Method for enrichment analysis of phthalate in indoor air based on MOFs composite sampling tube

Abstract

The invention discloses a method for enriching and analyzing phthalic acid ester in indoor air based on an MOFs composite sampling tube, and belongs to the field of analysis and test methods. The preparation method comprises the following steps: loading an MOFs material UiO-66-F4 on a white supporter to prepare an MOFs composite material UiO-66-F4 white supporter, filling a glass tube with the MOFs composite material, and blocking two ends of the glass tube with glass wool to prepare the MOFs composite sampling tube. The composite sampling pipe is connected with an atmosphere sampling instrument, and the composite material UiO-66-F4 at a white supporter is used as an adsorbent to enrich phthalate in indoor air. And placing the sampling tube after sampling in a thermal desorption instrument, and completing gas chromatography-mass spectrometry after thermal desorption. The MOFs composite sampling tube has good adsorption capacity on phthalate in air, and is good in stability and easy to reuse. The method has the advantages of simple operation, wide linear range, low detection limit and good accuracy, and can be used for measuring phthalate in an actual environment.

Description

Technical Field

[0001] The invention belongs to the technical field of analysis and testing methods, and specifically relates to a method for enriching and analyzing phthalates in indoor air using a MOFs composite sampling tube. Background Art

[0002] Phthalate esters (PAEs) are a common class of plasticizers that are widely used in plastic products, children's toys and medical devices. PAEs are mainly bonded to polymer molecules by van der Waals forces or hydrogen bonds. They are easily migrated and discharged into the environment during production and use, polluting the environment and endangering human health. Accurate monitoring of the content of PAEs in the environment is the basis for environmental pollution assessment and health effect research.

[0003] The sampling of PAEs in indoor air generally uses quartz fiber filter membrane, polyurethane foam, activated carbon and Tenax TA as adsorption materials. These adsorption materials generally have problems such as poor adsorption selectivity, limited adsorption capacity and difficulty in regeneration.

[0004] UiO-66 is a classic metal organic framework (MOFs) material, which is widely used to adsorb organic pollutants in the environment. Directly using it to adsorb PAEs has the problems of low adsorption capacity and poor stability. Monocarboxylic acid is introduced into UiO-66 to construct pore defects, and F atoms are introduced on the ligand to change the structure of UiO-66, which is then loaded on a white support to prepare a MOFs composite material UiO-66-F4@white support, which can improve the stability and adsorption capacity of the adsorption material. The composite material is used as an adsorbent for a sampling tube to make a composite sampling tube for enriching PAEs in the air. Combined with thermal desorption-gas chromatography-mass spectrometry, it can be used for the analysis of trace PAEs in the air. Summary of the invention

[0005] The present invention provides an analytical method for enriching PAEs in the air by using a MOFs composite material UiO-66-F4@white support as an adsorption material of an air sampling tube, and combining thermal desorption-gas chromatography-mass spectrometry technology for determination. The method comprises the following steps:

[0006] (1) Preparation of MOFs composite material UiO-66-F4@white support

[0007] Zirconium tetrachloride and 2,3,5,6-tetrafluoroterephthalic acid (molar ratio of 2:1 to 2.2:1) were added to an acetic acid aqueous solution (volume ratio of acetic acid to water was 2:3), and after ultrasonic dissolution, a white support was added, and after thorough mixing, the mixture was transferred to a tetrafluoroethylene-lined reactor and sealed, and the reaction was carried out at a constant temperature of 110°C for 24 hours. After cooling to room temperature, the product was filtered, washed with DMF and methanol several times, and the sample was vacuum dried at 60°C to obtain UiO-66-F4@ white support;

[0008] (2) Preparation of MOFs composite sampling tube

[0009] Weigh the MOFs composite material UiO-66-F4@white support and fill it into a cylindrical glass tube, plug both ends with glass wool, and then fix it with a stainless steel mesh. Activate the filled MOFs composite sampling tube at 250°C for 30 minutes at a nitrogen flow rate of 100mL / min. After activation, store it in a desiccator for later use; preferably, weigh 110mg of the MOFs composite material UiO-66-F4@white support and fill it into a cylindrical glass tube (90mm×6.36mm);

[0010] (3) Sampling

[0011] The activated MOFs composite sampling tube was connected to the atmospheric sampler to collect indoor air at a flow rate of 200 mL / min for 50 min.

[0012] (4) Analysis

[0013] After the MOFs composite sampling tube collects air, it is directly placed in a thermal desorber for thermal desorption-gas chromatography-mass spectrometry analysis.

[0014] Further preferred: in the preparation of the MOFs composite material in step (1) of the method, the white support is a 102 acid-washed white support with a particle size of 60 to 80 meshes.

[0015] Further preferred: In the preparation of the MOFs composite material in step (1) of the present method, the loading rate of UiO-66-F4 in the UiO-66-F4@white support is 10wt% to 30wt%, and the loading rate is calculated by weight percentage based on the ratio of the weight increase of the white support before and after loading to the UiO-66-F4@white support.

[0016] Further preferably, in the analysis of step (4) of the method, a second-order thermal desorption mode is adopted, the first stage is sample tube desorption, the desorption temperature is 160-220°C, the desorption time is 10-30min, the desorption flow rate is 30-50mL / min, and the corresponding cold trap capture temperature after desorption is -10-0°C; the second stage is cold trap desorption, the desorption temperature is 280-320°C, the desorption time is 2-5min, the heating rate is 40-60°C / s, and the trap mouth diversion is 0-9mL / min; a six-way valve is used for diversion, the six-way valve temperature is 230-250°C, and the transmission line temperature is 230-250°C.

[0017] Further preferably, in the analysis of step (4) of the method, the gas chromatography conditions are as follows: the gas chromatography column is an HP-5MS column (30m×0.25mm×0.25μm), the carrier gas is helium, the flow rate is 1mL / min, and the programmed temperature rise mode is adopted, the initial temperature is 100°C, maintained for 1min, increased to 200°C at a rate of 10°C / min, and then increased to 250°C at a rate of 6°C / min, and maintained for 10min.

[0018] Further preferably, in the analysis of step (4) of the method, the mass spectrometer adopts EI ionization, the electron energy is 70 eV, the transmission line temperature is 250°C, the ion source temperature is 250°C, the mass scanning range m / z is 50-500, the full scan mode is qualitative, and the selected ion scanning mode is quantitative.

[0019] When performing analysis in step (4), the external standard method is used for quantitative analysis. Under the same method conditions, the determined PAEs of different concentrations are measured, and a working curve is drawn with the mass as the horizontal axis and the peak area as the vertical axis; the concentration of the analyte is quantified according to the working curve.

[0020] The phthalate ester is one or more of dimethyl phthalate (DMP), diethyl phthalate (DEP), and di-n-butyl phthalate (DBP).

[0021] The method for determining PAEs in indoor air based on MOFs composite sampling tube enrichment combined with thermal desorption-gas chromatography-mass spectrometry described in the present invention not only has good adsorption performance for PAEs, but also shows good stability and reusability. The analytical method has a wide linear range and a low detection limit, and can be used to detect trace PAEs in the air. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM image of the white support

[0023] Figure 2 SEM image of MOFs composite material UiO-66-F4@white support

[0024] Figure 3 Comparison of different recycling times of MOFs composite sampling tubes. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0026] Example 1: Preparation of MOFs composite sampling tube

[0027] 3.0mmol of zirconium tetrachloride and 1.5mmol of 2,3,5,6-tetrafluoroterephthalic acid were added to 50mL of acetic acid aqueous solution (the ratio of acetic acid to water was 2:3), and after ultrasonic dissolution, 1.5g of white support was added, and after thorough mixing, it was transferred to a tetrafluoroethylene-lined reactor and sealed, and reacted at 110℃ for 24h. Cooled to room temperature, the product was filtered, washed with DMF and methanol several times, and the sample was vacuum dried at 60℃ to obtain the MOFs composite material UiO-66-F4@white support. 110 mg of MOFs composite material UiO-66-F4@white support was weighed and filled into a glass tube (90 mm × 6.36 mm), both ends were blocked with glass wool, and then fixed with a stainless steel mesh to obtain a MOFs composite sampling tube.

[0028] Determination of thermal desorption conditions:

[0029] In the first stage, the sample tube was thermally desorbed at a temperature of 180°C, a desorption time of 30 min, a desorption flow rate of 50 mL / min, and a cold trap temperature of -10°C. In the second stage, the cold trap was thermally desorbed at a temperature of 300°C, a desorption time of 5 min, a heating rate of 40°C / s, and a trap outlet diversion of 9 mL / min. The temperature of the six-way valve was 230°C, and the temperature of the transmission line was 240°C.

[0030] Working curve and detection limit:

[0031] Prepare mixed standard solutions of DMP, DEP and DBP with concentrations of 10, 20, 50, 100, 200, 500 and 1000 mg / L; accurately pipette 1.0 μL of mixed standard solutions of different concentrations (using acetonitrile solvent) and inject them into activated MOFs composite sampling tubes respectively, and purge them at a nitrogen flow rate of 100 mL / min for 5 min to make a series of standard tubes; perform thermal desorption-gas chromatography-mass spectrometry on the standard tubes of different concentrations, and draw a working curve with mass as the horizontal axis and peak area as the vertical axis.

[0032] Prepare a low-concentration mixed standard solution, perform parallel measurements 7 times, calculate the standard deviation S of the measurement results, and calculate the detection limit of the method according to Formula 1.

[0033] Formula 1

[0034] MDL=t (n-1,1-α＝0.99) S

[0035] In Formula 1, t is the t value of n-1 degrees of freedom at a confidence level of 99% (when n=7, t is 3.143), and S is the standard deviation of 7 consecutive analyses.

[0036] The results are shown in Table 1. The linear range of the method is 10-1000 mg / L, the correlation coefficient is greater than 0.99, and the linearity is good. The detection limit is 0.008-0.021 μg / m 3 The measurement requirements are met.

[0037] Table 1 Working curves and detection limits of PAEs

[0038] Example 2: Precision and Accuracy

[0039] The method for determining the accuracy is as follows: 1.0 μL of 1000 mg / L PAEs mixed standard solution was injected into the 5 activated sampling tubes respectively, and the mixture was purged for 5 min at a nitrogen flow rate of 100 mL / min. The mixture was measured by thermal desorption-gas chromatography-mass spectrometry, and the recovery rate was calculated by comparing with the direct injection of the PAEs standard solution. The calculation formula is shown in Formula 2. The accuracy of the method was investigated by the recovery rate. The method for determining the precision is as follows: 5 PAEs standard solutions of the same concentration were injected into the 5 activated sampling tubes respectively to prepare 5 standard tubes, and the 5 standard tubes were analyzed continuously. The precision was expressed by the relative standard deviation. The results are shown in Table 2. The relative standard deviation was between 0.8% and 2.1%, and the recovery rate was between 83.3% and 90.1%.

[0040] Formula 2

[0041]

[0042] Table 2 Recovery and precision of PAEs

[0045] Example 3: Recycling of MOFs composite sampling tubes The MOFs composite sampling tube was subjected to 150 adsorption / desorption cycle experiments. Figure 3 As shown, after being used 150 times, the MOFs composite sampling tube still has a high recovery rate for PAEs, indicating that the prepared MOFs composite sampling tube has a long service life, good stability, and is easy to reuse.

[0043] Example 4: Determination of PAEs Standards

[0044] The above method was used to determine the PAEs standard (where the concentrations of DMP, DEP and DBP were all 100 mg / L). The MOFs composite sampling tube adsorbed with the PAEs standard was placed in a thermal desorber for thermal desorption-gas chromatography-mass spectrometry analysis, and the concentrations of PAEs were measured as follows: DMP: 89.64 mg / L; DEP: 86.45 mg / L; DBP: 84.41 mg / L.

[0051] Example 5: Measurement of actual air samples

[0052] Using the above method, the MOFs composite sampling tube was connected to the atmospheric sampler in the living room and bedroom. After collecting air at a flow rate of 200 mL / min at room temperature for 50 min, the sampling tube was placed in a thermal desorber and thermal desorption-gas chromatography-mass spectrometry analysis was performed according to the established method. The concentrations of DMP and DEP in the living room were measured to be 1.62 and 0.84 μg / m 3 The concentrations of DMP and DEP in the bedroom were 0.58 and 0.86 μg / m 3 , DBP was not detected in the living room and bedroom.

Claims

1. A method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube, characterized in that: The following steps are involved: (1) Preparation of MOFs composite sampling tube Weigh the MOFs composite material UiO-66-F4@white support and fill it into a cylindrical glass tube, plug both ends with glass wool, and then fix it with a stainless steel mesh. Activate the filled MOFs composite sampling tube at 250°C for 30 minutes at a nitrogen flow rate of 100mL / min. After activation, store it in a desiccator for later use; preferably, weigh 110mg of the MOFs composite material UiO-66-F4@white support and fill it into a cylindrical glass tube (90mm×6.36mm); (2) Sampling The activated MOFs composite sampling tube was connected to an atmospheric sampler to collect indoor air at a flow rate of 200 mL / min for 50 min at room temperature; (3) Analysis After the MOFs composite sampling tube collects air, it is placed in a thermal desorber for thermal desorption-gas chromatography-mass spectrometry analysis.

2. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 1, characterized in that: Step (1) The MOFs composite material is UiO-66-F4@white support, and its preparation method is as follows: zirconium tetrachloride and 2,3,5,6-tetrafluoroterephthalic acid (molar ratio of 2:1 to 2.2:1) are added to an acetic acid aqueous solution (the volume ratio of acetic acid to water is 2:3), and after ultrasonic dissolution, the white support is added, and after sufficient mixing, it is transferred to a tetrafluoroethylene-lined reactor and sealed, and reacted at a constant temperature of 110°C for 24 hours. Cool to room temperature, filter the product, wash with DMF and methanol several times, and vacuum dry the sample at 60°C to obtain UiO-66-F4@white support.

3. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 2, characterized in that: Step (1) In the MOFs composite material UiO-66-F4@white support, the loading amount of UiO-66-F4 on the UiO-66-F4@white support is 10wt% to 30wt%.

4. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 1, characterized in that: Step (3) adopts a two-stage desorption mode, and the desorption gas is helium; the first stage is sample tube desorption, the desorption temperature is 160-220°C, the desorption time is 10-30min, the desorption flow rate is 30-50mL / min, and the corresponding cold trap capture temperature after desorption is -10-0°C; the second stage is cold trap desorption, the desorption temperature is 280-320°C, the desorption time is 2-5min, the heating rate is 40-60°C / s, and the trap mouth diversion is 0-9mL / min; a six-way valve is used for diversion, the six-way valve temperature is 230-250°C, and the transmission line temperature is 230-250°C.

5. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 1, characterized in that: Step (3) Gas chromatography conditions: The gas chromatography column is an HP-5MS column (30m×0.25mm×0.25μm), the carrier gas is helium, the flow rate is 1mL / min, and the programmed temperature mode is adopted. The initial temperature is 100°C, maintained for 1min, increased to 200°C at a rate of 10°C / min, and then increased to 250°C at a rate of 6°C / min, and maintained for 10min.

6. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 1, characterized in that: Step (3) The mass spectrometer adopts EI ionization, the electron energy is 70eV, the transmission line temperature is 250°C, the ion source temperature is 250°C, the mass scanning range m / z is 50-500, the full scanning mode is qualitative, and the selected ion scanning mode is quantitative.

7. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 1, characterized in that: During the analysis of step (3), the external standard method is used for quantitative analysis; under the same method conditions, different concentrations of phthalates are measured, and a working curve is drawn with mass as the horizontal axis and peak area as the vertical axis; the concentration of the analyte is quantified according to the working curve.

8. The method for enriching and analyzing phthalates in indoor air based on a MOFs composite sampling tube according to claim 1, characterized in that: The phthalates are: dimethyl phthalate (DMP), diethyl phthalate (DEP), and di-n-butylphthalate (DBP).

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