A method for particulate matter nitrosamine extraction and determination

Abstract

The present application relates to a kind of particulate matter nitrosamine extraction and determination method, comprising the following steps: S1: sample extraction and concentration purification;S2: constant temperature gasification injection: the sample to be measured is injected into the sample inlet of gas chromatograph, set the temperature of sample inlet, using non-split injection mode, with high-purity nitrogen as carrier gas, so that the sample to be measured gasification is introduced into chromatographic column;S3: high-resolution chromatography separation;S4: high temperature plasma pyrolysis;S5: constant current reaction gas luminescence detection: the combustion furnace of the nitrogen chemiluminescence detector is passed into reaction gas, set oxygen flow and hydrogen flow in reaction gas, generate ozone and occur chemiluminescence reaction with the nitric oxide, the light signal of specific wavelength is collected by photomultiplier tube;S6: standard curve and accurate quantification.

Description

Technical Field

[0001] This invention belongs to the field of environmental pollutant analysis and detection technology. In particular, it relates to a method for the extraction, purification, and high-resolution gas chromatography-nitrogen chemiluminescence detection of trace multi-structured nitrosamines in particulate matter. Background Technology

[0002] Trace amounts of nitrosamines adsorbed in fine particulate matter and complex microenvironments (such as underground parking lots) aerosols are highly carcinogenic. Due to the complex environmental matrix and extremely low concentration of the target analyte, coupled with the significant differences in the physicochemical properties of nitrosamines with different structures and their easy photodegradation, stringent technical requirements are placed on the extraction, purification, and accurate quantification of actual aerosol samples.

[0003] Currently, the quantitative analysis of nitrosamines in the environment mainly relies on gas chromatography-tandem mass spectrometry (GC-MS / MS) and liquid chromatography-high resolution mass spectrometry (LC-HRMS). However, in practical applications, LC-HRMS is susceptible to interference from high concentrations of inorganic salts in aerosol extracts, causing matrix inhibition at the mass spectrometry ion source and accelerating column wear; GC-MS / MS is prone to matrix cross-interference caused by nonpolar organic compounds such as fatty acids and aldehydes in particulate matter. A more prominent problem is that aromatic nitrosamines such as N-nitrosodiphenylamine (NDPhA) have poor thermal stability and are prone to thermal dissociation during conventional high-temperature vaporization injection, which cannot guarantee the accuracy of the test data.

[0004] Gas chromatography-nitrogen chemiluminescence detector (GC-NCD) theoretically avoids the aforementioned carbon matrix interference due to its specific response to nitrogen-containing compounds. However, directly applying conventional GC-NCD to the analysis of trace multi-structured nitrosamines in real environmental samples is objectively limited by the following technical bottlenecks: Firstly, there is the balance between the vaporization of high-boiling-point components and the dissociation of heat-sensitive substances. While a higher inlet temperature is beneficial for the vaporization of high-boiling-point substances, it directly leads to the thermal decomposition of components such as NDPhA. Secondly, separation of complex homologues is difficult. The polarity and boiling point range of straight-chain and cyclic / aromatic nitrosamines in fine particulate matter are large, and a single fixed temperature program rate can easily lead to co-elution of chromatographic peaks, making it difficult to achieve the baseline separation required for accurate quantification. Third, instrument drift caused by environmental matrix fluctuations. The concentration of non-nitrogenous carbon matrix in actual environmental samples fluctuates dramatically due to emission sources and seasons. When high-concentration carbon impurities enter the NCD detector, if the core pyrolysis temperature and the ratio of reactant gases are not precisely matched, it will cause a dramatic drift in the detector baseline, thereby masking the true signal of ultra-trace target substances.

[0005] Based on the above problems, a quantitative analysis method that combines environmental sample extraction process with the control of key parameters of GC-NCD is developed to overcome technical defects such as interference from complex matrices, dissociation of thermosensitive substances, and co-eluting of multiple components, which has a practical technical need. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for the extraction, purification and high-resolution gas chromatography-nitrogen chemiluminescence detection of trace multi-structured nitrosamines in particulate matter.

[0007] To achieve the above-mentioned objectives, the present invention provides the following steps: A method for extracting and determining particulate nitrosamines includes the following steps: S1: Sample extraction and concentration purification: A sample membrane of appropriate area is placed in an extraction container that has been deactivated, and chromatographic grade dichloromethane solvent is added for ultrasonic extraction; the extract is filtered and purified through a microporous membrane, concentrated, and then chromatographic grade dichloromethane is added again to make up to the set volume to obtain the sample to be tested; S2: Isothermal vaporization injection: The sample to be tested is injected into the injection port of the gas chromatograph, the injection port temperature is set, a splitless injection mode is adopted, and high-purity nitrogen is used as the carrier gas to vaporize the sample to be tested and introduce it into the chromatographic column, while inhibiting the thermal dissociation of the heat-sensitive nitrosamine component during the injection stage. S3: High-resolution chromatographic separation: The vaporized sample runs in the chromatographic column, and the linear nitrosamines and cyclic or aromatic nitrosamines in the sample are separated at baseline through a preset temperature program curve. S4: High-temperature plasma pyrolysis: The effluent after chromatographic separation enters the nitrogen chemiluminescence detector in sequence. The plasma pyrolysis temperature of the nitrogen chemiluminescence detector is set to pyrolyze the nitrosamine and convert it into nitric oxide. S5: Constant current reactive gas luminescence detection: Reactive gas is introduced into the combustion furnace of the nitrogen chemiluminescence detector, and the oxygen flow rate and hydrogen flow rate in the reactive gas are set to generate ozone and react with the nitric oxide in a chemiluminescence reaction. A light signal of a specific wavelength is collected by a photomultiplier tube. S6: Standard Curve and Accurate Quantification: Record the chromatographic peak areas at different retention times, and combine them with the pre-established multi-component nitrosamine external standard curve to calculate the accurate mass concentration of each nitrosamine component in the particulate matter sample.

[0008] Preferably, the area of ​​the sampling filter membrane and the volume of chromatographic grade dichloromethane solvent added in step S1 are determined in association with the pre-measured organic carbon concentration value in the particulate matter sample.

[0009] Preferably, in step S1, the duration of ultrasonic extraction is not less than 20 min to ensure that the organic matter adsorbed by the particulate matter is completely dissolved and transferred to the liquid phase; the microporous filter membrane is a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.45 μm.

[0010] Preferably, in step S2, the injection port temperature is set to 280 ℃, and the column flow rate is controlled to be constant at 1.0 mL / min.

[0011] Preferably, in step S3, the high-resolution chromatographic separation uses a one-dimensional capillary column, and its programmed temperature rise curve is set as follows: initial column temperature 40 ℃, held for 2 min; then rise to the target temperature of 320 ℃ at a heating rate of 25 ℃ / min, with the total running time controlled within 16 min.

[0012] Preferably, in step S5, the oxygen flow rate in the reaction gas is set to 10 mL / min and the hydrogen flow rate is set to 4 mL / min.

[0013] Preferably, in step S6, the operation of pre-establishing the standard curve is as follows: prepare a mixed standard solution containing nine nitrosamines including NDMA, NMEA, NDEA, NDPA, NDBA, NPIP, NPYR, NMOR and NDPhA, and set different concentration gradients to measure them sequentially to draw a calibration curve.

[0014] Preferably, in the chromatographic data processing obtained after sample testing, the target analytes are ensured to be within the same integration window. Manual integration is performed based on the retention time position to extract accurate peak areas, and finally the actual concentration of nitrosamines in the sample is calculated based on the concentration line.

[0015] Preferably, in the chromatographic data processing obtained after sample testing, the target analytes should be kept within the same integration window. Manual integration should be performed based on the retention time position to extract accurate peak areas, and finally, the actual concentration of nitrosamines in the sample should be calculated based on the concentration calibrator.

[0016] This invention features a simple and efficient pretreatment process, eliminating seasonal baseline drift caused by complex carbon impurities at the instrument level. It overcomes sensitivity bottlenecks and provides reliable technical support for the tracking and accurate assessment of pollution from fine particulate nitrogen-containing aerosols in microenvironments and complex urban atmospheres. The specific beneficial effects are as follows: Firstly, addressing the technical challenge of easily decomposing aromatic nitrosamines (such as NDPhA) under conventional instrumental analysis, making them difficult to measure, this invention precisely locks the temperature of the splitless injection port at 280 °C. This specific temperature condition ensures the full vaporization of high-boiling-point components in the aerosol extract while effectively cutting off the dissociation pathway of thermally unstable nitrosamines, thus solving the problem of inaccurate quantification caused by thermal degradation of the analyte at the instrument front end.

[0017] Secondly, in response to the physical characteristics of nitrosamine homologues in fine particulate matter, which have a large polarity range and significant differences in boiling points, this invention solves the problem of chromatographic peak co-elution caused by conventional single heating rate by matching a specific step-programmed heating curve. This method can completely separate linear nitrosamines and cyclic / aromatic nitrosamines, whose chromatographic peaks are very likely to overlap, and obtain mutually separated and symmetrical chromatographic peaks, so that the peak area of ​​the target component can be accurately integrated.

[0018] Finally, this invention fully utilizes the high selectivity and sensitivity of NCD for nitrogen atoms, eliminating the need for cumbersome and error-prone chemical derivatization steps. By simultaneously introducing matrix blank and matrix spiking experiments in each batch of detection for rigorous procedural control, this method maintains extremely low limits of detection (LOD) and quantitation (LOQ) even in complex aerosol matrices. It can accurately capture trace amounts of toxic substances at the ppt level in the environment, providing a standardized detection method with high precision and high recovery rate for long-term monitoring and health risk assessment of nitrosamines in particulate matter. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. It should be noted that the following embodiments are only used to demonstrate the implementation effects of the core technical parameters of the present invention, and should not be construed as limiting the scope of protection of the present invention.

[0020] Figure 1 This is the concentration standard curve of the target pollutant measured in this invention. Detailed Implementation

[0021] This invention provides a method for the extraction, purification, and high-resolution gas chromatography-nitrogen chemiluminescence detection of trace multi-structured nitrosamines in particulate matter, comprising the following steps: Step 1: Sample extraction and concentration / purification. A sample membrane of appropriate size is placed in a deactivated extraction container, and chromatographic-grade dichloromethane solvent is added for ultrasonic extraction. The extract is then purified by filtration through a microporous membrane, concentrated using a nitrogen blower, and finally diluted to the set volume with chromatographic-grade dichloromethane to obtain the sample to be tested. Step 2, isothermal vaporization injection. The sample to be tested is injected into the injection port of the gas chromatograph, the injection port temperature is set to 280 ℃, splitless injection mode is used, high-purity nitrogen is used as the carrier gas, and the column flow rate is controlled at a constant 1.0 mL / min, so that the sample is vaporized and introduced into the chromatographic column, while inhibiting the thermal dissociation of the heat-sensitive nitrosamine component during the injection stage; Step 3, high-resolution chromatographic separation. The vaporized sample runs in the chromatographic column, and through a preset temperature program, straight-chain nitrosamines with significant differences in polarity and boiling point are separated from cyclic or aromatic nitrosamines at baseline. Step four, high-temperature plasma pyrolysis. The effluent after chromatographic separation sequentially enters a nitrogen chemiluminescence detector, and the plasma pyrolysis temperature of the detector is set to 1000 °C, causing the nitrosamine to pyrolyze and convert into nitric oxide; Step 5, constant-flow reactive gas luminescence detection. Reactive gas is introduced into the combustion furnace of the detector, with the oxygen flow rate set to 10 mL / min and the hydrogen flow rate set to 4 mL / min. Ozone is generated and reacts with the nitric oxide in a chemiluminescent reaction. The light signal of a specific wavelength is collected by a photomultiplier tube. Step Six: Standard Curve and Accurate Quantification. Record the peak areas at different retention times, and calculate the accurate mass concentration of each nitrosamine component in the particulate sample using a pre-established multi-component external standard curve for nitrosamines.

[0022] Experimental Example 1: Particulate Matter (PM) in Underground Parking Lots 2.5 Extraction, purification, and high-resolution GC-NCD full-process quantitative analysis of trace nitrosamines with multiple structures in ) This embodiment uses PM2.5 collected in an underground parking lot environment (sampling time of 11 hours). 2.5 Taking particulate matter samples as an example, this document details the entire process from targeted extraction and purification at the front end to high-resolution quantitative analysis at the back end. The instrument used for testing is a gas chromatograph (Agilent 7890B) coupled with a nitrogen chemiluminescence detector (NCD). The specific operating steps are as follows: Step 1: All sample vials and aluminum foil used in the experiment must be placed in a muffle furnace and calcined at 450 ℃ for six hours to completely remove background organic matter from the consumables and avoid interference with ultra-trace analysis.

[0023] Step two, based on the pre-measured PM of the underground parking lot 2.5 The concentration of organic carbon (OC) in the sample was assessed, and a 40 mm diameter sampling membrane was cut. The cut membrane was placed in a deactivated sample vial, and 7 mL of chromatographic-grade dichloromethane solvent was accurately added. The vial was then sonicated for 20 min in an ultrasonic cleaner to ensure complete dissolution of the target organic matter on the filter membrane in the liquid phase. After sonication, the extract was filtered by injection using a 0.45 μm polytetrafluoroethylene (PTFE) microporous membrane to remove insoluble impurities. The collected clear filtrate was transferred to a test tube and completely dried using a nitrogen evaporator under a gentle nitrogen flow to obtain concentrated organic solute.

[0024] Step 3: Accurately add 100 μL of chromatographic-grade dichloromethane solvent to the dried solute to completely reconstitute it, obtaining the final sample that meets the conditions for instrumentation. If the sample obtained from this pretreatment is not immediately tested, it should be sealed and stored in the freezer at -20 ℃ in the dark.

[0025] Step four: Select a silica capillary column (e.g., Agilent VF-wax, 30 m × 0.32 mm × 0.25 μm) as the analytical column. Inject the sample prepared in step three into the gas chromatograph, with an injection volume of 1 μL. Precisely maintain the injection port temperature at 280 ℃, use splitless injection mode, and use high-purity nitrogen (≥99.999%) as the carrier gas. Set the column flow rate to a constant 1.0 mL / min. These conditions ensure complete vaporization of high-boiling-point substances while preventing the dissociation of heat-sensitive components such as NDPhA within the injection tubing.

[0026] The chromatographic column was run using a stepped temperature program: the initial column temperature was set at 40 °C and held for 2 min; then rapidly increased at a rate of 25 °C / min, with the total chromatographic run time controlled within 16 min. The detector interface temperature was set at 320 °C. This specific temperature program enables complete baseline separation of linear nitrosamines and cyclic / aromatic nitrosamines in the sample, which have significant differences in polarity and boiling point.

[0027] Step five: The chromatographic effluent sequentially enters the NCD detector and undergoes pyrolysis at 1000 °C in a plasma combustion furnace, converting into nitric oxide (NO). Using a high-precision mass flow controller, 10 mL / min of oxygen and 4 mL / min of hydrogen are introduced into the combustion furnace to generate ozone, which then undergoes a chemiluminescent reaction with nitric oxide. The light signal is collected by a photomultiplier tube. The specific reaction gas flow ratio of 10 mL / min oxygen to 4 mL / min hydrogen used in this invention is specifically designed to eliminate instrument baseline drift caused by differences in high concentrations of non-nitrogenous carbon matrix in complex microenvironments and urban atmospheric fine particulate aerosol samples.

[0028] Step Six: Formal PM2.5 measurement 2.5 Before sampling, a series of standard concentrations of the target analytes were prepared. A mixed standard solution containing nine nitrosamines, including NDMA, NMEA, NDEA, NDPA, NDBA, NPIP, NPYR, NMOR, and NDPhA, was diluted to five concentration gradients: 100 ppb, 200 ppb, 500 ppb, 1 ppm, and 2 ppm. The samples were then analyzed sequentially, and the corresponding concentration standard curves were plotted using the obtained peak areas (e.g., ...). Figure 1 (As shown).

[0029] After the baseline was drawn, a solvent blank containing only chromatographic grade dichloromethane was continuously injected and analyzed until no interfering peaks appeared in the instrument spectrum. Once the system baseline was confirmed to be clean, PM2.5 from the actual underground parking lot was analyzed. 2.5 The sample is injected for testing, and the components are manually integrated based on the retention time and position. Finally, the concentration of each component is calculated based on the concentration line.

[0030] Step seven: Under these optimized integrated extraction and detection conditions, five parallel determinations of nitrogen-containing compounds were performed. The results showed that this method effectively eliminated interference from complex environmental matrices, with the relative standard deviation (RSD) of the target component peak area controlled between 0.92% and 7.53%, and the recovery rate of the target component consistently between 96.30% and 105.10%. The limits of detection (LOD) of this complete analytical process ranged from 1.1 to 5.8 pg, and the limits of quantitation (LOQ) ranged from 3.6 to 19.3 pg, fully meeting the accurate quantification requirements for ppt-level multi-structure polar nitrogen-containing compounds in actual atmospheric microenvironment aerosols.

Claims

1. A method for extracting and determining particulate nitrosamines, characterized in that... Includes the following steps: S1: Sample extraction and concentration purification: A sample membrane of appropriate area is placed in an extraction container that has been deactivated, and chromatographic grade dichloromethane solvent is added for ultrasonic extraction; the extract is filtered and purified through a microporous membrane, concentrated, and then chromatographic grade dichloromethane is added again to make up to the set volume to obtain the sample to be tested; S2: Isothermal vaporization injection: The sample to be tested is injected into the injection port of the gas chromatograph, the injection port temperature is set, a splitless injection mode is adopted, and high-purity nitrogen is used as the carrier gas to vaporize the sample to be tested and introduce it into the chromatographic column, while inhibiting the thermal dissociation of the heat-sensitive nitrosamine component during the injection stage. S3: High-resolution chromatographic separation: The vaporized sample runs in the chromatographic column, and the linear nitrosamines and cyclic or aromatic nitrosamines in the sample are separated at baseline through a preset temperature program curve. S4: High-temperature plasma pyrolysis: The effluent after chromatographic separation sequentially enters a nitrogen chemiluminescence detector. The plasma pyrolysis temperature of the nitrogen chemiluminescence detector is set to 1000 ℃, so that nitrosamines are pyrolyzed and converted into nitric oxide. S5: Constant current reactive gas luminescence detection: Reactive gas is introduced into the combustion furnace of the nitrogen chemiluminescence detector, and the oxygen flow rate and hydrogen flow rate in the reactive gas are set to generate ozone and react with the nitric oxide in a chemiluminescence reaction. A light signal of a specific wavelength is collected by a photomultiplier tube. S6: Standard Curve and Accurate Quantification: Record the chromatographic peak areas at different retention times, and combine them with the pre-established multi-component nitrosamine external standard curve to calculate the accurate mass concentration of each nitrosamine component in the particulate matter sample.

2. The method according to claim 1, characterized in that, The area of ​​the sampling filter membrane and the volume of chromatographic grade dichloromethane solvent added in step S1 are determined in association with the pre-measured organic carbon concentration value in the particulate matter sample.

3. The method according to claim 1, characterized in that, In step S1, the duration of ultrasonic extraction is not less than 20 minutes to ensure that the organic matter adsorbed by the particulate matter is completely dissolved and transferred to the liquid phase; the microporous filter membrane is a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.45 μm.

4. The method according to claim 1, characterized in that, In step S2, the injection port temperature is set to 280℃ and the column flow rate is kept constant at 1.0 mL / min.

5. The method according to claim 1, characterized in that, In step S3, the high-resolution chromatographic separation uses a one-dimensional capillary column, and its programmed temperature rise curve is set as follows: initial column temperature 40℃, held for 2 min; then rise to the target temperature of 320℃ at a heating rate of 25℃ / min, with the total running time controlled within 16 min.

6. The method according to claim 1, characterized in that, In step S4, the plasma pyrolysis temperature of the nitrogen chemiluminescence detector is set to 1000℃.

7. The method according to claim 1, characterized in that, In step S5, the oxygen flow rate in the reaction gas is set to 10 mL / min and the hydrogen flow rate is set to 4 mL / min.

8. The method according to claim 1, characterized in that, In step S6, the operation of pre-establishing the standard curve is as follows: prepare a mixed standard solution containing nine nitrosamines including NDMA, NMEA, NDEA, NDPA, NDBA, NPIP, NPYR, NMOR and NDPhA, set different concentration gradients and measure them sequentially to draw the calibration curve.

9. The method according to claim 1, characterized in that, In the chromatographic data processing after sample analysis, the target analytes are ensured to be within the same integration window. Manual integration is performed based on the retention time position to extract accurate peak areas. Finally, the actual concentration of nitrosamines in the sample is calculated based on the concentration line.

Images