Gas chromatography-mass spectrometry determination method for residual quantity of tetraethyl pyrophosphate in polyphosphate flame retardant

Abstract

The invention discloses a gas chromatography-mass spectrometry determination method for the residual quantity of toxic and harmful synthetic intermediate tetraethyl pyrophosphate in a polyphosphate flame retardant, and relates to the technical field of chemical analysis and detection. The method comprises the following steps: preparing a tetraethyl pyrophosphate standard working solution, an internal standard solution and a sample solution, respectively injecting the tetraethyl pyrophosphate standard working solution and the sample solution into a gas chromatography-mass spectrometer, effectively separating to-be-detected components by adopting an HP-5MS quartz capillary column, carrying out rapid determination in a selected ion monitoring mode, and quantifying by adopting an internal standard method. The invention provides a method for determining and analyzing trace phosphorus-containing compounds in an organic phosphorus system, interference of high background on detection is effectively eliminated, the detection sensitivity is further improved, and the method is low in detection limit, good in accuracy and high in specificity and can qualitatively or quantitatively detect trace tetraethyl pyrophosphate in a polyphosphate flame retardant.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis and detection, and particularly relates to a gas chromatography-mass spectrometry method for determining the residual amount of tetraethyl pyrophosphate in a polyphosphate ester flame retardant. Background Art

[0002] With the continuous development of technology, the flame retardancy of materials has received more attention due to its importance in enhancing product safety and reducing fire accidents. Phosphorus-based flame retardants have been widely used in fields such as plastics, rubber, textiles, construction, and transportation due to their excellent flame retardant properties and environmental friendliness, and are considered flame retardants with broad application prospects. Organophosphorus flame retardants have the characteristics of being non-toxic, low-smoke, and halogen-free, and are a hot research direction for flame retardants. The polyphosphate ester flame retardant EPPE, as an efficient, green, and environmentally friendly organophosphorus flame retardant, can achieve the specified flame retardant effect with a relatively low dosage, and is particularly suitable for the flame retardant use of high-grade automobiles, furniture sponges, fabric materials, and coatings. Tetraethyl pyrophosphate (also known as TEPP), as an intermediate in the synthesis process, is highly toxic, and the residual amount of this toxic and harmful substance seriously affects the product quality and safety. Therefore, it is urgent to detect its residual amount for control.

[0003] Currently, there is a lack of detection standards and methods for tetraethyl pyrophosphate. Most of the detection and analysis methods focus on the detection of agricultural residues in grains, fruits, and vegetables. The common detection method for TEPP in grains mainly uses gas chromatography, and in order to improve the detection sensitivity, a flame photometric detector (FPD) is used for detection, but this method is difficult to apply to polyphosphate ester flame retardants. The polyphosphate ester flame retardant system is a mixture of organophosphorus compounds with complex components and many impurity peaks. Gas chromatography analysis only qualitatively determines by retention time, which is very likely to cause false positives and lead to deviations in the determination results. Summary of the Invention

[0004] The purpose of the present invention is to provide a gas chromatography-mass spectrometry method for determining the residual amount of tetraethyl pyrophosphate in a polyphosphate ester flame retardant, and to solve the problem that the existing method is difficult to accurately determine the residual amount of tetraethyl pyrophosphate in a polyphosphate ester flame retardant.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A gas chromatography-mass spectrometry method for determining the residual amount of tetraethyl pyrophosphate in a polyphosphate ester flame retardant, which is characterized by including the following steps:

[0006] S1. Prepare a tetraethyl pyrophosphate standard working solution and an internal standard solution;

[0007] S2. Prepare a sample solution: Weigh a sample of the polyphosphate ester flame retardant into a volumetric flask, add a certain amount of the internal standard solution, make up the volume with acetonitrile, shake well, and filter to obtain the sample solution to be tested;

[0008] S3. Inject the tetraethyl pyrophosphate standard working solution into the gas chromatography-mass spectrometer. Draw a standard curve based on the measurement results of the standard working solution. Use the peak area ratio (A / Ai) of tetraethyl pyrophosphate at each concentration in the standard working solution to the quantitative ion of the internal standard solution as the ordinate, and the relative concentration (C / Ci) of tetraethyl pyrophosphate to the internal standard as the abscissa. Inject the test sample solution into the gas chromatography-mass spectrometer, and obtain the concentration of tetraethyl pyrophosphate in the test sample solution according to the standard curve from the peak area ratio of the quantitative ions of tetraethyl pyrophosphate and the internal standard solution in the test sample solution.

[0009] A further technical solution is that the concentrations of tetraethyl pyrophosphate in the tetraethyl pyrophosphate standard working solution are 0.5 mg / L, 1 mg / L, 2 mg / L, 3 mg / L, 5 mg / L, 8 mg / L, and 10 mg / L in sequence.

[0010] A further technical solution is that the preparation method of the standard working solution is to respectively pipette 0.5 mL, 1.0 mL, 2.0 mL, 3.0 mL, 5.0 mL, 8.0 mL, and 10 mL of tetraethyl pyrophosphate standard solution with a concentration of 50 mg / L and 5 mL of internal standard standard solution with a concentration of 5 mg / L into a 50 mL volumetric flask, dilute with acetonitrile to the scale, and shake well.

[0011] A further technical solution is that the concentration of the internal standard solution is 0.5 mg / L, and the internal standard is dimethyl phthalate (DMP).

[0012] A further technical solution is that the preparation method of the sample solution is to weigh 3 g of the polyphosphate flame retardant sample into a 50 mL volumetric flask, add 5 mL of the internal standard standard solution with a concentration of 5 mg / L, dilute with acetonitrile to the scale, and shake well.

[0013] A further technical solution is that the filtration is carried out using a 0.22 μm organic filter membrane.

[0014] A further technical solution is that the measurement conditions of the gas chromatography-mass spectrometer are as follows:

[0015] a) Chromatographic column: HP-5MS fused silica capillary column, 30 m × 0.25 mm × 0.25 μm;

[0016] b) Column temperature: Initial temperature 80 °C, increase the temperature to 220 °C at a rate of 20 °C / min, hold for 2 min, then increase the temperature to 280 °C at a rate of 30 °C / min, and hold for 8 min;

[0017] c) Injection port temperature: 160 °C;

[0018] d) Mass spectrometry interface temperature: 280 °C;

[0019] e) Quadrupole temperature: 150 °C;

[0020] f) Ion source temperature: 280 °C;

[0021] g) Carrier gas: Helium, purity ≥ 99.999%, flow rate 1.2 mL / min;

[0022] h) Ionization mode: Electron impact ionization (EI);

[0023] i) Ionization energy: 70 eV;

[0024] j) Detection mode: Selected ion monitoring mode (SIM);

[0025] k) Injection volume: 1 μL;

[0026] l) Injection method: Split injection, split ratio at the injection port 20:1;

[0027] m) Solvent delay: 3 min.

[0028] A further technical solution is that the characteristic ions of tetraethyl pyrophosphate and their abundance ratios in the ion monitoring mode are 161:235:263 = 100:41:52, the quantitative ion mass-to-charge ratio is 161; the characteristic ions of dimethyl phthalate and their abundance ratios are 163:77:135 = 100:17:5, and the quantitative ion mass-to-charge ratio is 163.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. Dimethyl phthalate (DMP) is used as the internal standard solution, and a standard working solution of tetraethyl pyrophosphate is prepared. At the same time, a polyphosphate flame retardant is weighed and added to acetonitrile and the internal standard solution to prepare a test sample solution. The standard curve of the standard solution is constructed by a gas chromatography-mass spectrometer first, and then the content of tetraethyl pyrophosphate in the test sample solution is quickly determined according to the standard curve. A gas chromatography-mass spectrometry determination and analysis method for the residue of trace toxic and harmful substances tetraethyl pyrophosphate in polyphosphate flame retardants is established by a simple method.

[0031] 2. The method of the present invention has a low detection limit, good accuracy, and strong specificity. It can qualitatively or quantitatively detect trace tetraethyl pyrophosphate in polyphosphate flame retardants, and can be used as an important means for quality control of polyphosphate flame retardant products. At the same time, it provides guarantee for the safety in the actual use process. Description of the Drawings

[0032] Figure 1 a is the chromatogram of the standard product in the example, and b is the partial enlarged view of a.

[0033] Figure 2 b is the working standard curve diagram in the example.

[0034] Figure 3 It is the total ion chromatogram with the concentration of tetraethyl pyrophosphate being 0.1 μg / mL.

[0035] Figure 4 It is the mass spectrum with the concentration of tetraethyl pyrophosphate being 0.1 μg / mL.

[0036] Figure 5 It is the selected ion chromatogram with the concentration of tetraethyl pyrophosphate being 0.1 μg / mL. a is the selected ion chromatogram of the quantitative ion, and b is the selected ion chromatogram of the qualitative ion.

[0037] Figure 6 It is the chromatogram of the sample to be tested in the example, and b is the partially enlarged view of a. Specific Embodiments

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] The present invention discloses a gas chromatography-mass spectrometry method for determining the residual amount of tetraethyl pyrophosphate in polyphosphate flame retardants, which can effectively determine the residual amount of the toxic and harmful synthetic intermediate tetraethyl pyrophosphate (also known as TEPP) in polyphosphate flame retardants. The analysis and detection method is that the sample is dissolved in acetonitrile, dimethyl phthalate (DMF) is used as the internal standard, and an HP-5MS quartz capillary column (30 m × 0.25 mm × 0.25 μm) is used to effectively separate the components to be tested, and rapid determination is carried out under the selected ion monitoring mode (SIM), and quantitative analysis is carried out by the internal standard method.

[0040] In the present invention, the instruments, reagents and materials used include:

[0041] Agilent 8890-5977B gas chromatography-mass spectrometer (equipped with an electron impact ionization source (EI), Agilent Technologies, USA), HP-5MS capillary chromatographic column (30 m × 0.25 mm × 0.25 μm, Agilent Technologies, USA); METTLER ME204 electronic balance (METTLER TOLEDO, Switzerland).

[0042] Acetonitrile (chromatographic grade, Merck, USA); dimethyl phthalate (analytical grade, purity ≥ 99%), Shanghai Macklin Biochemical Technology Co., Ltd.).

[0043] TEPP (tetraethyl pyrophosphate) (1000 mg / L, Tianjin Aladdin Chemistry Co., Ltd.).

[0044] Example 1

[0045] This embodiment provides a gas chromatography-mass spectrometry analysis method for determining the residual amount of tetraethyl pyrophosphate in polyphosphate flame retardants, including:

[0046] (1) Preparation of tetraethyl pyrophosphate standard solution: Accurately pipette 2.5 mL of 1000 mg / L tetraethyl pyrophosphate standard stock solution into a 50 mL volumetric flask, dilute with acetonitrile, and make up to the mark, shake well to prepare a 50 mg / L tetraethyl pyrophosphate standard solution.

[0047] (2) Preparation of internal standard solution: Accurately weigh 0.1 g of dimethyl phthalate (DMP) into a 1000 mL volumetric flask, dilute with acetonitrile, and make up to the mark, shake well to prepare a 100 mg / L internal standard standard stock solution; accurately pipette 5 mL of 100 mg / L internal standard standard stock solution into a 100 mL volumetric flask, dilute with acetonitrile, and make up to the mark, shake well to prepare a 5 mg / L internal standard solution.

[0048] (3) Preparation of standard working solution: Pipette 0.5 mL, 1.0 mL, 2.0 mL, 3.0 mL, 5.0 mL, 8.0 mL, 10 mL of tetraethyl pyrophosphate standard solution and 5 mL of internal standard solution into a 50 mL volumetric flask respectively, dilute with acetonitrile, and make up to the mark, shake well to prepare standard working solutions with tetraethyl pyrophosphate concentrations of 0.5 mg / L, 1 mg / L, 2 mg / L, 3 mg / L, 5 mg / L, 8 mg / L, 10 mg / L and an internal standard concentration of 0.5 mg / L.

[0049] (4) Preparation of sample solution: Weigh 3 g of polyphosphate sample into a 50 mL volumetric flask, accurately pipette 5 mL of internal standard solution with a pipette, dilute to the mark with acetonitrile, and shake well. Filter through a 0.22 μm organic filter membrane to obtain the sample solution to be tested for gas chromatography-mass spectrometry determination. At the same time, perform a blank test (the blank test object here is a blank solution obtained only with internal standard solution and acetonitrile without adding polyphosphate sample).

[0050] (5) Determination: Inject the tetraethyl pyrophosphate standard working solutions into the gas chromatography-mass spectrometer in sequence, draw a standard curve according to the determination results of the standard working solutions, with the peak area ratio (A / Ai) of the quantitative ions of tetraethyl pyrophosphate and internal standard in the standard working solution as the ordinate and the relative concentration (C / Ci) of tetraethyl pyrophosphate and internal standard as the abscissa. Inject the sample solution to be tested into the gas chromatography-mass spectrometer, and obtain the concentration of tetraethyl pyrophosphate in the sample solution to be tested according to the standard curve from the peak area ratio of the quantitative ions of tetraethyl pyrophosphate and internal standard in the sample solution to be tested.

[0051] The gas chromatography-mass spectrometer is determined under the following conditions:

[0052] a) Chromatographic column: HP-5MS quartz capillary column, 30 m × 0.25 mm × 0.25 μm;

[0053] b) Column temperature: Initial temperature 80 °C, heated to 220 °C at a rate of 20 °C / min, held for 2 min, then heated to 280 °C at a rate of 30 °C / min, held for 8 min;

[0054] c) Injection port temperature: 160 °C;

[0055] d) Mass spectrometry interface temperature: 280 °C;

[0056] e) Quadrupole temperature: 150 °C;

[0057] f) Ion source temperature: 280 °C;

[0058] g) Carrier gas: Helium, purity ≥ 99.999%, flow rate 1.2 mL / min;

[0059] h) Ionization mode: Electron impact ionization (EI);

[0060] i) Ionization energy: 70 eV;

[0061] j) Determination mode: Selected ion monitoring mode (SIM), monitored ions are shown in Table 1 below:

[0062] Table 1 Characteristic ions of TEPP and DMP

[0063] Compound Name Abbreviation Molecular Formula Characteristic Ions and Their Abundance Ratios Quantitative Ion Mass-to-Charge Ratio Tetraethyl Pyrophosphate TEPP <![CDATA[C 8 H 20 O 7 P 2 > 161:235:263＝100:41:52 161 Dimethyl Phthalate DMP <![CDATA[C 10 H 10 O 4 > 163:77:135＝100:17:5 163

[0064] k) Injection volume: 1 μL;

[0065] l) Injection mode: Split injection, split ratio at the injection port 20:1;

[0066] m) Solvent delay: 3 min.

[0067] (6) Result calculation and representation

[0068] Qualitative analysis

[0069] Under the same experimental conditions, when performing sample determination, if the retention time of the chromatographic peak of the analyte in the sample differs from that of the standard by within 2.5%, and all ions appear, and the relative abundances of the qualitative ions in the sample spectrum are compared with those of the corresponding qualitative ions in the spectrum of the standard solution with similar concentrations, and the deviation does not exceed the range specified in Table 2, then it can be determined that the analyte exists in the sample.

[0070] Table 2 Maximum allowable deviation of relative ion abundances during qualitative confirmation

[0071] Relative Ion Abundance K K＞50 20＜K＜50 10＜K＜20 K≤10 Maximum Allowable Deviation / % ±20 ±25 ±30 ±50

[0072] Result calculation

[0073] The content X of tetraethyl pyrophosphate, the value is expressed in %, and is calculated according to the following formula:

[0074]

[0075] c - The value of the concentration of the component solution to be measured obtained from the standard working curve, the unit is milligram per liter (mg / L).

[0076] c 0 - The value of the concentration of the blank solution obtained from the standard working curve, the unit is milligram per liter (mg / L).

[0077] V - The value of the volume of the solution made up to a constant volume, the unit is milliliter (mL).

[0078] k - Dilution factor.

[0079] m - The value of the mass of the sample represented by the sample solution to be tested, the unit is gram (g).

[0080] (1) Standard curve

[0081] For a series of standard solutions with tetraethyl pyrophosphate concentrations of 0.5 mg / L to 10 mg / L and an internal standard dimethyl phthalate concentration of 0.5 mg / L, analyze and determine them in order from low to high concentration, Figure 1 The chromatographic peaks in are the dimethyl phthalate in the standard product (retention time 5.499 min) and tetraethyl pyrophosphate (retention time 6.205 min) respectively. Draw a standard curve according to the measurement results of the standard working solution. Take the peak area ratio (A / Ai) of the quantitative ions of tetraethyl pyrophosphate and the internal standard at each concentration in the standard working solution as the ordinate, and the relative concentration (C / Ci) of tetraethyl pyrophosphate and the internal standard as the abscissa. Its linear range, linear regression equation, and correlation coefficient are shown in Table 3. It can be seen from Table 3 that there is a good linear relationship within the linear range, meeting the requirements of quantitative analysis.

[0082] Table 3. Linear range, linear equation, and correlation coefficient of TEPP

[0083]

[0084] (2) Detection limit and lower limit of quantification

[0085] Prepare sample solutions with tetraethyl pyrophosphate concentrations of 0.05 mg / L, 0.1 mg / L, 0.15 mg / L, and 0.2 mg / L using a sample without tetraethyl pyrophosphate as the matrix. Independently detect each level 7 times and record signals such as peak height, noise, and signal-to-noise ratio (signal-to-noise ratio = (peak height - average noise) / (maximum noise - minimum noise)).

[0086] The signal-to-noise ratio of the sample solution with a tetraethyl pyrophosphate concentration of 0.1 μg / mL is 3.2. The corresponding total ion chromatogram is shown in Figure 3 , the mass spectrum and selected ion current Figures 4 - 5 . Figure 4 It shows that there is an obvious peak at a retention time of 6.20 min, Figure 4 and the corresponding ion abundances can be seen. When the TEPP concentration is 0.1 μg / mL, comparing the qualitative ions of 235 (m / z), 263 (m / z) with 161 (m / z), the relative abundances are 40.9% and 50.4% respectively, meeting the requirements of the maximum allowable deviation of relative ion abundances given in Table 12.4 of the Commission Decision of the European Communities authorizing the implementation of Council Directive 96 / 23 / EC on analytical methods and the interpretation of results (2002 / 657 / EC) for the use of mass spectrometry techniques. Therefore, it can be reasonably judged that the detection concentration of this method is 0.1 μg / mL. The sample weight in the method is 3 g. Converting it to the content in the sample, the detection limit of this method is calculated to be 0.0002%.

[0087] Take 3 times the detection limit as the lower limit of quantification. Through calculation, the lower limit of quantification of this method is 0.0006%.

[0088] (3) Precision and accuracy

[0089] Take samples of four concentrations, including low, medium, and high concentrations within the determination range, and calculate the average value and relative standard deviation. The typical chromatogram of sample determination is shown in Figure 6 , Figure 6 The determination results in it show that tetraethyl pyrophosphate and dimethyl phthalate (internal standard) determined by this method are completely separated from other impurities in the sample and have good peak shapes. The precision test results of samples with different concentrations are shown in Table 4. It can be seen from Table 4 that the RSD values for samples with different tetraethyl pyrophosphate concentrations are 2.5 - 3.6% (n = 6), meeting the requirements for precision in the verification of general analytical methods and being able to meet the actual determination requirements for the content of tetraethyl pyrophosphate in polyphosphate flame retardant samples.

[0090] Table 4 Accuracy of the determination of tetraethyl pyrophosphate in the sample

[0091]

[0092] The accuracy of the verification method was verified by adding a known amount of the target analyte to the sample. Low-concentration samples were weighed, and different spiking levels of high, medium, and low were set. For each concentration, 6 parallel independent tests were conducted. The samples were extracted according to this method, and the samples were detected in turn under the same chromatographic conditions. The spike recoveries at high, medium, and low concentrations were calculated respectively. The experimental data are shown in Table 5. The average spike recoveries at different spiking levels were between 97.4% and 115.5%, all meeting the analysis requirements.

[0093] Table 5 Accuracy of tetraethyl pyrophosphate detection in samples

[0094]

[0095] The present invention provides a gas chromatography-mass spectrometry method for determining the residual amount of tetraethyl pyrophosphate, a toxic and harmful intermediate in polyphosphate flame retardants. It is applicable to the detection of trace tetraethyl pyrophosphate in the organophosphorus system, effectively excluding the interference of high background on the detection and further improving the detection sensitivity. The method of the present invention has a low detection limit, good accuracy, and strong specificity, and can qualitatively or quantitatively detect trace tetraethyl pyrophosphate in polyphosphate flame retardants, ensuring the product quality of polyphosphate flame retardants and improving the safety during actual use.

[0096] Although the present invention has been described herein with reference to several illustrative embodiments of the invention, it should be understood that those skilled in the art can design many other modifications and embodiments that will fall within the scope of the disclosure of this application. More specifically, within the scope of the disclosure of this application, the drawings, and the claims, various deformations and improvements can be made to the components or the layout. In addition to the deformations and improvements to the components or the layout, other uses will also be obvious to those skilled in the art.

Claims

1. A gas chromatography-mass spectrometry method for determining the residual amount of tetraethyl pyrophosphate in a polyphosphate flame retardant, characterized in that The steps include: S1. Prepare tetraethyl pyrophosphate standard working solution and internal standard solution; S2. Preparation of sample solution: Weigh the polyphosphate flame retardant sample into a volumetric flask, add a certain internal standard solution, shake it to volume with acetonitrile, and filter to obtain a test sample solution; S3. Inject the tetraethyl pyrophosphate standard working solution into the gas chromatography-mass spectrometer, draw a standard curve according to the measurement results of the standard working solution, with the peak area ratio of the quantitative ion of tetraethyl pyrophosphate at each concentration in the standard working solution to the internal standard solution as the ordinate, and the relative concentration of tetraethyl pyrophosphate to the internal standard as the abscissa, inject the test sample solution into the gas chromatography-mass spectrometer, and obtain the concentration of tetraethyl pyrophosphate in the test sample solution according to the peak area ratio of the quantitative ion of the internal standard solution in the test sample solution according to the standard curve.

2. The method according to claim 1, characterized in that: The concentrations of tetraethyl pyrophosphate in the tetraethyl pyrophosphate standard working solution are 0.5 mg / L, 1 mg / L, 2 mg / L, 3 mg / L, 5 mg / L, 8 mg / L, and 10 mg / L, respectively.

3. The method according to claim 2, characterized in that: The standard working solution preparation method is to respectively transfer 0.5mL, 1.0mL, 2.0mL, 3.0mL, 5.0mL, 8.0mL, and 10mL of 50mg / L tetraethyl pyrophosphate standard solution and 5mL of 5mg / L internal standard standard solution into a 50mL volumetric flask, dilute to the scale with acetonitrile, and shake well.

4. The method according to claim 1, characterized in that: The concentration of the internal standard solution is 0.5 mg / L, and the internal standard substance is dimethyl phthalate.

5. The method according to claim 1, characterized in that: The sample solution is prepared by weighing 3 g of a polyphosphate flame retardant sample into a 50 mL volumetric flask, adding 5 mL of an internal standard solution with a concentration of 5 mg / L, diluting the solution to the mark with acetonitrile, and shaking the solution well.

6. The method according to claim 1, characterized in that: The filtration is carried out using a 0.22 μm organic filter membrane.

7. The method according to claim 1, characterized in that: The measurement conditions of the gas chromatography-mass spectrometer are as follows: a) Chromatographic column: HP-5MS quartz capillary column, 30m×0.25mm×0.25μm; b) Column temperature: initial temperature 80°C, increase the temperature to 220°C at a rate of 20°C / min, maintain for 2 min, then increase the temperature to 280°C at a rate of 30°C / min, maintain for 8 min; c) Inlet temperature: 160°C; d) Mass spectrometer interface temperature: 280°C; e) Quadrupole temperature: 150°C; f) Ion source temperature: 280°C; g) Carrier gas: helium, purity ≥ 99.999%, flow rate 1.2 mL / min; h) Ionization method: electron impact ionization (EI); i) Ionization energy: 70 eV; j) Determination method: selected ion monitoring mode (SIM); k) Injection volume: 1 μL; l) Injection mode: split injection, injection port split ratio 20:1; m) Solvent delay: 3 min.

8. The method according to claim 7, characterized in that: In the ion monitoring mode, the characteristic ion of tetraethyl pyrophosphate and its abundance ratio are 161:235:263=100:41:52, and the quantitative ion mass-to-charge ratio is 161; the characteristic ion of dimethyl phthalate and its abundance ratio are 163:77:135=100:17:5, and the quantitative ion mass-to-charge ratio is 163.

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