A quantitative method for indoor semi-volatile organic pollutants

Abstract

The present invention belongs to the technical field of semi-volatile organic pollutant air monitoring, and relates to a quantitative method for indoor semi-volatile organic pollutants, including a complete set of work processes including sample collection, pre-treatment, instrument analysis, and data processing. The present invention provides a passive air sampler with a compact size and easy operation, which improves the applicability of the passive sampler for on-site sampling; and provides a sampling rate prediction method that can predict the sampling rate of each compound, thereby improving the accuracy of air concentration quantification. The present invention solves the problem that the existing method has poor sampling applicability and is difficult to accurately quantify due to lack of calibration data.

Description

Technical Field

[0001] The present invention belongs to the technical field of air monitoring of semi-volatile organic pollutants, and relates to a method for quantifying indoor semi-volatile organic pollutants. Background Art

[0002] Semi-volatile organic pollutants (SVOCs) have adverse effects on human health. It is crucial to clarify the indoor occurrence and concentration of SVOCs for their risk prevention and control. Compared with conventional active air sampling, passive air sampling is a method that is noise-free, low-cost, and can provide time-weighted average concentrations, and has good application prospects indoors.

[0003] The passive air sampling technique is based on the principle of molecular diffusion and uses the concentration difference between the target substance in the air and the adsorbent as the driving force to complete enrichment. For kinetic passive air samplers, the sampling amount of a compound is proportional to the sampling time, and the slope of the linear curve between the two is the sampling rate (SR). With the help of SR, the sampling amount can be converted into air concentration, thereby realizing the quantification of air pollutants.

[0004] Currently, polyurethane passive samplers are often used in the passive sampling technique of SVOCs. However, its stainless steel shell (diameter: 30 cm at the top, 24 cm at the bottom) is large in volume and not convenient for indoor deployment. In addition, due to limited calibration data of compounds, many studies use a general SR to calculate the air concentration of different compounds, which increases the uncertainty of quantification.

[0005] Polydimethylsiloxane (PDMS) foam (diameter: 2 cm, thickness: 1 cm) is small in volume and has been proven to have excellent SVOCs sampling ability. However, no calibration data related to PDMS foam has been seen yet. Currently, there is a lack of a method that can accurately quantify indoor air pollutants. Summary of the Invention

[0006] The present invention aims to provide a method for quantifying SVOCs in indoor air, which involves a complete workflow of sample collection, pretreatment, instrumental analysis, and data processing. Aiming at the problems of large volume of the passive sampler and lack of SR data in the existing quantification methods, this method realizes the quantification of SVOCs in indoor air by improving the passive air sampler and constructing a sampling rate prediction model.

[0007] The technical solution of the present invention:

[0008] A method for quantifying indoor semi-volatile organic pollutants, comprising the following steps:

[0009] (1) Air sample collection:

[0010] Place the passive air sampler at the sampling point, open the glass protective cover for sealing, vertically place the wooden plug with the adsorbent on the indoor plane, and close the glass protective cover and the wooden plug after sampling for Δt days.

[0011] The sampling time Δt is preferably 14 days.

[0012] (2) Pretreatment of air samples:

[0013] Take out the adsorbent from the sampler, place it in the extraction cell of the accelerated solvent extractor, add the surrogate solution for extraction; concentrate the extract under nitrogen purging, and make up the volume after adding the internal standard solution;

[0014] The extraction conditions are as follows: use a mixed solution of n-hexane and ethyl acetate with a volume ratio of 1:1 as the extraction solvent, heat the extraction cell to 100 - 120 °C for 1 - 3 extraction cycles;

[0015] The surrogate is the isotope-labeled substance of the target compound, and the internal standards are hexamethylbenzene and diazinon-D10. The spiking amounts of the two are the same. Control the final concentrations of the surrogate and the target compound in the sample to be in the middle concentration range of the standard curve, that is, 100 - 300 μg·L -1 .

[0016] (3) GC-MS instrumental analysis:

[0017] Quantify by the internal standard method; integrate the chromatographic peak areas of the measured components and the internal standards in the sample through the GC-MS instrument, and calculate the quantitative results (m) of the measured components according to the standard curve.

[0018] The GC-MS instrumental analysis conditions are as follows: use an HP-5ms gas chromatography column, with parameters of 30 m (length) × 0.25 mm (inner diameter) × 0.25 μm (film thickness); GC programmed temperature rise conditions, hold at 60 °C for 1 min, rise to 300 °C at 5 °C·min -1 and hold for 2 min; the transfer line temperature is 290 °C, the mass spectrometry ion source is an EI source, SIM acquisition mode, the ion source temperature is 250 °C, the interface temperature is 290 °C, and the solvent delay time is 5 min.

[0019] (4) Prediction of sampling rate:

[0020] Input the molecular mass of the measured component and the n-octanol / air partition coefficient into the sampling rate prediction model to calculate the sampling rate of this component.

[0021] The sampling rate prediction model is: logSR = 1.25 + 0.125logK OA –1.240logMW (R 2= 0.480, p = 0.027); where SR is the sampling rate of the analyte, MW is the molecular weight of the analyte, K OA is the n-octanol / air partition coefficient of the analyte (at 25 °C), R 2 is the regression coefficient, and p is the significance level.

[0022] (5) Air concentration calculation:

[0023] Based on the quantitative result (m) of the analyte, the sampling rate (SR), and the sampling time (Δt), calculate the air concentration (C Air ) of the analyte.

[0024] The formula for calculating the air concentration of the analyte is: C Air = m / (SR·Δt).

[0025] The passive air sampler described above is composed of a glass protective cover, a stainless-steel needle, an adsorbent, and a sealing cork; the sealing cork serves as the base, the stainless-steel needle is vertically inserted into the sealing cork, the adsorbent is fixed on the stainless-steel needle, and the glass protective cover is placed on the sealing cork and directly sealed, enclosing the stainless-steel needle and the adsorbent within the glass protective cover.

[0026] The adsorbent is polydimethylsiloxane (PDMS) foam with a diameter of 2 cm and a thickness of 1 cm, and three pieces of PDMS foam are provided in each passive air sampler.

[0027] The preparation method of the adsorbent is as follows: Mix polydimethylsiloxane elastomer and a curing agent (Dow Corning DC184) in a volume ratio of 10:1 to obtain an elastomer mixture; then mix the elastomer mixture with sodium chloride in a mass ratio of 1:6, and the particle size of the sodium chloride particles is between 0.3 and 0.5 mm; then pour the mixture of the elastomer mixture and sodium chloride into a silicone mold and compact it, and cure it in an oven at 60 - 80 °C for 1 - 2 h; subsequently, demold the PDMS foam, wash it with water at 30 - 50 °C to dissolve the entrained salt, and dry it to obtain a flexible and porous PDMS foam adsorbent material.

[0028] To remove potential interfering components and contaminants in the adsorbent, further treatment of the PDMS foam is required: Place the PDMS foam in a tube furnace, heat it to 200 - 250 °C in a nitrogen atmosphere and hold for 1 - 2 h; then use an accelerated solvent extractor to wash the PDMS foam, and a mixed solution of n-hexane and ethyl acetate with a volume ratio of 1:1 is used as the extraction solvent, heat it to 100 - 120 °C for 1 - 3 extraction cycles; then place the PDMS foam in a vacuum oven, at 55 - 75 °C and 10 -4 ~10 -2Dry for 4 - 6 h under the condition of Pa. Assemble the adsorption material with other components of the sampler before sampling.

[0029] Advantages of the present invention:

[0030] The present invention provides a passive air sampler, which has a good adsorption effect on SVOCs. Compared with other samplers, it is small in size, low in cost (about 5 yuan), simple to operate, and suitable for wide deployment indoors.

[0031] The present invention provides a method for predicting the SR of SVOCs, which overcomes the problem of missing calibration data of compounds and can predict the sampling rate of each SVOC, thereby improving the accuracy of air concentration quantification. Description of the drawings

[0032] Figure 1 is the basic flowchart of the method of the present invention.

[0033] Figure 2 is the structural diagram of the passive air sampler prepared by the present invention. In the figure, 1 - glass protective cover; 2 - stainless steel needle; 3 - polydimethylsiloxane foam; 4 - sealing cork.

[0034] Figure 3 is the schematic diagram of the adsorption of gaseous and particulate semi - volatile organic compounds by polydimethylsiloxane foam.

[0035] Figure 4 is the sampling rate prediction model. In the figure, SR is the sampling rate, K OA is the octanol / air partition coefficient, and MW is the molecular mass. Detailed implementation manners

[0036] For a better understanding of the content of the present invention, the following further illustrates the present invention through examples, but the examples given do not limit the protection scope of the present invention.

[0037] Example 1

[0038] This example provides a method for quantifying indoor semi - volatile organic pollutants. The overall process of the method of the present invention is as Figure 1 shown.

[0039] (1) Collection of air samples

[0040] Use Figure 2 the passive sampler shown to achieve indoor air sampling. Place the passive sampler prepared by the present invention indoors in a building materials market. Open the glass protective cover 1, and place the sealing cork 4 fixed with PDMS foam 3 on the indoor plane. During sampling, recover 2 passive samplers on the 3rd, 7th, 14th, 21st, and 28th days respectively.

[0041] (2) Pretreatment of air samples

[0042] Take out the adsorbent from the sampler and place it in the extraction cell of the accelerated solvent extractor. Add the surrogate solution (the surrogate is the isotope-labeled compound of the target compound, with a concentration of 10 mg·L -1 , and the dosage is 10 μL), and then extract with a mixture of n-hexane and ethyl acetate with a volume ratio of 1:1. The extraction conditions are: heat to 120 °C for 2 extraction cycles; concentrate the extract under nitrogen purging, add the internal standard solution (the internal standards are hexamethylbenzene and diazinon-D10, with a concentration of 10 mg·L -1 , and the dosage is 10 μL), and then make up the volume to 1 mL.

[0043] (3) GC-MS detection

[0044] Establish a GC-MS analysis method for 71 SVOCs, determine the method detection limit and recovery rate of the target compounds, and then quantify the SVOCs in the samples based on the internal standard method. The specific implementation steps are as follows:

[0045] The GC-MS instrument analysis conditions are as follows: use an HP-5ms gas chromatography column with parameters of 30 m (length) × 0.25 mm (inner diameter) × 0.25 μm (film thickness); for the GC temperature programming conditions, hold at 60 °C for 1 min, increase to 300 °C at a rate of 5 °C·min-1, and hold for 2 min; the transfer line temperature is 290 °C, the mass spectrometry ion source is an EI source, in the SIM acquisition mode, the ion source temperature is 250 °C, the interface temperature is 300 °C, and the solvent delay time is 5 min.

[0046] Mass spectrometry information of the test compounds: The characteristic ions of the target compounds, surrogates and internal standards are shown in Table 1 and Table 2.

[0047] Table 1. Mass spectrometry information of target compounds

[0048]

[0049]

[0050] Table 2. Mass spectrometry information of surrogates and internal standards

[0051]

[0052]

[0053] Establish a standard curve: Prepare standard solutions of 71 target compounds with concentrations of 0.5, 1, 5, 10, 50, 100, 200, 500 μg·L -1 , and at the same time control the concentrations of the surrogates and internal standards in the standard solutions to be 100 μg·L -1. The standard solution was analyzed by GC-MS to establish the linear curve of response and concentration. The R of the standard curve 2 is shown in Table 3. The R of the standard curve of the target compound 2 is between 0.893 and 0.999, indicating a good linear relationship.

[0054] Method detection limit: For the target compound detected in the matrix blank sample, the method detection limit is the blank concentration + 3 times the standard deviation. For the target compound not detected in the matrix blank sample, the method detection limit is 3 times the signal-to-noise ratio of the low-concentration spiked sample.

[0055] Matrix spike recovery: The target compound and surrogate were added to the PDMS foam at a spiking level of 20 ng. The recoveries of the target compound in three replicate samples were calculated.

[0056] Table 3. Method detection limits of 71 target compounds

[0057]

[0058]

[0059]

[0060] Note: "-" represents not detected.

[0061] The detected compounds in the air sample are shown in Table 4. The adsorption of some detected compounds on the adsorbent was analyzed. As Figure 3 shown, effective enrichment of gaseous and particulate-phase SVOCs on the PDMS foam can be achieved within 14 days before sampling. As the sampling time increases, some volatile compounds escape from the adsorption material. The results show that the optimal passive sampling time is 14 days, which also proves the applicability of the PDMS foam passive sampler for indoor sampling.

[0062] Table 4. List of detected compounds

[0063]

[0064]

[0065] Note: The unit of molecular mass is g·mol -1 ; K OA is the octanol / air partition coefficient; logK OA is calculated by "KOAWIN v1.11" in the EPI Suite.

[0066] (4) Calculation of SVOCs air concentration

[0067] As Figure 4As shown, the sampling rate (SR) is positively correlated with the molecular weight (MW) and the n-octanol-air partition coefficient (K OA ). By performing multiple linear regression on the data, the prediction model for SR is obtained as: logSR = 1.25 + 0.125logK OA – 1.240logMW (R 2 = 0.480, p = 0.027).

[0068] For compounds without standards or sampling rates, the calibration curve of reference compounds can be used for quantification to obtain the content (m) of the determined components in the sample. Then, the MW and K OA values of the determined components are input into the sampling rate prediction model to calculate the corresponding SR. Finally, the air concentration (C) of indoor SVOCs is calculated from the above parameters [C = m / (Δt × SR)]. As shown in Table 5, through the method proposed by the present invention, the quantification of SVOCs in the air of building materials markets is achieved, demonstrating the feasibility of the method.

[0069] Table 5. Quantification results of SVOCs in the air of building materials markets

[0070]

[0071]

[0072] Note: K OA is the n-octanol / air partition coefficient; m is the sampling amount of the determined component; SR is the sampling rate of the determined component; C AIR is the air concentration of the determined component.

Claims

1. A quantitative method for indoor semi-volatile organic pollutants, characterized in that: The steps include: (1) Air sample collection: Place the passive air sampler at the sampling point, open the glass protective cover used for sealing, place the wooden plug fixed with the adsorbent vertically on the indoor plane, and close the glass protective cover and the wooden plug after sampling Δt days; The passive air sampler is composed of a glass protective cover, a stainless steel needle, an adsorbent and a sealed wooden plug; the sealed wooden plug serves as a base, the stainless steel needle is vertically inserted into the sealed wooden plug, the adsorbent is fixed on the stainless steel needle, the glass protective cover is covered on the sealed wooden plug, the two are directly sealed, and the stainless steel needle and the adsorbent are sealed in the glass protective cover; (2) Air sample pretreatment: The adsorbent is taken out from the sampler, placed in the extraction cell of the rapid solvent extractor, and the substitute solution is added for extraction; the extract is concentrated under nitrogen purge, and the internal standard solution is added to make it constant; (3) GC-MS instrument analysis: The internal standard method was used for quantification; The chromatographic peak areas of the measured components and internal standards in the sample are integrated by a GC-MS instrument, and the quantitative results m of the measured components are calculated according to the standard curve; (4) Sampling rate prediction: The molecular weight and n-octanol / air partition coefficient of the measured component are input into the sampling rate prediction model to calculate the sampling rate of the component; The sampling rate prediction model is: logSR = 1.25 + 0.125logK OA –1.240logMW; where SR is the sampling rate of the measured component, MW is the molecular weight of the measured component, and K OA To determine the n-octanol / air partition coefficient of the component at 25°C; (5) Calculation of air concentration: Calculate the air concentration C of the measured component based on the quantitative result m of the measured component, the sampling rate SR and the sampling time Δt Air ; The adsorbent is polydimethylsiloxane foam, 2 cm in diameter and 1 cm in thickness, and each passive air sampler is provided with 3 pieces of polydimethylsiloxane foam; In step (1), the sampling time Δt is 14 days; In step (2), the sample extraction conditions are: using a mixture of n-hexane and ethyl acetate in a volume ratio of 1:1 as the extraction solvent, heating the extraction cell to 100-120° C. and extracting for 1-3 cycles.

2. The method for quantifying indoor semi-volatile organic pollutants according to claim 1, characterized in that: The preparation method of the adsorbent is as follows: a polydimethylsiloxane elastomer of Dow Corning DC184 and a curing agent are mixed at a volume ratio of 10:1 to obtain an elastomer mixture; the elastomer mixture is then mixed with sodium chloride at a mass ratio of 1:6, and the particle size of the sodium chloride particles is between 0.3 and 0.5 mm; the mixture of the elastomer mixture and the sodium chloride is then poured into a silicone mold for compaction, and cured in a drying oven at 60 to 80° C. for 1 to 2 hours; the polydimethylsiloxane foam is then demolded, rinsed with water at 30 to 50° C. to dissolve the salt entrained therein, and dried to obtain a flexible and porous polydimethylsiloxane foam adsorption material.

3. A quantitative method for indoor semi-volatile organic pollutants according to claim 2, characterized in that: In order to remove potential interfering components and pollutants in the adsorbent, the polydimethylsiloxane foam needs to be further treated: the polydimethylsiloxane foam is placed in a tube furnace and heated to 200-250°C in a nitrogen atmosphere for 1-2 hours; then the polydimethylsiloxane foam is cleaned using a rapid solvent extractor, and a mixture of n-hexane and ethyl acetate in a volume ratio of 1:1 is used as the extraction solvent, heated to 100-120°C for 1-3 cycles; then the polydimethylsiloxane foam is placed in a vacuum oven and heated at 55-75°C and 10 -4 ~10 -2 Dry for 4 to 6 hours under the conditions of Pa; assemble the adsorption material with other components of the sampler before sampling.

4. The method for quantifying indoor semi-volatile organic pollutants according to claim 1, characterized in that: In step (2), in the sample extraction, the surrogate is the isotope labeled substance of the target substance, and the internal standard is hexamethylbenzene and diazinon-D10, and the spiked amounts of the two are the same, and the final concentrations of the internal standard, surrogate and target substance in the sample are controlled to be in the middle concentration range of the standard curve of 100 to 300 μg·L -1 .

5. The method for quantifying indoor semi-volatile organic pollutants according to claim 1, characterized in that: In step (3), the GC-MS instrument analysis conditions are: using an HP-5ms gas chromatography column with parameters of length 30m×inner diameter 0.25mm×film thickness 0.25μm; GC program temperature conditions, 60℃ for 1min, 5℃·min -1 Raise to 300℃ and maintain for 2min; the transfer line temperature is 290℃, the mass spectrometry ion source is EI source, SIM acquisition mode, ion source temperature is 250℃, interface temperature is 290℃, and solvent delay time is 5min.

6. The method for quantifying indoor semi-volatile organic pollutants according to claim 1, characterized in that: In step (5), the calculation formula for the air concentration of the measured component is: C Air =m / (SR·Δt).

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