot. The precipitate enriched with As(III) is dissolved in nitric acid and can be determined by graphite furnace atomic absorption spectrometry. The detection limit of As(III) is 0.034 g / L.

[0005] Although the above method reduces the detection limit of Cd determination, it still requires the use of a large amount of organic solvents, and requires operations such as desorption or extraction before determination, or complex subsequent processing steps such as acid digestion. Summary of the invention

[0006] The purpose of the present invention is to provide a method for the morphological determination of ultra-trace inorganic arsenic in water, which can effectively enrich, separate and morphologically determine the ultra-trace arsenic in water without using an organic solvent and can also achieve the morphological determination of inorganic arsenic.

[0007] The scheme adopted by the present invention to achieve the purpose is: a method for determining the form of ultra-trace inorganic arsenic in water, comprising the following steps:

[0008] (1) adding porous nano zinc oxide to a water sample to be analyzed to enrich ultra-trace arsenic in the water sample at room temperature;

[0009] (2) removing the aqueous phase from the porous nano zinc oxide enriched with ultra-trace arsenic in step (1) by suction filtration, and collecting the solid phase;

[0010] (3) adding the solid phase obtained in step (2) to a hydrochloric acid solution having a volume concentration of 2% to 12%, dissolving the solution and then fixing the volume to obtain a fixed volume solution;

[0011] (4) using citric acid solution as a carrier, and using hydride generation atomic fluorescence spectrometry to determine the content of trivalent arsenic ion As(III) in the fixed volume solution obtained in step (3);

[0012] (5) repeating steps (1) and (2), and dissolving the obtained solid phase in a hydrochloric acid solution having a volume concentration of 10% to 15%, adding a reducing agent, thiourea, and then fixing the volume with a hydrochloric acid solution having a volume concentration of 10% to 20% to obtain a fixed volume solution;

[0013] (6) using hydrochloric acid solution as a carrier, and using hydride generation atomic fluorescence spectrometry to determine the content of inorganic arsenic ions in the fixed volume solution obtained in step (5);

[0014] (7) Subtract the measurement result in step (4) from the measurement result in step (6) to obtain the concentration of pentavalent arsenic ions in the water sample.

[0015] Preferably, in the step (1), the concentration of porous nano zinc oxide after adding the water sample is 0.1-1.0 g / L, and the pH value of the solution is 5.5-8.0.

[0016] Preferably, in the step (1), the preparation method of porous nano zinc oxide is: weigh zinc acetate dihydrate and dissolve it in methanol to obtain a Zn(CH3COO)2-CH3OH solution; separately take potassium hydroxide and dissolve it in methanol to obtain a KOH-CH3OH solution; add the KOH-CH3OH solution to the Zn(CH3COO)2-CH3OH solution under stirring conditions to obtain a mixed solution; reflux the mixed solution at 50-70°C until the reaction is completed, centrifuge the product, collect the solid phase, wash and dry it, and grind the dried product into powder to obtain porous nano zinc oxide.

[0017] Preferably, the solid-liquid ratio of the Zn(CH3COO)2-CH3OH solution is 14.75 g / 60 ml; the solid-liquid ratio of the KOH-CH3OH solution is 7.4 g / 32 ml; and the volume ratio of the KOH-CH3OH solution to the Zn(CH3COO)2-CH3OH solution is 32:64.

[0018] Preferably, in step (1), the enrichment condition is to place it in a constant temperature shaker at 25°C and shake at a speed of 100-350 rpm for 5-30 min.

[0019] Preferably, in step (2), the filter membrane used for filtration is a water-based filter membrane with a pore size less than or equal to 0.45 m.

[0020] Preferably, in step (4), the volume concentration of the citric acid solution is 1%-5%.

[0021] Preferably, in steps (4) and (6), the measurement conditions of hydride atomic fluorescence spectrometry are negative high voltage 280V, argon gas flow rate of 350mL / min, hollow cathode lamp main current of 30mA, auxiliary current of 30mA, and atomic vaporization temperature of 180°C.

[0022] Preferably, in step (5), the amount of thiourea used is 7.5-15 mg / ml.

[0023] Preferably, in step (6), the volume concentration of the hydrochloric acid solution is 1%-5%.

[0024] The present invention has the following advantages and beneficial effects:

[0025] The method of the present invention utilizes the porous nano zinc oxide-hydride atomic fluorescence spectrometry method to effectively enrich, separate and morphologically determine ultra-trace arsenic in water, does not require the use of organic solvents, and the enriched arsenic only needs to be dissolved by a small amount of hydrochloric acid, does not require the use of a desorbent for desorption, and does not interfere with subsequent atomic fluorescence determination, and can achieve morphological analysis of inorganic arsenic ions in various aqueous solutions.

[0026] The method of the present invention first determines the concentration of trivalent arsenic ions (As(III)) in a water sample, and then determines the concentration of total arsenic in the water sample. The difference between the two is the pentavalent arsenic ions (As(V)) in the water. The method is simple, convenient and easy to operate.

[0027] The method of the present invention can achieve the speciation determination of inorganic arsenic by adjusting the reducing agent. Under the condition of 20-fold enrichment, the detection limits of the method for total inorganic arsenic and trivalent arsenic are 0.01 g / L and 0.02 g / L respectively. DETAILED DESCRIPTION

[0028] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0029] Example 1

[0030] Preparation of porous nano zinc oxide (ZnO):

[0031] 14.75 g of zinc acetate dihydrate was weighed and dissolved in 60 mL of methanol to obtain Zn(CH3COO)2-CH3OH. 7.4 g of potassium hydroxide was dissolved in 32 mL of methanol to obtain KOH-CH3OH. 32 mL of KOH-CH3OH solution was slowly added to 60 mL of Zn(CH3COO)2-CH3OH solution under magnetic stirring. The mixed solution was then transferred to a 250 mL round-bottom flask, refluxed in a water bath at 60° C. (the temperature is generally controlled to be 50-70° C., and 60° C. is preferred in this embodiment) for 72 h, and the product was centrifuged at 7000 r / min for 25 min. The product was washed with methanol several times and centrifuged to remove residual potassium hydroxide; finally, dried at 40° C. under vacuum for 6 h; the obtained product was ground into powder using an agate mortar to obtain porous nano zinc oxide.

[0032] A 1000 g / mL As(III) standard solution (GBW08611) was diluted to 0.1 g / L with ultrapure water, 500 mL of the solution was placed in a 1000 mL sample bottle, and the porous nano zinc oxide prepared in this example was added to a concentration of 0.2 g / L. After shaking in a constant temperature shaker at 25°C and 200 r / min for 10 min, the mixture was filtered with a 0.45 m microporous filter membrane, and then the porous nano zinc oxide retained on the filter membrane was washed with a hydrochloric acid solution with a volume concentration of 2% (generally, a hydrochloric acid solution with a volume concentration of 2%-12% was selected, and 2% was preferred in this embodiment). The washing solution was transferred to a 10 mL volumetric flask and fixed to volume with a hydrochloric acid solution with a volume concentration of 2% (enriched 50 times). A citric acid solution with a pH of 4 to 5 and a volume concentration of 1% (generally, a citric acid solution with a volume concentration of 1% to 5%, 1% is preferred in this embodiment) was used as a carrier current to measure the fluorescence value on an atomic fluorescence spectrophotometer. The measuring conditions were a negative high voltage of 280 V, an argon flow rate of 350 mL / min, a main current of a hollow cathode lamp of 30 mA, an auxiliary current of 30 mA, and an atomic vaporization temperature of 180°C. The As(III) concentration after enrichment was calculated by the standard curve method to be 4.94 g / L, and the relative standard deviation was 4.1% (n=3).

[0033] Example 2

[0034] 1000g / mL As(III) standard solution (GBW08611) and 1000g / mL As(V) standard solution (GSB04-1714-2004) were diluted step by step to prepare a mixed solution of 1g / L As(III) and 1g / L As(V). Two 200mL portions of the solution were placed in 250mL sample bottles, and the porous nano zinc oxide (ZnO) prepared in Example 1 was added to a concentration of 0.5g / L, and the mixture was shaken in a constant temperature shaker at 25°C and 250r / min for 20min. One portion was selected and analyzed according to the method in Example 1, and the As(III) concentration was 11.06g / L, with a relative standard deviation of 4.9% (n=3).

[0035] Another sample after shaking was filtered with a 0.45m microporous filter membrane, and then a 12% hydrochloric acid solution (a hydrochloric acid solution with a volume concentration of 10%-20% was generally selected, and 12% was preferred in this embodiment) was used to dissolve the porous nano zinc oxide trapped on the filter membrane, and the leaching solution was transferred to a 10mL colorimetric tube, 0.8mL of 150g / L thiourea was added, and then the volume was fixed to the scale with 12% hydrochloric acid. The fluorescence value was measured on an atomic fluorescence spectrophotometer using a hydrochloric acid solution with a volume concentration of 2% (a hydrochloric acid solution with a volume concentration of 1%-5% was generally selected, and 2% was preferred in this embodiment) as a carrier current, and the measurement conditions were negative high voltage 280V, argon flow rate of 350mL / min, hollow cathode lamp main current of 30mA, auxiliary current of 30mA, and atomic vaporization temperature of 180°C. The total arsenic concentration after enrichment was calculated by the standard curve method to be 20.31g / L, and the relative standard deviation was 3.8% (n=3).

[0036] The difference in the measurement results of the two samples shows that after ten-fold enrichment, the content of pentavalent arsenic in the solution is 9.25 g / L.

[0037] Example 3

[0038] Prepare a 200 mL solution containing 0.5 g / L As(III), 0.5 g / L As(V), 39 mg / L K + , 460mg / L Na + , 40mg / L Ca 2+ , 48mg / L Mg 2+ , 1491mg / L Cl - , 192mg / L SO4 2- , 62mg / L NO3 - , 45g / LF -, used for As(III) enrichment measurement. The porous nano zinc oxide prepared in Example 1 was added to the above solution to a concentration of 0.3 g / L, and after shaking in a constant temperature shaker at 25°C and 300 r / min for 15 min, it was filtered with a 0.22 m microporous filter membrane, and then the porous nano zinc oxide retained on the filter membrane was washed with a hydrochloric acid solution with a volume concentration of 2% (generally, a hydrochloric acid solution with a volume concentration of 2%-12% was selected, and 2% was preferred in this embodiment), and the washed solution was transferred to a 10 mL volumetric flask and fixed to volume with 2% hydrochloric acid (enrichment 20 times). A citric acid solution with a pH value of 4 to 5 and a volume concentration of 1% (a citric acid solution with a volume concentration of 1% to 5% is generally selected, and 1% is preferred in this embodiment) is used as a carrier current to measure the fluorescence value on an atomic fluorescence spectrophotometer. The measuring conditions are a negative high voltage of 280 V, an argon gas flow rate of 350 mL / min, a hollow cathode lamp main current of 30 mA, an auxiliary current of 30 mA, and an atomic vaporization temperature of 180°C. The As(III) concentration after enrichment is calculated by the standard curve method to be 5.03 g / L, and the relative standard deviation is 5.2% (n=3).

[0039] Example 4

[0040] Prepare a 200 mL solution containing 0.25 g / L As(III), 0.25 g / L As(V), 39 mg / L K + , 460mg / L Na + , 40mg / L Ca 2+ , 48mg / L Mg 2+ , 1491mg / L Cl - , 192mg / L SO4 2- , 62mg / L NO3 - , 45g / LF -, used for the enrichment measurement of total inorganic arsenic, the porous nano zinc oxide prepared in Example 1 was added to the above solution to a concentration of 0.3 g / L, and after shaking in a constant temperature shaker at 25°C and 300 r / min for 15 min, it was filtered using a 0.22 m microporous filter membrane, and then a 12% volume fraction hydrochloric acid solution (generally a hydrochloric acid solution with a volume concentration of 10%-20% is selected, and 12% is preferred in this embodiment) was used to dissolve the porous nano zinc oxide retained on the filter membrane, the dissolved solution was transferred to a 10 mL colorimetric tube, 0.8 mL of 150 g / L thiourea was added, and then the volume was fixed to the scale with 12% hydrochloric acid. The fluorescence value was measured on an atomic fluorescence spectrophotometer using a hydrochloric acid solution with a volume concentration of 2% (generally, a hydrochloric acid solution with a volume concentration of 1%-5%, preferably 2% in this embodiment) as a carrier. The measuring conditions were a negative high voltage of 280V, an argon flow rate of 350mL / min, a hollow cathode lamp main current of 30mA, an auxiliary current of 30mA, and an atomic vaporization temperature of 180°C. The total arsenic concentration after enrichment was calculated by the standard curve method to be 0.49g / L, and the relative standard deviation was 4.6% (n=3).

[0041] The determination results of Example 3 and Example 4 show that the coexisting ions do not interfere with the determination of As(III) and total inorganic arsenic. Therefore, the method of the present invention can also be used for the speciation analysis of inorganic arsenic in hard water.

[0042] Example 5

[0043] Take 2 1000ml lake water samples, add 0.1g of the porous nano ZnO (0.3g / L) prepared in Example 1, and shake on a shaker at a speed of 200r / min for 30min. Then determine the As(III) and total inorganic arsenic in the lake water samples according to the method of Example 2. Calculated by the standard working curve method, the As(III) concentration in the lake water sample is 0.050±0.005mg / L (n=3), and the spike recovery rate is 91(±3)%; the concentration of total inorganic arsenic is 1.690±0.008mg / L (n=3), and the spike recovery rate is 101(±3)%, and the content of pentavalent arsenic can be calculated.

[0044] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for determining the speciation of ultra-trace inorganic arsenic in water, characterized in that: The steps include: (1) Add porous nano zinc oxide to the water sample to be analyzed to enrich the ultra-trace arsenic in the water sample at room temperature; (2) removing the aqueous phase from the porous nano zinc oxide enriched with ultra-trace arsenic in step (1) by suction filtration, and collecting the solid phase; (3) adding the solid phase obtained in step (2) into a hydrochloric acid solution having a volume concentration of 2% to 12% to dissolve the solution and then fix the volume to obtain a fixed volume solution; (4) using citric acid solution as carrier, and using hydride generation atomic fluorescence spectrometry to determine the content of trivalent arsenic ion As(III) in the fixed volume solution obtained in step (3); (5) repeating steps (1) and (2), and adding the obtained solid phase to a hydrochloric acid solution with a volume concentration of 10%-15% to dissolve it, adding a reducing agent thiourea, and then using a hydrochloric acid solution with a volume concentration of 10%-20% to make up the volume to obtain a fixed volume solution; (6) using hydrochloric acid solution as a carrier, and using hydride generation atomic fluorescence spectrometry to determine the content of inorganic arsenic ions in the fixed volume solution obtained in step (5); (7) Subtracting the result of step (4) from the result of step (6) yields the concentration of pentavalent arsenic ions in the water sample; In step (4), the volume concentration of the citric acid solution is 1%-5%; In the step (5), the amount of thiourea used is 7.5-15 mg / ml; In step (6), the volume concentration of the hydrochloric acid solution is 1%-5%; Under the condition of 20-fold enrichment, the detection limits of this method for total inorganic arsenic and trivalent arsenic were 0.01 g / L and 0.02 g / L, respectively.

2. The method for speciation determination of ultra-trace inorganic arsenic in water according to claim 1, characterized in that: In the step (1), after adding the water sample, the concentration of the porous nano zinc oxide is 0.1-1.0 g / L, and the pH value of the solution is 5.5-8.

0.

3. The method for speciation determination of ultra-trace inorganic arsenic in water according to claim 1, characterized in that: In the step (1), the preparation method of porous nano zinc oxide is as follows: zinc acetate dihydrate is weighed and dissolved in methanol to obtain a Zn(CH3COO)2-CH3OH solution; potassium hydroxide is dissolved in methanol to obtain a KOH-CH3OH solution; the KOH-CH3OH solution is added to the Zn(CH3COO)2-CH3OH solution under stirring to obtain a mixed solution; the mixed solution is refluxed at 50-70°C until the reaction is completed, the product is centrifuged, the solid phase is collected, washed, and dried, and the dried product is ground into powder to obtain porous nano zinc oxide.

4. The method for speciation determination of ultra-trace inorganic arsenic in water according to claim 3, characterized in that: The solid-liquid ratio of the Zn(CH3COO)2-CH3OH solution is 14.75g / 60ml; the solid-liquid ratio of the KOH-CH3OH solution is 7.4g / 32ml; the volume ratio of the KOH-CH3OH solution to the Zn(CH3COO)2-CH3OH solution is 32:

64.

5. The method for speciation determination of ultra-trace inorganic arsenic in water according to claim 1, characterized in that: In the step (1), the enrichment condition is to place it in a constant temperature shaker at 25°C and shake at a speed of 100-350 rpm for 5-30 minutes.

6. The method for speciation determination of ultra-trace inorganic arsenic in water according to claim 1, characterized in that: In the step (2), the filter membrane used for filtration is a water-based filter membrane with a pore size of less than or equal to 0.45 μm.

7. The method for speciation determination of ultra-trace inorganic arsenic in water according to claim 1, characterized in that: In the steps (4) and (6), the measurement conditions of the hydride atomic fluorescence spectrometry are negative high voltage 280V, argon gas flow rate 350mL / min, hollow cathode lamp main current 30mA, auxiliary current 30mA, and atomic vaporization temperature 180°C.