Method for calibrating perfluorinated / polyfluorinated compound liquid chromatogram retention time database

Abstract

The invention belongs to the technical field of analytical chemistry, and particularly relates to a method for calibrating a perfluorinated / polyfluorinated compound liquid chromatogram retention time database, which comprises the following steps: establishing an initial RT database and PFCA-RI; establishing a PFSAs retention index (RI) database; and based on the RI of the PFSAs and the RT of the PFCAs under the new method, calibrating the RT of other PFSAs, and establishing an RT database of the PFSAs under the new method. On the basis of PFCA-RI calibration, RT deviation caused by change of chromatographic conditions is improved, and the compatibility and accuracy of a database when PFASs are identified by different chromatographic methods, liquid chromatograms or laboratories are improved. The method is suitable for database-based quasi-targeted PFSAs analysis in the field of analytical chemistry, and aims to establish a PFSAs database based on PFCA-RI calibration and realize rapid qualitative analysis of PFSAs under the condition of no standard reference substance.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry, and in particular relates to a method for calibrating a perfluorinated / polyfluorinated compound liquid chromatography retention time database. Background Art

[0002] The number of known perfluorinated / polyfluorinated compounds (PFASs) in the environment is huge. The U.S. Environmental Protection Agency has compiled a list of more than 14,700 perfluorinated / polyfluorinated compounds of global concern. With the global ban on traditional PFCAs and perfluorosulfonic acids (PFSAs), new perfluorinated alternatives are comprehensively replacing traditional perfluorinated / polyfluorinated compounds and gradually becoming the main pollutants in the environment.

[0003] In the field of analytical chemistry, there are two main methods for discovering perfluorinated / polyfluorinated compounds: quasi-targeted and non-targeted screening. The non-targeted screening method mainly relies on the Kendrick Mass Defect (KMD), homologous series (HS) and characteristic secondary fragments (CFIs) of PFASs to discover features and characterize their structures. The advantage is that unknown PFASs can be discovered, but it is easy to miss some mass features (MFs) that lack homologous series or secondary mass spectrometry fragment information, especially those MFs with low mass spectrometry response.

[0004] As a supplement to non-targeted methods, quasi-targeted methods can be used to make up for these shortcomings, mainly relying on the precise mass-to-charge ratio (m / z), isotopic profiles (IPs) and CFIs of the compounds to confirm the compounds. However, many PFASs have in-source collision-induced dissociation (CID) phenomenon, which can easily lead to false positives in the qualitative results of the compounds. Since this phenomenon occurs at the front end of the mass spectrometer, it is difficult to solve even with the use of ion mobility (IM) technology, and can only be confirmed by chromatographic RT (Retention Time, RT).

[0005] Due to the differences in equipment and methods between different laboratories (such as chromatographic columns, mobile phases, tubing lengths and gradients, etc.), it is difficult to reproduce the RT database established using standards on one device and method for different methods and equipment. Therefore, the transplantation of methods between laboratories, especially the effective application of RT between different laboratories, helps reduce false positive annotations, which is currently a difficulty and focus in the field of analytical chemistry. Summary of the invention

[0006] The present invention aims to solve the problem of database information not being universal due to the variability of liquid chromatography time, and provides a method for calibrating a perfluorinated / polyfluorinated compound liquid chromatography retention time database to overcome the above-mentioned shortcomings.

[0007] To achieve the above-mentioned purpose, the present invention is implemented by the following technical solutions: In a first aspect, the present invention provides a method for calibrating a perfluorinated / polyfluorinated compound liquid chromatography retention time database, comprising the following steps: (S.1) Under the same chromatographic conditions, all perfluorinated / polyfluorinated compounds to be tested are subjected to gradient elution using liquid chromatography-quadrupole high-resolution mass spectrometry to obtain the retention times of all perfluorinated / polyfluorinated compounds, thereby establishing an initial perfluorinated / polyfluorinated compound retention time database; (S.2) selecting straight-chain perfluorocarboxylic acids as reference substances from the initial perfluoro / polyfluoro compound retention time database according to the order of elution peaks, calculating the retention indexes of the reference substances and the remaining compounds, and establishing a perfluoro / polyfluoro compound retention index database; (S.3) Changing the chromatographic conditions, testing the retention time of the reference substance, and updating the retention times of all perfluorinated / polyfluorinated compounds according to the perfluorinated / polyfluorinated compound retention index database and the retention time of the newly obtained reference substance, thereby obtaining a calibrated perfluorinated / polyfluorinated compound retention time database.

[0008] Retention index (RI) is widely used in gas chromatography-mass spectrometry equipment. The inventors of the present application have found that on the same chromatographic column, the RI database constructed using a certain reference compound and its homologues can maintain good reproducibility even under different chromatographic conditions (such as programmed temperature or flow rate). The calculation formula is as shown below: Where t is the object to be tested, RT t , RT m and RT n are the RT and RI of the corresponding reference compound and its homologues (with carbon numbers m and n) before and after the analyte and the analyte respectively. t is the RI value of the object to be tested t.

[0009] The present application transfers the concept of RI value from gas chromatography to liquid chromatography, but due to the diversity of compound types and their properties, the retention of compounds on the chromatographic column comes from multiple factors, so it is still necessary to use homologues with similar physicochemical properties to the target compound to obtain better calibration effect and reproducibility. Therefore, after testing perfluorinated / polyfluorinated compounds, the present application found that after using linear perfluorinated carboxylic acids (PFCAs) as reference substances, the retention index and retention time of perfluorinated / polyfluorinated compounds have good calibration effect and reproducibility.

[0010] The reason is that PFCAs are a series of homologues containing perfluorinated fatty chain structures of different chain lengths (C2-C21) with carboxylic acid groups at the ends. When reverse phase chromatography is used for analysis, due to the hydrophobic straight chain alkane fillers (such as C18 and C8, etc.) used as stationary phases, PFCAs will be adsorbed and retained by the stationary phase on the filler through hydrophobic forces and van der Waals forces, and their retention capacity will gradually increase with the growth of the perfluorinated alkane chain. PFCAs have the following advantages as RT reference substances: (1) PFCAs are stable and not easily degraded, and can be stably analyzed in LC-MS systems; (2) PFCAs basically cover the chromatographic RT of existing perfluorinated / polyfluorinated compound standards and are evenly distributed in each RT segment; (3) PFCAs homologues will not have the problem of peak order interchange in the reverse phase chromatography system due to differences in methods.

[0011] Therefore, in the process of calibrating the retention time database of perfluorinated / polyfluorinated compounds under different chromatographic conditions, the present application selects to use straight-chain perfluorocarboxylic acids (PFCAs) as reference substances, which can greatly improve the problem of unavailability of the RT database caused by RT deviation caused by changes in chromatographic conditions, making it possible to migrate the database between different methods, and also eliminating the impact of RT on the instability of the chromatographic system, thereby greatly improving the matching degree of the compound database during identification.

[0012] Preferably, the perfluoro / polyfluoro compounds in step (S.1) include linear perfluorocarboxylic acid compounds and perfluorosulfonic acid compounds.

[0013] Preferably, the linear perfluorocarboxylic acid compounds include linear perfluorocarboxylic acid isotope standards contained in, externally added to, or stabilized in environmental, food, and biological samples.

[0014] Preferably, the linear perfluorocarboxylic acid compounds include linear perfluorocarboxylic acid isotope standards contained in, externally added to, or stabilized in environmental, food, and biological samples.

[0015] Preferably, the straight-chain perfluorocarboxylic acid compound contains a carbon chain with a length of C2 to C21.

[0016] Preferably, the retention index in step (S.2) is calculated as follows: the retention index of the reference product is artificially defined as the number of carbon atoms × 100 (such as the RI of perfluorooctanoic acid PFOA is 800) based on the order of peak elution, and the retention index of the remaining compounds is calculated according to formula (1): Among them, RT t , RT m , RT n Respectively represent the retention time of a target substance t and the two linear perfluorocarboxylic acid reference substances m and n adjacent to each other in elution order, RT m <RT t <RT n RI t , RI m , RI n They represent the retention indices of the target substance t and the two adjacent linear perfluorocarboxylic acid reference substances m and n in the elution order.

[0017] Preferably, the number of the linear perfluorocarboxylic acid used as the reference substance is 10-15.

[0018] Preferably, the number of the straight-chain perfluorocarboxylic acids used as the reference substances is 14. The 14 PFCAs reference substances selected in this application and their corresponding RIs are shown in Table 1 below.

[0019] Table 1. 14 PFCAs benchmarks and their corresponding RI Serial number Compound Name CAS Abbreviation Chemical formula <![CDATA[[M-H] - ]]> RI 1 Trifluoroacetic acid 76-05-1 TFA <![CDATA[C 2 HF 3 O 2 ]]> 112.9856 200 2 Perfluoro-n-butyric acid 375-22-4 PFBA <![CDATA[C 4 HF 7 O 2 ]]> 212.9792 400 3 Perfluoropentanoic acid 2706-90-3 PFA <![CDATA[C 5 HF 9 O 2 ]]> 262.9760 500 4 Perfluorohexanoic acid 307-24-4 PFh <![CDATA[C 6 HF 11 O 2 ]]> 312.9728 600 5 Perfluoro-n-heptanoic acid 375-85-9 PFHpA <![CDATA[C 7 HF 13 O 2 ]]> 362.9696 700 6 Perfluorooctanoic acid 335-67-1 PFOA <![CDATA[C 8 HF 15 O 2 ]]> 412.9664 800 7 Perfluorononanoic acid 375-95-1 PFNA <![CDATA[C 9 HF 17 O 2 ]]> 462.9632 900 8 Perfluorodecanoic acid 335-76-2 PFDA <![CDATA[C 10 HF 19 O 2 ]]> 512.9600 1000 9 Perfluoroundecanoic acid 2058-94-8 PfA <![CDATA[C 11 HF 21 O 2 ]]> 562.9568 1100 10 Perfluoro-n-dodecanoic acid 307-55-1 PFDoA <![CDATA[C 12 HF 23 O 2 ]]> 612.9537 1200 11 Perfluorotridecanoic acid 72629-94-8 PFTrDA <![CDATA[C 13 HF 25 O 2 ]]> 662.9505 1300 12 Perfluorotetradecanoic acid 376-06-7 PFTeDA <![CDATA[C 14 HF 27 O 2 ]]> 712.9473 1400 13 Perfluorohexadecanoic acid 67905-19-5 PxD <![CDATA[C 16 HF 31 O 2 ]]> 812.9409 1600 14 Perfluorooctadecanoic acid 16517-11-6 PFODA <![CDATA[C 18 HF 35 O 2 ]]> 912.9345 1800 .

[0020] Preferably, when the chromatographic conditions are changed in step (S.3), the retention time of the linear perfluorocarboxylic acid standard is first measured; The calibrated retention times of all per / polyfluorinated compounds in the initial database were then calculated according to Equation 2: Among them, RT t , RT m , RT n Represents the retention time of a target substance t and its two adjacent linear perfluorocarboxylic acid reference substances m and n in the elution order, RT m <RT t <RT n RI t , RI m , RI nrespectively represent the retention indices of the corresponding target analyte t and the two adjacent linear perfluorocarboxylic acid reference standards m and n before and after its elution order.

[0021] Preferably, the retention time determination of the linear perfluorocarboxylic acid reference standard needs to accurately identify the linear perfluorocarboxylic acid reference standard based on the exact molecular weight, isotope profile, and any one or more characteristic secondary ion fragments after the addition of each linear perfluorocarboxylic acid reference standard, and then determine the retention time of the linear perfluorocarboxylic acid reference standard.

[0022] Preferably, the upper and lower limits of the retention index coverage range in step (2) are determined by the compounds with the maximum and minimum retention times of the linear perfluorocarboxylic acid reference standards respectively, and the coverage range of the retention index can be expanded by obtaining linear perfluorocarboxylic acid reference standards with longer or shorter carbon chains.

[0023] Theoretically, PFCAs need to cover the entire RT range to meet the calculation of RI and the calibration of RT for all compounds in the database. Otherwise, compounds outside the RT coverage range of the PFCAs reference cannot calculate RI. The lower limit of the RI coverage should be determined by the shortest carbon chain PFCA, and the upper limit is determined by the longest carbon chain PFCA. However, currently, neither trifluoroacetic acid (TFA) with the shortest carbon chain nor perfluorooctadecanoic acid (PFODA) with the longest carbon chain can cover a small number of compounds in terms of their RT.

[0024] Therefore, preferably, this method uses the standards of the two PFCAs with the most forward and most backward RTs to establish a linear fitting curve, and predicts the RI and RT outside the RT coverage range by extending the curve, where RT t , RT m and RT n respectively represent the RTs of the analyte and m and n in the two PFCA references with the maximum / minimum RT, and RT m <RT n , RI m and RI n represent their RI, a and b respectively represent the slope and intercept of the equation in formula 3 (formula 4). This method uses the RT and RI of the two PFCAs with the most backward / forward RTs to draw a fitting curve to推算 the RI values of compounds outside the range. After the method is changed, the RT of new compounds can also be calculated by formula 5, where RT’t, RT’m, and RT’n respectively represent the RTs of the analyte and the two PFCA references m and n in the new method, and RT’m < RT’n, RI’m and RI’n represent their RI, c and d respectively represent the slope and intercept of the equation in formula 5 (formula 6).

[0025] RI t = RT t×a+b (3) Among them, RT t , RT m and RT n Represents the retention time of m and n of the analyte and the two linear perfluorocarboxylic acid standards with the largest / smallest retention time, respectively, and RT m <RT n RI m and RI n represents its retention index, a and b represent the slope and intercept of the equation in Formula 3, respectively, and the calculation method is shown in Formula 4; RT' t RT' m and RT' n represents the retention time of the analyte and two two-chain perfluorocarboxylic acid standards m and n in the new method, and RT' m <RT’ n , R.I.' m and RI' n represents its retention index, c and d represent the slope and intercept of the equation in Formula 5, respectively, and the calculation method is shown in Formula 6.

[0026] Therefore, the present invention has the following beneficial effects: The method of the present invention greatly improves the problem of unavailability of RT database caused by RT deviation caused by changes in chromatographic conditions, makes it possible to migrate databases between different methods, eliminates the influence of chromatographic system instability on RT, and greatly improves the matching degree of compound database during identification. At the same time, this method is not only applicable to RT databases established based on standards, but also can be used for RT databases predicted by machine learning models to perform broad-spectrum, high-throughput and rapid qualitative analysis of PFSAs in complex samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The distribution of RT corresponding to RI of 14 PFCAs based on PFCA-RI.

[0028] Figure 2 Schematic diagram of the RT deviation of perfluorinated / polyfluorinated compounds relative to the initial method before calibration with different methods.

[0029] Figure 3 Schematic diagram of the RT deviation of perfluorinated / polyfluorinated compounds after calibration with different methods relative to the initial method. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0031] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0032] Example 1 Experimental instruments and materials 1. Instrument An Ultimate 3000 chromatography system and a Q Exactive mass spectrometry system (Thermo Scientific) were used.

[0033] 2. Standards and Reagents Formic acid, methanol, and acetonitrile were all of mass spectrometry grade (Thermo Scientific). Ultrapure water used for sample treatment and chromatographic mobile phase was from the Milli-Q ultrapure water system (Millipore Corporation). Chromatographically grade standards (purity > 95%) were purchased from Wellington Laboratories. Chromatographically grade ammonium formate was purchased from Merck.

[0034] Example 1: RT database calibration based on mixed standards of perfluorinated / polyfluorinated compounds 2.1 Preparation of standard substances In this example, 66 perfluorinated / polyfluorinated compounds (including 14 PFCAs) that can be detected in the negative mode of ESI are selected as research objects. The polarity range of the selected compounds is large, and each RT of the reverse phase chromatography can be completely covered. A mixed standard of each compound concentration at the ppb level is prepared using a 50% methanol aqueous solution and stored in a -20°C refrigerator for later use. The information of the 66 perfluorinated / polyfluorinated compounds is shown in Table 2 below.

[0035] Table 2 Information on 66 perfluorinated / polyfluorinated compounds contained in the mixed standard

[0036] 2. Chromatographic and mass spectrometry conditions 2.1 Chromatographic conditions In this embodiment, the initial chromatographic condition is the M1 method (Table 3), and 8 other different chromatographic methods (M2 to M9) are combined according to different gradients, flow rates, column temperatures and chromatographic columns to verify the RT calibration effect of the present invention.

[0037] Table 3. Conditions of different chromatographic methods (A) Gradient, flow rate and column temperature

[0038] 2.2 Mass spectrometry conditions The mass spectrometry acquisition mode was data-dependent scanning mode (FS-ddMS 2 ), 1 full scan with 5 secondary scans, the ion source and scanning parameters are shown in Table 4.

[0039] Table 4. Mass spectrometry source and scan parameters

[0040] 2.3 Data processing Firstly, a database was established based on the chemical formula and characteristic secondary mass spectrometry fragments of 66 standard substances. The precise molecular mass and characteristic secondary fragment data of the adduct form ([MH]-) of PFASs compounds after ionization on the ESI source were compared with the self-built database. The original data of standard samples based on methods M1 to M9 were imported into the TraceFinder software to extract the chromatographic peaks that met the requirements one by one, and the RT of each standard substance in different methods was determined.

[0041] 2.4 Database matching accuracy The measured data under the M1 method was used as the initial RT database, and the RI of all PFSAs in the database was calculated using the PFCAs benchmark and the extended method. The distribution of the RT corresponding to the RI of the 14 PFCAs is shown in the following figure: Figure 1 shown.

[0042] Then, based on the RT of the PFCAs measured in each method M2-M9, the calibration RT database under each method is established according to the RI of the PFSAs. In order to verify the matching accuracy of the initial and calibration databases with the measured RT data of each method M2-M9, this embodiment establishes linear regression curves between the measured RT data (y) under different methods and the calibration / initial database data RT (x). In addition, the parameter ΔRT is defined i The RT deviation of each perfluorinated / polyfluorinated compound before and after database calibration was investigated as the RT deviation value. The following summarizes the linear regression equation parameters (intercept, slope and R 2 ) and ΔRT i Statistical data (see Table 5 and Table 6). Compared with the original database, it was found that the equation slope and R 2 are closer to 1, the intercept value and ΔRT iThe values ​​are closer to 0, proving that the matching degree between the calibrated database and the measured values ​​has been significantly improved.

[0043] ΔRT i The calculation formula of the value is shown in Formula 7: ΔRT i =RT experimental -RT (Original / Adjusted) (5).

[0044] Table 5. Linear regression equations and parameters of measured RT and database RT of perfluorinated / polyfluorinated compounds method Measured vs Calibrated Actual vs Initial M2 <![CDATA[y=0.9994x+0.0102R 2 =0.9999]]> <![CDATA[y=1.0239x-0.4643R 2 =0.9981]]> M3 <![CDATA[y=0.9947x+0.0537R 2 =0.9997]]> <![CDATA[y=1.0494x-0.9674R 2 =0.9916]]> M4 <![CDATA[y=0.998x+0.0179R 2 =0.9999]]> <![CDATA[y=0.997x+0.3344R 2 =0.9994]]> M5 <![CDATA[y=0.9947x+0.0493R 2 =0.9997]]> <![CDATA[y=0.9992x+0.7088R 2 =0.9974]]> M6 <![CDATA[y=1.0023x-0.0155R 2 =0.9999]]> <![CDATA[y=1.0006x+0.0923R 2 =0.9998]]> M7 <![CDATA[y=1.004x-0.0281R 2 =0.9997]]> <![CDATA[y=1.0007x+0.1937R 2 =0.9993]]> M8 <![CDATA[y=0.9976x+0.0706R 2 =0.9958]]> <![CDATA[y=0.9649x+1.9156R 2 =0.9668]]> M9 <![CDATA[y=1.0039x+0.0109R 2 =0.9957]]> <![CDATA[y=0.9815x+1.3211R 2 =0.9807]]> .

[0045] Table 6. ΔRT of perfluorinated / polyfluorinated compounds in the initial and calibration databases i Statistics summary

[0046] From the data in the table, we can see that compared with M1, method M2-M3 only changes in the liquid phase gradient, changing the composition of the initial aqueous phase and organic phase, from 95% initial aqueous phase in M1 to 90% (M2) and 85% (M3). The increase in the initial organic phase makes the RT of the compound move forward as a whole, with the maximum RT drift of 1.27min. Through linear regression and deviation statistics (Table 5), the correlation (R 2 ) is normal, but the intercept and mean deviation (ΔRT i ) are relatively large, such as M3's y=1.0494x-0.9674, R 2 =0.9916, ΔRT i =-0.55±0.25, the correlation of the fitting is general but the intercept is large, indicating that there is a certain gap between the RT of the two methods. After calibration, the equation becomes y=0.9947x+0.0537, R 2 =0.9997, ΔRT i =-0.01±0.05, which shows great improvement in terms of linearity, intercept and deviation.

[0047] Compared with M1, method M4-M5 only changed in liquid phase flow rate, from 0.4mL / min of M1 to 0.35mL / min (M4) and 0.3mL / min (M5). The reduction in flow rate led to the overall RT shift of perfluorinated / polyfluorinated compounds, with the largest RT drift at 0.93min. Although the linearity of M4 and M5 was good, the intercepts (0.3344 and 0.7088, respectively) were large. After calibration, the intercepts of the equation (0.0179 and 0.0493, respectively) were significantly reduced, and the ΔRT i The deviation has also been significantly improved.

[0048] Compared with M1, method M6-M7 only changed the liquid column temperature, from 40℃ in M1 to 35℃ (M6) and 30℃ (M7). The change in column temperature caused the RT of perfluorinated / polyfluorinated compounds to drift slightly backward, with the maximum RT drift at 0.39min. Except that the intercept of methods M6 and M7 was slightly larger, the other parameters were acceptable, but the intercept was greatly improved after calibration.

[0049] Methods Compared with M1, M8-M9 only changed in the HPLC column, from the Accucore aQ C18 (2.1x150 mm: 2.6μm) column of M1 to the ACQUITY UPLC BEH C18 (2.1x150 mm: 1.7μm) column of M8 and the InfinityLab Poroshell 120EC-C18 (2.1x150 mm: 2.7μm) column of M9. Although the length and inner diameter of the column were the same, the different processes (core-shell and non-core-shell) and particle sizes (2.6 and 1.7μm) of the column caused the retention of perfluorinated / polyfluorinated compounds on the column to shift significantly. Compared with non-core-shell columns, the biggest advantage of core-shell columns is that they have better column efficiency at the same particle size, which can even be consistent with the column efficiency of non-core-shell columns with 1.7μm particles. Therefore, in order to reduce the maximum pressure of the chromatographic system, the particle size of the core-shell column is generally around 2.6μm. The results show that the maximum drift of the compound RT under the M8 and M9 methods is 2.66min, and the correlation, intercept and average deviation of the equation are poor. However, after calibration, except for the absolute deviation of individual substances in M8 and M9 greater than 0.5min (probably due to the difference in the chromatographic column stationary phase process), the rest are good in terms of correlation, intercept and ΔRT. i All have been significantly improved.

[0050] In summary, the RT of the compounds in methods M2-M9 has a non-negligible deviation compared with the initial method M1 under the changes of parameters such as gradient, flow rate, column temperature and chromatographic column ( Figure 2 ), these deviations were significantly improved after calibration of 14 PFCAs markers ( Figure 3 ), indicating that the database calibrated with PFCA-RI can maintain good reproducibility under different chromatographic conditions.

[0051] Example 2: RT calibration based on environmental samples 1. Pretreatment of leachate samples After the landfill leachate sample was taken out of the -20℃ refrigerator and thawed to room temperature, 500μL of the sample was accurately transferred to a 3mL EP tube using a pipette, and 500μL of methanol was added and vortexed to mix. After standing for 3 minutes, the supernatant was filtered through a 0.22μm nylon filter membrane and placed in a 2mL chromatographic injection bottle for injection; the mixed standard solution of 14 PFCAs was determined at the same time.

[0052] 2. Chromatographic and mass spectrometry conditions The chromatographic and mass spectrometric conditions selected in this example are the M1 method described in Example 1, except that a different batch but the same specification of Accucore aQ C18 chromatographic column is selected as the method M10 of this experiment.

[0053] 3. Data processing The PFCAs standard based on the M10 method was extracted using TraceFinder to obtain RTs, and the corresponding new RTs in M10 were calculated in combination with the RI values ​​of the 66 perfluorinated substances database in M0 to generate a new database under the M10 method. The landfill leachate sample data based on the M10 method was then imported into TraceFinder for peak extraction, and the extracted characteristic ions were compared with the new database. The characteristic ions whose matching results met the requirements (the response of the parent ion was >1e5 and Δm / z<5ppm, the isotope matching degree was >70% and the allowed intensity deviation was <30%, the deviation of the compound RT from the M10 database was <1.0min, the characteristic secondary fragments of the parent ion were >2 and Δm / z<10ppm) were retained, and the suspicious features with isomerism were also excluded, and the RT of each compound characteristic peak was finally determined.

[0054] 4. Comparison of database matching accuracy From the M10 method, a total of 11 characteristic ions were matched to the leachate sample as the research object, and all RTs were recorded. Compared with the M0 database method, the RTs of these substances were all shifted forward. Without calibration, the maximum deviation of the compound RT relative to the M0 database was -0.93min (PFBS), while after calibration, the deviation was only -0.21min. After the M10 database was calibrated, the largest RT deviation among the 11 compounds was -0.33min (5:3FTCA), which was significantly improved compared to the deviation of the M0 database (-0.82min) (Table 7).

[0055] Table 7. Perfluorinated / polyfluorinated compounds detected in landfill leachate and their RT information

[0056] The specific embodiments described herein are merely examples of the spirit of the present invention. A person skilled in the art of the present invention may make various modifications or additions to the specific embodiments described or replace them in a similar manner, but this will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for calibrating a perfluorinated / polyfluorinated compound liquid chromatography retention time database, characterized in that: The following steps are involved: (S.1) Under the same chromatographic conditions, all perfluorinated / polyfluorinated compounds to be tested are subjected to gradient elution using liquid chromatography-quadrupole high-resolution mass spectrometry to obtain the retention times of all perfluorinated / polyfluorinated compounds, thereby establishing an initial perfluorinated / polyfluorinated compound retention time database; (S.2) selecting straight-chain perfluorocarboxylic acids as reference substances from the initial perfluoro / polyfluoro compound retention time database according to the order of elution peaks, calculating the retention indices of the reference substances and the remaining compounds, and establishing a perfluoro / polyfluoro compound retention index database; (S.3) Changing the chromatographic conditions, testing the retention time of the reference substance, and updating the retention times of all perfluorinated / polyfluorinated compounds according to the perfluorinated / polyfluorinated compound retention index database and the retention time of the newly obtained reference substance, thereby obtaining a calibrated perfluorinated / polyfluorinated compound retention time database.

2. The method according to claim 1, characterized in that: The perfluoro / polyfluoro compounds in the step (S.1) include straight-chain perfluorocarboxylic acid compounds and perfluorosulfonic acid compounds.

3. The method according to claim 1 or 2, characterized in that: The linear perfluorocarboxylic acid compounds include linear perfluorocarboxylic acid isotope standards contained in, externally added to or stabilized in environmental, food and biological samples.

4. The method according to claim 1 or 2, characterized in that: The straight-chain perfluorocarboxylic acid compound contains a carbon chain with a length of C2 to C21.

5. The method according to claim 1, characterized in that: The calculation method of the retention index in the step (S.2) is as follows: The retention index of the reference product is artificially defined as the number of carbon atoms × 100 based on the order of peak elution, and the retention index of the remaining compounds is calculated according to formula (1): Wherein, RTt, RTm, and RTn represent the retention times of a target substance t and two adjacent linear perfluorocarboxylic acid reference substances m and n in the elution order, respectively, RTm < RTt < RTn; RIt, RIm, and RIn represent the retention indices of the corresponding target substance t and two adjacent linear perfluorocarboxylic acid reference substances m and n in the elution order, respectively.

6. The method according to claim 5, characterized in that The number of the linear perfluorocarboxylic acid used as the reference product is 10-15.

7. The method according to claim 5 or 6, characterized in that: The upper and lower limits of the retention index coverage in step (2) are determined by the compounds with the largest and smallest retention times of the linear perfluorocarboxylic acid reference material, respectively. The retention index coverage can be expanded by obtaining linear perfluorocarboxylic acid reference materials with longer or shorter carbon chains.

8. The method according to claim 7, characterized in that: When the upper / lower limit range cannot be covered by the linear perfluorocarboxylic acid standard, the retention time and retention index of the two linear perfluorocarboxylic acid standards with the latest / earliest retention times are used to draw a fitting curve, and the retention index values ​​of the compounds outside the range are estimated using Formula 3; After the chromatographic conditions are changed, the retention time of the new compound can be calculated based on the retention index value and formula 5: RIt=RTt×α+b(3); Wherein, RTt, RTm and RTn represent the retention times of m and n of the analyte and the two linear perfluorocarboxylic acid standards with the largest / smallest retention times, respectively, and RTm < RTn; RIm and RIn represent their retention indices, a and b represent the slope and intercept of the equation in Formula 3, respectively, and the calculation method thereof is shown in Formula 4; RT't, RT'm and RT'n represent the retention times of the analyte and the two linear perfluorocarboxylic acid standards m and n, respectively, on the new method, and RT'm < RT'n, RI'm and RI'n represent their retention indices, c and d represent the slope and intercept of the equation in Formula 5, respectively, and the calculation method thereof is shown in Formula 6.

9. The method according to claim 1, characterized in that: When the chromatographic conditions are changed in step (S.3), the retention time of the linear perfluorocarboxylic acid standard is first measured; then the calibration retention time of all perfluoro / polyfluoro compounds in the initial database is calculated according to Formula 2: Wherein, RTt, RTm, and RTn represent the retention times of a target substance t and two linear perfluorocarboxylic acid reference substances m and n adjacent to each other in the elution order, respectively, RTm < RTt < RTn; RIt, RIm, and RIn represent the retention indices of the target substance t and two linear perfluorocarboxylic acid reference substances m and n adjacent to each other in the elution order, respectively.

10. The method according to claim 9, characterized in that The retention time determination of the linear perfluorocarboxylic acid standard requires accurate identification of the linear perfluorocarboxylic acid standard based on the precise molecular weight, isotope profile and any one or more characteristic secondary ion fragments of each linear perfluorocarboxylic acid standard after addition, and further determination of the retention time of the linear perfluorocarboxylic acid standard.

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