Method for separating iodide and glyphosate in high-salt water through two-dimensional ion chromatography

Abstract

The invention belongs to the technical field of water quality detection, and provides a method for separating iodide and glyphosate in heavy salt water by two-dimensional ion chromatography, which comprises the following steps: A, making standard curves: respectively establishing conductivity peak area-concentration standard curves of iodide and glyphosate by ion chromatography; b, sample collection: collecting a water sample, adjusting the pH value of the water sample to 10-12 by using a saturated sodium hydroxide solution, and taking the water sample as a to-be-detected solution; c, sample treatment: filtering the solution to be detected in the step B, and waiting for analysis on a machine; and D, sample detection: carrying out ion chromatography analysis on the solution to be detected collected in the step C, respectively detecting the chromatographic peak areas of the iodide and the glyphosate in the solution to be detected, and substituting the chromatographic peak areas into the conductivity peak area-concentration standard curve of the iodide and the glyphosate prepared in the step A to obtain the concentration values of the iodide and the glyphosate in the solution to be detected. The method can realize simultaneous determination of iodide and glyphosate in high-salt underground water, and has the advantages of fast analysis speed, simple operation, less interference and high sensitivity.

Description

Technical Field

[0001] The invention belongs to the technical field of water quality detection and relates to a method for separating iodide and glyphosate in high-salt water by two-dimensional ion chromatography. Background Art

[0002] Glyphosate (Gly) is a broad-spectrum, non-selective, lethal herbicide with low price and excellent weed control performance. It has been widely used as a low-toxic environmentally friendly pesticide in the world for weed control in low-till and no-till fields and directional protective spraying between rows of tall crop fields. Glyphosate has low volatility and is difficult to vaporize. It is not retained on conventional reversed-phase columns, so it is difficult to separate and determine directly using gas chromatography; and glyphosate is similar in structure to amino acids and amino sugars existing in nature, lacks chromophores, and is difficult to detect directly using ultraviolet and fluorescence detectors, so it is difficult to detect directly using liquid chromatographs or liquid chromatography-tandem mass spectrometry (LC-MS / MS). Iodide and glyphosate are respectively classified as conventional indicators and non-conventional indicators of groundwater quality in the Groundwater Quality Standard (GB / T14848-2017). In order to reduce interference, ion chromatography and derivatization liquid chromatography are usually used for determination. Derivatization liquid chromatography for glyphosate determination requires strict control of derivatization conditions, and the operation is relatively cumbersome. It can be seen that using two methods for determination at the same time is time-consuming and labor-intensive. An ion chromatography column can also be used for simultaneous determination, but for conventional anions (F - , Cl - 、NO2 - 、NO3 - PO4 3- 、SO4 2- Groundwater with high content of anions (such as ) is greatly affected by conventional anions. The two compounds are affected by tailing peaks, the baseline is raised, the recovery rates of the measurements are poor, and accurate quantification is impossible.

[0003] Based on this, it is of great significance to develop a method for simultaneously detecting iodide and glyphosate in water. Summary of the invention

[0004] The invention provides a method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography. The method can realize the simultaneous determination of iodide and glyphosate in high salt water, has fast analysis speed, simple operation, less interference and high sensitivity.

[0005] The technical solution of the present invention is achieved in this way: A method for separating iodide and glyphosate in high-salt water by two-dimensional ion chromatography comprises the following steps: A. Preparation of standard curves: Conductivity peak area-concentration standard curves of iodide and glyphosate were established by ion chromatography; B. Sample collection: Collect water samples and adjust the pH of the water samples to 10-12 with saturated sodium hydroxide solution as the test solution; glyphosate decomposes slower in an alkaline environment than in an acidic and neutral environment, so adjusting the pH to 12 is optimal; C. Sample processing: filter the solution to be tested in step B and wait for analysis; D. Sample testing: The solution to be tested collected in step C is subjected to ion chromatography analysis to respectively measure the chromatographic peak areas of iodide and glyphosate in the solution to be tested, and the chromatographic peak areas are respectively inserted into the conductivity peak area-concentration standard curve of iodide and glyphosate prepared in step A to obtain the iodide and glyphosate concentration values ​​in the solution to be tested; In step A and step D, the test conditions used are as follows: One-dimensional chromatographic column model: IonPac AS19, 4mm×250mm; its chromatographic conditions include: Eluent: 32 mmol / L potassium hydroxide or sodium hydroxide; Eluent flow rate: 1 mL / min; Suppressor current: 80~90mA; Column temperature: 25~30℃; Detection pool temperature: 30~35℃; Two-dimensional chromatography column model: IonPac AS19, 2mm×250mm; its chromatographic conditions include: Eluent: 25~30mmol / L potassium hydroxide or sodium hydroxide; Eluent flow rate: 0.3 mL / min; Suppressor current: 19~23mA; Column temperature: 25~30℃; Detection pool temperature: 30~35℃; Enrichment column model: IonPac AG19, 4mm×100mm; The two-dimensional six-way valve was switched at 7.5 min for enrichment, and the enrichment time was 4.5 min. Detector: conductivity detector; Injection volume: 100 μL.

[0006] Furthermore, the chromatographic conditions of the one-dimensional chromatographic column are: The eluent was 32 mmol / L sodium hydroxide; Suppressor current 80mA; Column temperature: 30°C; The detection cell temperature was 35°C.

[0007] Furthermore, the chromatographic conditions of the two-dimensional chromatographic column are: The eluent was 28 mmol / L potassium hydroxide; Suppressor current 21mA; Column temperature: 30°C; The detection cell temperature was 35°C.

[0008] Further, the steps of establishing the conductivity peak area-concentration standard curve of iodide and glyphosate in step A include: Equal amounts of iodide and glyphosate are dissolved in ultrapure water, and diluted step by step to prepare several groups of mixed standard solutions with concentration gradients, wherein the concentration gradient range of the mixed standard solutions is 0.00-1.00 μg / ml; and then ion chromatography is performed respectively, and the measured chromatographic peak area is used as the ordinate and the corresponding mass concentration of iodide and glyphosate is used as the abscissa to establish the conductivity peak area-concentration standard curve of iodide and glyphosate.

[0009] Furthermore, the test solution in step B is refrigerated and stored at 0°C-4°C away from light.

[0010] Furthermore, in step B, the pH of the water sample is adjusted to 12 with a saturated sodium hydroxide solution.

[0011] Furthermore, the filtration step in step C is: filtering the solution to be tested through an aqueous filter membrane with a pore size of 0.45 μm and a Na-type purification column in sequence.

[0012] Furthermore, after filtration, 5 ml of the primary filtrate was discarded, and 1.5 ml of the sample was collected in a sample injection bottle for analysis.

[0013] The working principle and beneficial effects of the present invention are: 1. The present invention provides a method for separating iodide and glyphosate in high-salt water by two-dimensional ion chromatography, using a conductivity detector and two ion chromatography columns to simultaneously separate iodide and glyphosate in high-salt groundwater. The retention time period of the two compounds is determined by a one-dimensional ion chromatography column, and after enrichment by an enrichment column, the two-dimensional ion chromatography column is switched to, and then quantitatively determined by a conductivity detector. The analysis speed is fast, the operation is simple, the interference is small, the sensitivity is high, and the accuracy is good. The detection limit is determined by referring to HJ168-2020. The detection limits of iodide and glyphosate in the present invention are 0.002mg / L and 0.004mg / L, respectively.

[0014] 2. In the present invention, the ion chromatography columns used in the first and second dimensions are both of the AS19 model, with different inner diameters of 4 mm and 2 mm, respectively. This is because the first-dimensional chromatography column can determine the retention time range of the target. After switching to the 2-dimensional 2 mm ion chromatography column, the use of a 2 mm thin column in the second dimension helps to improve the sensitivity of the method; The retention times of iodide and glyphosate separated on the AS19 chromatographic column are close. The present invention can meet the measurement requirements by using simple isocratic elution, without the need for complicated gradient elution that affects the baseline. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0016] Figure 1 The chromatogram of the spiked sample No. 7 measured by a one-dimensional ion chromatography column in Example 1 of the present invention; Figure 2 The chromatogram of the spiked sample No. 7 measured by a two-dimensional ion chromatography column in Example 1 of the present invention; Figure 3 is a chromatogram of the 1 μg / ml mixed standard solution in Example 1 of the present invention; Figure 4 This is the chromatogram of the 1 μg / ml mixed standard solution in Example 2 of the present invention; Figure 5 is the chromatogram of the 1 μg / ml mixed standard solution in Example 3 of the present invention; Figure 6 This is the ion chromatogram of the sample measured by a one-dimensional ion chromatography column in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Unless otherwise specified, the equipment used in this embodiment is conventional equipment, the reagents used are conventional reagents, all of which can be commercially obtained, and the operating methods used are all recorded in textbooks in this field.

[0019] As shown in Table 1, there is information about the raw materials and instruments used in the present invention.

[0020] Example 1 A method for separating iodide and glyphosate in high-salt water by two-dimensional ion chromatography comprises the following steps: A. Preparation of standard curve: including the following steps: (1) Preparation of 1000 mg / L glyphosate standard stock solution: Accurately weigh 10.44 mg of glyphosate (purity and manufacturer are shown in Table 1), dissolve it in deionized water, make up to 10 mL with water, transfer to a polypropylene reagent bottle, and store at 0°C in the dark until use; The 1000 mg / L iodide standard stock solution was purchased directly, and the manufacturer is shown in Table 1.

[0021] Take 1 mL of 1000 mg / L iodide and glyphosate respectively, dilute to 100 mL volumetric flask to obtain a mixed standard with a concentration of 100 mg / L, dilute the mixed standard 10 times to obtain a 10 mg / L mixed standard intermediate solution, and dilute the intermediate mixed standard 10 times again to obtain a 1 mg / L mixed standard standard working solution.

[0022] The mixed standard series solution includes 6 groups of solutions, and the concentrations of iodide and glyphosate in each group of solutions are the same, namely 0.00µg / ml, 0.02µg / ml, 0.05µg / ml, 0.08µg / ml, 0.10µg / ml, 0.50µg / ml and 1.00µg / ml; (2) The mixed standard series solution prepared in step (1) is subjected to ion chromatography to obtain ion chromatographic standard spectra of iodide and glyphosate, and a standard curve is drawn with the chromatographic peak area as the ordinate and the corresponding mass concentration as the abscissa, and a linear regression equation of iodide and a linear regression equation of glyphosate are obtained respectively; ultrapure water is directly subjected to ion chromatography to serve as a blank experiment; Figure 3 , is the chromatogram of the 1 μg / ml mixed standard solution in this example; The linear regression equation of the iodide is Y1=0.8284X1-0.0165, R 2 is 0.9990; the linear regression equation of glyphosate is Y2=0.5786X2-0.0077, R 2 is 0.9996; y is the conductivity peak area, in μS*min; x is the mass concentration of the target substance, in μg / ml; a and b are dimensionless coefficients; B. Sample collection: Collect water samples in polypropylene containers or glass bottles, adjust the pH of the water samples to 12 with saturated sodium hydroxide solution, and store them as the test solution at 0°C in a dark place. C. Sample treatment: Take the solution to be tested in step B, pass it through a 0.45µm aqueous phase needle filter and a 1g Na type cation purification column, discard 5ml of the initial filtrate, collect 1.5ml of the sample in a sample injection bottle, and wait for analysis on the machine; D. Sample testing: Perform ion chromatography analysis on the test solution collected in step C to obtain the chromatographic peak area, which is respectively substituted into y1 and y2 in step A to perform quantitative and qualitative measurement of iodide and glyphosate in the test solution.

[0023] In the ion chromatography determination in steps A and D, an ion chromatography instrument is used for analysis, and the chromatographic conditions used are as follows: First-dimension chromatography column model: Dionex IonPac TM AS19 (RTIC TM 4mm×250mm Separator); Its chromatographic conditions are: Eluent: 32mmol / L sodium hydroxide; Eluent flow rate: 1 mL / min; Suppressor current: 80mA; Column temperature: 30°C; Detection cell temperature: 35°C; Two-dimensional chromatography column model: Dionex IonPac TM AS19 (2mm×250mm); its chromatographic conditions are: Eluent: 28mmol / L potassium hydroxide; Eluent flow rate: 0.3 mL / min; Suppressor current: 21mA; Column temperature: 30°C; Detection cell temperature: 35°C; Enrichment column model: Dionex IonPac TM AG19 (4mm×100mm); The two-dimensional six-way valve was switched at 7.5 min for enrichment, and the enrichment time was 4.5 min; Detector: conductivity detector; Injection volume: 100 μL; Total running time: 28 minutes.

[0024] In order to ensure that the two compounds are completely transferred to the two-dimensional chromatographic column for separation, the switching time of the two-dimensional six-way valve is set at 7.5 minutes. After 4.5 minutes of enrichment, it is switched back. By changing the concentration of the eluent in the first dimension, the peak time of the target will also change, and the separation from the conventional ions will also change. In order to ensure separation, the eluent concentration of the one-dimensional chromatographic column is 32moml / L.

[0025] like Figure 1 is a chromatogram of the spiked sample No. 7 (the spiked sample No. 7 in the following recovery test) measured by a one-dimensional ion chromatography column in Example 1, Figure 2 This is the chromatogram of spiked sample No. 7 measured using a two-dimensional ion chromatography column, where the spiked amount of iodide is 0.3 mg / L and the spiked amount of glyphosate is 0.5 mg / L. Figure 1It can be seen that the chromatographic peaks of iodide and glyphosate are seriously interfered by conventional ions and there are no obvious chromatographic peaks. Figure 2 It can be seen that iodide and glyphosate have achieved baseline separation. By comparing the two chromatograms, it can be clearly seen that the advantage of the present invention of using two-dimensional ion chromatography to determine iodide and glyphosate in high salt water.

[0026] Example 2 The only difference from Example 1 is that the chromatographic conditions used in the ion chromatography determination in steps A and D are different, specifically: First-dimension chromatography column model: Dionex IonPac TM AS19 (RTIC TM 4mm×250mm Separator); Its chromatographic conditions are: Eluent: 32mmol / L sodium hydroxide; Eluent flow rate: 1 mL / min; Suppressor current: 80mA; Column temperature: 30°C; Detection cell temperature: 35°C; Two-dimensional chromatography column model: Dionex IonPac TM AS19 (2mm×250mm); its chromatographic conditions are: Eluent: 25mmol / L potassium hydroxide; Eluent flow rate: 0.3 mL / min; Suppressor current: 19mA; Column temperature: 30°C; Detection cell temperature: 35°C; Enrichment column model: IonPac AG19, 4mm×100mm; The two-dimensional six-way valve was switched at 7.5 min for enrichment, and the enrichment time was 4.5 min; Detector: conductivity detector; Injection volume: 100 μL; Total running time: 30 minutes.

[0027] like Figure 4 , which is the chromatogram of the 1 μg / ml mixed standard solution in this example, the separation between iodide and glyphosate is good, and the distance between the two chromatographic peaks is far.

[0028] Example 3 The only difference from Example 1 is that the chromatographic conditions used in the ion chromatography determination in steps A and D are different, specifically: First-dimension chromatography column model: Dionex IonPac TM AS19 (RTIC TM4mm×250mm Separator); Its chromatographic conditions are: Eluent: 32mmol / L sodium hydroxide; Eluent flow rate: 1 mL / min; Suppressor current: 80mA; Column temperature: 30°C; Detection cell temperature: 35°C; Two-dimensional chromatography column model: Dionex IonPac TM AS19 (2mm×250mm); its chromatographic conditions are: Eluent: 30mmol / L potassium hydroxide; Eluent flow rate: 0.3 mL / min; Suppressor current: 23mA; Column temperature: 30°C; Detection cell temperature: 35°C; Enrichment column model: IonPac AG19, 4mm×100mm; The two-dimensional six-way valve was switched at 7.5 min for enrichment, and the enrichment time was 4.5 min; Detector: conductivity detector; Injection volume: 100 μL; Total running time: 28 minutes.

[0029] like Figure 5 , is the chromatogram of the 1 μg / ml mixed standard solution in this example, iodide and glyphosate can be baseline separated.

[0030] Comparative Example 1 The only difference from Example 1 is that in the ion chromatography determination in steps A and D, the chromatographic conditions used are different, and only one-dimensional ion chromatography is used, specifically: Chromatographic column model: Dionex IonPac TM AS19 (2mm×250mm); Eluent: 28mmol / L potassium hydroxide; Eluent flow rate: 0.3 mL / min; Suppressor current: 21mA; Column temperature: 30°C; Detection cell temperature: 35°C; Under this chromatographic condition, the same high-salinity groundwater with a spiked amount of 0.5 mg / L was measured, and the chromatogram was as follows Figure 6 As shown in the figure, it can be seen that the chromatographic peak of the target substance is seriously affected by the tailing peak of the conventional ion and cannot be accurately integrated. It can be seen that the use of a one-dimensional chromatographic column cannot achieve accurate qualitative and quantitative analysis of iodide and glyphosate in high saline water.

[0031] 1. Method detection limit test According to the detection limit test requirements of HJ 168-2020, a laboratory blank test was first conducted, using experimental water and following the test steps of 5.6.2 standard solution. The test result was not detected. Therefore, the method detection limit was determined by using 0.01 mg / L iodide ion and 0.02 mg / L glyphosate mixed standard solution for 7 parallel tests. According to all the steps of sample analysis, the blank test was repeated n (≥7) times, and each test result was converted into the concentration or content in the sample to calculate n The standard deviation of the replicates was used to calculate the detection limit of the method according to formula (1).

[0032] MDL = t ( n -1,0.99)×S (1) Where: MDL – method detection limit; n - the number of parallel determinations of samples; t——degrees of freedom n -1, when the confidence level is 99% t Distribution (one-sided); S—— n Standard deviation of the replicates.

[0033] The degrees of freedom are n -1, the confidence level is 99%, when n When t ( n -1,0.99) = 3.143. In this study, different standard solutions were measured 7 times in parallel, and the concentrations used were 3 to 5 times the estimated detection limit. The standard deviation was calculated and the detection limit results are shown in Table 2.

[0034] Table 2 Method detection limit and determination lower limit (II) Recovery rate test Seven high-salinity groundwater samples were selected, and different concentrations of iodide and glyphosate standard solutions were added thereto. The method of the present invention (chromatographic conditions were the same as in Example 1) was used for parallel determination twice. The results are shown in Tables 3-4. When the iodide addition amount was 0.020-0.300 mg / L, the spiked recovery rate was 73.3%-115%; when the glyphosate addition amount was 0.02-0.500 mg / L, the spiked recovery rate was 72.4%-115%.

[0035] Table 3 Data results of the determination of iodide in high-salinity groundwater by two-dimensional ion chromatography Table 4 Data results of determination of glyphosate in high-salinity groundwater by two-dimensional ion chromatography The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography, characterized in that: The steps include: A. Preparation of standard curves: Conductivity peak area-concentration standard curves of iodide and glyphosate were established by ion chromatography; B. Sample collection: Collect water samples and adjust the pH of the water samples to 10-12 with saturated sodium hydroxide solution as the test solution; C. Sample processing: filter the solution to be tested in step B and wait for analysis; D. Sample testing: The solution to be tested collected in step C is subjected to ion chromatography analysis to respectively measure the chromatographic peak areas of iodide and glyphosate in the solution to be tested, and the chromatographic peak areas are respectively inserted into the conductivity peak area-concentration standard curve of iodide and glyphosate prepared in step A to obtain the iodide and glyphosate concentration values ​​in the solution to be tested; In step A and step D, the test conditions used are as follows: One-dimensional chromatographic column model: IonPac AS19, 4mm×250mm; its chromatographic conditions include: Eluent: 32 mmol / L potassium hydroxide or sodium hydroxide; Eluent flow rate: 1 mL / min; Suppressor current: 80~90mA; Column temperature: 25~30℃; Detection pool temperature: 30~35℃; Two-dimensional chromatography column model: IonPac AS19, 2mm×250mm; its chromatographic conditions include: Eluent: 25~30mmol / L potassium hydroxide or sodium hydroxide; Eluent flow rate: 0.3 mL / min; Suppressor current: 19~23mA; Column temperature: 25~30℃; Detection pool temperature: 30~35℃; Enrichment column model: IonPac AG19, 4mm×100mm; The two-dimensional six-way valve was switched at 7.5 min for enrichment, and the enrichment time was 4.5 min; Detector: conductivity detector; Injection volume: 100 μL.

2. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 1, characterized in that: Chromatographic conditions of the one-dimensional chromatographic column: The eluent was 32 mmol / L sodium hydroxide; Suppressor current 80mA; Column temperature: 30°C; The detection cell temperature was 35°C.

3. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 1, characterized in that: Chromatographic conditions of the two-dimensional chromatographic column: The eluent was 28 mmol / L potassium hydroxide; Suppressor current 21mA; Column temperature: 30°C; The detection cell temperature was 35°C.

4. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 1, characterized in that: The steps for establishing the conductivity peak area-concentration standard curve of iodide and glyphosate in step A include: Equal amounts of iodide and glyphosate are dissolved in ultrapure water, and diluted step by step to prepare several groups of mixed standard solutions with concentration gradients, wherein the concentration gradient range of the mixed standard solutions is 0.00-1.00 μg / ml. Then, ion chromatography is performed to establish a conductivity peak area-concentration standard curve of iodide and glyphosate, with the measured chromatographic peak area as the ordinate and the corresponding mass concentration of iodide and glyphosate as the abscissa.

5. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 1, characterized in that: The test solution in step B is stored in a refrigerator at 0°C-4°C and protected from light.

6. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 1, characterized in that: In step B, the pH of the water sample is adjusted to 12 with saturated sodium hydroxide solution.

7. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 1, characterized in that: The filtration step in step C is: filtering the solution to be tested through an aqueous filter membrane with a pore size of 0.45 μm and a Na-type purification column in sequence.

8. The method for separating iodide and glyphosate in high salt water by two-dimensional ion chromatography according to claim 7, characterized in that: After filtration, discard 5 ml of the initial filtrate and collect 1.5 ml of the sample in a sample injection bottle for analysis.

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