An on-line mass spectrometry analysis method and on-line analysis system for volatile organic compounds based on a gas phase quantitative ring

Abstract

This invention belongs to the field of volatile organic compound (VOC) detection technology, and provides an online mass spectrometry analysis method and system for VOCs based on a gas-phase quantitative loop. The method includes: collecting human exhaled breath using a gas sampling bag; switching the gas-phase quantitative loop to Load mode to deliver the gas from the sampling bag to the loop; switching the loop to Inject mode and introducing a carrier gas to compress and enrich the gas in the loop, then delivering it to an ion source for mass spectrometry analysis. This invention eliminates the need for adsorption enrichment and thermal desorption steps, simplifying the gas sample pretreatment process and significantly shortening the mass spectrometry analysis time. By combining the gas sampling bag and the gas-phase quantitative loop, the high-flow-rate carrier gas compresses and enriches the analyte gas within the loop, improving detection sensitivity and making it suitable for determining extremely low concentrations of VOCs. Quantitative analysis of VOCs is achieved by controlling the volume of the gas-phase quantitative loop.

Description

Technical Field

[0001] This invention relates to the field of volatile organic compound (VOC) detection technology, and in particular to an online mass spectrometry analysis method and system for VOCs based on a gas-phase quantitative loop. Background Technology

[0002] Changes in the composition and content of volatile organic compounds (VOCs) in exhaled breath are closely related to changes in human physiological state. Some characteristic biomolecules produced by human metabolism, such as disease marker molecules, are exhaled. Therefore, accurately measuring disease markers in exhaled breath can effectively monitor the occurrence and development of related diseases. Modern medicine, through research on disease pathogenesis and clinical trials, has strongly demonstrated that some diseases are indeed closely related to certain components in human exhaled breath. These compounds are also used as diagnostic markers for corresponding diseases. For example, acetone in exhaled breath is a marker for diagnosing diabetes; the concentration of hydrogen in exhaled breath after lactose intake is a marker for diagnosing gastrointestinal diseases; labeled carbon dioxide in exhaled breath after taking 13C-labeled urea is a marker for determining Helicobacter pylori infection; and nitric oxide is a marker for diagnosing asthma. In recent years, studying the composition and concentration of various metabolites in exhaled breath to find biomarkers that can be used for disease screening has become a research hotspot in related fields.

[0003] Traditional VOCs detection methods mainly include gas chromatography (GC), gas sensors, laser spectroscopy, and electronic nose systems composed of sensor arrays. These methods are often limited to the detection of specific volatile components and have very limited sensitivity. However, human metabolites contain over 200,000 compounds, yet only about 3,000 have been detected in exhaled breath to date. Therefore, traditional detection methods are insufficient for systematically studying the relationship between various exhaled metabolites and disease diagnosis. Modern mass spectrometry offers advantages such as fast analysis speed, high resolution, and accurate results. Its extremely high sensitivity and various ionization methods also greatly facilitate the study of volatile and non-volatile chemical components. Currently, methods for exhaled VOCs analysis are mainly classified according to ionization methods into gas chromatography-mass spectrometry (GC-MS), selected ion tube mass spectrometry (SELECTI-MS), proton transfer reaction mass spectrometry (PTS-MS), and extraction electrospray ionization mass spectrometry (ESI-MS). These technologies provide important means for characterizing human exhaled metabolites and have become core tools driving exhaled breath analysis research.

[0004] Although various volatile metabolites in exhaled breath have a significant impact on disease diagnosis, metabolic pathway research, and human health, mass spectrometry-based methods for analyzing exhaled VOCs still face challenges such as insufficient analytical sensitivity and difficulty in quantitative analysis due to their diverse types, low concentrations, and complex structures. Furthermore, traditional VOCs enrichment analysis methods involve lengthy sample pretreatment times, hindering high-throughput analysis and failing to meet the needs of real-time clinical monitoring.

[0005] Therefore, it is necessary to develop a rapid, efficient, and highly sensitive online mass spectrometry method for analyzing VOCs in human exhaled breath. Summary of the Invention

[0006] The purpose of this invention is to provide an online mass spectrometry analysis method and system for volatile organic compounds based on a gas-phase quantitative loop, addressing the shortcomings of existing technologies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an online mass spectrometry analysis method for volatile organic compounds based on gas-phase quantitative loops, comprising the following steps: 1) Collect human exhaled breath using a gas sampling bag; 2) Switch the gas phase quantitative loop to Load mode to deliver the gas in the gas sampling bag to the gas phase quantitative loop; 3) Switch the gas phase quantitative loop to Inject mode, introduce carrier gas to compress and enrich the gas in the gas phase quantitative loop, and then transport it to the ion source for mass spectrometry analysis.

[0008] Preferably, the volume of the gas sampling bag in step 1) is 1~4L.

[0009] Preferably, the volume of the gas phase metering loop in step 2) is 200~500mL.

[0010] Preferably, in step 2), the gas in the gas sampling bag is delivered to the gas phase quantitative loop using a vacuum pump. The flow rate of the air pump is 1.5~3L / min.

[0011] Preferably, the carrier gas in step 3) comprises nitrogen or synthetic air.

[0012] Preferably, the flow rate of the carrier gas in step 3) is adjusted by a mass flow controller, and the flow rate of the carrier gas is 6~12L / min.

[0013] Preferably, the ion source in step 3) includes an extraction electrospray ion source or a dielectric barrier discharge ion source.

[0014] The present invention also provides an online analysis system for the online mass spectrometry analysis method for volatile organic compounds based on the gas phase quantitative loop, the online analysis system comprising a gas sampling bag, a gas phase quantitative loop, and an ion source; The gas sampling bag is connected to a gas phase metering loop via a vacuum pump. The gas-phase metering loop is connected to the ion source.

[0015] The beneficial effects of this invention are: This invention eliminates the need for adsorption enrichment and thermal desorption steps, greatly simplifying the gas sample pretreatment process and significantly shortening the mass spectrometry analysis time, with a single injection analysis time of only about 10 seconds. By combining a gas sampling bag and a gas phase quantitative loop, the analyte gas is compressed and enriched within the gas phase quantitative loop using a high-flow-rate carrier gas, improving detection sensitivity and making it suitable for the determination of VOCs at extremely low concentrations (pptv-ppbv level). By controlling the volume of the gas phase quantitative loop, quantitative analysis of VOCs can be achieved within a certain concentration range, with a linearity of over 0.99. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the online analysis system of the present invention; Figure 2 The results are the optimized values ​​of the carrier gas flow rate and volume of the gas phase metering loop. Among them, (a) is the relationship between the carrier gas flow rate and the signal-to-noise ratio, (b) is the relationship between the carrier gas flow rate and the pressure difference before and after the six-way valve of the gas phase metering loop, (c) is the relationship between the volume of the gas phase metering loop and the signal-to-noise ratio, and (d) is the relationship between the volume of the gas phase metering loop and the peak area. Figure 3 The standard curves are for four representative VOCs, where (a) is cyclohexanone, (b) is acetone, (c) is 2-pentanone, and (d) is triethylamine. Figure 4 The results are for stability testing, where (a) is the first-order mass spectrum, (b) is the second-order mass spectrum, and (c) is the EIC spectrum at m / z=81. Figure 5 The results are for the analysis of acetone gas at 1 ppmv, where (a) is the self-made acetone test gas and (b) is the acetone standard gas. Figure 6 The analysis results are for manual sample injection and automatic sample injection using a vacuum pump. Detailed Implementation

[0017] This invention provides an online mass spectrometry analysis method for volatile organic compounds based on gas-phase quantitative loops, comprising the following steps: 1) Collect human exhaled breath using a gas sampling bag; 2) Switch the gas phase quantitative loop to Load mode to deliver the gas in the gas sampling bag to the gas phase quantitative loop; 3) Switch the gas phase quantitative loop to Inject mode, introduce carrier gas to compress and enrich the gas in the gas phase quantitative loop, and then transport it to the ion source for mass spectrometry analysis.

[0018] In this invention, the volume of the gas sampling bag in step 1) is preferably 1-4L, more preferably 2-3L. This volume setting of the gas sampling bag can meet the requirements for multiple sample injection analyses of environmental VOCs and human exhalation samples.

[0019] In this invention, the volume of the gas phase metering loop in step 2) is preferably 200~500mL, and more preferably 300~400mL.

[0020] In this invention, the material of the gas-phase quantitative ring in step 2) is preferably polytetrafluoroethylene (PTFE). PTFE can prevent VOCs adsorption and improve detection accuracy.

[0021] In this invention, the gas in the gas sampling bag in step 2) is preferably delivered to the gas phase metering loop via a vacuum pump; The flow rate of the vacuum pump is preferably 1.5~3 L / min, more preferably 1.8~2.5 L / min, and even more preferably 2~2.3 L / min. The flow rate setting of the vacuum pump can ensure that the original gas in the gas phase metering loop is completely replaced in about 10 seconds.

[0022] In this invention, the carrier gas in step 3) preferably contains nitrogen or synthetic air.

[0023] In this invention, the flow rate of the carrier gas in step 3) is preferably adjusted by a mass flow controller, and the preferred flow rate is 6~12 L / min, more preferably 7~11 L / min, and even more preferably 8~10 L / min. A high-flow-rate carrier gas helps to compress and enrich the gas sample within the gas phase quantitative loop.

[0024] In this invention, the ion source in step 3) preferably includes an extractive electrospray ion source or a dielectric barrier discharge ion source.

[0025] In this invention, steps 2) and 3) are preferably performed by switching the working mode of the gas phase metering loop using a six-way valve; the six-way valve can be switched manually or automatically.

[0026] The present invention also provides an online analysis system for the online mass spectrometry analysis method for volatile organic compounds based on the gas phase quantitative loop, the online analysis system comprising a gas sampling bag, a gas phase quantitative loop, and an ion source; The gas sampling bag is connected to a gas phase metering loop via a vacuum pump. The gas-phase metering loop is connected to the ion source.

[0027] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0028] The human exhaled breath used in the embodiments and comparative examples of this invention was prepared by the individual.

[0029] The conditions for mass spectrometry analysis were as follows: ion transfer tube temperature 275℃; S-lens RF level 60%; maximum injection time 100ms; number of microscans 1; ion source voltage +3.5kV; the extract consisted of water, methanol and formic acid, with methanol having a mass fraction of 4.8% and formic acid having a mass fraction of 0.2%; and the syringe pump flow rate 10μL / min.

[0030] Example 1

[0031] A 5 μL solution of cyclohexanone with a concentration of 32.03 mg / L was placed in a 4 L gas sampling bag. Nitrogen gas with a purity of 99.999% was used as the balancing gas. The gas sampling bag was filled with a balancer to obtain a cyclohexanone test gas with a concentration of 10 ppbv.

[0032] The online analysis system includes a gas sampling bag, a gas phase metering loop, and an ion source. The gas sampling bag is connected to the gas phase metering loop via a vacuum pump, and the gas phase metering loop is connected to the extraction electrospray ion source.

[0033] The online mass spectrometry analysis method for volatile organic compounds based on a gas phase quantitative loop is as follows: The gas phase quantitative loop (300 mL, made of polytetrafluoroethylene) is switched to Load mode via a six-way valve. The analyte gas from the gas sampling bag is then transferred to the gas phase quantitative loop via a vacuum pump at a flow rate of 1.6 L / min. Next, the gas phase quantitative loop is switched to Inject mode via the six-way valve, and nitrogen gas (99.999% purity) is introduced at a flow rate of 10 L / min using a mass flow controller. This compresses and enriches the analyte gas in the gas phase quantitative loop, which is then transferred to an extraction electrospray ionization source for mass spectrometry analysis.

[0034] Example 2

[0035] The difference from Example 1 is that a mass flow controller is used to regulate the flow of nitrogen gas (purity 99.999%) at a flow rate of 6 L / min, so that the gas to be tested in the gas phase quantitative loop is compressed and enriched, and then transported to the extraction electrospray ionization source for mass spectrometry analysis.

[0036] Example 3

[0037] The difference from Example 1 is that a mass flow controller is used to regulate the flow of nitrogen gas (purity 99.999%) at a flow rate of 8 L / min, so that the gas to be tested in the gas phase quantitative loop is compressed and enriched, and then transported to the extraction electrospray ion source for mass spectrometry analysis.

[0038] Example 4

[0039] The difference from Example 1 is that a mass flow controller is used to regulate the flow of nitrogen gas (purity 99.999%) at a flow rate of 12 L / min, so that the gas to be tested in the gas phase quantitative loop is compressed and enriched, and then transported to the extraction electrospray ionization source for mass spectrometry analysis.

[0040] Example 5

[0041] The volume of the gas phase metering loop in Example 1 was modified to 200 mL, and everything else remained the same as in Example 1.

[0042] Example 6

[0043] The volume of the gas phase metering loop in Example 1 was modified to 400 mL, and everything else remained the same as in Example 1.

[0044] Example 7

[0045] The volume of the gas phase metering loop in Example 1 was modified to 500 mL, and everything else remained the same as in Example 1.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that a mass flow controller is used to regulate the flow of nitrogen gas (purity 99.999%) at a flow rate of 4 L / min, so that the gas to be tested in the gas phase quantitative loop is compressed and enriched, and then transported to the extraction electrospray ionization source for mass spectrometry analysis.

[0048] Comparative Example 2

[0049] The difference from Example 1 is that a mass flow controller is used to regulate the flow of nitrogen gas (purity 99.999%) at a flow rate of 2 L / min, so that the gas to be tested in the gas phase quantitative loop is compressed and enriched, and then transported to the extraction electrospray ionization source for mass spectrometry analysis.

[0050] Comparative Example 3

[0051] The volume of the gas phase metering loop in Example 1 was modified to 100 mL, and everything else remained the same as in Example 1.

[0052] Figure 2The optimized results for the carrier gas flow rate and volume of the gas-phase metering loop are shown, where (a) represents the relationship between carrier gas flow rate and signal-to-noise ratio (SNR), (b) represents the relationship between carrier gas flow rate and the pressure difference before and after the six-way valve of the gas-phase metering loop, (c) represents the relationship between the gas-phase metering loop volume and SNR, and (d) represents the relationship between the gas-phase metering loop volume and peak area. Figure 2 As shown in (a) and (b), when the carrier gas flow rate is 2 L / min, no cyclohexanone detection signal is observed in the mass spectrum. At this time, the carrier gas not only compresses and delivers the sample to the quantitative loop, but also acts as the nebulizer for the composite ion source. As the carrier gas flow rate increases from 2 L / min to 10 L / min, the signal-to-noise ratio (SNR) of cyclohexanone continuously increases and reaches its maximum value. Further increasing the carrier gas flow rate to 12 L / min, the SNR of cyclohexanone no longer increases. With the increase of the carrier gas flow rate, the pressure difference before and after the six-way valve of the gas phase quantitative loop shows a trend of first gradually increasing and then stabilizing, reaching its highest value at a carrier gas flow rate of 10 L / min. The consistent trend of the pressure difference and the SNR confirms that the compression and enrichment of the analyte gas in the gas phase quantitative loop is the main reason for improving the detection SNR. (c) and (d) show that as the gas phase quantitative loop volume gradually increases from 100 mL to 300 mL, the signal-to-noise ratio (SNR) of the target component cyclohexanone shows a significant upward trend, which may be related to the increase in the total amount of sample reaching the ion source. When the gas phase quantitative loop volume is further increased, the ionization of the target component reaches a dynamic equilibrium, and the SNR is in a stable region. Within the gas phase quantitative loop volume range of 50–500 mL, the chromatographic peak area increases linearly with the gas phase quantitative loop volume, and R0... 2 It reached 0.995. Figure 2 The method of the present invention has been verified to have good quantitative analysis performance.

[0053] The limits of detection (LOD) and limits of quantitation (LOQ) of four representative VOCs (cyclohexanone, acetone, 2-pentanone, and triethylamine) were tested using the standard curve method under the conditions of Example 1 to evaluate the sensitivity and accuracy of the online analytical method of the present invention. Each concentration of the analyte gas was measured three times, and the average value was taken. The LOD and LOQ of the four representative VOCs are shown in Table 1.

[0054] Table 1. Limit of Detection (LOD) and Limit of Quantification (LOQ) for four representative VOCs

[0055] As shown in Table 1, the method of the present invention has a detection limit (LOD) as low as pptv for cyclohexanone, 2-pentanone, and triethylamine, exhibiting high sensitivity. The LOD for acetone is 670 pptv. The concentration of acetone in normal human exhaled breath reaches 300-900 ppbv, while the concentration of acetone in the exhaled breath of diabetic patients is significantly higher than this range. This indicates that the detection sensitivity of the method of the present invention for acetone meets the analytical requirements of actual human exhaled breath samples.

[0056] Figure 3 Standard curves for four representative VOCs are shown: (a) cyclohexanone, (b) acetone, (c) 2-pentanone, and (d) triethylamine. Cyclohexanone, 2-pentanone, and triethylamine, with higher molecular weights, were quantified using secondary spectra, with ion pair information of 99>81, 87>69, and 102>74, respectively. Acetone was quantified using primary spectra. Figure 3 It can be seen that the four representative VOCs all achieved good linearity (R0) over a wide concentration range. 2 The linear relationships were 0.995 to 0.998 for cyclohexanone, 0.1 to 500 ppbv for acetone, 10 to 2000 ppbv for 2-pentanone and triethylamine, and 0.1 to 1000 ppbv for 2-pentanone and triethylamine.

[0057] The measurement was repeated three times under the conditions of Example 1 to evaluate the stability of the analytical method. Figure 4 The results are for stability testing, where (a) is the primary mass spectrum, (b) is the secondary mass spectrum, and (c) is the EIC spectrum at m / z=81. Figure 4 As can be seen, a very strong [M+H] group is observed in the first-order mass spectrum. + The signal, with an m / z of 99, lost one neutral water molecule after CID fragmentation, and the fragment ion had an m / z of 81. Using a signal with an m / z of 81 as a reference, the EIC chromatograms of repeated measurements showed good peak shapes overall, with a small amount of tailing at the peak ends. The RSD of the peak area of ​​the three measurements was only 2.1%, proving that the method has good repeatability and meets the requirements for quantitative analysis of gas phase metabolite molecules.

[0058] The accuracy of the self-made test gas samples was analyzed: 5 μL of acetone solution with a concentration of 1.90 g / L was placed in a 4 L gas sampling bag. Nitrogen gas with a purity of 99.999% was used as the equilibrium gas to fill the gas sampling bag, resulting in a self-made acetone test gas with a concentration of 1 ppmv. Online analysis of the 1 ppmv self-made acetone test gas and the 1 ppmv acetone standard gas (purchased from Dalian Date Gas Co., Ltd.) was performed according to the conditions of Example 1, with each sample analyzed three times.

[0059] Figure 5 The results are for the analysis of acetone gas at 1 ppmv, where (a) is the self-prepared acetone test gas, and (b) is the acetone standard gas. Figure 5 It can be seen that the average peak area of ​​the three repeated measurements of the self-made acetone test gas at 1 ppmv was 6.05 × 10⁻⁶. 7 The average peak area of ​​1 ppmv acetone standard gas is 5.99 × 10⁻⁶. 7 The error between the two is no more than 1.0%. This proves that the self-made method of the test gas used in the embodiments and comparative examples of the present invention is reliable.

[0060] Using manual injection (with the same injection volume as the gas phase quantitative loop) as a baseline, the accuracy of automatic injection using a vacuum pump was analyzed under the conditions of Example 1, and the process was repeated twice. Figure 6 The analysis results are for manual sample injection and automatic sample injection using a vacuum pump. (From...) Figure 6 It can be seen that the peak areas of the target component (acetone) in the two automatic injections by the vacuum pump were 8.89 × 10⁻⁶ and 8.89 × 10⁻⁶, respectively. 7 8.83×10 7 The peak areas of the two manual injections were 8.86 × 10⁻⁶. 7 8.90×10 7 The peak areas are very close. This proves that the present invention can completely replace the original gas in the gas phase quantitative loop in a short time through automatic sample injection using a vacuum pump, thereby ensuring the reliability of the detection results.

[0061] As can be seen from the above embodiments, the present invention provides an online mass spectrometry analysis method and system for volatile organic compounds based on a gas phase quantitative loop. By combining a gas sampling bag and a gas phase quantitative loop, and controlling the volume and carrier gas flow rate of the gas phase quantitative loop, the gas to be measured is compressed and enriched within the gas phase quantitative loop, thereby improving detection sensitivity and achieving the determination of VOCs at extremely low concentrations (pptv-ppbv level) with a linearity of over 0.99. At the same time, it simplifies the gas sample pretreatment process and significantly shortens the mass spectrometry analysis time.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An online mass spectrometry analysis method for volatile organic compounds based on gas-phase quantitative loop, characterized in that, It includes the following steps: 1) Collect human exhaled breath using a gas sampling bag; 2) Switch the gas phase quantitative loop to Load mode to deliver the gas in the gas sampling bag to the gas phase quantitative loop; 3) Switch the gas phase quantitative loop to Inject mode, introduce carrier gas to compress and enrich the gas in the gas phase quantitative loop, and then transport it to the ion source for mass spectrometry analysis.

2. The online mass spectrometry analysis method according to claim 1, characterized in that, Step 1) The volume of the gas sampling bag is 1~4L.

3. The online mass spectrometry analysis method according to claim 1 or 2, characterized in that, Step 2) The volume of the gas phase metering loop is 200~500mL.

4. The online mass spectrometry analysis method according to claim 3, characterized in that, In step 2), the gas in the gas sampling bag is delivered to the gas phase metering loop via a vacuum pump; The flow rate of the air pump is 1.5~3L / min.

5. The online mass spectrometry analysis method according to claim 4, characterized in that, Step 3) The carrier gas contains nitrogen or synthetic air.

6. The online mass spectrometry analysis method according to claim 4 or 5, characterized in that, Step 3) The flow rate of the carrier gas is adjusted by a mass flow controller, and the flow rate of the carrier gas is 6~12L / min.

7. The online mass spectrometry analysis method according to claim 6, characterized in that, Step 3) The ion source includes an extraction electrospray ion source or a dielectric barrier discharge ion source.

8. An online analysis system for the online mass spectrometry analysis method for volatile organic compounds based on gas-phase quantitative loops as described in any one of claims 1 to 7, characterized in that, The online analysis system includes a gas sampling bag, a gas phase quantitative loop, and an ion source; The gas sampling bag is connected to a gas phase metering loop via a vacuum pump. The gas-phase metering loop is connected to the ion source.

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