A method for determining arsenic content in natural water using headspace single drop microextraction-spectroscopic pipette method

Abstract

The present invention provides a method for determining the arsenic content in natural water using a headspace single drop microextraction-spectroscopic pipette method, which belongs to the field of detection technology. The equipment used in the detection method of the present invention has low cost, good portability, and is easy to operate. The sampling strategy can be adjusted in time to meet the needs of any specific environment. ‑1 The detection method of the present invention is sensitive, robust, reliable, simple and practical, and can quickly measure the nanomolar concentration of different forms of arsenic in natural water bodies in the field. The linear detection range of the detection method of the present invention for arsenic is 0.3-65nM (R 2 =0.9980), the detection limit is 0.1nM, the RSDs for 25nM As(III) measurement are <2.0% (n=10), and the recovery rate of As at different concentration levels (5, 10 and 20nM) in different samples (rivers, lakes, ponds and reservoirs) is 91.7%-97.4%. The method provided by the present invention is very suitable for field analysis of the content of various forms of arsenic in natural water bodies, and has broad application prospects.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and in particular relates to a method for determining the arsenic content in natural water by utilizing a headspace single drop microextraction-spectroscopic pipette method. Background Art

[0002] Arsenic is a metalloid element that is mainly found in soil, air and water. Arsenic is present in trace amounts in almost all organisms. Arsenic is one of the essential trace elements in organisms. Trace arsenic has the effect of inhibiting oxidation and promoting assimilation. Excessive intake can lead to poisoning and cause teratogenic and carcinogenic effects. Arsenic exists mainly in the form of arsenic compounds such as arsenite (As(III)), arsenic acid (As(V)), methylarsonic acid (MMA) and dimethylarsonic acid (DMA) in soil, water and terrestrial plants. In seafood, it mainly exists in the form of arsenobetaine (AsB), arsenocholine (AsC) and more complex arsenosugars. The toxicity and bioavailability of the element depend on its chemical form. The toxicity of the main arsenic compounds is in the following order: As(III)>As(V)>MMA>DMA, while AsB and AsC are generally considered to be non-toxic.

[0003] Water is the source of life. With the improvement of public health and environmental awareness in recent years, ensuring water quality safety is particularly important. Therefore, it is of great significance to accurately detect the arsenic forms and the arsenic content in each form in water.

[0004] Atomic fluorescence spectrometry is also known as hydride generation-atomic fluorescence spectrometry (HG-AFS). This method is to use KBH 4 The arsenic hydride is reduced to arsenic hydride, which is then introduced into an atomizer for atomization. Finally, the arsenic content is obtained based on the measured fluorescence intensity. The sensitivity of atomic fluorescence spectroscopy is 10 to 10 times that of photometry. 4 It has the advantages of simple spectral lines, good selectivity, and wide linear range. Hydride generation-atomic fluorescence spectrometry has been widely used in the detection of arsenic and arsenic forms in various waters.

[0005] However, the equipment used in the HG-AFS method is complex, costly, and inconvenient to carry around, which is not conducive to on-site analysis of the arsenic content in various forms in natural water bodies in the wild. Summary of the invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a simple, compact, portable, low-cost method for determining the arsenic content in natural water using headspace single drop microextraction-spectroscopic pipette (HS-SDME-SP).

[0007] The present invention provides a method for determining the concentration of As(III) in water, the method comprising the following steps:

[0008] (1) Add the water to be tested, a buffer solution with a pH value of 3.50 to 4.50, and a reducing agent into a container, seal the container, and react to generate AsH 3 gas;

[0009] (2) performing headspace extraction on the system of step (1) using an extractant; the extractant is capable of reacting with AsH 3 The reaction generates a substance with a characteristic ultraviolet absorption peak;

[0010] (3) Using an ultraviolet spectrometer, the absorbance of the extractant after the headspace extraction in step (2) is tested, and the concentration of As(III) in the water to be tested is calculated based on a standard curve of absorbance and As(III) concentration.

[0011] Furthermore, in step (1), the pH value of the buffer solution is 4.30 to 4.50; the buffer solution is an acetic acid buffer solution, and the concentration of the acetic acid buffer solution is 0.2M to 0.8M;

[0012] In step (1), the reducing agent is a borohydride salt;

[0013] In step (1), the volume ratio of the water to be tested to the acetic acid buffer is 1:(0.10-0.40), and the volume mass ratio of the water to be tested to the reducing agent is 1:(0.8-1.5) mL / mg.

[0014] Furthermore, in step (1), the pH value of the acetate buffer is 4.46; the concentration of the acetate buffer is 0.5 M;

[0015] In step (1), the borohydride salt is KBH 4 ;

[0016] In step (1), the volume ratio of the water to be tested to the acetic acid buffer is 1:0.25, and the volume mass ratio of the water to be tested to the reducing agent is 1:(1.0-1.1) mL / mg.

[0017] Further, in step (2), the headspace extraction is headspace single drop microextraction;

[0018] And / or, the substance having ultraviolet characteristic absorption peak is Fe(o-phen) 3 (SDS) 2 ;

[0019] And / or, the extractant is prepared from a buffer solution with a pH value of 3.50 to 4.50, an Ag(I) aqueous solution, an Fe(III) aqueous solution, an o-phenanthroline aqueous solution and a dodecyl sulfate aqueous solution.

[0020] Furthermore, the operation of step (2) is: inserting a spectroscopic pipette filled with an extractant into the container of step (1) and placing it at the headspace position of the water body to be tested; then discharging the extractant in the spectroscopic pipette from the spectroscopic pipette to form a hanging droplet below the spectroscopic pipette; after 2 to 6 minutes, sucking the hanging droplet into the ultraviolet spectrophotometric colorimetric cell of the spectroscopic pipette; the spectroscopic pipette is a pipette provided with an ultraviolet spectrophotometric colorimetric cell;

[0021] The operation of step (3) is: using an ultraviolet spectrometer to test the absorbance of the liquid in the ultraviolet spectrophotometric colorimetric cell of step (2), and calculating the concentration of As(III) in the water body to be tested based on a standard curve of absorbance and As(III) concentration.

[0022] Furthermore, in the extractant of step (2), the buffer is an acetic acid buffer, and the dodecyl sulfate is sodium dodecyl sulfate; the pH value of the acetic acid buffer is 4.30-4.40, and the concentration ratio of the acetic acid buffer, the Ag(I) aqueous solution, the Fe(III) aqueous solution, the o-phenanthroline aqueous solution, and the sodium dodecyl sulfate aqueous solution is 0.5M:5mM:25mM:0.3M:0.3M.

[0023] Furthermore, in the extractant of step (2), the pH value of the acetic acid buffer is 4.37, and the concentration of the acetic acid buffer is 0.5M; the concentration of the Ag(I) aqueous solution is 5mM; the concentration of the Fe(III) aqueous solution is 25mM; the concentration of the o-phenanthroline aqueous solution is 0.3M; and the concentration of the sodium dialkyl sulfate is 0.3M.

[0024] Furthermore, in the extractant of step (2), the volume ratio of the acetic acid buffer, the Ag(I) aqueous solution, the Fe(III) aqueous solution, the o-phenanthroline aqueous solution, and the sodium dodecyl sulfate aqueous solution is 1:1:1:1:1.

[0025] Furthermore, in step (2), a hanging droplet is formed below the spectroscopic pipette, and then the hanging droplet is sucked into the ultraviolet spectrophotometric colorimetric cell of the spectroscopic pipette 4 minutes later.

[0026] Further, in step (3), the wavelength of the absorbance test is 500-520 nm, preferably 510 nm;

[0027] And / or, the standard curve of absorbance and As(III) concentration is: absorbance=(0.0207×10 -4 )×[As(III)],R 2 =0.9988; wherein [As(III)] is the As(III) concentration in nM.

[0028] The present invention also provides a method for determining the total concentration of As(III) and As(V) in water, the method comprising the following steps:

[0029] (a) Add the water to be tested and concentrated hydrochloric acid into the container, control the pH value of the liquid in the container to 0.52-0.54, add the reducing agent, seal the container, and react to generate AsH 3 gas; preferably, the pH value of the liquid in the container is controlled to be 0.53;

[0030] (b) performing headspace extraction on the system of step (a) using an extractant, wherein the operations of the extractant and the headspace extraction are as described in the above step (2);

[0031] (c) using an ultraviolet spectrometer to test the absorbance of the extractant after the headspace extraction in step (b), and calculating the concentration of As(III)' in the water body to be tested based on a standard curve of absorbance and As(III)' concentration; the As(III)' concentration at this time is the total concentration of As(III) and As(V).

[0032] Furthermore, in step (1), the reducing agent is a borohydride salt; the volume ratio of the water body to be tested to concentrated hydrochloric acid is 1:(0.010-0.040), and the volume mass ratio of the water body to be tested to the reducing agent is 1:(0.50-1.00) mL / mg;

[0033] Preferably, the borohydride salt is KBH 4 ; The volume ratio of the water to be tested to concentrated hydrochloric acid is 1:0.025, and the volume mass ratio of the water to be tested to the reducing agent is 1:0.84mL / mg;

[0034] In step (3), the wavelength of the absorbance test is 500-520 nm, preferably 510 nm, and the standard curve of absorbance and As(III) concentration is: absorbance = (0.0207 × 10 -4 )×[As(III)'],R 2 =0.9988; wherein, [As(III)'] is the total concentration of As(III) and As(V), in nM.

[0035] The present invention also provides a method for determining the concentration of As(V) in water, the method comprising the following steps:

[0036] (1) Determine the As(III) concentration in the water body to be tested using the above method;

[0037] (2) Determine the total concentration of As(III) and As(V) in the water body to be tested using the above method;

[0038] (3) Subtract the As(III) concentration from the total As(III) and As(V) concentration to obtain the As(V) concentration in the water to be tested.

[0039] In the present invention, As(III) refers to trivalent arsenic ions, i.e., As 3+ ; As(V) refers to pentavalent arsenic ion, i.e. As 5+ ; Ag(I) refers to monovalent silver ion, i.e. Ag + ; Fe(III) refers to trivalent iron ion, namely Fe 3+ .

[0040] Room temperature refers to 25±2℃.

[0041] The detection principle of the headspace single drop microextraction-spectroscopic pipette method of the present invention is:

[0042] As(III) and As(V) in water samples are catalyzed by KBH under different pH conditions. 4 Reduction to AsH 3 (gas):

[0043] As(OH) 3 +3BH 4 - +3H + +6H 2 O→AsH 3 (g)+3B(OH) 3 +9H 2 (g) (1)

[0044] As(O)(OH) 3 +4BH 4 - +4H + +6H 2 O→AsH 3 (g)+4B(OH) 3 +10H 2 (g) (2)

[0045] Generated AsH 3 The following reactions occur with the extractant:

[0046] AH 3 +6Ag + →6Ag+As 3+ +3H + (3)

[0047] 6Ag+6Fe 3+ →6Ag + +6Fe 2+ (4)

[0048] 6Fe2+ +18(o-phen)→6[Fe(o-phen) 3 ] 2+ (5)

[0049] 6[Fe(o-phen) 3 ] 2+ +12SDS - →6Fe(o-phen) 3 (SDS) 2 (6)

[0050] Overall reaction:

[0051] AH 3 +6Fe 3+ +18(o-phen)+12SDS - →6Fe(o-phen) 3 (SDS) 2 +As 3+ +3H + (7)

[0052] The final Fe(o-phen) 3 (SDS) 2 There is a characteristic ultraviolet absorption peak at 510nm.

[0053] Under the pH conditions of Example 1 of the present invention, the reducing agent KBH 4 After that, only As(III) in the water sample will react with the reducing agent KBH 4 The reaction generates AsH 3 , so the final measured As(III) concentration is the As(III) concentration in the water sample to be tested.

[0054] Experiments have shown that when the pH value of the acetic acid buffer in step (1) of Example 1 is controlled to be 4.46, the HS-SDME-SP method of the present invention can be used to detect the As(III) concentration in the water sample to be tested.

[0055] Under the pH conditions of Example 2 of the present invention, the reducing agent KBH 4 After that, As(III) and As(V) in the water sample can react with the reducing agent KBH 4 The reaction generates AsH 3 Therefore, the final measured "As(III) concentration" is actually the total concentration of As(III) and As(V) in the water sample to be tested.

[0056] Experiments have shown that when the pH value of the sample after adding concentrated hydrochloric acid in step (1) of Example 2 is controlled to be 0.53, the HS-SDME-SP method of the present invention can be used to detect the total concentration of As(III) and As(V) in the water sample to be tested.

[0057] In order to determine the concentration of As(V) in the water sample to be tested, it is necessary to subtract the concentration of As(III) from the total concentration of As(III) and As(V).

[0058] The spectroscopic pipette used in the present invention is a powerful multifunctional tool that can be used as an extractant processor, a microdroplet holder, and a micro-cutting tube in HS-SDME and in-situ absorbance measurement procedures; in the method of the present invention, gas-liquid absorption, redox reaction and color development reaction, and absorbance measurement can all be completed in one step.

[0059] The equipment used in the detection method of the present invention is simple, compact and portable (weight 1.1 kg), easy to operate, and the sampling strategy can be adjusted in time to meet the needs of any specific environment. -1 The detection method of the present invention has low cost, and the equipment cost is only 1 / 5 of that of the HG-AFS method.

[0060] The detection method of the present invention is sensitive, robust, reliable, simple and practical, and can quickly measure the nanomolar concentration of arsenic in natural water bodies in the field, and is suitable for on-site analysis of natural water bodies. The linear detection range of the detection method of the present invention for arsenic is 0.3-65nM (R 2 =0.9980), the detection limit is 0.1nM, the RSDs for 25nM As(III) measurements are <2.0% (n=10), and the recovery of As at different concentration levels (5, 10 and 20nM) in different samples (rivers, lakes, ponds and reservoirs) is 91.7%-97.4%. The method provided by the present invention is very suitable for field analysis of the content of various forms of arsenic in natural water bodies.

[0061] Obviously, according to the above contents of the present invention, in accordance with common technical knowledge and customary means in the art, without departing from the above basic technical ideas of the present invention, other various forms of modification, replacement or change may be made.

[0062] The above contents of the present invention are further described in detail below through specific implementation methods in the form of embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples. All technologies realized based on the above contents of the present invention belong to the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1. Schematic diagram of the process of determining arsenic concentration in water samples using headspace single drop microextraction-spectroscopic pipette method in the present invention: (a) pre-loading 5 μL of extractant in the spectroscopic pipette; (b) using KBH 4 Reduction of As(III) and / or As(V) to AsH 3 ; (c) During headspace single drop microextraction, AsH 3 is absorbed and reacts with the extractant solution in the suspended microdroplets; (d) absorbance measurement is performed in situ.

[0064] Figure 2 .Photo of the device for determining the arsenic concentration in water samples using the headspace single drop microextraction-spectroscopic pipette method of the present invention.

[0065] Figure 3 The concentrations of As(III) and As(V) in different freshwater samples were measured and compared using the HS-SDME-SP method and the HG-AFS method of the present invention; wherein the horizontal axis value represents the test result of the HS-SDME-SP method, the vertical axis value represents the test result of the HG-AFS method, the solid line represents the fitting graph of the actual result, and the dotted line represents the 1:1 fitting line.

[0066] Figure 4 . The influence of different buffer types and their pH on the extraction effect of the method of the present invention. In the figure, Citrate buffer represents a citrate buffer solution, Acetate buffer represents an acetic acid buffer solution, and Phosphate buffer represents a phosphate buffer solution.

[0067] Figure 5 .The effect of the concentration of Ag(I) aqueous solution on the extraction effect in the extractant composition.

[0068] Figure 6 .The effect of Fe(III) aqueous solution concentration on the extraction effect in the extractant composition.

[0069] Figure 7 .The effect of o-phen aqueous solution concentration on the extraction effect in the extractant composition.

[0070] Figure 8 .The effect of SDS aqueous solution concentration on the extraction effect in the extractant composition.

[0071] Fig. 9 .Effect of extraction time with / without SDS aqueous solution.

[0072] Fig.10 .Generate AsH 3 Effect of pH on gas processes. DETAILED DESCRIPTION

[0073] The raw materials and equipment used in the present invention are all known products, which are obtained by purchasing commercially available products.

[0074] 1. Reagent preparation:

[0075] 1.1.0 mM As(III) and As(V) stock solutions were prepared by mixing 0.049 g As 2 O 3 (≥99.95%, Merck, Darmstadt, Germany) and 0.0575g As 2 O 5 (≥99.99%, Merck, Darmstadt, Germany) were dissolved in 250 ml of water. 1.0 μM As(III) and As(V) working solutions were prepared by diluting the stock solutions with water every day.

[0076] 2. Use potassium tetrahydroborate (KBH 4 ; ≥97%, Sinopharm Chemical Reagent Co., Shanghai, China) as a reducing agent for the generation of arsine.

[0077] 3. Prepare acetate buffer (0.5 M) by adding 7.19 mL of acetic acid (≥99.5%, Macklin, Shanghai, China) to 100 mL of water, and then adjust the solution to the desired pH with 2 M NAOH and 2 M HCL. Then transfer the solution to a 250 mL volumetric flask and make up to volume with water. According to this method, a 0.5 M acetate buffer with a pH of 4.37 was prepared.

[0078] Citric acid buffer (0.5 M) was prepared by dissolving 26.40 g of citric acid monohydrate (≥99.5%, Chron Chemicals, Chengdu, China) in 100 mL of water, and the pH was adjusted with 2 M NaOH and 2 M HCL. The citric acid buffer was then diluted to 250 mL with water as in the preparation of acetate buffer.

[0079] Phosphate buffer solutions (0.5 M) of different pH values ​​were prepared by mixing appropriate amounts of sodium dihydrogen phosphate (0.5 M) and sodium hydrogen phosphate (0.5 M).

[0080] 4. 8.51 g AgNO 3 (≥99.8%, Chron Chemicals, Chengdu, China) was dissolved in 100 mL of water to prepare a 0.5 M Ag(I) stock solution. 13.65 g FeCl 3 6H 2O (≥99%, Macklin, Shanghai, China) to prepare 0.5M Fe(III) stock solution. 0.1M Fe(III) working solution and 0.05M Ag(I) working solution were prepared by diluting the stock solution with water every day. According to this method, 5mM Ag(I) aqueous solution and 25mM Fe(III) aqueous solution were prepared.

[0081] 5. Dissolve 10.01 g o-phenanthroline monohydrate (≥99%, Chron Chemicals, Chengdu, China) in 2.5 mL ethanol and dilute to 50 mL with water to prepare a 1 M o-phenanthroline (o-phen) aqueous solution. Prepare a 0.3 M SDS aqueous solution in this way.

[0082] 6. Sodium dodecyl sulfate (SDS) working solution was prepared by dissolving SDS (≥98%, Chron Chemicals, Chengdu, China) in water on the same day. A 0.3 M o-phen aqueous solution was prepared according to this method.

[0083] 7. The extractant for headspace single-drop microextraction was prepared by mixing the following reagents: 1 μL of 0.5 M acetate buffer at pH 4.37, 1 μL of 5 mM Ag(I) aqueous solution, 1 μL of 25 mM Fe(III) aqueous solution, 1 μL of 0.3 M o-phen aqueous solution, and 1 μL of 0.3 M SDS aqueous solution.

[0084] The water used in the preparation of all the above reagents was ultrapure water from the Milli-Q Integral 3 system of Millipore (MA, USA). All the above reagents were stored at 5°C in the dark.

[0085] 2. Equipment:

[0086] A USB 2000+ UV spectrometer (Ocean Optics, FL, USA) equipped with a DH-mini tungsten-halogen light source (Ocean Optics, FL, USA) was used to measure absorbance.

[0087] A spectrophotometric pipette (Ideaoptics, Shanghai, China) used as a spectrophotometric sampling device for spectral analysis of samples, the spectrophotometric pipette has the functions of a pipette gun and a UV spectrophotometric colorimetric cell, and is a pipette with a UV spectrophotometric colorimetric cell at the lower tip. Figure 1As shown in Figure d, the sample can be pumped and discharged through a highly transparent quartz piston in the spectroscopic pipette, which is controlled by turning the button clockwise and counterclockwise. The UV spectrophotometric cell at the tip of the spectroscopic pipette also serves as the sample optical unit. The spectroscopic pipette is protected by a stainless steel housing, and a quartz sleeve is installed inside the pipette as a guide between the piston and the housing.

[0088] Example 1: Determination of As(III) concentration in natural water using headspace single drop microextraction-spectroscopic pipette method

[0089] 1. Detect water

[0090] This example uses freshwater samples from Qingshui River (Chengdu, China) as the samples to be tested. A 50 mL polypropylene (PP) syringe equipped with a 0.22 μm polyethersulfone (PP) filter was used to collect water samples at a water depth of 0.2 m, and then the water samples were collected in a 50 mL polypropylene (PE) bottle. Then, 5.0 mL of the water sample to be tested was taken from the collected water sample and transferred to a 10 mL glass test tube.

[0091] 2. Determine the concentration of As(III) in the water sample to be tested

[0092] according to Figure 1 The flow chart shown in the figure detects the concentration of As(III) in the water sample. The operation is carried out at room temperature. The specific operation is as follows:

[0093] (1) Add 1.25 mL of 0.5 M acetic acid buffer with a pH value of 4.46 to 5.0 mL of the water sample to be tested, mix, and then add 5.2 mg of pre-weighed and packaged KBH 4 , and immediately cover the test tube with a screw cap with a silicone gasket to seal it.

[0094] (2) Then, a spectroscopic pipette pre-loaded with 5 μL of extractant (the extractant is prepared by 1 μL of 0.5 M acetic acid buffer with a pH value of 4.37, 1 μL of 5 mM Ag(I) aqueous solution, 1 μL of 25 mM Fe(III) aqueous solution, 1 μL of 0.3 M o-phen aqueous solution and 1 μL of 0.3 M SDS aqueous solution) is inserted into the test tube through the silicone gasket (the gasket is pierced using a tilted base) and placed at the headspace position of the water sample to be tested (0.5 cm from the liquid surface). Then, by turning the knob on the spectroscopic pipette, the extractant is discharged from the ultraviolet spectrophotometric cell at the tip of the spectroscopic pipette, forming a suspended microdroplet on one side of the tip. After 4 minutes, the suspended microdroplet is sucked into the ultraviolet spectrophotometric cell, and the absorbance of the microdroplet is measured on-site at 510 nm using an ultraviolet spectrometer ( Figure 1 d).

[0095] According to the standard curve of absorbance and As(III) concentration, the As(III) concentration in the water sample to be tested is measured. The standard curve is: Absorbance = (0.0207 × 10 -4 )×[As(III)](nM),

[0096] R 2 =0.9988; where [As(III)] is the As(III) concentration.

[0097] Example 2: Determination of As(III)+As(V) concentration in natural water using headspace single drop microextraction-spectroscopic pipette method

[0098] 1. Detect water

[0099] Another 5.0 mL of the water sample to be tested was taken from the water sample collected in Example 1 and transferred to a 10 mL glass test tube.

[0100] 2. Determine the total concentration of As(III) and As(V) in the water sample to be tested

[0101] according to Figure 1 The flow chart shown in the figure detects the total concentration of As(III) and As(V) in the water sample. The operation is carried out at room temperature. The specific operation is as follows:

[0102] (1) Add 0.125 mL of concentrated hydrochloric acid to 5.0 mL of the water sample to make the pH value of the sample 0.53, and then add 4.2 mg of pre-weighed and packaged KBH 4 , and immediately cover the test tube with a screw cap with a silicone gasket to seal it.

[0103] (2) Then, a spectroscopic pipette pre-loaded with 5 μL of extractant (the extractant is prepared by 1 μL of 0.5 M acetic acid buffer with a pH value of 4.37, 1 μL of 5 mM Ag(I) aqueous solution, 1 μL of 25 mM Fe(III) aqueous solution, 1 μL of 0.3 M o-phen aqueous solution and 1 μL of 0.3 M SDS aqueous solution) is inserted into the test tube through the silicone gasket (the gasket is pierced using a tilted base) and placed at the headspace position of the water sample to be tested (0.5 cm from the liquid surface). Then, by turning the knob on the spectroscopic pipette, the extractant is discharged from the ultraviolet spectrophotometric cell at the tip of the spectroscopic pipette, forming a suspended microdroplet on one side of the tip. After 4 minutes, the suspended microdroplet is sucked into the ultraviolet spectrophotometric cell, and the absorbance of the microdroplet is measured on-site at 510 nm using an ultraviolet spectrometer ( Figure 1 d).

[0104] According to the standard curve of absorbance and the total concentration of As(III) and As(V), the total concentration of As(III) and As(V) in the water sample to be tested was measured. The standard curve is: Absorbance = (0.0207 × 10 -4 )×[As(III)+As(V)](nM), R 2 =0.9988; where [As(III)+As(V)] is the total concentration of As(III) and As(V).

[0105] Example 3: Determination of As(V) concentration in natural water using headspace single drop microextraction-spectroscopic pipette method

[0106] 1. The As(III) concentration in the water sample to be tested was measured using the method of Example 1;

[0107] 2. The total concentration of As(III) and As(V) in the water sample to be tested was measured using the method of Example 1;

[0108] 3. Subtract the As(III) concentration from the total concentration of As(III) and As(V) to obtain the As(V) concentration in the water sample to be tested.

[0109] The beneficial effects of the present invention are demonstrated by experimental examples below.

[0110] Experimental Example 1: Establishing a standard curve between absorbance and As(III) concentration

[0111] The absorbance of freshwater samples doped with As(III) at different concentrations (concentration range: 0.5-25 nM) was measured using the method of Example 1 of the present invention to obtain a standard curve of absorbance versus As(III) concentration. A linear calibration of As(III) in the range of 0.5 to 25 nM was performed to obtain an R of 0.9988. 2 Values ​​and the following regression equation;

[0112] Absorbance=(0.0207×10 -4 )×[As(III)](nM)

[0113] Table 1. Analytical performance of the HS-SDME-SP method for the determination of As(III) concentrations in natural waters

[0114]

[0115] In Table 1, a : The calculation result is 3 times the signal-to-noise ratio; b : The calculation result is 10 times the signal-to-noise ratio; c : By measuring fresh water samples doped with 25 nM As(III) (n=10 replicates).

[0116] The limit of detection (LOD) calculated from the three-fold signal-to-noise ratio was 0.1 nM, and the method was linear in the range of 0.3-65 nM (R 2 =0.9980), and the RSDs of 25 nM As(III) was 2.0% (n=10), indicating that the method had good reproducibility.

[0117] Experimental Example 2: Recovery Rate Test

[0118] 1. Experimental methods

[0119] By analyzing different natural water matrices (rivers, lakes, reservoirs and ponds; for details, see Figure 3 ) was used to study the recovery rate of the test method of the present invention.

[0120] Lake samples were collected from Donghu Lake (University of Electronic Science and Technology of China, Chengdu, China), Sancha Lake (Chengdu, China) and Longquan Lake (Chengdu, China); pond samples were collected from a wetland in Pidu District (Chengdu, China); river samples were collected from different locations along the Qingshui River and Pihe River (Chengdu, China); reservoir samples were collected from Zipingpu, Tuanjie and Heilongtan reservoirs (Chengdu, China).

[0121] Sampling was performed using a 50 mL plastic syringe equipped with a 0.22 μm membrane filter. The syringe was filled with water at a depth of approximately 10 cm and the collected samples were stored in a foamed polypropylene cooling box at approximately 4°C in the dark until they were analyzed.

[0122] The known hydride generation-atomic fluorescence spectrometry (HG-AFS) was used as a control. The HG-AFS method uses a flow injection-hydride generation atomic fluorescence spectrometer (AFS-9130 Beijing Jitian Instrument Company) to measure:

[0123] (1) Determination steps of As(III) concentration: After the sample is collected, it is filtered with a 0.22 μm filter head and then directly placed in a flow injection-hydride generation atomic fluorescence spectrometer for analysis. The operating parameters of the flow injection-hydride generation atomic fluorescence spectrometer are shown in Table 2.

[0124] (2) Determination of As(V) concentration: After the sample was collected, it was filtered with a 0.22 μm filter head, and then 25 mL of the sample was taken into a 40 mL test tube, 1.5 mL of concentrated hydrochloric acid and 1 mL of 10% (m / v) thiourea solution were added, and after being fully mixed, it was placed at room temperature for 20 min, and then placed in a flow injection-hydride generation atomic fluorescence spectrometer for analysis. The operating parameters are shown in Table 2. At this time, the test result is the total concentration of As(III) and As(V), and the result minus the As(III) concentration measured above is the As(V) concentration value.

[0125] Table 2. HG-AFS operating parameters for measuring As(III) concentration

[0126]

[0127] 2. Experimental results

[0128] The test results are shown in Table 3 and Figure 3 .

[0129] Table 3. Measurement of As content in different natural water bodies using HS-SDME-SP method (n=3)

[0130]

[0131] In Table 3, a : Natural water samples collected; b : 1.0 nM As(III) and 5.0 nM As(V) were added to the sample; c : 5.0 nM As(III) and 10 nM As(V) were added to the sample; d : 10nM As(III) and 20nM As(V) were added to the sample.

[0132] As can be seen from Table 3, the recovery rate of AS(III) is 93.2-97.4% and the recovery rate of As(V) is 91.7-97.0% when the method of the present invention is used for detection, indicating that the method of the present invention has good accuracy in detecting As content in natural water bodies.

[0133] from Figure 3 It can be seen that when testing the As(III) concentration and As(V) concentration in various water bodies, the detection results of the HS-SDME-SP method of the present invention are equivalent to those of the HG-AFS method, indicating that the test method of the present invention has reliable results.

[0134] Experimental Example 3: Verification of Detection Accuracy

[0135] This experimental example used two certified reference materials to verify the detection accuracy of the HS-SDME-SP method of Example 2 of the present invention. Among them, GSB 07-3171-2014 (surface fresh water) came from the Institute of Standard Samples of the Ministry of Environmental Protection of China, and GBW (E) 080230 (seawater) came from the National Institute of Metrology of China.

[0136] Table 4. Analysis of As in standard reference materials (n=3)

[0137]

[0138] In Table 4, a Measured as the total concentration of As(III) and As(V); b The sample was diluted 10 times before testing; c α=0.05; df=4.

[0139] The validation results are shown in Table 4. The experimental values ​​and the validation values ​​(i.e., recommended values) show good consistency. The concentration factor of the 25 nM As(III) solution, i.e., the ratio of the analyte concentration in the extraction phase to the aqueous sample phase, is 166.

[0140] The above results show that the HS-SDME-SP method provided by the present invention has high accuracy in detecting the total concentrations of As(III) and As(V) in GSB 07-3171-2014 (surface fresh water) and GBW(E)080230 (seawater).

[0141] Experimental Example 4: Screening experiment of extraction agent and extraction time

[0142] 1. Screening experiment of buffer types and pH in extractants

[0143] The determination method of Example 1 was referred to, except that the type of buffer and pH value in the extractant composition of step (2) were changed. The absorbance was used as an indicator to evaluate the measurement effect under each buffer type and pH value.

[0144] The results are as follows Figure 4 The results show that the extraction effect is best when the acetic acid buffer solution with pH = 4.37 is used.

[0145] 2. Screening experiment of the amount of Ag(I), Fe(III) and o-phen in the extractant composition

[0146] The determination method of Example 1 was used with reference to the method of Example 1, except that the concentrations of the Ag(I) aqueous solution, Fe(III) aqueous solution, and o-phen aqueous solution in the extractant composition of step (2) were changed. The absorbance was used as an indicator to evaluate the measurement effect at each concentration.

[0147] The results are as follows Figure 5-Figure 7 The results show that the best extraction effect is achieved when the concentrations of Ag(I) aqueous solution, Fe(III) aqueous solution and o-phen aqueous solution are 5mM, 25mM and 0.3M respectively.

[0148] 3. Screening experiment of SDS dosage in extractant composition

[0149] The determination method of Example 1 was referred to, except that the concentration of the SDS aqueous solution in the extractant composition of step (2) was changed. The absorbance was used as an indicator to evaluate the measurement effect at each concentration.

[0150] The results are as follows Figure 8 The results show that in the composition of the extractant, a good extraction effect can be achieved when the concentration of the SDS aqueous solution is 0.3M, and further increasing the concentration of the SDS aqueous solution will not improve the extraction efficiency.

[0151] 4. Screening experiment of extraction time

[0152] The determination method of Example 1 is referred to, except that the presence or absence of the SDS aqueous solution in the extractant composition is controlled (when the SDS aqueous solution is present, the amount used is the same as in Example 1), and the interval between forming a suspended micro-droplet on the tip side and sucking the suspended micro-droplet into the ultraviolet spectrophotometric colorimetric cell in step (2) is changed (i.e., the extraction time). The absorbance is used as an index to evaluate the measurement effect at each extraction time when the SDS aqueous solution is present or not.

[0153] The results are as follows Fig. 9 The results show that the presence or absence of SDS aqueous solution in the extractant has a great influence on the extraction effect. In the absence of SDS aqueous solution, it is difficult for the extraction to reach equilibrium. When the concentration of the extractant SDS aqueous solution is 0.3M, the extraction equilibrium time is greatly shortened, and the extraction equilibrium can be reached when the extraction time is 4 minutes.

[0154] Experimental Example 5: Generation of AsH 3 Effect of pH on Gas Processes

[0155] In order to achieve the purpose of separating the total concentration of As(III) and [As(III)+As(V)] in the sample in steps, the present invention generates AsH 3 The pH value of the gas process was investigated and compared. Fig.10 When the sample pH is 0.53, both As(III) and As(V) can be separated from the sample; when the pH is 4.46, only As(III) can form AsH 3 Thus, separation from the matrix is ​​achieved, while As(V) is retained in the sample.

[0156] Therefore, when measuring the As(III) concentration in the water sample to be tested, the present invention controls the pH value of the hydride generating system to be 4.46 by adding 1.25 mL of 0.5 M acetic acid buffer having a pH value of 4.46 to 5.0 mL of the water sample to be tested; when measuring the total concentration of [As(III)+As(V)], the pH value of the hydride generating system is controlled to be 0.53 by adding 0.125 mL of concentrated hydrochloric acid to 5.0 mL of the water sample to be tested.

[0157] In summary, the present invention provides a method for determining the arsenic content in natural water using headspace single drop microextraction-spectroscopic pipette method. The equipment used in the detection method of the present invention has low cost, good portability (1.1 kg), easy operation, and the sampling strategy can be adjusted in time to meet the needs of any specific environment. The arsenic content in natural water can be obtained in 5 minutes on site. -1 The detection method of the present invention is sensitive, robust, reliable, simple and practical, and can quickly measure the nanomolar concentration of different forms of arsenic in natural water bodies in the field. The linear detection range of the detection method of the present invention for arsenic is 0.3-65nM (R 2 =0.9980), the detection limit is 0.1nM, the RSDs for 25nM As(III) are <2.0% (n=10), and the recovery of As at different concentration levels (5, 10 and 20nM) in different samples (rivers, lakes, ponds and reservoirs) is 91.7%-97.4%. The method provided by the present invention is very suitable for field analysis of the content of various forms of arsenic in natural water bodies, and has broad application prospects.

Claims

1. A method for determining the concentration of As(III) in water, characterized in that: The method comprises the following steps: (1) adding water to be tested, a buffer solution, and a reducing agent into a container, sealing the container, and reacting to generate AsH3 gas; the pH value of the buffer solution is 4.46, the buffer solution is an acetic acid buffer solution, and the concentration of the acetic acid buffer solution is 0.5M; and the reducing agent is a borohydride salt; (2) performing headspace extraction on the system of step (1) using an extractant; the extractant can react with AsH3 to generate a substance having a characteristic ultraviolet absorption peak; the extractant is prepared from a buffer solution with a pH value of 3.50 to 4.50, an Ag(I) aqueous solution, an Fe(III) aqueous solution, an o-phenanthroline aqueous solution and a dodecyl sulfate aqueous solution; (3) Using an ultraviolet spectrometer, the absorbance of the extractant after the headspace extraction in step (2) is tested, and the concentration of As(III) in the water to be tested is calculated based on a standard curve of absorbance and As(III) concentration.

2. The method according to claim 1, characterized in that: In step (1), the volume ratio of the water to be tested to the acetic acid buffer is 1:(0.10-0.40), and the volume mass ratio of the water to be tested to the reducing agent is 1:(0.8-1.5) mL / mg.

3. The method according to claim 2, characterized in that: In step (1), the borohydride salt is KBH4; In step (1), the volume ratio of the water to be tested to the acetic acid buffer is 1:0.25, and the volume mass ratio of the water to be tested to the reducing agent is 1:(1.0-1.1) mL / mg.

4. The method according to claim 1, characterized in that: In step (2), the headspace extraction is headspace single drop microextraction; The substance with ultraviolet characteristic absorption peak is Fe(o-phen)3(SDS)2.

5. The method according to claim 1, characterized in that: The operation of step (2) is as follows: inserting a spectroscopic pipette filled with an extractant into the container of step (1) and placing it at the headspace position of the water body to be tested; then discharging the extractant in the spectroscopic pipette from the spectroscopic pipette to form a hanging droplet below the spectroscopic pipette; after 2 to 6 minutes, sucking the hanging droplet into the ultraviolet spectrophotometric colorimetric cell of the spectroscopic pipette; the spectroscopic pipette is a pipette provided with an ultraviolet spectrophotometric colorimetric cell; The operation of step (3) is: using an ultraviolet spectrometer to test the absorbance of the liquid in the ultraviolet spectrophotometric colorimetric cell of step (2), and calculating the concentration of As(III) in the water body to be tested based on a standard curve of absorbance and As(III) concentration.

6. The method according to claim 5, characterized in that: In the extractant of step (2), the buffer is an acetic acid buffer, and the dodecyl sulfate is sodium dodecyl sulfate; the pH value of the acetic acid buffer is 4.30-4.40, and the concentration ratio of the acetic acid buffer, the Ag(I) aqueous solution, the Fe(III) aqueous solution, the o-phenanthroline aqueous solution, and the sodium dodecyl sulfate aqueous solution is 0.5M:5mM:25mM:0.3M:0.3M.

7. The method according to claim 6, characterized in that: In the extractant of step (2), the pH value of the acetic acid buffer is 4.37, and the concentration of the acetic acid buffer is 0.5M; the concentration of the Ag(I) aqueous solution is 5mM; the concentration of the Fe(III) aqueous solution is 25mM; the concentration of the o-phenanthroline aqueous solution is 0.3M; and the concentration of the dialkyl sodium sulfate is 0.3M.

8. The method according to claim 7, characterized in that: In the extractant of step (2), the volume ratio of the acetic acid buffer, the Ag(I) aqueous solution, the Fe(III) aqueous solution, the o-phenanthroline aqueous solution, and the sodium dodecyl sulfate aqueous solution is 1:1:1:1:

1.

9. The method according to claim 5, characterized in that: In step (2), a hanging droplet is formed below the spectroscopic pipette, and then the hanging droplet is sucked into the ultraviolet spectrophotometric colorimetric cell of the spectroscopic pipette 4 minutes later.

10. The method according to any one of claims 1 to 9, characterized in that: In step (3), the wavelength of the absorbance test is 500-520 nm; The standard curve of absorbance and As(III) concentration is: absorbance = (0.0207 × 10 -4 )×[As(III)],R 2 =0.9988; wherein [As(III)] is the As(III) concentration in nM.

11. The method according to claim 10, characterized in that: In step (3), the wavelength of the absorbance test is 510 nm.

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