Method for quantitatively determining 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol in electronic cigarette liquid

Abstract

The invention relates to a method for quantitatively determining 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol in electronic cigarette liquid, which belongs to the technical field of component detection of electronic cigarette liquid, and is characterized in that a sample pretreatment effect is improved by adopting a method of firstly carrying out purification pretreatment on an electronic cigarette liquid sample by using a saturated saline solution and n-hexane and then carrying out extraction; a sample is further purified through vortex, centrifugation, drying and membrane passing, and 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol in the electronic cigarette liquid is detected by combining a gas chromatography-mass spectrometer technology. The method has the advantages of simplicity in operation, environmental friendliness, high sensitivity and capability of extracting a target object from a complex electronic cigarette liquid matrix and accurately quantifying, and can meet the requirement on accurate detection of 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanediol in the electronic cigarette liquid.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic cigarette liquid composition detection, and particularly relates to a pretreatment method of purification and extraction, and a gas chromatography-mass spectrometry (GC-MS) analysis method for determining 2,2,4,4-tetramethyl-1,3-cyclobutanediol in electronic cigarette liquid. BACKGROUND

[0002] The polymer of dimethyl terephthalate, 1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (referred to as: PCTG resin, and the trade name is Tritan) is the most commonly used plastic material in electronic cigarettes, and is in contact with electronic cigarette liquid for a long time, generally between 18 months and 24 months. Since 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) is a monomer required for the synthesis of Tritan, there is a safety risk of TMCD migrating into electronic cigarette liquid.

[0003] TMCD (CAS number: 3010-96-6), molecular formula C8H 16 O2, molecular weight 144.21, boiling point about 115-220℃. Due to the presence of a four-membered ring and two hydroxyl groups in the molecule, there are cis and trans isomers, and the structure is shown in the following formula.

[0004] Cis structure Trans structure The database of the European Chemicals Agency (ECHA) shows that the oral daily maximum intake of TMCD is 0.63 mg / kgbw / day. At present, both China and the European Union have regulations and standards to control TMCD, and give clear migration limit requirements, i.e. not higher than 5 mg / kg.

[0005] At present, the test method for TMCD is only concentrated in the field of food contact materials, and the detection method in water, ethanol, acetic acid, olive oil and other food simulants is specified. Because electronic cigarette liquid is a mixture composed of propylene glycol, glycerol, and various natural extracts and flavor ingredients, it is more complex than food simulant substrate, and the published method cannot meet the detection of electronic cigarette liquid.

[0006] Therefore, it is urgent to establish an analysis method for TMCD in electronic cigarette liquid. SUMMARY The purpose of the present application is to find a pretreatment method that is simple to operate, environmentally friendly, and can extract the target substance from the complex electronic cigarette liquid substrate, and to find the optimal chromatographic conditions by combining gas chromatography-mass spectrometry technology, so as to realize the detection of TMCD in electronic cigarette liquid. The method is accurate, sensitive and easy to operate.

[0007] The purpose of the present application is achieved by the following technical solutions: A method for detecting TMCD in electronic cigarette liquid, first, a purification pretreatment solution is added to the electronic cigarette liquid to be detected for pretreatment, then an organic solvent is used for extraction, and then a drying agent is used for drying, and the detection of TMCD in the electronic cigarette liquid is realized by combining gas chromatography mass spectrometry technology, and the specific steps are as follows: (1) Sample purification pretreatment: add saturated brine and n-hexane to the sample, vortex, centrifuge, discard the supernatant, and leave the lower liquid; The specific process is: weigh 2 g of electronic cigarette liquid sample in a 15 mL centrifuge tube, add 5 mL of saturated brine and 5 mL of n-hexane, vortex for 5 min, centrifuge at 5000 r / min for 5 min, and discard the supernatant.

[0008] (2) Sample extraction: add ethyl acetate to the lower liquid after centrifugation in step (1), continue to vortex and centrifuge, take the supernatant, dry with anhydrous sodium sulfate, and filter for detection.

[0009] The specific process is: add 5 mL of ethyl acetate to the centrifuge tube, vortex for 5 min, centrifuge at 5000 r / min for 5 min, take the supernatant, dry with anhydrous sodium sulfate, and filter through a 0.22 μm microporous filter membrane.

[0010] (3) Sample detection: analyze the sample liquid by gas chromatography mass spectrometry, use an external standard method, and use a standard curve for quantitative analysis; The GC-MS analysis conditions are as follows: Chromatographic column: DB-WAX capillary chromatographic column (30 m x 0.2 mm x 0.2 μm), injection port temperature 250℃, injection amount 0.8~1 μL; programmed temperature; injection mode: splitless injection; carrier gas: helium; constant flow mode, flow rate 1.0 mL / min; ionization mode: electron impact ionization, ion source temperature 230℃; quadrupole temperature 150℃. Collection mode: selected ion monitoring (SIM) mode.

[0011] In the present application, the solvent used for purification pretreatment is saturated brine and n-hexane, and saturated brine and isooctane can also be used. In the early stage, TMCD solubility experiments in common reagents (methanol, ethanol, water, ethyl acetate, propylene glycol, dichloromethane, isooctane, n-hexane) were carried out, and it was found that TMCD was easily soluble in methanol, ethanol, water, ethyl acetate, propylene glycol, dichloromethane, and difficultly soluble in n-hexane and isooctane. Therefore, n-hexane and isooctane are used as the solvent for purification pretreatment, and comparative experiments are carried out, and the peak area of TMCD obtained by using n-hexane is slightly higher than that of isooctane (about 5%).

[0012] In this invention, the extraction solvent is ethyl acetate, but dichloromethane can also be used. The extraction capabilities of commonly used laboratory extraction solvents such as methanol, dichloromethane, ethyl acetate, and isooctane for TMCD were investigated. The results showed that: 1) Methanol, as the extraction solvent, is completely miscible with e-cigarette liquid, and even after adding saturated saline solution, it cannot separate into layers; 2) Isooctane, as the extraction solvent, resulted in poor extraction due to matrix interference, with the target peak unable to be effectively separated from the interfering matrix peaks; 3) Dichloromethane, as the extraction solvent, resulted in the water layer on top and the organic layer below, effectively separating the two TMCD peaks; 4) Ethyl acetate, as the extraction solvent, resulted in the water layer below and the organic layer above, effectively separating the two TMCD peaks. When using dichloromethane and ethyl acetate as extraction solvents, the peak areas of TMCD were not significantly different, but dichloromethane contained more interfering matrix peaks.

[0013] In this invention, the standard curve quantification is achieved by establishing a standard working curve using the external standard method, and calculating the content of the component based on the detection results and the standard curve of the target analyte.

[0014] In this invention, the purification pretreatment serves the following purposes: removing various impurities from the e-cigarette liquid, reducing interference with the target substance, and thus obtaining a better peak shape.

[0015] In this invention, the programmed temperature rise process in the GC-MS analysis conditions is as follows: initial temperature 80℃, hold for 3 min, rise to 180℃ at 5℃ / min, hold for 3 min, and run at 230℃ for 5 min.

[0016] In this invention, the mass spectrometry conditions in the GC-MS analysis are as follows: the ionization source is EI; the ion source temperature is 230℃; the quadrupole temperature is 150℃; the solvent delay is 17.0 min; the acquisition mode is ion monitoring (SIM) mode; the quantitative ion (m / z) is 72, and the qualitative ions are 57 and 97.

[0017] Compared with the prior art, the method of the present invention has the following superior effects: (1) The present invention uses “saturated saline solution + n-hexane” for purification and pretreatment and ethyl acetate for extraction. The operation is simple and fast, low cost, low solvent consumption, and environmentally friendly, realizing the accurate detection of TMCD in e-cigarette liquid.

[0018] (2) In this invention, “saturated saline solution + n-hexane” is used for purification pretreatment, and then ethyl acetate is used for extraction. This can effectively remove various flavor components in e-cigarette liquid, reduce interference with the target substance, and obtain better peak shape.

[0019] (3) The common impurity in propylene glycol is 1-[1-methyl-2-(2-propenyl-oxy)ethoxy]-2-propanol (CAS No. 55956-25-7, molecular weight 174.24, characteristic ion 43, 57, 103), which is difficult to separate from TMCD due to the close molecular weight and characteristic ion. The DB-WAX capillary chromatographic column is used in the present application to separate the substance from the target substance.

[0020] (4) The present method optimizes the corresponding quantitative ion and qualitative ion pair for TMCD, without standard spectrum library retrieval, so that the qualitative analysis of the compound is more accurate, and the method has higher sensitivity, better precision and repeatability.

[0021] (5) The present application establishes a standard curve for absolute quantification, which has higher accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Total ion current chromatogram of the standard solution on the GC-MS; Figure 2 Chromatographic comparison chart of the actual e-liquid using the purification pretreatment step. DETAILED DESCRIPTION

[0023] The present application is further described below in combination with examples.

[0024] Example 1: Accurately weigh 2.0 g of e-cigarette liquid in a 15 mL centrifuge tube, add 5 mL of saturated brine and 5 mL of n-hexane, vortex for 5 min, centrifuge at 5000 r / min for 5 min, and discard the supernatant. Continue to add 5 mL of ethyl acetate to the centrifuge tube, vortex for 5 min, centrifuge at 5000 r / min for 5 min, take the supernatant, dry with anhydrous sodium sulfate, filter through a 0.22 μm microporous filter membrane, and carry out GC-MS test.

[0025] The GC-MS analysis conditions are as follows: The gas chromatography conditions are as follows: DB-WAX capillary chromatographic column (30 m x 0.2 mm x 0.2 μm), carrier gas is helium, flow rate is 1.0 mL / min, splitless mode, injection volume is 1 μL, injection port temperature is 250℃, programmed temperature: initial temperature is 80℃, hold for 3 min, increase to 180℃ at a rate of 5℃ / min, hold for 3 min, run for 5 min at 230℃.

[0026] The mass spectrometry conditions are as follows: ionization source is EI; ion source temperature is 230℃; quadrupole rod temperature is 150℃; solvent delay is 17.0 min; acquisition mode is selected ion monitoring (SIM); quantitative ion (m / z) is 72, and qualitative ion is 57, 97.

[0027] The concentrations of the matrix-matched standard working solutions were 0.1, 0.5, 1.0, 2.0, and 5.0 mg / kg. These standard solutions were analyzed by GC-MS and linear regression analysis was performed. The standard curves showed good linearity, with correlation coefficients r0. 2 It is 0.9996.

[0028] The main components of e-cigarette liquid are propylene glycol and glycerol (accounting for about 90%). Three e-cigarette liquids with different propylene glycol to glycerol ratios of 67:33, 48:52 and 11:89 were selected, and recovery tests were conducted at four addition levels of 0.2, 0.5, 2 and 5 mg / kg. The average recovery rate of the target substance at the four addition levels was between 92% and 107%, and the RSD was less than 4%. Detailed data are shown in Table 1.

[0029] The limits of detection (LOD) and quantitation (LOQ) were calculated using signal-to-noise ratios of 3 and 10 times, respectively. The LOD for all targets was 0.02 mg / kg, and the LOQ was 0.04 mg / kg. The results indicate that this method has good recovery, precision, sensitivity, and stability, and can meet the needs of analytical detection.

[0030] Five parallel experiments were conducted within the day and five parallel experiments were conducted between the day, following the above procedures. The intra-day precision and inter-day precision of the measurement results were calculated, and the intra-day precision and inter-day precision were 0.31~2.48% and 0.47~3.82%, respectively. The results show that the method has good precision and good stability, and can meet the needs of analytical detection.

[0031] Table 1. Recovery rates of the target analyte (n=5) and relative standard deviations Example 2: To investigate the effect of purification pretreatment steps on sample pretreatment, two e-cigarette liquids were selected: e-cigarette liquid A (without TMCD) and e-cigarette liquid B (containing TMCD). 2 g of e-cigarette liquid was weighed into four 15 mL centrifuge tubes, and the following experiments were performed sequentially: (1) Add 5 mL of saturated saline and 5 mL of ethyl acetate, vortex for 5 min, centrifuge at 5000 r / min for 5 min, take the supernatant, dry with anhydrous sodium sulfate, and filter through a membrane for analysis. (2) Add 5 mL of saturated saline and 5 mL of n-hexane, vortex for 5 min, centrifuge at 5000 r / min for 5 min, discard the supernatant, add 5 mL of ethyl acetate to the lower layer, continue vortexing for 5 min, centrifuge at 5000 r / min for 5 min, take the supernatant, dry with anhydrous sodium sulfate, and filter through a membrane for analysis. Comparative chromatograms are shown below. Figure 2 .

[0032] Depend on Figure 2It can be seen that the baseline noise of the chromatogram after the n-hexane purification step is significantly reduced, the impurity peaks are fewer, and various flavor components and impurities in the electronic cigarette liquid can be well removed, the interference on the target is reduced, and a better peak shape is obtained.

[0033] Example 3: Ten different brands of electronic cigarette liquid samples were detected by the method of Example 1, and the experimental date was 12-18 months away from the production date of the electronic cigarette liquid. Six of the 10 samples were detected, with a detection rate of 60%, and the maximum value was 1.14 mg / kg. The specific results are shown in Table 2. It shows that this method can meet the detection needs of actual samples.

[0034] Table 2 Detection values of TMCD in 10 electronic cigarette liquids Serial number Detection value Serial number Detection value 1 Not detected 6 0.54 2 1.09 7 0.61 3 1.14 8 Not detected 4 Not detected 9 0.67 5 0.68 10 Not detected

Claims

1. A method for quantitative determination of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in e-cigarette liquid: The method improves sample pretreatment by first purifying and pretreating with saturated saline and n-hexane before extraction. The sample is then further purified by vortexing, centrifugation, drying, and membrane filtration. Gas chromatography-mass spectrometry is then used to detect 2,2,4,4-tetramethyl-1,3-cyclobutanediol in e-cigarette liquid. The specific steps are as follows: (1) Sample purification and pretreatment: Add saturated saline and n-hexane to the sample, vortex and centrifuge, discard the supernatant, and leave the liquid layer; (2) Sample extraction: Add ethyl acetate to the lower layer liquid, continue vortexing and centrifugation, take the supernatant, dry it with anhydrous sodium sulfate, and filter it through a membrane for analysis; (3) Sample detection: The sample was detected by gas chromatography-mass spectrometry, and a standard curve was prepared using matrix-matched standard working solution. The standard curve was used for quantification. GC-MS analysis conditions: Column: DB-WAX capillary column, 30m×0.2mm×0.2μm, injection port temperature 250℃, injection volume 0.8~1μL, temperature programmed; Injection method: splitless injection; Carrier gas: Helium; constant flow mode, flow rate 1.0 mL / min; ionization mode: electron bombardment ionization, ion source temperature 230℃; quadrupole temperature 150℃; Acquisition mode: Select Ion Monitoring (SIM) mode.

2. The method according to claim 1, characterized in that: In step (1), the sample purification and pretreatment method is to take 2.0g of e-cigarette liquid into a 15mL centrifuge tube, add 5mL of saturated saline and 5mL of n-hexane, vortex for 5min, centrifuge at 5000r / min for 5min, and discard the supernatant.

3. The method according to claim 1, characterized in that: In step (2), the sample extraction method is to add 5 mL of ethyl acetate to a centrifuge tube, vortex for 5 min, centrifuge at 5000 r / min for 5 min, take the supernatant, dry it with anhydrous sodium sulfate, and filter it through a 0.22 μm microporous membrane.

4. The method according to claim 1 or 2, characterized in that: The solvent n-hexane used in step (1) can be replaced by isooctane. 。 5. The method according to claim 1 or 3, characterized in that: In step (2), the extraction solvent ethyl acetate can be replaced by dichloromethane.

6. The method according to claim 1, characterized in that: The volume ratio of the extraction solvent ethyl acetate to saturated brine is 2:1, 1:1, or 1:2, preferably 1:

1.

7. The method according to claim 1, characterized in that: The aforementioned standard curve quantification involves establishing a standard working curve using the external standard method, and calculating the content of the component based on the test results and the standard curve of the target analyte.

8. The method according to claim 1, characterized in that: The temperature ramp-up process in the GC-MS analysis conditions is as follows: initial temperature 80℃, hold for 3 min, increase to 180℃ at 5℃ / min, hold for 3 min, and run at 230℃ for 5 min.

9. The method according to claim 1, characterized in that: The mass spectrometry conditions were as follows: EI ionization source; ion source temperature: 230℃; quadrupole temperature: 150℃; solvent delay: 17.0 min; acquisition mode: ion monitoring (SIM) mode; quantitative ion (m / z) setting: 72; qualitative ion setting: 57, 97.

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