CN112526011B - Method for synchronously extracting and measuring concentrations of sulfate ions and sulfide ions in environmental medium based on DGT technology and application - Google Patents
Method for synchronously extracting and measuring concentrations of sulfate ions and sulfide ions in environmental medium based on DGT technology and application Download PDFInfo
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Abstract
The invention relates to a method for synchronously extracting and measuring the concentration of sulfate radical and sulfide ions in an environmental medium based on a DGT technology, which adopts a layered double hydroxide polyacrylamide gel film as a binding membrane to assemble a double-sided DGT device with the same binding membrane, the double-sided DGT device is put into soil, water and sediment to adsorb sulfate radical and sulfide, 2 binding membranes in the DGT device are taken out, 2 eluents are adopted to respectively elute, then an extracting solution is diluted and the concentration of the sulfate radical ions is simultaneously measured by using an ion chromatography, the concentration of the sulfide ions in the extracting solution is obtained by using a differential subtraction method, and finally the concentrations of the sulfate radical and the sulfide ions in the binding membrane are respectively calculated according to the Fick's first diffusion law. The method simplifies the determination method, only needs to determine sulfate ions, obtains the concentration of sulfide ions by a subtraction method, avoids the complexity of different extraction methods and different devices in detection, and improves the detection efficiency and convenience.
Description
Technical Field
The invention belongs to the technical field of simultaneous detection of specific sulfur form ions, and particularly relates to a method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in an environmental medium based on a DGT (differential global positioning system) technology and application thereof.
Background
Sulfur is widely distributed in the natural environment and exists in various forms, and sulfur, which is mainly concerned in water and soil, is mainly sulfate and sulfide. The sulfate concentration in natural waters can range from a few milligrams per liter to several thousand milligrams per liter. A small amount of sulfate in water has no influence on human health, but when the concentration of the sulfate in water exceeds 150mg/L, the water has bitter taste, and when the concentration exceeds 250mg/L, the human body has a diarrhea phenomenon; in the oil field sewage, sulfate is reduced into S (-II) under the condition of reducing bacteria, the S (-II) is corrosive, and the product is ferric sulfide which is a black colloidal suspended substance insoluble in water and is easy to cause water to become black and smelly. At present, sulfate and sulfide are listed as one of important pollutants in water environment. Accurate, rapid, and reliable measurement techniques are therefore important to understand sulfate and sulfide distribution and levels.
At present, various methods are applied to the detection of sulfate radicals and sulfide ions in soil, water and sediments, including gravimetric method, barium chromate volumetric method, colorimetric method, capillary electrophoresis method, ion selective electrode method, gas chromatography, flow injection analysis method, methylene blue spectrophotometry, reversible optical fiber sensor and the like. However, these methods have limitations in terms of operation steps, detected concentrations, and measurement ranges, and they are usually combined with active sampling, so that conversion between forms of sulfide ions cannot be avoided, and only instantaneous concentrations at a specific point and at a specific time can be detected. Therefore, it is necessary to develop a new method for synchronously measuring sulfate and sulfide ions in the environment in situ at multiple scales.
The film diffusion gradient in thin-films (DGT) technology is an in-situ passive sampling technology and is a new technology for element morphology analysis. The measurement result is more representative because the average concentration of the object to be measured in soil, water and sediment per unit time is measured. The DGT device is composed of a protective film, a diffusion film and a combined film, wherein the protective film is mainly used for preventing solid particles in an environment to be detected from entering the device, the diffusion film can enable ions to freely diffuse into the combined film and form a linear gradient on the diffusion film, the combined film can adsorb and combine substances to be detected, the dynamic concentration of the substances in the environment can be quantitatively detected according to the adsorption quantity of the substances to be detected, and different adsorbing materials can be selected to be used as the combined film according to the difference of the ions to be detected. In short, the DGT technology is an ideal method for in-situ collection and detection of element forms, and has the advantages of convenience in use, in-situ detection, strong selectivity, wide application, high detection sensitivity and the like.
The DGT-binding membrane is usually made of silver iodide, and can efficiently adsorb S element and dissociate in an acid or alkali solution, but only the concentration of sulfide can be measured, and sulfate and sulfide cannot be distinguished. This limits their application to the detection of sulfate ions in water, sediments and especially in soil. Layered Double Hydroxides (LDH) S ) Due to the characteristics of controllable intercalation assembly and laminate composition structure, LDH can be utilized S So as to adsorb sulfate radical and sulfide ion simultaneously, thereby improving the portability of detection.
Therefore, the difficulty of extracting and measuring sulfate and sulfide ions in soil, water and sediment is solved. The invention provides a method for synchronously measuring sulfate radicals and sulfides based on DGT.
Through searching, no patent publication related to the present patent application has been found.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in an environmental medium based on a DGT (differential global positioning system) technology and application thereof.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in an environmental medium based on DGT technology adopts a layered double hydroxide polyacrylamide gel film, namely LDH S -NO 3 The membrane is a binding membrane, and double-sided LDH assembled to have the same binding membrane S -NO 3 The membrane DGT device is placed in soil, water body and sediment to adsorb sulfate radicals and sulfides, 2 binding membranes in the DGT device are taken out, and 2 eluents are adopted to respectively elute, wherein one of the eluentsSulfate ions and sulfide ions are eluted and extracted by one eluent, sulfate ions and sulfide ions in the form of sulfate ions are eluted and extracted by the other eluent, then the concentration of the sulfate ions is simultaneously measured by ion chromatography after the extracting solution is diluted, the concentration of the sulfide ions in the extracting solution is obtained by utilizing a subtraction method, and finally the concentrations of the sulfate ions and the sulfide ions in the binding membrane are respectively calculated according to Fick's first diffusion law.
Furthermore, the double-sided LDH S -NO 3 The assembly of the membrane DGT device is as follows: the first protective film, LDH S -NO 3 The membrane, the diffusion membrane, the second protective membrane and the protective shell of the DGT device are sequentially placed on one surface of a bottom plate of the DGT device, and the other surface of the bottom plate is placed in the same order, namely the double-sided LDH is completed S -NO 3 Assembling a membrane DGT device;
alternatively, the LDH S -NO 3 The membrane is a layered double hydroxide gel film made of magnesium nitrate, aluminum nitrate and polyacrylamide with the mass ratio of 2:3:1, and is recorded as LDH S -NO 3 And (3) a membrane.
And the double-sided DGT device is placed for 2-4 days, and when the sulfate ion concentration in the environmental medium is less than 100 mu g/L, the DGT device is placed for 4 days, and the sulfate ion concentration is more than 200 mu g/L, the DGT device is placed for 2 days.
And the 2 elution extracting solutions are respectively 0.5M of HNO 3 Eluent and 0.5M HON 3 -(1M～3M)H 2 O 2 Eluent of 0.5M HNO 3 Sulfate ions and sulfide ions are eluted and extracted by the eluent, and sulfide is not oxidized into sulfate radicals; 0.5M HON 3 -(1M H 2 O 2 ～3MH 2 O 2 ) The same sulfate ions and sulfide ions are eluted and extracted by the eluent, but the sulfide ions are oxidized into a sulfate ion form by hydrogen peroxide, and finally the total concentration of the sulfate ions and the sulfide ions represented by the sulfate ion form is obtained.
And the volume ratio of the binding membrane to the eluent is 1: 10-1: 80, and the elution time is 20-30min until the binding membrane is completely melted to be colorless and transparent.
Furthermore, the extract was diluted at least 30 times before the sulfate concentration was measured by ion chromatography.
The concentration of sulfide ions in the extract (S (-II)) obtained by the subtraction method is calculated according to the following equation:
C S(-Ⅱ) ＝C [SO4(Ⅱ)+S(-Ⅱ)] g-C SO4(Ⅱ) g
wherein C is [SO4(Ⅱ)+S(-Ⅱ)] Is carried out with 0.5M HON 3 -(1M～3M)H 2 O 2 Concentration of sulfate ion, C, measured after dilution of the eluent SO4(Ⅱ) Is carried out with 0.5M HNO 3 And g is the dilution multiple.
And the concentrations of sulfate ions and sulfide ions in the combined film are respectively calculated according to Fick's first diffusion law and are calculated according to the following formula:
M＝C e V g /f e
C DGT ＝MΔ g /D g At
wherein C is e Is the concentration of sulfate and sulfide ions in the extract, V g Is the volume of the extraction liquid volume and the binding membrane, f e For elution efficiency, LDH S -NO 3 The elution efficiency of the membrane was 100%, negligible; delta g Is the thickness (cm) of the diffusion film; d g Is the diffusion coefficient (cm) of the ion 2 ·s -1 ) (ii) a A is DGT window area (cm) 2 ) (ii) a t is a unit time(s).
Use of a method as described above for the analysis and evaluation of sulphur morphological transformation and/or bioavailability and/or pollution in an environmental medium.
Moreover, the environmental medium is: the pH range is 5-9, and the ionic strength is 0.005-0.1 mol/L.
The invention has the advantages and positive effects that:
1. the method adopts LDH prepared from magnesium nitrate, aluminum nitrate and polyacrylamide S -NO 3 The film is a bonding film which is formed by bonding,realizes synchronous extraction and synchronous determination of sulfate radical and sulfide ions in environmental medium based on DGT technology, namely LDH S -NO 3 The combined membrane has high capacity, strong anti-interference capability and convenient operation, and expands the types and the synchronous determination quantity of the DGT for the sulfur ion determination.
2. The method of the invention improves the elution efficiency. The invention develops a synchronous elution and one-step conversion method: with 0.5M HNO 3 And 0.5M HNO 3 -(1M～3M)H 2 O 2 LDH was eluted with two eluents S -NO 3 The sulfate radical and sulfide on the membrane are completely eluted, and 0.5M HNO is adopted 3 -1M H 2 O 2 All sulfides in one combined membrane can be oxidized into sulfate radicals during elution, and the elution time is only 20-30min, so that the sulfate radicals and sulfides can be efficiently eluted.
3. The method simplifies the determination method, only needs to determine sulfate ions, obtains the concentration of sulfide ions by a subtraction method, avoids the complexity of different extraction methods and different devices required in detection, and improves the detection efficiency and convenience.
The method overcomes the defect that the existing DGT technology can not be used for synchronous extraction, separation and determination of sulfate radical and sulfide ions, is a method for synchronously adsorbing and determining the sulfate radical and the sulfide ions in soil, water and sediment media by using a double-sided DGT technology combined with a membrane, and can be used for analysis and evaluation of sulfur form conversion, biological effectiveness and pollution in an environment medium.
5. The method of the invention LDH S -NO 3 The membrane is used for in-situ synchronous extraction of sulfate radicals and sulfides, is simple to operate and convenient to use, avoids the change of the form between sulfate radicals and sulfides during active sampling, and improves the detection efficiency and accuracy by using the same combined membrane.
6. The invention develops a method for extracting and converting ions of the same element with different valence states in one step, which is based on the LDH S -NO 3 By combining with the membrane, the extraction (elution + conversion) method of the invention can significantly improve the elution efficiency and the conversion rate, and avoid the need of measuring sulfate ions and sulfide ions without the need of measuringThe same extraction method and the complicated operation of different devices. Based on different binding films, HNO 3 And H 2 O 2 The mixed reagent is used as an eluent for extraction by other DGT technologies, the concentration of the two reagents is generally 0.5M, and the extraction time is required to be more than 2-3h to obtain better elution efficiency; in the determination of S for different binding membranes 2- 、SO4 2- When ionic, it is necessary to be on S 2- 、SO4 2- The ions are extracted step by step, and different detection instruments are used for detection, so that the operation is complex and time-consuming. In the present invention, LDH is used S -NO 3 Combined with membrane, extraction method using 0.5M HNO 3 And 0.5M HNO 3 -(1M H 2 O 2 ～3MH 2 O 2 ) The two eluents, which are subjected to one-step extraction, elution and conversion and then can be simultaneously measured using ion chromatography, are based on the following 3 facts: 1) despite the introduction of large amounts of NO in the present invention 3 - The concentration of sulfate ions can be still well measured through ion chromatography after the extracting solution is diluted by 30 times, and the diluted extracting solution has no influence on the detection of the sulfate ions; 2) use of 0.5M HNO 3 When sulfate radicals and sulfides are eluted, the elution time is only 20-30min, the elution rate can reach 100 +/-5%, and the sulfides cannot be oxidized into sulfate radicals; 3) by adding (1M-3M) H 2 O 2 Can completely convert sulfide into sulfate radical, and realizes synchronous extraction, separation and determination of sulfate radical and sulfide by using a differential subtraction method.
Drawings
FIG. 1 is a schematic diagram of a double-sided bonded film DGT device configuration of the present invention;
FIG. 2 is a diagram of the application of the DGT device in soil (under flooding conditions) in the present invention, i.e. the variation of the concentration of sulfide ions measured by DGT in different soil depths with time;
FIG. 3 is a diagram of the application of the DGT device in the soil (under flooding conditions) in the present invention, i.e. the variation of the concentration of sulfate ions measured by DGT in different soil depths with time;
FIG. 4 is a graph showing the effect of different pH values on DGT measurement of sulfide and sulfate ions in the present invention;
FIG. 5 is a graph showing the effect of different ion strengths on DGT measurement of sulfide and sulfate ions in the present invention;
FIG. 6 is a graph of the amount of sulfide accumulated by a DGT unit in accordance with the invention as a function of sulfide ion concentration in solution;
FIG. 7 is a graph of the amount of sulfate accumulated by a DGT apparatus according to the invention as a function of the sulfate ion concentration in solution.
Detailed Description
The present invention is further illustrated by the following examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.
The raw materials used in the invention are all conventional commercial products if no special description is provided, the method used in the invention is all conventional methods in the field if no special description is provided, and the mass of all the materials used in the invention is the conventional use mass.
A method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in an environmental medium based on DGT technology adopts a layered double hydroxide polyacrylamide gel film, namely LDH S -NO 3 The membrane is a binding membrane, and double-sided LDH assembled to have the same binding membrane S -NO 3 The membrane DGT device is placed in soil, water and sediment to adsorb sulfate and sulfide, 2 binding membranes in the DGT device are taken out, 2 kinds of eluents are adopted to respectively elute, one eluent elutes sulfate ions and sulfide ions, the other eluent elutes sulfate ions and sulfide ions in the form of sulfate ions, then the extracting solution is diluted and simultaneously the concentration of the sulfate ions is determined by ion chromatography, the concentration of the sulfide ions in the extracting solution is obtained by using a differential subtraction method, and finally the concentrations of the sulfate ions and the sulfide ions in the binding membranes are respectively calculated according to the first diffusion law of Fick's.
Preferably, the double-sided LDH is as shown in FIG. 1 S -NO 3 The assembly of the membrane DGT device is as follows: the first protective film 1, LDH S -NO 3 The membrane 2, the diffusion membrane 3, the second protective membrane 4 and the protective shell 5 of the DGT device are sequentially arrangedOn one side of the substrate 6 of the DGT device, the other side of the substrate is placed in the same order, i.e. to complete a double-sided LDH S -NO 3 Assembling a membrane DGT device;
alternatively, the LDH S -NO 3 The membrane is a layered double hydroxide gel film made of magnesium nitrate, aluminum nitrate and polyacrylamide with the mass ratio of 2:3:1, and is recorded as LDH S -NO 3 And (3) a membrane.
Preferably, the double-sided DGT device is placed for 2-4 days, and when the sulfate ion concentration in the environmental medium is less than 100 mu g/L, the DGT device is placed for 4 days, and the sulfate ion concentration is more than 200 mu g/L, the DGT device is placed for 2 days.
Preferably, the 2 kinds of elution extracting solutions are respectively 0.5M of HNO 3 Eluent and 0.5M HON 3 -(1M～3M)H 2 O 2 Eluent of 0.5M HNO 3 Sulfate ions and sulfide ions are eluted and extracted by the eluent, and sulfide is not oxidized into sulfate radicals; 0.5M HON 3 -(1M H 2 O 2 ～3MH 2 O 2 ) The same sulfate ions and sulfide ions are eluted and extracted by the eluent, but the sulfide ions are oxidized into a sulfate ion form by hydrogen peroxide, and finally the total concentration of the sulfate ions and the sulfide ions represented by the sulfate ion form is obtained.
Preferably, the volume ratio of the binding membrane to the eluent is 1: 10-1: 80, and the elution time is 20-30min until the binding membrane is completely melted to be colorless and transparent.
Preferably, the extract is diluted at least 30 times before the sulfate concentration is determined by ion chromatography.
Preferably, the concentration of sulfide ions in the extract (S (-II)) obtained by the differential subtraction is calculated according to the following formula:
C S(-Ⅱ) ＝C [SO4(Ⅱ)+S(-Ⅱ)] g-C SO4(Ⅱ) g
wherein C is [SO4(Ⅱ)+S(-Ⅱ)] Is carried out with 0.5M HON 3 -(1M～3M)H 2 O 2 Concentration of sulfate ion, C, measured after dilution of the eluent SO4(Ⅱ) Is carried out with 0.5M HNO 3 And g is the dilution multiple.
Preferably, the concentrations of sulfate ions and sulfide ions in the binding membrane are respectively calculated according to Fick's first diffusion law and calculated according to the following formula:
M＝C e V g /f e
C DGT ＝MΔ g /D g At
wherein C is e Is the concentration of sulfate and sulfide ions in the extract, V g Is the volume of the extraction liquid volume and the binding membrane, f e For elution efficiency, LDH S -NO 3 The elution efficiency of the membrane was 100%, negligible; delta g Is the thickness (cm) of the diffusion film; d g Is the diffusion coefficient (cm) of the ion 2 ·s -1 ) (ii) a A is DGT window area (cm) 2 ) (ii) a t is a unit time(s).
Use of a method as described above for the analysis and evaluation of sulphur morphological transformation and/or bioavailability and/or pollution in an environmental medium.
Preferably, the environmental medium is: the pH range is 5-9, and the ionic strength is 0.005-0.1 mol/L.
Specifically, the preparation and detection are as follows:
in the following process, LDH S -NO 3 The membrane is a laminated hydroxide adsorbing material prepared from magnesium nitrate and aluminum nitrate, laminated hydroxide powder is prepared into a combined membrane through acrylamide, and the combined membrane can be specifically prepared according to a method disclosed by Chinese invention patent CN 106568689A.
Example 1
According to the method for synchronously measuring sulfate radical and sulfide ions in the environmental medium based on the DGT technology, the time-dependent change of the sulfate radical and the sulfide ions in different depths of the soil under the flooding condition is measured. Selecting 5kg of acid soil in Hunan through a 2mm sieve, filling the soil in a 6L round bucket, leveling the soil surface, adding deionized water, keeping a 2cm submerged layer, and assembling the double-sided LDH S -NO 3 Long DGT devices for films are described in items 1, 3,5. Inserting the membrane into soil for 7, 9, 11 and 16 days, wherein a window 2cm above the DGT is kept in a flooded layer and represents the soil depth of 0cm, a window 15cm below the DGT is kept in the soil, the soil depth of 5cm, 10cm and 15cm is respectively represented by the depth of every 5cm, taking out the device after standing for 48 hours, eluting and measuring sulfate and sulfide ions on the binding membrane to obtain the amount of the sulfate and sulfide accumulated in the binding membrane, and finally respectively obtaining the concentration of the sulfate and sulfide ions according to the first diffusion law of Fick's.
The method comprises the following specific operation steps:
(1) double-sided LDH S -NO 3 Assembly of membrane DGT: the first protective film, LDH S -NO 3 The membrane, the diffusion membrane, the second protective membrane and the DGT protective shell are sequentially placed on one surface of the DGT, and the other surface of the DGT protective shell is placed in the same order to complete the assembly of the double-sided DGT;
(2) nitrogen charging protection: putting the assembled DGT into deionized water, and filling nitrogen to remove oxygen in the DGT device;
(3) placement of DGT device: respectively inserting the soil into the flooded soil on days 1, 3, 5, 7, 9, 11 and 16, keeping a window 2cm above the DGT in the flooded layer, and taking out the device after standing for 48 h;
(4)LDH S -NO 3 slicing the film; and taking out 2 binding membranes after the DGT device is taken out, washing the binding membranes by deionized water, horizontally placing the binding membranes on a glass plate, marking one binding membrane as an A surface and one binding membrane as a B surface for later operation convenience, slicing the binding membrane of A, B surfaces 2cm above the binding membrane into a centrifugal tube, respectively marking the slicing membrane as A/B-0, slicing the remaining binding membranes by 5cm, putting the slicing membrane into the centrifugal tube, and sequentially marking the slicing membrane as A/B-5 and the slicing membrane as A/B-10.
(5) Sulfate ion and sulfide ion elution: according to LDH S -NO 3 The volume ratio of the membrane to the eluent is 1: 20 adding eluent into the centrifuge tube, wherein one side (A or B side) is 0.5M HNO 3 Eluting for 20min, and applying 0.5M HNO on the other side 3 -1M H 2 O 2 Eluting the eluent for 20 min;
(6) determination of sulfate ion and sulfide ion: extracting appropriate amount of extractive solution from step (5) and dilutingAfter 30-fold release, simultaneous measurement was performed by ion chromatography, with 0.5M HNO 3 The elution was measured as the concentration of sulfate ions in the extract, 0.5M HNO 3 -1M H 2 O 2 The elution was measured as the total concentration of sulfate and sulfide ions in the eluate, and the concentration of sulfide ions in the extract (S (-II)) was obtained by the subtraction method according to the following formula:
C S(-Ⅱ) ＝C [SO4(Ⅱ)+S(-Ⅱ)] g-C SO4(Ⅱ) g
wherein C is [SO4(Ⅱ)+S(-Ⅱ)] Is carried out with 0.5M HON 3 -1MH 2 O 2 Concentration of sulfate ion, C, measured after dilution of eluent SO4(Ⅱ) Is carried out with 0.5M HNO 3 And g is the dilution multiple.
(7) The concentrations of sulfate ions and sulfide ions in the combined membrane are respectively calculated according to Fick's first diffusion law and calculated according to the following formula:
M＝C e V g /f e
C DGT ＝MΔ g /D g At
wherein C is e Is the concentration of sulfate and sulfide ions in the extract, V g Is the volume of the extraction liquid volume and the binding membrane, f e For elution efficiency (LDH) S -NO 3 The elution efficiency of the membrane is 100%, negligible); delta g Is the thickness (cm) of the diffusion film; d g Is the diffusion coefficient (cm) of the ion 2 ·s -1 ) (ii) a A is DGT window area (cm) 2 ) (ii) a t is a unit time(s).
Fig. 2 and 3 are cross-sectional views of sulfate and sulfide ions measured by the method and changing with time at different depths in flooded soil. The change of sulfate and sulfide ions with time under different soil depths measured by DGT can be clearly seen from the figures 2 and 3: the concentration of sulfide ions is gradually increased along with the prolonging of time, and the concentration of sulfate ions is gradually reduced along with the prolonging of time, mainly because sulfate is subjected to reduction under a strong reduction condition under a flooding condition; different soilsUnder the depth of soil, the concentration difference of sulfide and sulfate ions is large, the concentration of sulfide ions is gradually increased along with the increase of the depth of soil in the first 4 days, the increase of the concentration of sulfide ions in middle layer soil (-5cm) is obvious from the 4 th day to the 10 th day and is higher than that of upper layer soil (0cm) and lower layer soil (-10cm), and the concentration of sulfide ions in the upper layer soil is higher than that of the middle layer soil after the 10 th day, possibly because the activity of microorganisms in the soil at different depths, redox conditions and competitive ions are different, the concentration of sulfide ions between soil layers is different; the concentration of sulfate ions in the sulfate is obviously higher in the middle and lower layers than in the upper layer soil, but the concentration difference of the sulfate ions in the middle and lower layer soil is not large, mainly because the concentration of the sulfate ions in the soil is large under a flooding condition, although the redox conditions are different at different depths, the distance between soil layers is small (only 5cm), and the change of the sulfate caused by the reduction action or the oxidation action of the sulfuric acid is not obvious as that of the sulfide. It can thus be seen that LDH is utilized S -NO 3 The DGT prepared by combining the membrane is used for synchronously measuring the concentrations of sulfate radicals and sulfide ions in situ, so that the method has stronger practicability, and particularly, the method has more environmental significance for discussing the changes of the sulfate radicals and the sulfate ions in soil, water and sediments at different depths.
Example 2
Preparing Na with different pH values 2 S solution, K 2 SO 4 The total volume of the solution ( pH 4, 5, 6, 7, 8, 9) was 2L, wherein the concentrations of sulfate ion and sulfide ion were both 50. mu.g/L, and the nitrate ion strength was 0.01 mol/L. The specific operation is as follows: placing the manufactured round DGT devices in Na with different pH values respectively 2 S solution, K 2 SO 4 The solution was kept for 6h, and then the binding membrane in the device was removed, where it was placed in K 2 SO 4 Bound membranes in solution were treated with 9mL of 0.5M HNO 3 Eluting for 20min, and standing in Na 2 Binding membrane of S solution 9mL of 0.5M HNO 3 -1M H 2 O 2 Eluting for 20min (adsorbed sulfide is converted into sulfate ion after elution), respectively extracting appropriate amount of extractive solution, diluting by 30 times, and measuring elution with ion chromatographyThe concentrations of sulfate and sulfide ions in the liquid are calculated according to a formula to obtain the concentration (C) measured by DGT DGT ) And with the concentration in solution (C) SOl ) By contrast, if the ratio (C) DGT /C SOl ) Between 1.0 + -0.1 indicates that DGT can adsorb sulfate and sulfide ions simultaneously. The results are shown in FIG. 4, and the ratios are in the range of 1.0. + -. 0.1 except for pH 4, indicating that DGT can be used in an environment of pH 5-9.
Example 3
Configuring Na with different ionic strengths 2 S solution, K 2 SO 4 The total volume of the solution (ionic strength: 0.001, 0.005, 0.01, 0.05, 0.1, 0.5mol/L) was 2L, wherein the sulfate ion and sulfide ion concentrations were 50. mu.g/L, and the pH was 5.5. The specific operation is as follows: placing the manufactured round DGT devices on Na with different ionic strengths respectively 2 S solution, K 2 SO 4 The solution was allowed to stand for 6h, and the bound membrane was removed from the device. The procedure was substantially the same as in example 2. As shown in FIG. 5, the ratio was 1.0. + -. 0.1 except for the ionic strengths of 0.001 and 0.7mol/L, indicating that DGT can be applied to the environment having an ionic strength of 0.005 to 0.1 mol/L.
Example 4
Configuring Na with different concentrations 2 S solution (0, 0.5, 1, 5, 10, 20, 40, 80, 100, 120mg/L), K 2 SO 4 The total volume of the solution (0, 0.5, 1, 5, 10, 20, 40, 80, 100, 120mg/L) was 2L, wherein the pH was 6 and the ionic strength was 0.01 mol/L. The specific operation is as follows: placing the manufactured round DGT devices in Na with different concentrations respectively 2 S solution, K 2 SO 4 The solution was kept for 36h, and then the binding membrane in the device was removed. The measurement procedure was essentially the same as in example 2, except that only the amount of sulfate and sulfide accumulated in the bound membrane was calculated, and the DGT concentration was not calculated. The results are shown in FIGS. 6 and 7, which indicate that LDH is present S -NO 3 The binding membrane has a stronger adsorption capacity for sulfate, while the adsorption capacity for sulfide is relatively low.
Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that: various substitutions, changes and modifications are possible without departing from the spirit and scope of the invention and the appended claims, and therefore the scope of the invention is not limited to the embodiments disclosed.
Claims (9)
1. A method for synchronously extracting and measuring the concentration of sulfate radical and sulfide ions in an environmental medium based on a DGT technology is characterized by comprising the following steps: the method adopts a layered double hydroxide polyacrylamide gel film (LDH) S -NO 3 The membrane is a binding membrane, and double-sided LDH assembled to have the same binding membrane S -NO 3 The membrane DGT device is placed in soil, water and sediment to adsorb sulfate and sulfide, then 2 binding membranes in the DGT device are taken out, 2 kinds of eluents are adopted to respectively elute, wherein one eluent elutes and extracts sulfate ions and sulfide ions, the other eluent elutes and extracts sulfate ions and sulfide ions in a sulfate ion form, then the extracting solution is diluted and simultaneously the concentration of the sulfate ions is determined by ion chromatography, the concentration of the sulfide ions in the extracting solution is obtained by using a differential subtraction method, and finally the concentrations of the sulfate ions and the sulfide ions in the binding membranes are respectively calculated according to Fick's first diffusion law;
the 2 kinds of eluents are respectively HNO of 0.5M 3 Eluent and 0.5M HON 3 -1M ~3MH 2 O 2 Eluent of 0.5M HNO 3 Sulfate ions and sulfide ions are eluted and extracted by the eluent, and sulfide is not oxidized into sulfate radicals; 0.5M HON 3 -1M H 2 O 2 ~3MH 2 O 2 The same sulfate ions and sulfide ions are eluted and extracted by the eluent, but the sulfide ions are oxidized into a sulfate ion form by hydrogen peroxide, and finally the total concentration of the sulfate ions and the sulfide ions represented by the sulfate ion form is obtained.
2. The method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in the environmental medium based on the DGT technology as claimed in claim 1, wherein: the double-sided LDH S -NO 3 Assembly of membrane DGT deviceThe following were used: the first protective film, LDH S -NO 3 The membrane, the diffusion membrane, the second protective membrane and the protective shell of the DGT device are sequentially placed on one surface of a bottom plate of the DGT device, and the other surface of the bottom plate is placed in the same order, namely the double-sided LDH is completed S -NO 3 Assembling a membrane DGT device;
alternatively, the LDH S -NO 3 The membrane is a layered double hydroxide gel film made of magnesium nitrate, aluminum nitrate and polyacrylamide with the mass ratio of 2:3:1, and is recorded as LDH S -NO 3 And (3) a membrane.
3. The method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in the environmental medium based on the DGT technology as claimed in claim 1, wherein: the double-sided DGT device is placed for 2-4 days, and when the concentration of sulfate ions in the environmental medium is less than 100 mug/L, the DGT device is placed for 4 days, and the concentration of the sulfate ions is more than 200 mug/L, the DGT device is placed for 2 days.
4. The method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in the environmental medium based on the DGT technology as claimed in claim 1, wherein: the volume ratio of the binding membrane to the eluent is 1: 10-1: 80, and the elution time is 20-30min until the binding membrane is completely melted to be colorless and transparent.
5. The method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in the environmental medium based on the DGT technology as claimed in claim 1, wherein: the concentration of sulfate can be determined by ion chromatography after the extract is diluted at least 30 times.
6. The method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in the environmental medium based on the DGT technology as claimed in claim 1, wherein: the concentration S (-II) of sulfide ions in the extracting solution is obtained by using a subtraction method, and is calculated according to the following formula:
C S(-Ⅱ) =C ［SO4(Ⅱ)+S(-Ⅱ)] g-C SO4(Ⅱ) g
whereinC ［SO4(Ⅱ)+S(-Ⅱ)] Is carried out with 0.5M HON 3 -1M ~3MH 2 O 2 The concentration of sulfate ion is measured after the eluent is diluted,C SO4(Ⅱ) is carried out with 0.5M HNO 3 And g is the dilution multiple.
7. The method for synchronously extracting and measuring the concentrations of sulfate ions and sulfide ions in the environmental medium based on the DGT technology as claimed in any one of claims 1 to 6, wherein: the concentrations of sulfate ions and sulfide ions in the combined membrane are respectively calculated according to Fick's first diffusion law and calculated according to the following formula:
M=C e V g /f e
C DGT =MΔ g /D g At
whereinC e Is the concentration of sulfate and sulfide ions in the extract, V g Is the volume of the extraction liquid volume and the binding membrane, f e For elution efficiency, LDH S -NO 3 The elution efficiency of the membrane was 100%, negligible; delta g Is the thickness cm of the diffusion film; d g Is the diffusion coefficient cm of the ion 2 •s -1 (ii) a A is DGT window area cm 2 (ii) a t is a unit time s.
8. Use of a method according to any one of claims 1 to 7 for the analysis and evaluation of sulfur morphological transformation and/or bioavailability and/or contamination in an environmental medium.
9. Use according to claim 8, characterized in that: the environment medium is as follows: the pH range is 5-9, and the ionic strength is 0.005-0.1 mol/L.
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