CN113495108B - A method for the simultaneous detection of 63 persistent organic pollutants in soil - Google Patents

Abstract

The invention provides a method for simultaneously detecting 63 persistent organic pollutants in soil, which comprises the following steps: s1, preparing instruments, reagents and materials; s2, preparing standard curves of 6 concentration series of 63 POPs; s3, sample treatment; s4, measuring organic pollutants. The method solves the problems of large reagent consumption, long extraction time, relatively low ultrasonic extraction efficiency and poor stability in the traditional detection method, has the advantages of higher batch processing advantage compared with the accelerated solvent extraction, and has the advantages of high recovery rate, good reproducibility, low reagent consumption, rapidness, convenience and capability of realizing batch processing of samples.

Description

A method for simultaneous detection of 63 persistent organic pollutants in soil

Technical Field

The present invention relates to the technical field of soil pollutant detection, and in particular to a method for simultaneously detecting 63 persistent organic pollutants in soil.

Background Art

Polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs) and phthalates (PAEs) are typical persistent organic pollutants (POPs) that are widely present in the environment. POPs in soil can migrate and transform in the atmosphere, surface water and groundwater through volatilization and diffusion, and will eventually enter the food chain through bioaccumulation, posing a threat to the ecological environment and human health. Therefore, the study of persistent organic pollutants in soil has always been the focus of attention at home and abroad.

The determination of POPs in soil mainly includes extraction, concentration, purification and instrumental determination. The analysis cycle is long, the consumption of reagents and consumables is large, and the labor input is high. The detection methods for single organic pollutants at home and abroad are relatively mature. In recent years, researchers tend to tend to the simultaneous analysis of multi-component compounds. These types of pollutants are compounds with low polarity and similar properties. The pretreatment and instrumental analysis methods have many similarities. In theory, multi-component simultaneous detection can be achieved. If simultaneous analysis is possible, the timeliness of the method will be improved and the monitoring cost can be reduced. However, there are still few high-throughput analysis methods for simultaneous pretreatment and instrumental determination of the above four types of persistent organic pollutants in soil.

Most of the existing standard analytical methods in China are aimed at the analysis of certain compounds, and soil samples are generally required to be extracted 7 to 10 days after collection, which requires high timeliness. As the country's soil environmental control becomes more and more stringent, the requirements for soil monitoring are increasing, such as the national soil survey of a large number of samples of multi-component organic analysis projects, and the development of high-throughput analytical methods for the simultaneous determination of multi-component POPs in soil is of great significance.

From the extraction perspective, the current traditional extraction methods such as Soxhlet extraction have the disadvantages of large reagent consumption, long extraction time, relatively low extraction efficiency and poor stability of ultrasonic extraction. Researchers prefer fast and efficient extraction technologies such as Accelerated Solvent Extraction (ASE) and Microwave Extraction (MAE) to extract organic pollutants from soil. Compared with accelerated solvent extraction, microwave-assisted extraction technology has lower reagent consumption, fewer instrument pipelines, simple experimental operation, and can process more than 40 samples at the same time, which has the advantage of batch processing. It is a new green and environmentally friendly extraction technology and is often used to extract POPs from soil.

From the perspective of purification, commonly used purification methods for determining organic pollutants include acid washing, composite silica gel chromatography columns, gel permeation chromatography, solid phase extraction, etc. Acid washing or acid silica gel purification effects are good, but organochlorine pesticides, polycyclic aromatic hydrocarbons and phthalate compounds will be oxidized by concentrated sulfuric acid. Gel permeation chromatography equipment investment is high, and there are many instrument pipelines, which are easy to introduce PAEs interference. In order to achieve high-throughput analysis methods, the purification of environmental matrix samples often chooses the more broad-spectrum magnesium silicate column solid phase extraction purification.

Low-temperature partition extraction (LTPE) is a purification technology that has been proven to have superior performance in recent years and has been used to analyze organic pollutants in different matrices. Detection instruments include high-performance liquid chromatography (HPLC), gas chromatography (GC-ECD), gas chromatography-mass spectrometer (GC-MS), gas chromatography-tandem mass spectrometer (GC-MS/MS), high-resolution magnetic mass spectrometer (HRGC-HRMS), etc. GC-MS equipment is popular and uses selected ion scanning mode for detection, which reduces the probability of false positive samples. It has high sensitivity and selectivity, and the measurement results are accurate and reliable.

In this paper, a high-throughput analysis method for simultaneous experimental treatment and instrumental detection of 18 polychlorinated biphenyls, 23 organochlorine pesticides, 16 polycyclic aromatic hydrocarbons and 6 phthalates in soil was established by microwave-assisted extraction-low temperature distribution purification-gas chromatography-mass spectrometry. The experiment showed that the method had high recovery rate and good parallelism, which could meet the requirements for the detection and analysis of these 63 POPs in soil. When analyzing large quantities of samples, it had the advantage of batch processing, which would greatly improve the work efficiency.

Summary of the invention

The technical problem solved by the present invention is that the current determination of POPs in soil mainly includes the steps of extraction, concentration, purification and instrumental determination, wherein the analysis cycle of the extraction and purification steps is long, the consumption of reagents and consumables is large, the labor input is high, and the effects of high throughput and batch processing cannot be achieved.

The technical solution of the present invention is as follows:

A method for simultaneous detection of 63 persistent organic pollutants in soil:

The 63 persistent organic pollutants are: naphthalene, dimethyl phthalate, acenaphthylene, acenaphthene, diethyl phthalate, fluorene, α-BHC, hexachlorobenzene, γ-BHC, phenanthrene, anthracene, β-BHC, PCB28, δ-BHC, heptachlor, dibutyl phthalate, PCB152, aldrin, heptachlor epoxide B, fluoranthene, PCB101, γ-chlordane, α-chlordane, endosulfan I, pyrene, p,p'-DDE, dieldrin, PCB81, PCB77, endrin, P CB123, o,p'-DDT, PCB118, PCB114, p,p'-DDT, endosulfan II, PCB153, endrin aldehyde, PCB105, butyl benzyl phthalate, p,p'-DDT, PCB138, endosulfan sulfate, PCB126, PCB167, endrin ketone, methoxychlor, PCB156, di(2-ethylhexyl) phthalate, PCB157, benzo(a)anthracene, PCB180, Mirex, PCB169, PCB189, di-n-octyl phthalate, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, indeno(1,2,3-cd)pyrene, benzo(ghi)perylene;

A gas chromatography-mass spectrometer was used to detect 63 persistent organic pollutants. The measuring conditions were as follows: a chromatographic column was Rxi-XLB, which was 30 m long, 0.25 μm in inner diameter, and 0.25 mm in coating. The gas chromatograph injection port temperature was 280°C, the carrier gas was 99.999% pure helium, the column flow rate was 1.0 mL/min, the injection volume was 1 μL, and non-split injection was used. The heating program was as follows: after keeping at 70°C for 2 min, the temperature was increased to 140°C at a rate of 20°C/min, the temperature was increased to 180°C at a rate of 15°C/min, and maintained for 5 min, then the temperature was increased to 210°C at a rate of 8°C/min, the temperature was increased to 270°C at a rate of 3°C/min and maintained for 4 min, and finally the temperature was increased to 320°C at a rate of 15°C/min and maintained for 6 min. The mass spectrometry conditions were as follows: the ion source was an EI source, the electron energy was 70 eV, the ion source temperature was 300 °C, and the transfer line temperature was 300 °C;

The following steps are involved:

S1. Preparation of instruments, reagents and materials

The materials include: 16 PAH mixed standards, 23 OCPs mixed standards, 18 PCBs mixed standards, 6 phthalates mixed standards, among which the extraction internal standards include: 5 deuterated PAH mixed standards, 5 13C labeled organochlorine pesticides, 5 13C labeled polychlorinated biphenyls, and the injection internal standards include: D10-pyrene, 13C-p,p'-DDE, 13C-PCB138;

S2. Prepare standard curves of 63 POPs in 6 concentration series

The concentration range of PCBs was 0.005, 0.01, 0.05, 0.1, 0.2, 0.5 μg·mL ^-1 , and the concentration of the internal standard for extraction and injection was 0.1 μg·mL ^-1 ; the concentration range of OCPs was 0.02, 0.05, 0.1, 0.5, 1.0, 5.0 μg·mL ^-1 , and the concentration of the internal standard for extraction and injection was 0.5 μg·mL ^-1 ; the concentration range of PAHs and PAEs was 0.1, 0.25, 0.5, 1.0, 5.0, 10.0 μg·mL ^-1 , and the concentration of the internal standard for extraction and injection was 1.0 ng·mL ^-1 ;

S3. Sample processing

Mix and grind fresh soil with an appropriate amount of anhydrous sodium sulfate, add n-hexane:acetone mixed reagent for extraction, place in a low-temperature refrigerator and let stand for 4 hours, then filter for testing;

S4. Measurement of organic pollutants

Organic pollutants were measured by gas chromatography-mass spectrometry.

Further, in step S1, the instruments of the control experiment include: a gas chromatograph-mass spectrometer, a microwave extractor, a rotary evaporator, and a nitrogen blowdown instrument; the reagents include: n-hexane and acetone; the instruments of the purification method comparison experiment include: a gas chromatograph-mass spectrometer, a microwave extractor, a rotary evaporator, a nitrogen blowdown instrument, and a solid phase extraction device; the reagents include: n-hexane, dichloromethane, acetone, magnesium silicate solid phase extraction column, microporous filter membrane, quartz sand, and low-temperature distribution technology is based on the principle of like dissolves like. Under low temperature conditions, the solubility of strongly polar impurities or interfering matrices in weakly polar organic solvents decreases rapidly and is resolved, or filtered with the help of microporous filter membranes to achieve the purpose of purification. The freezing time and the solubility of the extractant in the compound are important factors affecting the low-temperature distribution.

Furthermore, in step S1, the materials also include: 18 certified standard substances of PCBs in soil, 23 certified standard substances of OCPs in soil, 16 certified standard substances of PAHs in soil, and 6 certified standard substances of PAEs in soil, to facilitate the subsequent calculation of sample precision and accuracy.

Furthermore, the five deuterated PAHs mixed standards include: D8-naphthalene, D10-acenaphthene, D10-phenanthrene, D12- D12-perylene is convenient for the subsequent calculation of sample precision and accuracy.

Furthermore, five 13C-labeled organochlorine pesticides include: 13C-α-BHC, 13C-γ-chlordane, 13C-o,p'-DDE, 13C-p,p'-DDD, 13C-p,p'-DDT, and five 13C-labeled polychlorinated biphenyls include: 13C-PCB28, 13C-PCB52, 13C-PCB 101, 13C-PCB153, 13C-PCB180, which facilitates the subsequent calculation of sample precision and accuracy.

Preferably, step S3 specifically includes the following sub-steps:

S31, take 10.0g of fresh soil and mix with an appropriate amount of anhydrous sodium sulfate, grind, and put into a Teflon microwave oven;

S32, adding isotope extraction internal standard, adding 30 mL of a mixed reagent with a volume ratio of n-hexane: acetone of 1:1, and microwave extraction at 115°C for 15 min;

S33. The extract is concentrated by rotary evaporation and dissolved in n-hexane and blown with nitrogen to about 0.5 mL. After standing in a low-temperature refrigerator at an ambient temperature of -20°C for 4 hours, take the supernatant or filter it into a sampling bottle using a microporous filter membrane, add the injection internal standard, and wait for measurement.

Preferably, in step S4, the organic pollutants are measured by a gas chromatography-mass spectrometer. During the measurement, the instrument conditions include gas chromatography conditions and mass spectrometry conditions. The gas chromatography-mass spectrometer is equipped with a Z-shaped channel at the rear end of the ion source, which can effectively remove the interference of neutral impurities in the sample, thereby reducing the matrix effect during sample detection, which is manifested in its superior noise reduction performance. The compound chromatographic peak can obtain a higher signal-to-noise ratio, so that there is no obvious difference in the signal-to-noise ratio of the chromatographic peak of the sample with a similar measurement matrix.

Preferably, the gas chromatography conditions are: the chromatographic column is Rxi-XLB, the injection port temperature is 280°C, the carrier gas is 99.999% pure helium, the column flow rate is 1.0 mL/min, the injection volume is 1 μL, non-split injection, and the temperature program is: after keeping at 70°C for 2 minutes, increase the temperature to 140°C at a rate of 25°C/min, then increase the temperature to 240°C at a rate of 10°C/min, increase the temperature to 280°C at a rate of 5°C/min and hold for 4 minutes, and finally increase the temperature to 320°C at a rate of 10°C/min and hold for 5 minutes. The programmed temperature increase of the gas chromatograph has the advantages of improving separation, narrowing the peak, reducing the detection limit and saving time.

Further preferably, the mass spectrometry conditions are: the ion source is an EI source, the electron energy is 70eV, the ion source temperature is 300°C, and the transmission line temperature is 300°C. The ion source, as one of the main components of the mass spectrometer, is composed of an ionization chamber, an ion beam acceleration field, a focusing lens, etc. Its function is to ionize the analyte into molecular ions or fragment ions, thereby realizing the sample ionization area.

The beneficial effects of the present invention are:

This method is fast and simple, with high recovery rate and good reproducibility. It can meet the detection requirements of 63 POPs in soil. Compared with conventional pretreatment purification, this method is simple to operate and has the advantages of batch processing. When analyzing large quantities of samples, it can greatly improve work efficiency and save monitoring costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a graph showing the change in the signal-to-noise ratio of target PCBs with low-temperature storage time;

FIG2 is a graph showing the change in the signal-to-noise ratio of target PAEs with low-temperature storage time;

FIG3 is a graph showing the change in the signal-to-noise ratio of the target OCPs with the cryopreservation time;

FIG4 is a graph showing the change in the signal-to-noise ratio of the target PAHs with low-temperature storage time;

FIG5 is a schematic diagram of the signal-to-noise ratio of the chromatographic peaks in a non-purification test;

Fig. 6 is a schematic diagram of the signal-to-noise ratio after cryogenic distribution purification;

Fig. 7 is a schematic diagram of the signal-to-noise ratio after solid phase extraction purification;

FIG. 8 is a flow chart of the present invention.

DETAILED DESCRIPTION

In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all 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.

The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

It should be understood that although the terms first, second, third, etc. may be used to describe ... in the embodiments of the present invention, these ... should not be limited to these terms. These terms are only used to distinguish .... For example, without departing from the scope of the embodiments of the present invention, the first ... may also be referred to as the second ..., and similarly, the second ... may also be referred to as the first ....

Example

As shown in Figure 8, a method for simultaneously detecting 63 persistent organic pollutants in soil:

The 63 persistent organic pollutants are: naphthalene, dimethyl phthalate, acenaphthylene, acenaphthene, diethyl phthalate, fluorene, α-BHC, hexachlorobenzene, γ-BHC, phenanthrene, anthracene, β-BHC, PCB28, δ-BHC, heptachlor, dibutyl phthalate, PCB152, aldrin, heptachlor epoxide B, fluoranthene, PCB101, γ-chlordane, α-chlordane, endosulfan I, pyrene, p,p'-DDE, dieldrin, PCB81, PCB77, endrin, P CB123, o,p'-DDT, PCB118, PCB114, p,p'-DDT, endosulfan II, PCB153, endrin aldehyde, PCB105, butyl benzyl phthalate, p,p'-DDT, PCB138, endosulfan sulfate, PCB126, PCB167, endrin ketone, methoxychlor, PCB156, di(2-ethylhexyl) phthalate, PCB157, benzo(a)anthracene, PCB180, Mirex, PCB169, PCB189, di-n-octyl phthalate, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, indeno(1,2,3-cd)pyrene, benzo(ghi)perylene;

A gas chromatography-mass spectrometer was used to detect 63 persistent organic pollutants. The measuring conditions were as follows: a chromatographic column of Rxi-XLB, which was 30 m long, 0.25 μm in inner diameter, and 0.25 mm in coating. The gas chromatograph injection port temperature was 280°C, the carrier gas was 99.999% pure helium, the column flow rate was 1.0 mL/min, the injection volume was 1 μL, and non-split injection was performed. The heating program was as follows: after keeping at 70°C for 2 min, the temperature was increased to 140°C at a rate of 20°C/min, the temperature was increased to 180°C at a rate of 15°C/min, and maintained for 5 min, then the temperature was increased to 210°C at a rate of 8°C/min, the temperature was increased to 270°C at a rate of 3°C/min and maintained for 4 min, and finally the temperature was increased to 320°C at a rate of 15°C/min and maintained for 6 min. The mass spectrometry conditions were as follows: the ion source was an EI source, the electron energy was 70 eV, the ion source temperature was 300 °C, and the transfer line temperature was 300 °C;

The following steps are involved:

S1. Preparation of instruments, reagents and materials

Gas chromatography-mass spectrometer (Thermo, TSQ 8000EVO), gas chromatography-mass spectrometer (Waters, Micromass Quattro), microwave extractor (Milestone, ETHOS UP 44-bit), rotary evaporator (BUCHI, V-100), nitrogen blowdown instrument (EYELA, MG-2200), and low-temperature refrigerator (Haier, DW-40W380).

n-Hexane, dichloromethane, acetone (Honeywell, pesticide residue grade), magnesium silicate solid phase extraction column (CNW, 1 g, glass material), microporous filter membrane (Anpu, 0.22 um), anhydrous sodium sulfate (Guangzhou brand chemical reagent, analytical grade), quartz sand (Guangzhou brand chemical reagent, analytical grade).

16 PAHs mixed standards, 23 OCPs mixed standards, 18 PCBs mixed standards, and 6 phthalates mixed standards were purchased from Accustandard. Extraction internal standards: 5 deuterated PAHs mixed standards (including D8-naphthalene, D10-acenaphthene, D10-phenanthrene, D12- D12-perylene) was purchased from Accustandard; 5 13C-labeled organochlorine pesticides (including 13C-α-BHC, 13C-γ-chlordane, 13C-o,p'-DDE, 13C-p,p'-DDD, 13C-p,p'-DDT) were purchased from CIL; 5 13C-labeled polychlorinated biphenyls (including 13C-PCB28, 13C-PCB52, 13C-PCB 101, 13C-PCB153, 13C-PCB180) were purchased from CIL. Injection internal standard: D10-pyrene was purchased from Accustandard; 13C-p,p'-DDE and 13C-PCB138 were purchased from CIL.

There are certified reference materials for 18 PCBs in soil (Sigma-Aldrich, CRM962), 23 OCPs in soil (ERA, 093), 16 PAHs in soil (ERA, 722), and 6 PAEs in soil (Dongguan Longchang Intelligent Technology Research Institute, RUM001).

S2. Prepare standard curves of 63 POPs in 6 concentration series

The concentration range of PCBs was 0.005, 0.01, 0.05, 0.1, 0.2, and 0.5 μg·mL ^-1 .

The concentration of the internal standard for extraction and injection was 0.1 μg·mL ^-1 , the concentration range of OCPs was 0.02, 0.05, 0.1, 0.5, 1.0, 5.0 μg·mL ^-1 , the concentration of the internal standard for extraction and injection was 0.5 μg·mL ^-1 ,

The concentration ranges of PAHs and PAEs were 0.1, 0.25, 0.5, 1.0, 5.0, and 10.0 μg·mL ^-1 , and the concentrations of the internal standards for extraction and injection were both 1.0 ng·mL ^-1 ;

S3, sample processing, sample processing specifically includes the following sub-steps:

S31. Take 10.0g of fresh soil and mix with an appropriate amount of anhydrous sodium sulfate, grind and put into a Teflon microwave oven.

S32, add isotope extraction internal standard, add 30mL of n-hexane:acetone (1:1) mixed reagent, and microwave extraction at 115℃ for 15min.

S33, the extract is concentrated by rotary evaporation and dissolved in n-hexane and blown with nitrogen to about 0.5 mL, and then placed in a low-temperature refrigerator at an ambient temperature of -20°C for 4 hours, and the supernatant is taken or filtered into a sample injection bottle using a microporous filter membrane, and the internal standard is added for testing;

S4. Measurement of organic pollutants

Organic pollutants were measured by gas chromatography-mass spectrometry. During the measurement, the gas chromatography conditions were as follows: the chromatographic column was Rxi-XLB, the injection port temperature was 280°C, the carrier gas was 99.999% pure helium, the column flow rate was 1.0 mL/min, the injection volume was 1 μL, and non-split injection was performed. The heating program was as follows: after keeping at 70°C for 2 min, the temperature was increased to 140°C at a rate of 25°C/min, then increased to 240°C at a rate of 10°C/min, increased to 280°C at a rate of 5°C/min and maintained for 4 min, and finally increased to 320°C at a rate of 10°C/min and maintained for 5 min. The mass spectrometry conditions were as follows: the ion source was an EI source, the electron energy was 70 eV, the ion source temperature was 300°C, the transmission line temperature was 300°C, the ion scanning mode was selected, and the isotope internal standard method was used for quantification. Table 1 lists the retention times, quantitative ions, qualitative ions and quantitative relationships of 18 PCBs, 23 OCPs, 16 PAHs and 6 PAEs and internal standards.

Table 1 Retention time, quantitative ion, auxiliary ion and quantitative internal standard of the compounds

Experimental example

Experimental verification of the optimal time for low temperature distribution purification

Low temperature distribution technology is based on the principle that like dissolves like. Under low temperature conditions, the solubility of strongly polar impurities or interfering matrices in weakly polar organic solvents decreases rapidly and they are resolved, or filtered with the help of microporous membranes to achieve the purpose of purification. The freezing time and the solubility of the extractant in the compound are important factors affecting low temperature distribution.

Considering that the target substances PCBs, OCPs, PAHs and PAEs are not very polar, this experiment used certified reference substances as samples, and the solvent system for low-temperature distribution of the extract selected n-hexane, which has a lower polarity and is commonly used in organic experimental pretreatment, as the reagent. A time gradient of 0, 1, 2, 3, 4, 6, 8, and 16 h was designed under -20°C conditions, and the changes in the signal-to-noise ratio of the compound chromatographic peaks were determined in full scan mode.

The compound response was good when measured by gas chromatography-mass spectrometry (Thermo, TSQ 8000), and the signal-to-noise ratio of the chromatographic peaks under different time conditions was not different. The principle is that the gas chromatography-mass spectrometer is equipped with a Z-shaped channel at the rear end of the ion source, which can effectively remove the interference of neutral impurities in the sample, thereby reducing the matrix effect during sample detection, which is manifested in its superior noise reduction performance. The compound chromatographic peak can obtain a higher signal-to-noise ratio, so that the signal-to-noise ratio of the chromatographic peaks of samples with similar matrices is not significantly different.

Therefore, a gas chromatograph-mass spectrometer with relatively weak noise reduction function (Waters, Micromass Quattro) was used to set the same detection conditions.

The results showed that samples with low content, such as PCB126, PCB157, and benzo[a]pyrene, had a signal-to-noise ratio of less than 20, and the reliability of the comparison difference was low. Some organochlorine pesticides, such as endosulfan, aldrin, and mirex, had very low responses on this instrument, with a signal-to-noise ratio of less than 10, and no statistical analysis was performed.

The change of the signal-to-noise ratio of the target PCBs with the low-temperature storage time is shown in Figure 1, the change of the signal-to-noise ratio of the target PAEs with the low-temperature storage time is shown in Figure 2, the change of the signal-to-noise ratio of the target OCPs with the low-temperature storage time is shown in Figure 3, and the change of the signal-to-noise ratio of the target PAHs with the low-temperature storage time is shown in Figure 4. As shown in Figures 1 to 4, with the extension of the storage time, the signal-to-noise ratio of the chromatographic peaks of most compounds can be increased by 1.5 to 3 times at about 4 hours. After 4 hours, the signal-to-noise ratio fluctuates slightly but has no significant difference. It is speculated that the low-temperature distribution reaches phase equilibrium after 4 hours, which is similar to the conclusion of the researcher S.M.Goulart (2010) that -20℃ for 3 hours is the best extraction condition.

Therefore, it can be proved that the best condition for purifying the extract using low-temperature distribution is to maintain it at -20℃ for 4 hours.

Method performance parameter determination experiment

Quartz sand blank spiked with PCBs content of 1μg·kg ^-1 , OCPs content of 5μg·kg ^-1 , PAHs and PAEs content of 10μg·kg ^-1 were analyzed in parallel 8 times. 2.998 times the standard deviation of the determination results was calculated as the method detection limit, and 4 times the method detection limit was taken as the determination lower limit.

The soil matrix spiked samples at two concentration levels were analyzed in parallel 6 times, and the precision and accuracy of the samples were calculated. The measurement results are shown in Table 2.

As shown in Table 2, when the sample volume is 10.0 g and the final volume is 0.5 mL:

The detection limit of PCBs is between 0.1 and 0.2 μg·kg ^-1 , the lower limit of determination is between 0.4 and 0.8 μg·kg-1, the spiked recoveries of soil matrices with contents of 2.0 μg·kg ^-1 and 5.0 μg·kg ^-1 range from 96% to 113%, and the relative standard deviation (RSD) is between 0.9% and 4.1%.

The method detection limit of OCPs is between 0.3 and 1.5 μg·kg ^-1 , the lower limit of determination is between 1.2 and 6.0 μg·kg ^-1 , the spiked recoveries of soil matrices with contents of 10.0 μg·kg ^-1 and 50.0 μg·kg ^-1 range from 80% to 119%, and the relative standard deviation (RSD) is between 0.5% and 7.9%.

The method detection limit of PAHs is between 0.4 and 1.9 μg·kg ^-1 , and the lower limit of determination is between 1.6 and 7.6 μg·kg ^-1. The spiked recoveries of soil matrices with contents of 20.0 μg·kg ^-1 and 200 μg·kg ^-1 range from 76% to 111%, and the relative standard deviation (RSD) is from 0.4% to 3.8%.

The method detection limit of PAEs is between 1.0 and 2.2 μg·kg ^-1 , the lower limit of determination is between 4.0 and 8.8 μg·kg ^-1 , the spiked recoveries of soil matrices with contents of 20.0 μg·kg ^-1 and 200 μg·kg ^-1 range from 91% to 116%, and the relative standard deviation (RSD) is 1.7% to 4.8%.

Table 2 Performance parameter determination table of 63 POPs

Actual soil sample analysis

The actual soil samples were analyzed in parallel three times, and the test results showed that the recovery rate of the internal standard of isotope extraction ranged from 79% to 119%. None of the 18 PCBs were detected, and most of the OCPs were not detected. Only δ-BHC, p,p'-DDE, p,p'-DDD, and p,p'-DDT were detected, with a concentration range of 0.5-14.5μg·kg ^-1 (RSD: 1.9%-7.0%). The detection rate of 16 PAHs was 100%, with a concentration range of 28.0μg·kg ^-1 —400μg·kg ^-1 (RSD: 0.2%-11.1%). The detection indicators of PAEs included dibutyl phthalate, butylbenzyl phthalate, and di(2-ethyl)hexyl phthalate, with a concentration range of 1.5-10.5μg·kg ^-1 (RSD: 0.7%-1.5%).

The present method was used to analyze PCBs, OCPs, PAHs and PAEs standard substances in soil (n=3). As shown in Table 3, the determination results of PCBs, OCPs and PAHs were all within the quality control range of the compounds. The certified standard substances for PAEs in soil only gave expanded uncertainties but no qualified intervals. The determination results are shown in Table 4. The recovery rates of the target substances were between 56% and 89%, and the RSDs were between 0.1% and 3.2%.

Table 3 Determination results of PCBs, OCPs and PAHs standard substances in soil

Table 4 Determination results of PAEs standard substances in soil

Comparison with related purification methods

The existing environmental standards recommended a magnesium silicate column solid phase extraction purification with high universality for comparison with low temperature distribution purification. The extract of the certified reference material of soil was used and concentrated to 0.5 mL as a control sample without purification. The solid phase extraction purification test referred to HJ835 and a commercial glass magnesium silicate column (1 g) was selected. It was eluted with 9 mL of n-hexane: acetone (9:1) and then concentrated to 0.5 mL. The low temperature distribution purification test was carried out according to the above steps, and each treatment method was analyzed in parallel three times.

The determination results are shown in Table 5. The recovery rate of the compound is between 50% and 119%. There is no significant difference in the recovery rate of the same compound under different treatment methods, showing a trend of no purification control (54%-119%) > low temperature distribution purification (50%-114%) > magnesium silicate solid phase extraction purification (49%-112%).

This shows that the experimental process is long, there are many operations, there will be a certain loss of samples, and the recovery rate tends to decrease. The results of the three treatment methods are all within the qualified range for PCBs, OCPs and PAHs. The certified reference material content of PAEs is high, the relative concentration multiple of the synchronous experiment is large, and the recovery rate of the compound determination is 56%-90%, but the standard material does not give a qualified range, and the determination results are used as a reference. The relative standard deviation of the determination results shows that compared with the control without purification (1.1%-13.0%), the RSD of low-temperature distribution purification (0.1%-10.6%) is generally smaller, and the magnesium silicate solid phase extraction purification (0.23%-14.2%) varies from high to low. It is speculated that the RSD of the sample is better after purification because the sample matrix background is reduced after purification, and the sample repeatability is better, while the deterioration of RSD may be due to the extension of the experimental steps and the deterioration of the parallelism of the compounds.

Table 5 Recovery and relative standard deviation of compounds in three purification methods

The signal-to-noise ratio of the compound chromatographic peaks was analyzed. Compared with the control test without purification, the instrument response of individual compounds in the low-temperature distribution purification and solid phase extraction purification tests was lower, and the signal-to-noise ratio comparison was not made. Figure 5 is a schematic diagram of the signal-to-noise ratio of some chromatographic peaks in the test without purification, Figure 6 is a schematic diagram of the signal-to-noise ratio of some chromatographic peaks in the low-temperature distribution purification, and Figure 7 is a schematic diagram of the signal-to-noise ratio of some chromatographic peaks in the solid phase extraction purification.

As shown in Figures 5 to 7, the signal-to-noise ratio can be improved by about the same amount after low-temperature distribution purification and solid phase extraction purification, which is about 1.5 to 3 times. Therefore, after the extract is distributed at low temperature, it can reduce certain background interference, improve the signal-to-noise ratio of the chromatographic peak, and has the same purification effect as magnesium silicate solid phase extraction. Because the method is simple in processing, its parallelism and repeatability are better than magnesium silicate solid phase extraction. This method only needs to place the extract concentrate in a low-temperature refrigerator, and the purification process does not require manual operation. At the same time, it reduces the input of reagents and consumables, simplifies the experimental process, and reduces the secondary pollution of PAHs and PAEs in particular. In addition, compared with the non-purification test, the sample can reduce the matrix background after low-temperature distribution treatment, which is beneficial to the protection of the detection instrument.

in conclusion

This method uses microwave-assisted extraction-low-temperature distribution purification-GC/MS to establish a method for the simultaneous analysis of 18 polychlorinated biphenyls, 23 organochlorine pesticides, 16 polycyclic aromatic hydrocarbons and 6 phthalates in soil. It realizes the simultaneous extraction, purification and determination of these types of compounds in soil samples, meets the detection requirements of relevant environmental standard methods, improves the efficiency of large-scale sample analysis and testing, and reduces monitoring costs. It is an analytical method worthy of promotion.

Claims (5)

1. A method for simultaneously detecting 63 persistent organic pollutants in soil, which is characterized in that:

the 63 persistent organic pollutants are: naphthalene, dimethyl phthalate, acenaphthylene, acenaphthene, diethyl phthalate, fluorene, alpha-hexahexa-hexa-chloro, gamma-hexa-chloro, phenanthrene, anthracene, beta-hexa- -chloro, PCB28, delta-hexa-chloro, hepta-chloro, dibutyl phthalate, PCB152, aishi agent, epoxy hepta-chloro B, fluoranthene, PCB101, gamma-chlordane, alpha-chlordane, thiodane I, pyrene, p '-dribbling, di-reagent, PCB81, PCB77, isodieldrin, PCB123, o, p' -dribbling, PCB118, PCB114, p, p '-drop, thiodane ii, PCB153, isodieldrin aldehyde, PCB105, butylbenzyl phthalate, p' -drop, PCB138, thiodane sulfate, PCB126, PCB167, isodieldrin ketone, methoxydrop, PCB156, di (2-ethylhexyl) phthalate, PCB157, benzo (a) anthracene, PCB180, chrysene, miracle, PCB169, PCB189, di-n-octyl phthalate, benzo (B) fluoranthene, benzo (k) fluoranthene, benzo (a) pyrene, dibenzo (a, h) anthracene, indeno (1, 2, 3-cd) pyrene, benzo (ghi) perylene;

detecting 63 persistent organic pollutants by using a gas chromatography-mass spectrometer under the measurement conditions that a chromatographic column is Rxi-XLB, the Rxi-XLB is 30m long, the inner diameter is 0.25 mu m, the coating is 0.25mm, the temperature of a gas chromatography sample inlet is 280 ℃, the carrier gas is helium with 99.999% purity, the flow rate of the column is 1.0mL/min, the sample injection amount is 1 mu L, sample injection is not split, and the temperature rising program is as follows: after heat preservation at 70 ℃ for 2min, heating to 140 ℃ at a speed of 20 ℃/min, heating to 180 ℃ at a speed of 15 ℃/min, maintaining for 5min, heating to 210 ℃ at a speed of 8 ℃/min, heating to 270 ℃ at a speed of 3 ℃/min, maintaining for 4min, and finally heating to 320 ℃ at a speed of 15 ℃/min, maintaining for 6min; the mass spectrum conditions are as follows: the ion source is an EI source, the electron energy is 70eV, the temperature of the ion source is 300 ℃, and the temperature of a transmission line is 300 ℃;

the method comprises the following steps:

s1, preparation of instruments, reagents and materials

Wherein the material comprises: the target compound standard substance dissolved in the organic solvent is used for preparing a standard curve, and comprises 16 polycyclic aromatic hydrocarbon mixed standard substances, 23 OCPs mixed standard substances, 18 PCBs mixed standard substances and 6 phthalate mixed standard substances, and internal standards are extracted: 5 deuterated polycyclic aromatic hydrocarbon mixed standard substances and 5 ¹³ C marked organochlorine pesticide, 5 kinds ¹³ C, marking polychlorinated biphenyl, and feeding an internal standard: d (D) ₁₀ Pyrene, ¹³ C-p,p'DDE (direct digital Emotion) ¹³ C-PCB138；

S2, preparing standard curves of 6 concentration series of 63 POPs

PCBs concentration ranges of 0.005, 0.01, 0.05, 0.1, 0.2 and 0.5. Mu.g.multidot.mL ^-1 The concentration of the extraction internal standard and the sample injection internal standard are 0.1 mug.mL ^-1 OCPs concentration ranges of 0.02, 0.05, 0.1, 0.5, 1.0 and 5.0. Mu.g.multidot.mL ^-1 The concentration of the extraction internal standard and the sample injection internal standard are 0.5 mug.mL ^-1 PAHs and PAEs concentrations ranged from 0.1, 0.25, 0.5, 1.0, 5.0 and 10.0. Mu.g.mL ^-1 The concentration of the extraction internal standard and the sample injection internal standard is 1.0 ng.mL ^-1 ；

S3, sample treatment

Mixing fresh sample soil with proper amount of anhydrous sodium sulfate, grinding, and adding n-hexane: extracting an acetone mixed reagent, concentrating to about 0.5mL, placing in a low-temperature refrigerator, standing for 4h, and filtering to be detected, wherein the method comprises the following substeps:

s31, taking 10.0g of fresh soil, uniformly mixing and grinding the fresh soil with a proper amount of anhydrous sodium sulfate, filling the mixture into a Teflon material microwave tank,

s32, adding an isotope extraction internal standard, and adding 30mL of n-hexane according to the volume ratio: the acetone is a mixed reagent with the ratio of 1:1, and is subjected to microwave extraction for 15min at the temperature of 115 ℃,

s33, concentrating the extracting solution by rotary evaporation, blowing n-hexane to about 0.5mL by converting dissolved nitrogen, standing for 4 hours in a low-temperature refrigerator with the ambient temperature of-20 ℃, taking supernatant or filtering the supernatant into a sample injection bottle by using a microporous filter membrane, adding a sample injection internal standard, and measuring;

s4, organic pollutant measurement

The organic contaminants were measured by gas chromatography-mass spectrometry.

2. A method for simultaneous detection of 63 persistent organic pollutants in soil according to claim 1, wherein in said step S1, the control experimental apparatus comprises: a gas chromatograph-mass spectrometer, a microwave extraction instrument, a rotary evaporator and a nitrogen blower; the reagent comprises: n-hexane and acetone; the apparatus for the purification method comparison experiment comprises: a gas chromatograph-mass spectrometer, a microwave extraction instrument, a set of rotary evaporator, a nitrogen blower and a set of solid phase extraction device; the reagent comprises: n-hexane, dichloromethane, acetone, magnesium silicate solid phase extraction column, microporous filter membrane and quartz sand.

3. A method for simultaneously detecting 63 persistent organic pollutants in soil according to claim 1, wherein in step S1, said material further comprises: the standard substance with the target compound in the soil is used for experimental tests, and comprises 18 PCBs standard substances in the soil, 23 OCPs standard substances in the soil, 16 PAHs standard substances in the soil and 6 PAEs standard substances in the soil.

4. The method for simultaneously detecting 63 persistent organic pollutants in soil as recited in claim 1, wherein said 5 deuterated polycyclic aromatic hydrocarbon mixed standards comprise: d (D) ₈ Naphthalene, D ₁₀ Acenaphthene, D ₁₀ Phenanthrone, D ₁₂ chrysene and D ₁₂ Perylene.

5. A method for simultaneously detecting 63 persistent organic pollutants in soil according to claim 1, wherein said 5 types of pollutants are selected from the group consisting of ¹³ The C-labeled organochlorine pesticide comprises: ¹³ C-α-six, ¹³ C-γChlordane, ¹³ C-o,p'-DDE， ¹³ C-p, p'-DDD， ¹³ C-p,p'DDT,5 kinds ¹³ The C-labeled polychlorinated biphenyl includes: ¹³ C-PCB28、 ¹³

C-PCB52、 ¹³ C-PCB 101、 ¹³ C-PCB153 ¹³ C-PCB180。