Method for adsorbing and desorbing six phenoxy carboxylic acid herbicides in water by nitrate radical type hydrotalcite adsorbent
Technical Field
The invention belongs to the field of application of adsorbents of analytical chemistry, and particularly relates to an adsorption and desorption method of nitrate radical type hydrotalcite adsorbents to six phenoxy carboxylic acid herbicides in water.
Background
The mandatory standard GB 5749 domestic drinking water 2006 in China strictly stipulates the limited value of herbicide residues, wherein various phenoxy carboxylic acid herbicides exist. Phenoxy carboxylic acid herbicides represented by 2,4-D are the second most selective herbicide varieties in agricultural production and are widely applied to paddy fields, non-cultivated lands, pastures and the like. The herbicide is dissolved in water in an anion form, can be rapidly diffused after being applied, and pollutes the source water of people along with the transportation of the water body. With the increasing use amount and the use range, the substances become important factors for the water quality safety of drinking water.
The limit value of 2,4-D in drinking water is 0.03mg/L according to national standard regulation, and the limit value of phenoxy carboxylic acid herbicides such as 2,4-D propionic acid, 2-methyl-4-chloropropionic acid and the like is 0.002-0.9 mg/L according to the drinking water standard regulation of the world health organization, so that the requirement is strict. At present, the detection method of phenoxy carboxylic acid herbicides in water mainly comprises a chromatography and mass spectrum combined method; the pretreatment method goes through two stages, liquid-liquid extraction enrichment is adopted in the early stage, namely the pH value of a water sample is adjusted, then an organic solvent is used for extraction, and then people adopt a solid phase extraction column to directly adsorb and enrich. However, the enrichment of the liquid-liquid extraction method has the defects of large amount of used organic solvent, complex operation and the like; the solid phase extraction method has the defects of single type of alternative adsorbents, low adsorption rate, high price and the like. Therefore, the difficulty of detecting the trace phenoxy carboxylic acid herbicide residue in water in order to realize effective enrichment is high, and the research of an effective enrichment adsorbent and the development of an application method thereof are urgently needed.
Hydrotalcite (LDHS) is a typical anionic Layered material, has the characteristics of small-size effect, surface effect, macroscopic quantum tunneling effect and the like, and has the characteristics of large specific surface area, strong ion exchange capacity, high adsorption capacity and the like, so that the hydrotalcite has good adsorption performance on trace residues, and becomes an anionic adsorbent with wide application and development prospects in the field of analysis and testing. Currently, hydrotalcite is reported as an adsorbent for inorganic and organic anionic pollutants, for example, hydrotalcite is used as an adsorbent for adsorbing dyes and pesticides such as chlorpyrifos and glyphosate; the static adsorption report of the hydrotalcite as the adsorbent to 2, 4-drops in water shows the application prospect of the hydrotalcite adsorbent in the field of phenoxy carboxylic acid herbicide adsorption.
Aiming at the current situation that the prior phenoxy carboxylic acid herbicide efficient adsorbent in water is lacked and the application method thereof, and combining the characteristic that hydrotalcite has strong adsorption capacity to anions, the invention provides a method for adsorbing and desorbing six phenoxy carboxylic acid herbicides (related information is shown in table 1) in water by taking nitrate type hydrotalcite prepared by a double-drop coprecipitation method as an adsorbent. The method has the advantages of simple operation, high adsorption efficiency, easy elution and the like.
TABLE 1 information on six phenoxy carboxylic acid herbicides
Disclosure of Invention
Aiming at the problem of lack of high-efficiency adsorbents of phenoxy carboxylic acid herbicides in water and application methods thereof, the invention aims to provide methods for adsorbing and desorbing six phenoxy carboxylic acid herbicides in water by using nitrate radical type hydrotalcite as an adsorbent.
The present invention solves the above problems by the following technical solutions.
A method for adsorbing and desorbing six phenoxy carboxylic acid herbicides in water by a nitrate radical type hydrotalcite adsorbent comprises the following steps:
step one, adjusting the pH value: adjusting the pH value of an aqueous solution in which six phenoxy carboxylic acid herbicides are dissolved;
step two, adsorption: weighing a proper amount of nitrate type hydrotalcite adsorbent in a centrifuge tube, adding six phenoxy carboxylic acid herbicide aqueous solutions with the pH values adjusted, carrying out vortex, oscillation and centrifugation, and removing supernatant;
step three, washing: adding deionized water into a centrifugal tube, carrying out vortex, centrifuging and removing a supernatant;
step four, desorption: adding a desorption solvent into a centrifugal tube, whirling, oscillating and centrifuging, and obtaining supernate which is a desorption solution containing six phenoxy carboxylic acid herbicides.
Wherein,
the six phenoxy carboxylic acid herbicides are 2, 4-dichlorophenoxyacetic acid, 2, 4-dichlorophenoxypropionic acid, 2, 4-dichlorophenoxybutyric acid, 2-methyl-4-chlorophenoxyacetic acid, 2-methyl-4-chlorophenoxybutyric acid and 2,4, 5-trichlorophenoxyacetic acid.
The water is drinking water.
In the first step, the pH value of the aqueous solution is adjusted to be 4.0-10.0.
The dosage of the nitrate type hydrotalcite is 0.2g to 0.4 g.
The vortex time is 1-3 min, the oscillation time is 10-30 min, the centrifugal rotating speed is 2500-4500 r/min, and the time is 3-5 min.
And the amount of deionized water for washing in the third step is 10-15 mL.
In the fourth step, the desorption agent is 0.2-0.4 mol/L disodium hydrogen phosphate solution, and the volume of the desorption agent added is 2.00 mL.
The invention has the advantages that:
(1) the nitrate radical type hydrotalcite adsorbent selected by the invention has high-efficiency adsorption capacity on six phenoxy carboxylic acid herbicides, and has good dispersity and high adsorption efficiency in aqueous solution.
(2) The adsorption and desorption provided by the invention are carried out by adopting a dispersed solid phase extraction mode, and compared with the solid phase extraction operation, the adsorption and desorption are simple, convenient, feasible, quick and efficient.
(3) The method does not need to use an organic solvent to extract the phenoxy carboxylic acid herbicide, and is more suitable for the concept of environmental protection compared with liquid-liquid extraction.
Drawings
FIG. 1 is a typical chromatogram of six phenoxy carboxylic acid herbicides, wherein 1 is MCPA, 2 is 2,4-D, 3 is 2,4-DB, 4 is 2,4,5-T, 5 is 2,4-DP, and 6 is MCPB;
FIG. 2 is a chromatogram of adsorption and desorption comparison of six phenoxy carboxylic acid herbicides, wherein A is a chromatogram of a standard solution, B is a chromatogram of a supernatant after centrifugation after adsorption, C is a chromatogram of a supernatant after centrifugation after desorption, and the concentrations of A and C are both 2.0 mg/L.
Detailed Description
For further disclosure, but not limitation, the present invention is described in further detail below with reference to examples.
(1) The reagent medicines involved in the embodiments of the present invention are as follows:
a) the preparation method of the nitrate type hydrotalcite adsorbent comprises the following steps: dissolving 190g of magnesium nitrate (0.04mol) and 93g of aluminum nitrate (0.02mol) in 500mL of deionized water from which carbon dioxide is removed, dissolving 79g of sodium hydroxide (0.12mol) in 500mL of deionized water from which carbon dioxide is removed, respectively dropwise adding the solution into a three-necked bottle, intensively stirring under the protection of nitrogen, adjusting the dropping speed to keep the pH value at about 10, crystallizing the obtained colloidal solution at 75 ℃ for 20 hours after the dropwise adding is finished, performing suction filtration, washing a filter cake with hot water until the pH value is less than 8, and performing vacuum drying to obtain nitrate type hydrotalcite.
b) Acetonitrile, formic acid, ammonium formate: carrying out chromatographic purification; the water is first-grade water meeting the GB/T6682 specification.
c) Six phenoxy carboxylic acid herbicides solid standard: purity 98.0% or more, Dr.
d) Preparation of six phenoxy carboxylic acid herbicide standard stock solutions: weighing appropriate amount of six herbicide standards, dissolving with deionized water and fixing volume to prepare 1000mg/L stock solution, and storing at-4 deg.C for use.
(2) Liquid chromatography test conditions:
a) a chromatographic column: c18The separation column is 150mm multiplied by 4.6mm, and the particle size is 5 mu m; front connected C18The column size was 12.5 mm. times.4.6 mm, and the particle size was 5 μm.
b) Temperature of the column: at 25 ℃.
c) Mobile phase: the solvent A is acetonitrile and water which are 80+20 in volume ratio; the solvent B is water; wherein both solvents A and B contained 3mM formic acid and 3mM ammonium formate buffer solution.
d) Elution gradient: solvent a rose from 25% to 75% within 40 min.
e) Flow rate: 1.0 mL/min.
f) Detection wavelength: 230 nm.
g) Sample introduction amount: 100 μ L.
Example 1
(1) Adjusting the pH of an aqueous solution
Accurately transferring 1.0mL (accurate to 0.01mL) of the stock solution, diluting with tap water to 100.0mL to obtain six phenoxy carboxylic acid herbicide aqueous solutions with the concentration of 10mg/L, adjusting the pH value to 4.0, sealing, marking, filtering the liquid, and performing high performance liquid chromatography.
(2) Adsorption
Weighing 0.2g of nitrate type hydrotalcite in a 50mL centrifuge tube, taking 10.0mL of the diluted solution, vortexing for 3min, oscillating for 10min, centrifuging for 3min at the rotating speed of 4500r/min, taking 1.0mL of supernatant, and filtering for high performance liquid chromatography analysis.
(3) Washing machine
Adding 10mL of deionized water into the centrifugal tube, vortexing for 3min, oscillating for 10min, centrifuging at the rotating speed of 4500r/min for 5min, and discarding the supernatant;
(4) desorption and adsorption
Adding 2.00mL of 0.2mol/L disodium hydrogen phosphate solution into the centrifuge tube, vortexing for 3min, oscillating for 10min, centrifuging at the rotating speed of 4500r/min for 5min, and filtering supernate to be analyzed by high performance liquid chromatography;
(5) liquid chromatography assay
And (4) taking the liquid to be analyzed filtered in the steps (1), (2) and (4) for analysis test, wherein the concentration in the step (1) is 10.0mg/L, and the theoretical concentration in the step (4) is 50 mg/L.
The results of the analytical tests on the above solutions are shown in table 2. The results in table 2 show that the adsorbent has high adsorption capacity for six phenoxy carboxylic acid herbicides, the adsorption rate is up to more than 98.5%, and the desorption rate using disodium hydrogen phosphate as the desorption agent is also up to more than 96.0%, so that the effect is good.
TABLE 2 concentrations of six phenoxy carboxylic acid herbicides (n ═ 3)
Example 2
(1) Adjusting the pH of an aqueous solution
Accurately transferring 2.0mL (accurate to 0.01mL) of the stock solution, diluting with well water to 100.0mL to obtain six phenoxy carboxylic acid herbicide aqueous solutions with the concentration of 20mg/L, adjusting the pH value to 10.0, sealing, marking, filtering the liquid, and performing high performance liquid chromatography.
(2) Adsorption
Weighing 0.4g of nitrate type hydrotalcite in a 50mL centrifuge tube, taking 10.0mL of the diluted solution, vortexing for 3min, oscillating for 15min, centrifuging for 3min at the rotating speed of 2500r/min, taking 1.0mL of supernatant, and filtering for high performance liquid chromatography analysis.
(3) Washing machine
Adding 10mL of deionized water into the centrifugal tube, vortexing for 3min, oscillating for 15min, centrifuging at the rotating speed of 3500r/min for 3min, and discarding the supernatant;
(4) desorption and adsorption
Adding 2.00mL of 0.4mol/L disodium hydrogen phosphate solution into the centrifuge tube, vortexing for 3min, oscillating for 15min, centrifuging at the rotating speed of 4500r/min for 3min, and filtering supernate to be subjected to high performance liquid chromatography;
(5) liquid chromatography assay
In the above steps, the retention time of the six phenoxy carboxylic acid herbicides was measured to be the same as that in example 1, and the peak areas were different.
And (4) taking the liquid to be analyzed filtered in the steps (1), (2) and (4) for analysis test, wherein the concentration in the step (1) is 20.0mg/L, and the theoretical concentration in the step (4) is 100 mg/L.
The results of the analytical tests on the above solutions are shown in Table 3. The results in table 3 show that the adsorbent has high adsorption capacity for six phenoxy carboxylic acid herbicides, the adsorption rate is as high as more than 99.0%, and the desorption rate using disodium hydrogen phosphate as the desorption agent is as high as more than 96.4%, so that the effect is good.
TABLE 3 concentration of six phenoxy carboxylic acid herbicides (n ═ 3)
The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the spirit of the invention, which falls within the scope of the invention, and therefore the scope of the patent of the invention shall be governed by the appended claims.