A method for simultaneously determining nicotine, volatile and non-volatile organic acids in e-liquid of electronic cigarette

Abstract

The present application relates to a kind of method for simultaneously determining nicotine, volatile and non-volatile organic acid in electronic cigarette liquid, which comprises the following steps: (1) electronic cigarette liquid is weighed, an extracting agent is added, and after being sealed with a cover, it is extracted by vortex oscillation to obtain an extract; (2) the extract obtained in step (1) is filtered through a 0.22 μm water phase filter membrane, and then subjected to high performance liquid chromatography analysis; (3) the content of the target substance in the sample is calculated. The present application realizes the simultaneous analysis of nicotine, DL-tartaric acid, malic acid, lactic acid, acetic acid, citric acid, propionic acid, acetylpropionic acid, butyric acid and 2-methylbutyric acid in electronic cigarette liquid.

Description

Technical Field

[0001] This invention belongs to the field of tobacco chemical analysis technology, specifically relating to a method for simultaneously determining nicotine, volatile and non-volatile organic acids in e-cigarette liquids. Background Technology

[0002] In recent years, nicotine salts (nicotine + organic acids) have replaced free nicotine and become the main form of nicotine added to e-cigarettes. The national standard GB 41700 "E-cigarettes" stipulates that the nicotine concentration in e-cigarette liquid should not exceed 20 mg / g. It also specifies the permitted additives in the liquid and their maximum usage, including 10 volatile and non-volatile organic acids such as DL-tartaric acid (10 mg / g), acetic acid (50 mg / g), propionic acid (2.5 mg / g), butyric acid (50 mg / g), 2-methylbutyric acid (50 mg / g), lactic acid (20 mg / g), citric acid (50 mg / g), benzoic acid (26 mg / g), levulinic acid (28 mg / g), and malic acid (24 mg / g).

[0003] Currently, gas chromatography (GC) is the primary method for determining nicotine content in e-cigarette liquids. Methods for determining organic acids mainly include GC, GC-MS, liquid chromatography (LC), and LC-tandem mass spectrometry (LC-MS). GC and GC-MS require derivatization reactions for non-volatile organic acids, which are time-consuming and labor-intensive, and the accuracy for volatile organic acids is relatively low. LC-MS has high sensitivity for determining nicotine and non-volatile organic acids, but because the mass spectrometry ion source requires high-temperature ionization, it is not suitable for determining volatile organic acids. While LC can determine volatile organic acids, most methods for simultaneously determining two types of organic acids only measure a few non-volatile acids and one or two volatile acids. Compared to other detection methods such as GC, LC can only determine two types of organic acids. However, due to the similar structures of organic acids, it is essential to simultaneously separate the chromatographic peaks of multiple organic acids.

[0004] Therefore, it is of great significance to establish a method with high accuracy and sensitivity for simultaneously determining nicotine, volatile and non-volatile organic acids in e-cigarette liquids. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned technical shortcomings by establishing an analytical method for the simultaneous determination of nicotine and 10 volatile and non-volatile organic acids in e-cigarette liquids. This method, based on high-performance liquid chromatography (HPLC), achieves the simultaneous separation and analysis of nicotine, DL-tartaric acid, acetic acid, propionic acid, butyric acid, 2-methylbutyric acid, lactic acid, citric acid, benzoic acid, levulinic acid, and malic acid. It has the advantages of simple operation, high separation, accurate quantification, good recovery rate, and high repeatability, making it suitable for the simultaneous determination of nicotine and 10 organic acids in e-cigarette liquids.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for simultaneously determining nicotine, volatile and non-volatile organic acids in e-cigarette liquids, the method comprising the following steps:

[0008] (1) Weigh the e-cigarette liquid, add the extractant, seal the cap and vortex to extract the extract;

[0009] (2) The extract obtained in step (1) was filtered through a 0.22 μm aqueous phase filter membrane and then analyzed by high performance liquid chromatography.

[0010] (3) Calculate the content of the target substance in the sample.

[0011] Preferably, in step (1), the extractant is an aqueous phosphoric acid solution, particularly a 0.085 w / v% aqueous phosphoric acid solution (mass percentage); the aqueous phosphoric acid solution (e.g., a 0.085 w / v% aqueous phosphoric acid solution (mass percentage)) may contain methanol, wherein the volume percentage of methanol is 0%-10%, preferably 0%-5%. That is, in this invention, the extractant can be an aqueous phosphoric acid solution, particularly a 0.085 w / v% aqueous phosphoric acid solution (mass percentage). The extractant may or may not contain methanol; the present invention preferably uses a 0.085 w / v% aqueous phosphoric acid solution (mass percentage) without methanol. When methanol is included, the volume percentage of methanol is 0%-10%, preferably 0%-5%.

[0012] Preferably, in step (1), the volume of the extractant is 10 mL.

[0013] Preferably, in step (1), the extraction method is vortex oscillation or ultrasonic extraction, preferably vortex oscillation.

[0014] Preferably, in step (1), the extraction time is 5-30 min, preferably 10 min.

[0015] Preferably, in step (2), the conditions for the high-performance liquid chromatography analysis include: the chromatographic column is a Waters Atlantis. TM T3 column (4.6 mm × 250 mm, 5 μm); column temperature 30 °C; flow rate 1 mL / min.

[0016] Preferably, in step (2), the conditions for the high performance liquid chromatography analysis further include: the mobile phase is a 0.085 w / v% aqueous phosphoric acid solution (phase A) and a 0.085 w / v% methanolic phosphoric acid solution (phase B), and the gradient elution program is: 0–11.5 min, phase A is maintained at 99%; 11.5–15 min, phase A decreases from 99% to 75%; 15–28 min, phase A decreases from 75% to 10%; 28.01–31 min, phase A is maintained at 1%; 31.01–35 min, phase A is maintained at 99%.

[0017] Preferably, in step (2), the conditions for the high performance liquid chromatography analysis further include: injection volume of 5 μL; detection wavelength: 0.00-25.80 min, wavelength 210 nm; 25.80-35.00 min, wavelength 250 nm.

[0018] Preferably, in step (3), the content of the target analyte in the sample is quantitatively calculated using the external standard curve method. The external standard curve method is as follows: prepare a series of standard working solutions containing the target analyte (the concentration range of each target analyte is 0.005 to 2.5 mg / mL), and construct a standard working curve with the peak area ratio of the target analyte in each standard working solution as the ordinate and the content of the target analyte in each standard working solution as the abscissa; substitute the analysis results of step (2) into the standard working curve to obtain the content of the target analyte in the test solution, and then further calculate the content of each target analyte in the sample.

[0019] Preferably, the volatile or non-volatile organic acids are DL-tartaric acid, acetic acid, propionic acid, butyric acid, 2-methylbutyric acid, lactic acid, citric acid, benzoic acid, acetylpropionic acid, and malic acid.

[0020] Acetic acid, propionic acid, butyric acid, and 2-methylbutyric acid are volatile organic acids. DL-tartaric acid, lactic acid, citric acid, benzoic acid, levulinic acid, and malic acid are non-volatile organic acids.

[0021] Preferably, the concentration range of each target analyte in the series of standard working solutions is 0.005 to 2.5 mg / mL.

[0022] In one specific implementation, the method includes the following steps:

[0023] (1) Weigh 0.5g of sample into a 10mL stoppered colorimetric tube, dilute to the mark with 0.085w / v% phosphoric acid aqueous solution, seal and vortex for 10min to obtain the extract;

[0024] (2) The extract obtained in step (1) was filtered through a 0.22 μm aqueous membrane and then subjected to high performance liquid chromatography analysis under the following conditions:

[0025] Chromatographic column: Waters Atlantis™ T3 column, 4.6 mm × 250 mm, 5 μm; Mobile phase A: 0.085 w / v % aqueous phosphoric acid solution, Mobile phase B: 0.085 w / v % methanolic phosphoric acid solution; Gradient elution program: 0–11.5 min, phase A maintained at 99%; 11.5–15 min, phase A decreased from 99% to 75%; 15–28 min, phase A decreased from 75% to 10%; 28.01–31 min, phase A maintained at 1%; 31.01–35 min, phase A maintained at 99%; Column temperature: 30 °C; Flow rate: 1 mL / min; Injection volume: 5 μL; Detection wavelength: 0.00–25.80 min, wavelength 210 nm; 25.80–35.00 min, wavelength 250 nm.

[0026] (3) The content of the target analyte in the sample is quantitatively calculated using the external standard curve method. The external standard curve method is as follows: prepare a series of standard working solutions containing the target analyte (the concentration range of each target analyte is 0.005 to 2.5 mg / mL), and construct a standard working curve with the peak area ratio of the target analyte in each standard working solution as the ordinate and the content of the target analyte in each standard working solution as the abscissa; substitute the analysis results of step (2) into the standard working curve to obtain the content of the target analyte in the test solution, and then further calculate the content of each target analyte in the sample.

[0027] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0028] This invention establishes an analytical method for nicotine and 10 organic acids in e-cigarette liquids based on high-performance liquid chromatography (HPLC). It enables the simultaneous separation and analysis of nicotine and 10 volatile and non-volatile organic acids, including DL-tartaric acid, acetic acid, propionic acid, butyric acid, 2-methylbutyric acid, lactic acid, citric acid, benzoic acid, levulinic acid, and malic acid. This invention offers advantages such as simple operation, high separation, accurate quantification, good recovery, and high repeatability, making it suitable for the analysis of nicotine and 10 organic acids in e-cigarette liquids.

[0029] This invention provides for the first time a method for simultaneously determining volatile and non-volatile organic acids in electronic cigarettes.

[0030] This invention can simultaneously separate all target substances, namely nicotine and 10 organic acids, by adjusting the chromatographic conditions.

[0031] This invention enables the simultaneous detection of highly reactive target (benzoic acid) and other target substances by changing the absorption wavelength. Attached Figure Description

[0032] Figure 1The chromatograms are of the target analytes in the standard working solution, where: 1. DL-tartaric acid; 2. Nicotine; 3. Malic acid; 4. Lactic acid; 5. Acetic acid; 6. Citric acid; 7. Propionic acid; 8. Vetylpropionic acid; 9. Butyric acid; 10. 2-Methylbutyric acid; 11. Benzoic acid;

[0033] Figure 2 This is a comparison chart showing the separation effects under different chromatographic column conditions. The components are: 1. DL-tartaric acid; 2. Nicotine; 3. Malic acid; 4. Lactic acid; 5. Acetic acid; 6. Citric acid; 7. Propionic acid; 8. Vinegaric acid; 9. Butyric acid; 10. 2-Methylbutyric acid; 11. Benzoic acid. Figure 2 A is the chromatogram of 11 target analytes separated by a Spurtil C18 column. Figure 2 B is the chromatogram of 11 target analytes separated by an ODS Hypersil C18 column. Figure 2 C is the chromatogram of 11 target analytes separated by a Waters HSS T3 column. Figure 2 D stands for Waters Atlantis TM Chromatograms of 11 target analytes separated by a T3 column;

[0034] Figure 3 This is a comparison chart showing the separation effects under different mobile phase gradient conditions;

[0035] Figure 4 Chromatograms of nicotine and 10 organic acids extracted with different extractants;

[0036] Figure 5 Isoabsorption diagrams of nicotine and 10 organic acids;

[0037] Figure 6 UV spectra of nicotine and 10 organic acids;

[0038] Figure 7 The effect of vortex extraction at different times on the extraction efficiency of nicotine and 10 organic acids;

[0039] Figure 8 The effect of ultrasonic extraction at different times on the extraction efficiency of nicotine and 10 organic acids. Detailed Implementation

[0040] The technical solution of the present invention will be further described below in conjunction with specific implementation methods.

[0041] Unless otherwise specified, all percentages mentioned in the following examples are volume percentages.

[0042] Example 1 A high-performance liquid chromatography method for the analysis of nicotine and 10 organic acids in e-cigarette liquid.

[0043] (1) Instruments and reagents

[0044] 1260Infinity II high performance liquid chromatograph, equipped with a diode array detector (Agilent Technologies, USA); vortex mixer (DATI Instruments Technology Co., Ltd.); electronic balance (Sartorius GmbH, Germany).

[0045] Nicotine (purity >99%, National Tobacco Quality Supervision and Inspection Center), Acetic Acid (purity ≥99.8%, Beijing Manhag Biotechnology Co., Ltd.), Propanoic Acid (purity ≥99.8%, Beijing Manhag Biotechnology Co., Ltd.), Butyric Acid (purity 99.7%, Dr. Ehrenstorfer GmbH, Germany), 2-Methylbutyric Acid (purity 99.6%, Shanghai Anpu Cuishi Standard Technology Service Co., Ltd.), DL-tartaric acid (purity 99.7%, Beijing Tanmo Quality Inspection Standard Material Center), Lactic acid (purity 90.2%, Beijing Manhag Biotechnology Co., Ltd.), Citric acid (purity 99.7%, Beijing Tanmo Quality Inspection Standard Material Center), Levulinic acid (purity 99%, Shanghai Anpu Cuishi Standard Technology Service Co., Ltd.), Malic acid Benzoic acid (purity 99.8%, Shanghai Anpu Cuishi Standard Technical Service Co., Ltd.), benzoic acid (purity 99.5%, Dr. Ehrenstorfer GmbH, Germany), phosphoric acid (USA, purity 85%, Alfa Aesar), and methanol (chromatographic grade, Shanghai Keyi Chemical Technology Co., Ltd.) were used. Ultrapure water was used in the experiments, prepared using a Milli-Q system (Milford, MA, USA).

[0046] (2) Instrument operating conditions

[0047] Chromatographic column: Waters Atlantis™ T3 column, 4.6 mm × 250 mm, 5 μm; Mobile phase A: 0.085 w / v % aqueous phosphoric acid solution, Mobile phase B: 0.085 w / v % methanolic phosphoric acid solution; Gradient elution program: 0–11.5 min, phase A maintained at 99%; 11.5–15 min, phase A decreased from 99% to 75%; 15–28 min, phase A decreased from 75% to 10%; 28.01–31 min, phase A maintained at 1%; 31.01–35 min, phase A maintained at 99%; Column temperature: 30 °C; Flow rate: 1 mL / min; Injection volume: 5 μL; Detection wavelength: 0.00–25.80 min, wavelength 210 nm; 25.80–35.00 min, wavelength 250 nm.

[0048] (3) Sample pretreatment

[0049] Weigh 0.5 g of sample into a 10 mL stoppered colorimetric tube, dilute to the mark with 0.085 w / v phosphate aqueous solution, seal and vortex for 10 min. Take the extract, filter it through a 0.22 μm aqueous filter membrane and perform high performance liquid chromatography analysis.

[0050] (4) Preparation of phosphoric acid aqueous solution

[0051] Transfer 1 mL of phosphoric acid to a 1 L volumetric flask and dilute to the mark with ultrapure water.

[0052] (5) Preparation of standard working solution

[0053] ① Preparation of primary standard solutions: Weigh 500 mg each of nicotine, DL-tartaric acid, malic acid, lactic acid, citric acid, and levulinic acid into separate 10 mL volumetric flasks, and dilute to volume with 0.085 w / v phosphate water; weigh 500 mg each of acetic acid, propionic acid, and butyric acid into the same 10 mL volumetric flask, and dilute to volume with 0.085 w / v phosphate water; weigh 500 mg each of 2-methylbutyric acid and benzoic acid into the same 10 mL volumetric flask, and dilute to volume with methanol. Primary standard solutions with a concentration of 50 mg / mL are obtained and stored at 4℃.

[0054] ② Preparation of secondary standard solutions: Transfer 1 mL of each of the above primary standard solutions to a 10 mL volumetric flask, and dilute to volume with 0.085 w / v % phosphoric acid aqueous solution to obtain secondary standard solutions with a concentration of 5 mg / mL. Store at 4℃.

[0055] ③ Preparation of standard working solutions

[0056] Using a gradient dilution method, secondary standard solutions were prepared to create standard working curves with concentrations of 0.005, 0.02, 0.05, 0.1, 0.2, 0.5, 1, and 2.5 mg / mL.

[0057] (6) Sample determination

[0058] The standard working solution obtained in step (5) and the sample solution obtained in step (3) were analyzed by high performance liquid chromatography (HPLC). The chromatograms of the target analytes in the standard working solution are shown below. Figure 1 As shown. A standard working curve is constructed with the peak area ratio of the target substances in each standard working solution as the ordinate and the content of the target substances in each standard working solution as the abscissa. The analysis results of step (3) are substituted into the standard curve to obtain the content of the target substances in the test solution, and then the content of each target substance in the sample is further calculated.

[0059] (7) Method Validation

[0060] The limit of detection (LOD) of this method was calculated based on a signal-to-noise ratio of 3. The recoveries were calculated using three spiking levels (low, medium, and high), with five parallel samples added at each level. The precision was calculated based on the parallel test results. The linear range, linear coefficient, LOD, average recoveries, and average precision of this method are shown in Table 1.

[0061] Table 1. Linear range, linear coefficient, limit of detection, average spiked recovery, and average precision of each target analyte.

[0062]

[0063]

[0064] (8) Actual sample analysis

[0065] Based on the above determination method, 20 e-cigarette liquid samples were selected, and the content of the target substance was measured as shown in Table 2.

[0066] Table 2. Results of target substance content in typical e-cigarette liquid samples (unit: mg / g)

[0067]

[0068]

[0069] Note: "ND." indicates not detected.

[0070] Example 2 Selection of chromatographic column

[0071] This method compares the performance of Spurtil C18 column (4.6 × 250 mm, 5 μm), ODS Hypersil C18 column (4.6 × 250 mm, 5 μm), Waters HSS T3 column (2.1 × 150 mm, 1.8 μm), and Waters Atlantis column. TMFour types of columns were used: T3 column (4.6 × 250 mm, 5 μm). Results showed that most organic acids exhibited asymmetrical peak shapes and leading peaks on the Spurtil C18 column, and baseline separation was not achieved for nicotine and malic acid (see [link to study]. Figure 2 A); When using the ODS Hypersil C18 column, nicotine did not elute, while the peak shapes of the other 10 target compounds were all good (see...). Figure 2 B); Baseline separation of nicotine and malic acid peaks was not achieved in the Waters HSS T3 column (see...). Figure 2 C); Baseline separation of 11 target analytes was achieved on the Waters Atlantis™ T3 column, with symmetrical peak shapes (see...). Figure 2 Therefore, the Waters Atlantis™ T3 column was ultimately chosen for the next step of analysis.

[0072] Example 3 Selection of mobile phase system

[0073] This invention investigated the effect of different mobile phase systems on the detection method. The mobile phases were: 0.085 w / v% aqueous phosphoric acid-methanol system, 0.085 w / v% aqueous phosphoric acid-acetonitrile system, and 0.085 w / v% aqueous phosphoric acid-0.085 w / v% aqueous phosphoric acid-methanol system. The remaining methods are as described in Example 1.

[0074] turn out:

[0075] ① When the mobile phase is selected as a 0.085 w / v% phosphoric acid aqueous solution-methanol system, benzoic acid causes interference, and the baseline is not stable when the gradient is too large.

[0076] ② When the mobile phase is selected as a 0.085 w / v% phosphoric acid aqueous solution-acetonitrile system, the baseline is stable, but the nicotine peak bifurcates at the top.

[0077] ③ When the mobile phase is selected as 0.085 w / v% phosphoric acid aqueous solution-0.085 w / v% phosphoric acid methanol system, the peak shapes of all target compounds are good.

[0078] Therefore, a 0.085 w / v% aqueous phosphoric acid solution-0.085 w / v% methanolic phosphoric acid solution was ultimately selected as the mobile phase.

[0079] Example 4 Selection of mobile phase gradient

[0080] This invention investigated the effect of different mobile phase gradients on the separation of 11 compounds. The mobile phase gradients were as follows: ① 0-5 min: 0.085 w / v% phosphoric acid solution maintained at 99%, 5-11.5 min: decreased to 80%, 11.5-11.6 min: decreased from 80% to 5%, 15 min: increased from 5% to 99%, equilibrated for 5 min, total 20 min; ② 0-11.5 min: 0.085 w / v% phosphoric acid solution maintained at 99%, 11.5-14 min: decreased to 90%, 14-19 min: decreased from 90% to 1% and maintained for 1 min, then immediately increased to 99%, equilibrated for 5 min, total 25 min; ③ 0-11.5 min... The following steps were performed: First, 0.085 w / v% phosphoric acid solution was maintained at 99% for 11.5-14 min, then decreased to 90% for 11.5-14 min, then decreased from 90% to 1% for 2 min for 14-24 min, and immediately increased to 99% for 4 min, for a total of 30 min. Second, 0.085 w / v% phosphoric acid solution was maintained at 99% for 0-11.5 min, then decreased to 75% for 11.5-15 min, then decreased from 75% to 10% for 15-28 min, then maintained at 1% for 28.01-31 min, and finally maintained at 99% for 31.01-35 min. All mobile phase gradients were performed at an absorption wavelength of 210 nm. The remaining methods followed the procedures in Example 1, and the results are as follows. Figure 3 As shown.

[0081] The results showed that when the mobile phase gradient condition was ①, propionic acid and levulinic acid overlapped, failing to meet the separation requirements. Furthermore, due to the gradual increase in the organic phase ratio, the chromatographic baseline rose after 15 minutes, and the butyric acid peak overlapped with the baseline noise, making separation impossible. 2-Methylbutyric acid overlapped with benzoic acid. When the mobile phase gradient condition was ②, propionic acid and levulinic acid were separated, butyric acid was separated from the baseline noise, while 2-methylbutyric acid and benzoic acid were not completely separated. When the mobile phase gradient condition was ③, 2-methylbutyric acid and benzoic acid were separated, but the interval between the chromatographic peaks of 2-methylbutyric acid and benzoic acid was small, making it impossible to change the absorption wavelength. When the mobile phase gradient condition was ④, the interval between the chromatographic peaks of 2-methylbutyric acid and benzoic acid was wider than that under mobile phase gradient condition ③, allowing for switching of the absorption wavelength.

[0082] Therefore, the final selected mobile phase gradient conditions are as follows: 0–11.5 min, 0.085 w / v% phosphoric acid water is maintained at 99%; 11.5–15 min, it is reduced to 75%; 15–28 min, it is reduced from 75% to 10%; 28.01–31 min, 0.085 w / v% phosphoric acid water is maintained at 1%; 31.01–35 min, 0.085 w / v% phosphoric acid water is maintained at 99%; for a total of 35 min.

[0083] Example 5 Selection of Extractant

[0084] Malic acid, DL-tartaric acid, and citric acid, among non-volatile organic acids, contain two or more carboxylic acid structures and exhibit different pKa values. Therefore, 0.085 w / v% phosphoric acid was added to the extraction solution to improve peak shape. This method compares the effects of aqueous solutions containing 0.085 w / v% phosphoric acid on the extraction of nicotine and ten organic acids at methanol-free, 1% methanol, 2% methanol, 3% methanol, 4% methanol, 5% methanol, 6% methanol, 7% methanol, 8% methanol, 9% methanol, and 10% methanol ratios. The remaining methods are as described in Example 1, and the results are as follows. Figure 4 As shown.

[0085] The results showed that different proportions of methanol-water solution had a significant impact on the chromatographic peak shape of the target compound. At a methanol ratio of 3%, the response of nicotine began to decrease; at a methanol ratio of 5%, the peak shape began to show a leading edge and signs of bifurcation; and at a methanol ratio of 6%, nicotine split into two peaks. Therefore, considering the influence of different extractants on the peak shape of the target compound, a 0.085 w / v% phosphoric acid aqueous solution was selected as the extractant, resulting in a good peak shape. Since the main components of e-cigarette liquid are propylene glycol and glycerol, which have good solubility in aqueous solution, and to avoid excessive organic matter content in the extractant interfering with the peak shape of the target compound, a 0.085 w / v% phosphoric acid aqueous solution was ultimately chosen as the extraction solution.

[0086] Example 6 Optimization of absorption wavelength

[0087] To obtain the maximum absorption wavelength of various organic acids and determine the most suitable absorption wavelength for the method, this method uses a diode array detector (DAD) to detect the target compound in the full spectrum of 190-400 nm. Other methods are described in Example 1. Isoabsorption diagrams are shown below. Figure 5 As shown.

[0088] The results show that the signal intensities of nicotine and benzoic acid are significantly higher than those of other organic acids. Analysis of the spectra of each target compound ( Figure 6 It can be seen that the maximum absorption wavelength of DL-tartaric acid, malic acid, lactic acid, acetic acid, and citric acid is around 210 nm; the maximum absorption wavelength of propionic acid, levulinic acid, butyric acid, and 2-methylbutyric acid is between 190-200 nm; the maximum absorption wavelengths of nicotine are 192 nm and 260 nm; and benzoic acid has two optimal absorption wavelengths, 200 nm and 234 nm. Considering the terminal absorption phenomenon of methanol contained in the mobile phase, in order to obtain the optimal response of each target analyte, 210 nm was selected as the detection wavelength at 25.8 min (before the benzoic acid peak), and 250 nm was selected as the detection wavelength after 25.8 min.

[0089] Example 7 Selection of extraction method

[0090] To compare the effects of vortex extraction and ultrasonic extraction on the extraction efficiency of nicotine and 10 organic acids in e-cigarettes, the effects of different extraction times (5 min, 10 min, 15 min, 20 min, 25 min, and 30 min) on vortex and ultrasonic extraction were investigated. The results are as follows: Figure 7 and Figure 8 As shown in the figure. The results show that vortex extraction and ultrasonic extraction have basically the same effect on the recovery rate of the target substance. Considering that vortex extraction is more convenient, vortex oscillation extraction was selected as the extraction method, and the extraction time was 10 min.

Claims

1. A method for simultaneously determining nicotine, volatile and non-volatile organic acids in e-cigarette liquid, wherein the volatile organic acids include acetic acid, propionic acid, butyric acid and 2-methylbutyric acid, and the non-volatile organic acids include DL-tartaric acid, lactic acid, citric acid, benzoic acid, levulinic acid and malic acid, the method comprising the following steps: (1) Weigh the e-cigarette liquid, add 0.085 w / v % phosphoric acid aqueous solution as the extractant, seal the container and vortex to extract the extract; (2) The extract obtained in step (1) was filtered through a 0.22 μm aqueous phase filter membrane and then analyzed by high performance liquid chromatography. The conditions for the high-performance liquid chromatography analysis are as follows: the chromatographic column is a Waters Atlantis. TM T3 column, 4.6 mm × 250 mm, 5 μm; column temperature 30 °C; flow rate 1 mL / min; mobile phase A was 0.085 w / v % aqueous phosphoric acid solution, mobile phase B was 0.085 w / v % methanolic phosphoric acid solution, gradient elution program: 0–11.5 min, phase A maintained at 99%; 11.5–15 min, phase A decreased from 99% to 75%; 15–28 min, phase A decreased from 75% to 10%; 28.01–31 min, phase A maintained at 1%; 31.01–35 min, phase A maintained at 99%; detection wavelength: 0.00–25.80 min, wavelength 210 nm; 25.80–35.00 min, wavelength 250 nm. (3) Calculate the content of the target substance in the sample.

2. The method according to claim 1, characterized in that, In step (1), the volume of the extractant is 10 mL.

3. The method according to claim 1, characterized in that, In step (1), the extraction method is vortex oscillation or ultrasonic extraction.

4. The method according to claim 1, characterized in that, In step (1), the extraction method is vortex oscillation.

5. The method according to claim 1, characterized in that, In step (1), the extraction time is 5-30 min.

6. The method according to claim 1, characterized in that, In step (1), the extraction time is 10 min.

7. The method according to claim 1, characterized in that, The injection volume was 5 μL.

8. The method according to any one of claims 1 to 7, characterized in that, In step (3), the content of the target substance in the sample is quantitatively calculated using the external standard curve method. The external standard curve method is as follows: prepare a series of standard working solutions containing the target substance, and construct a standard working curve with the peak area ratio of the target substance in each standard working solution as the ordinate and the content of the target substance in each standard working solution as the abscissa; substitute the analysis results of step (2) into the standard working curve to obtain the content of the target substance in the test solution, and then further calculate the content of each target substance in the sample.

9. The method according to claim 8, characterized in that, The concentration range of each target analyte in the series of standard working solutions is 0.005~2.5 mg / mL.

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