A method for determining isopropylamine in groundwater using headspace gas chromatography

Abstract

The application discloses a method for determining isopropylamine in groundwater by using a headspace gas chromatograph, and comprises the following steps: S1, sample collection and preservation: a glass bottle is used to collect a sample, the sample should fill the sample bottle and be sealed with a cover, and the sample is stored and transported under refrigeration below 4 DEG C and in the dark, and analysis is completed within 7 days after sampling; S2, sample pretreatment: the collected groundwater sample is restored to room temperature, 10.0 mL of the sample is accurately taken into a headspace bottle in which 3.2 g of sodium chloride and 1.0 g of potassium sulfate are added in advance, 500 muL of a 50% sodium hydroxide solution and 100 muL of ammonia water are added, the headspace bottle is immediately sealed, the salt is shaken to be completely dissolved, and a sample to be tested is obtained. In the application, a pretreatment system is optimized according to the characteristics of the groundwater matrix, a sodium chloride-potassium sulfate composite salting-out system is used to improve the volatilization efficiency of isopropylamine, and alkalization treatment is used to eliminate the interference of the water matrix, so that the method is suitable for the detection of different types of groundwater samples, including clean groundwater, slightly polluted groundwater and the like.

Description

Technical Field

[0001] This invention relates to the field of water environment monitoring and analytical chemistry, and in particular to a method for determining isopropylamine in groundwater using a headspace gas chromatograph. Background Technology

[0002] Isopropylamine is an important organic chemical raw material widely used in pharmaceuticals, pesticides, rubber, dyes and other industrial fields. It is highly volatile and easily soluble in water. During production, storage, use and wastewater discharge, it can easily enter the groundwater environment through surface runoff, leaching and infiltration. Isopropylamine has certain irritant and toxic properties. Long-term exposure or ingestion can damage the human respiratory system and central nervous system, and can also disrupt the stability of the groundwater ecosystem, threatening drinking water safety. Therefore, establishing a rapid, sensitive and accurate method for detecting isopropylamine in groundwater is of great significance for groundwater pollution investigation, environmental risk assessment and drinking water safety assurance.

[0003] Currently, the main methods for detecting organic amine compounds in water bodies include solution absorption-headspace / gas chromatography, ion chromatography, and liquid chromatography-mass spectrometry. Among these, headspace / gas chromatography has become a commonly used method for detecting volatile organic amines in water bodies due to its advantages such as simple pretreatment, minimal matrix interference, and low detection cost. The current standard, "Determination of Trimethylamine in Ambient Air and Exhaust Gas: Solution Absorption-Headspace / Gas Chromatography" (HJ...), is also used. 1042-2019) is the typical application specification of this technology, but the existing technology still has the following shortcomings in the application of the detection of isopropylamine in groundwater: (1) The existing methods are mostly for water bodies with complex matrices such as industrial wastewater and domestic sewage, and are not suitable for the detection of low concentrations of isopropylamine in groundwater. The detection limit and sensitivity of the methods are difficult to meet the detection requirements of trace pollution in groundwater; (2) The sample pretreatment conditions are not optimized enough. The salting-out system and alkalization conditions are not adjusted according to the characteristics of the groundwater matrix, resulting in poor volatilization efficiency of the target substance and low detection recovery rate; (3) The instrument detection parameters are not specifically optimized for the physicochemical properties of isopropylamine, resulting in poor separation effect of the target substance, easy tailing of the peak shape, and insufficient precision and stability of the detection results; (4) The quality control system of the existing methods is not perfect and is difficult to adapt to the large-scale and standardized detection requirements of groundwater samples.

[0004] In view of this, the present invention establishes a headspace gas chromatography method for the determination of isopropylamine in groundwater by optimizing the groundwater sample collection and preservation method, sample pretreatment system, headspace sampling and gas chromatography detection parameters, aiming to solve the problems of insufficient sensitivity, low recovery rate, poor precision and weak adaptability to groundwater matrix in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining isopropylamine in groundwater using a headspace gas chromatograph to solve the above-mentioned problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for determining isopropylamine in groundwater using headspace gas chromatography includes the following steps:

[0008] S1. Sample collection and preservation: Samples are collected using glass bottles. The sample bottles should be filled and sealed. They should be stored and transported at 4°C or below, protected from light. The analysis should be completed within 7 days after sampling.

[0009] S2. Sample pretreatment: After the collected groundwater sample is brought to room temperature, accurately transfer 10.0 mL of sample into a headspace vial containing 3.2 g sodium chloride and 1.0 g potassium sulfate. Add 500 μL of 50% sodium hydroxide solution and 100 μL of ammonia water. Immediately seal the headspace vial and gently shake until the salt is completely dissolved to obtain the sample to be tested.

[0010] S3. Preparation of standard curve: Using pure water as solvent, prepare a series of isopropylamine standard solutions with concentration gradients of 2.215 mg / L, 4.430 mg / L, 8.860 mg / L, 17.720 mg / L, 22.150 mg / L, and 44.300 mg / L. Pretreat the standard solutions of each concentration according to the operation in step S2 to obtain the standard series samples.

[0011] S4. Headspace sampling process: The test sample obtained in step S2 and the standard series samples obtained in step S3 are placed in a fully automatic headspace sampler, heated to equilibrium and headspace sampled to achieve thermodynamic equilibrium between the gas and liquid phases, and the target component in the gas phase is obtained.

[0012] S5. Gas Chromatography Detection: The target component obtained by headspace injection is injected into a gas chromatograph for separation and detected by a flame ionization detector. The retention time and peak area of ​​the target analyte are recorded.

[0013] S6. Qualitative and quantitative analysis: Qualitative analysis is performed by comparing the retention time of the target analyte with that of isopropylamine in a series of standard solutions. A standard curve is established with the concentration of isopropylamine in the standard solutions as the abscissa and the corresponding peak area as the ordinate. The content of isopropylamine in groundwater is quantitatively calculated using the external standard method.

[0014] S7. Data Validation: Quality control of test results is carried out through precision experiments, recovery rate experiments, detection limit validation, and blank experiments.

[0015] Preferably, in step S2, when adding sodium hydroxide solution and ammonia, the reagents should be added to the bottom of the headspace vial to avoid the loss of the target compound isopropylamine.

[0016] Preferably, in step S4, the operating conditions of the headspace sampler are: heating equilibrium temperature 75°C, heating equilibrium time 30 min, sampling needle temperature 100°C, transfer line temperature 105°C, and injection volume 1.0 mL.

[0017] Preferably, in step S5, the operating conditions of the gas chromatograph are as follows: the chromatographic column is an HP-5 capillary column, the tail purge flow rate is 25 mL / min, and the split ratio is 10:1; the programmed temperature is: the initial temperature of the column oven is 35°C, held for 6 min, and then increased to 150°C at a heating rate of 30°C / min; the vaporization chamber temperature is 150°C, and the detection chamber temperature is 250°C.

[0018] Preferably, in step S7, the method detection limit is 0.6 mg / L, the quantitation limit is 2.4 mg / L, the recovery rate of groundwater samples is 70.5%~101%, and the relative standard deviation (RSD) is ≤4.5%.

[0019] Preferably, in step S7, experimental water is used instead of groundwater sample in the blank experiment, and the detection is performed according to the operation of steps S2-S5, and the detection result of isopropylamine in the blank sample should be lower than the method detection limit.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] 1. This application has strong adaptability to detection: the pretreatment system is optimized for the characteristics of groundwater matrix, and the sodium chloride-potassium sulfate composite salting-out system is used to improve the volatilization efficiency of isopropylamine. Combined with alkalization treatment to eliminate interference from water matrix, it is suitable for the detection of different types of groundwater samples, including clean groundwater and slightly polluted groundwater.

[0022] 2. This application features high detection efficiency: sample pretreatment does not require complex extraction and purification steps, and the combination of headspace sampling and gas chromatography detection can realize automated processing of batch samples, with a single sample detection cycle of ≤40min, meeting the rapid detection needs of large batches of groundwater samples.

[0023] 3. The method in this application has high sensitivity: by optimizing the headspace equilibrium parameters and gas chromatography detection conditions, the method detection limit is as low as 0.6 mg / L and the quantitation limit is 2.4 mg / L, which can accurately detect low concentrations of isopropylamine in groundwater and meet the trace detection needs of groundwater pollution investigation.

[0024] 4. In this application, the test results are stable and reliable: the external standard method is used for quantification, and the separation effect and peak symmetry of the target analytes are effectively improved by optimizing the instrument parameters. The linear correlation coefficient of the standard curve is r≥0.997, the spiked recovery rate of groundwater samples is 70.5%~101%, the method precision RSD≤4.5%, and the accuracy and precision of the test results meet the requirements of the "Technical Guidelines for the Formulation of Standards for Environmental Monitoring and Analysis Methods" (HJ 168-2020).

[0025] 5. This application is simple to operate and easy to promote: the instruments and equipment used are conventional equipment in environmental monitoring laboratories, the pretreatment operation process is simple, there is no need to use expensive reagents and complex equipment, the detection cost is low, and it is easy to promote and apply in grassroots monitoring laboratories. Attached Figure Description

[0026] Figure 1 A chromatogram provided according to an embodiment of the present invention is shown;

[0027] Figure 2 A schematic diagram of instrument and equipment information provided according to an embodiment of the present invention is shown;

[0028] Figure 3 A schematic diagram illustrating the use of reagents according to an embodiment of the present invention is shown. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figure 1-3 The present invention provides a technical solution:

[0031] A method for determining isopropylamine in groundwater using headspace gas chromatography includes the following steps:

[0032] S1. Sample collection and preservation: Samples should be collected in glass bottles. The sample bottles should be filled and sealed. They should be refrigerated below 4℃, protected from light, and transported. The analysis should be completed within 7 days after sampling. Groundwater samples should be collected in accordance with the relevant provisions of HJ / T91 "Technical Specification for Surface Water and Wastewater Monitoring" and HJ / T164 "Technical Specification for Groundwater Environmental Monitoring". 100mL hard ground glass bottles or threaded glass bottles with polytetrafluoroethylene caps should be used for sampling. The sample bottles should be filled completely during sampling, leaving no top space. The bottles should be sealed immediately after sampling.

[0033] S2. Sample Pretreatment: After the collected groundwater sample is brought to room temperature, accurately transfer 10.0 mL of sample into a headspace vial containing 3.2 g of sodium chloride and 1.0 g of potassium sulfate. Add 500 μL of 50% sodium hydroxide solution and 100 μL of ammonia. Immediately seal the headspace vial and gently shake until the salt is completely dissolved to obtain the test sample. When adding sodium hydroxide solution and ammonia, the reagents should be added to the bottom of the headspace vial to avoid the loss of the target compound isopropylamine.

[0034] S3. Preparation of standard curve: Using pure water as solvent, prepare a series of isopropylamine standard solutions with concentration gradients of 2.215 mg / L, 4.430 mg / L, 8.860 mg / L, 17.720 mg / L, 22.150 mg / L, and 44.300 mg / L. Pretreat the standard solutions of each concentration according to the operation in step S2 to obtain the standard series samples.

[0035] Preparation of standard stock solution: Take isopropylamine standard with a purity ≥99.0%, dilute with pure water to prepare isopropylamine standard stock solution with a concentration of 886 mg / L, store in a sealed container below 4℃ away from light, and the shelf life is 3 months.

[0036] Preparation of standard series solutions: Take an appropriate amount of isopropylamine standard stock solution and dilute it stepwise with pure water to prepare a series of isopropylamine standard solutions with six concentration points: 2.215 mg / L, 4.430 mg / L, 8.860 mg / L, 17.720 mg / L, 22.150 mg / L, and 44.300 mg / L. Preparation of standard series samples: Following the sample pretreatment operation in step S2, accurately transfer 10.0 mL of each concentration of standard series solution into a headspace vial containing 3.2 g of sodium chloride and 1.0 g of potassium sulfate. Add the same amount of sodium hydroxide solution and ammonia water, seal, and shake until the salt dissolves to obtain the standard series samples.

[0037] Standard curve establishment: The standard series samples were sequentially headspace-injected and gas-chromatographically detected in order of increasing concentration. The concentration of isopropylamine in the standard series solutions was used as the abscissa (x), and the corresponding peak area was used as the ordinate (y). A linear regression equation was established, and the correlation coefficient was calculated. The linear equation of the standard curve was Y = 56.9082x - 108.6398, and the linear correlation coefficient r = 0.997, which meets the technical requirement of r ≥ 0.995 in HJ168-2020.

[0038]

[0039] S4. Headspace Sampling Processing: The test sample obtained in step S2 and the standard series samples obtained in step S3 are placed in a fully automatic headspace sampler for heating equilibrium and headspace sampling to achieve thermodynamic equilibrium between the gas and liquid phases, thereby obtaining the target component in the gas phase. The working conditions of the headspace sampler are: heating equilibrium temperature 75℃, heating equilibrium time 30min, sampling needle temperature 100℃, transfer line temperature 105℃, and injection volume 1.0mL. The instrument automatically completes the sample heating equilibrium, headspace sampling, and injection operations according to the preset program, so that the isopropylamine in the sample reaches thermodynamic dynamic equilibrium between the gas and liquid phases, and then the target component in the gas phase is sent into the gas chromatograph.

[0040] S5. Gas Chromatography Detection: The target components obtained by headspace injection are injected into the gas chromatograph for separation and detection using a flame ionization detector. The retention time and peak area of ​​the target analytes are recorded. The operating conditions of the gas chromatograph are as follows: HP-5 capillary column, tail purge flow rate 25 mL / min, split ratio 10:1; programmed temperature: initial column oven temperature 35℃, held for 6 min, then increased to 150℃ at a rate of 30℃ / min; vaporization chamber temperature 150℃, detection chamber temperature 250℃.

[0041]

[0042]

[0043] S6. Qualitative and quantitative analysis: Qualitative analysis is performed by comparing the retention time of the target analyte with that of isopropylamine in a series of standard solutions. A standard curve is established with the concentration of isopropylamine in the standard solutions as the abscissa and the corresponding peak area as the ordinate. The content of isopropylamine in groundwater is quantitatively calculated using the external standard method.

[0044]

[0045]

[0046] S7. Data Validation: Quality control of the detection results was performed through precision experiments, recovery experiments, limit of detection (LOD) validation, and blank experiments. For the blank experiments, experimental water was used instead of groundwater samples, and the detection was performed according to steps S2-S5. The detection result of isopropylamine in the blank sample should be lower than the method detection limit (LOD), which is 0.6 mg / L and the quantitation limit (LOQ) is 2.4 mg / L. The recovery rate of the groundwater samples was 70.5%–101%, and the relative standard deviation (RSD) was ≤4.5%.

[0047] (1) Precision experiment

[0048] Three concentration levels of isopropylamine-spiked pure water samples were prepared, with spiked concentrations of 4.4 mg / L, 11.5 mg / L, and 31.0 mg / L, respectively. Six parallel samples were prepared for each concentration level, and the measurements were performed according to steps S2-S5. The average value and relative standard deviation (RSD) of the six parallel measurements were calculated.

[0049] Verification results: The average detected value of the sample at the 4.4 mg / L concentration level was 4.5 mg / L, with an RSD of 4.1%; the average detected value of the sample at the 11.5 mg / L concentration level was 11.2 mg / L, with an RSD of 3.5%; and the average detected value of the sample at the 31.0 mg / L concentration level was 31.9 mg / L, with an RSD of 4.5%. The RSDs of all three concentration levels were ≤4.5%, meeting the precision requirements of HJ168-2020.

[0050] (2) Accuracy and recovery rate experiment

[0051] ① Pure water matrix spiking experiment: Spiked pure water samples at the above low, medium and high concentration levels were measured, and the relative error was calculated. The results showed that the relative error range of the 4.4 mg / L concentration level sample was -2.3%~6.8%; the relative error range of the 11.5 mg / L concentration level sample was -7.0%~2.6%; and the relative error range of the 31.0 mg / L concentration level sample was -4.2%~8.7%, indicating good method accuracy.

[0052] ② Groundwater matrix spiking experiment: Three groundwater samples from different sources (all without detectable background levels of isopropylamine) were selected and spiked at three concentration levels: low, medium, and high. The spike concentrations were 4.4 mg / L, 8.9 mg / L, and 35.4 mg / L, respectively. Six parallel samples were prepared for each concentration level and measured according to steps S2-S5. The spike recovery rate was calculated.

[0053] Validation results: The spiked recoveries of groundwater samples at a concentration level of 4.4 mg / L ranged from 70.5% to 86.4%; the spiked recoveries of groundwater samples at a concentration level of 8.9 mg / L ranged from 74.2% to 101%; and the spiked recoveries of groundwater samples at a concentration level of 35.4 mg / L ranged from 77.7% to 92.4%. All recoveries met the quality control requirements for the detection of organic pollutants in environmental monitoring.

[0054] According to the provisions of HJ168-2020, seven samples of pure water with a low concentration of isopropylamine (2.22 mg / L) were prepared and parallel determinations were performed according to steps S2-S5. The standard deviation S of the seven determinations was calculated and then calculated using the formula... ( -Method detection limit, - Degrees of freedom are At a confidence level of 99% distributed( ), - Standard deviation of multiple parallel determinations The limit of detection (LOD) is calculated based on the number of parallel determinations of the sample, where n=7 and the t-value at a 99% confidence level is 3.143; the LOD is set at 4 times the LOD.

[0055] Validation results: The standard deviation S of 7 parallel determinations was 0.1902 mg / L, the limit of detection was 0.6 mg / L, and the limit of quantitation was 2.4 mg / L; the ratio of the mean value to the limit of detection was 4.2, which meets the requirement of 3-5 times in HJ168-2020, indicating that the limit of detection is reliable.

[0056] (4) Blank experiment

[0057] Using experimental water instead of groundwater samples, blank samples were prepared and tested according to steps S2-S5. The results showed that isopropylamine was not detected in the blank samples, and no interfering peaks affected the qualitative and quantitative analysis of the target analytes, meeting the method detection requirements.

[0058] The limits of detection and limits of quantitation for the assay method are as follows:

[0059]

[0060] According to the HJ168-2020 standard, the ratio of the measured average value to the detection limit meets the standard requirements.

[0061]

[0062] The above description of the embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining isopropylamine in groundwater using headspace gas chromatography, characterized in that, Includes the following steps: S1. Sample collection and preservation: Samples are collected using glass bottles. The sample bottles should be filled and sealed. They should be stored and transported at 4°C or below, protected from light. The analysis should be completed within 7 days after sampling. S2. Sample pretreatment: After the collected groundwater sample is brought to room temperature, accurately transfer 10.0 mL of sample into a headspace vial containing 3.2 g sodium chloride and 1.0 g potassium sulfate. Add 500 μL of 50% sodium hydroxide solution and 100 μL of ammonia water. Immediately seal the headspace vial and gently shake until the salt is completely dissolved to obtain the sample to be tested. S3. Preparation of standard curve: Using pure water as solvent, prepare a series of isopropylamine standard solutions with concentration gradients of 2.215 mg / L, 4.430 mg / L, 8.860 mg / L, 17.720 mg / L, 22.150 mg / L, and 44.300 mg / L. Pretreat the standard solutions of each concentration according to the operation in step S2 to obtain the standard series samples. S4. Headspace sampling process: The test sample obtained in step S2 and the standard series samples obtained in step S3 are placed in a fully automatic headspace sampler, heated to equilibrium and headspace sampled to achieve thermodynamic equilibrium between the gas and liquid phases, and the target component in the gas phase is obtained. S5. Gas Chromatography Detection: The target component obtained by headspace injection is injected into a gas chromatograph for separation and detected by a flame ionization detector. The retention time and peak area of ​​the target analyte are recorded. S6. Qualitative and quantitative analysis: Qualitative analysis is performed by comparing the retention time of the target analyte with that of isopropylamine in a series of standard solutions. A standard curve is established with the concentration of isopropylamine in the standard solutions as the abscissa and the corresponding peak area as the ordinate. The content of isopropylamine in groundwater is quantitatively calculated using the external standard method. S7. Data Validation: Quality control of test results is carried out through precision experiments, recovery rate experiments, detection limit validation, and blank experiments.

2. The method for determining isopropylamine in groundwater using headspace gas chromatography according to claim 1, characterized in that, In step S2, when adding sodium hydroxide solution and ammonia, the reagents should be added to the bottom of the headspace vial to avoid the loss of the target compound isopropylamine.

3. The method for determining isopropylamine in groundwater using headspace gas chromatography according to claim 1, characterized in that, In step S4, the operating conditions of the headspace sampler are: heating equilibrium temperature 75℃, heating equilibrium time 30min, sampling needle temperature 100℃, transfer line temperature 105℃, and injection volume 1.0mL.

4. The method for determining isopropylamine in groundwater using headspace gas chromatography according to claim 1, characterized in that, In step S5, the operating conditions of the gas chromatograph are as follows: the column is an HP-5 capillary column, the tail purge flow rate is 25 mL / min, and the split ratio is 10:1; the programmed temperature is: the initial temperature of the column oven is 35℃, held for 6 min, and then increased to 150℃ at a rate of 30℃ / min; the vaporization chamber temperature is 150℃, and the detection chamber temperature is 250℃.

5. The method for determining isopropylamine in groundwater using headspace gas chromatography according to claim 1, characterized in that, In step S7, the method detection limit is 0.6 mg / L, the quantitation limit is 2.4 mg / L, the recovery rate of groundwater samples is 70.5%~101%, and the relative standard deviation (RSD) is ≤4.5%.

6. The method for determining isopropylamine in groundwater using headspace gas chromatography according to claim 1, characterized in that, In step S7, experimental water is used instead of groundwater sample for blank experiment, and detection is performed according to the operation of steps S2-S5. The detection result of isopropylamine in blank sample should be lower than the method detection limit.

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