A method for detecting solvent components in ink

Abstract

The present invention provides a method for detecting solvent components in ink, and belongs to the technical field of document material inspection. The method of the present invention comprises the following steps: S1. preparing a mixed standard solution: preparing mixed standard solutions of different concentrations with standard products of internal standard substances and target compounds; S2. preparing a sample solution: sampling the sample to be tested using a sampler, immersing the sample obtained in an extractant containing an internal standard substance, centrifuging after extraction, and taking the supernatant as the sample solution; S3. performing qualitative or quantitative detection by gas chromatography. The detection method of the present invention greatly shortens the detection time by reasonably selecting an internal standard substance, preparing a sample solution, and setting appropriate gas chromatography analysis conditions; the method of the present invention only uses gas chromatography for detection and analysis, and does not need to be combined with a mass spectrometer for detection, thereby achieving a high-sensitivity, high-accuracy, and high-precision detection effect while reducing operating costs and reducing instrument use.

Description

Technical Field

[0001] The invention relates to the technical field of document material inspection, in particular to a method for detecting solvent components in ink. Background Art

[0002] The analysis and identification of ink in handwriting has always been a hot topic in document inspection, including the identification of ink types and the identification of writing time. The authenticity of signatures on contracts, promissory notes and other documentary evidence, whether the content has been added or modified, and the time of writing all involve the analysis and identification of ink components. Studying the types of volatile solvents in ink and the law of their residual amount changing over time is an important means of identifying the writing time of ink.

[0003] The common solvent components in ballpoint pen inks include benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether. The common solvent components in neutral and water-based pen inks include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, etc.

[0004] In recent years, the qualitative and quantitative analysis methods of polyols reported in the literature mainly use gas chromatography and gas chromatography-mass spectrometry. Because polyols are widely used as humectants, the tobacco chemical industry has established qualitative and quantitative analysis methods for some polyols (such as literature [1] Duan Yuanxing, Wu Yiqin, Yang Wei, et al. Simultaneous determination of five alcohol compounds in electronic cigarette smoke emissions by GC / MS [J]. Tobacco Science and Technology. 2015, 48(10): 43-47; literature [2] Zhang Jie, Li Peng, Sun Shihao, et al. Simultaneous detection of 1,2-propylene glycol, glycerol and triethylene glycol in smokeless tobacco products by GC / MS [J]. Tobacco Science and Technology. 2011(03): 36-42; Chinese patent application CN111272938A). Although some alcohol solvents are also present in ink, due to different application ranges, common solvent components in ink such as ethylene glycol, 1,3-propylene glycol, benzyl alcohol, 2-phenoxyethanol, diethylene glycol ethyl ether, etc., have no research data in the polyol detection method of the tobacco chemical industry, and these components may not be completely separated using existing methods. In addition, due to the huge differences in sample types, sample pretreatment and internal standard selection are also very different, so the polyol detection method of the tobacco chemical industry cannot be directly applied to the analysis of solvent components in ink.

[0005] In the field of document inspection research, there are many literatures on qualitative determination of polyol types, but few on quantitative determination of their contents. Moreover, quantitative determination is mostly characterized by the relative content of the sample itself, and its results are not convenient for peer researchers to conduct horizontal comparison and verification. For example, Guo Dongdong et al. (Guo Dongdong, Lv Yinni, Zhang Haipeng. GC analysis of solvent components in black water-based pen and neutral pen ink [J]. Fujian Analysis and Testing. 2015, 24(04): 48-52.), Niu Fan et al. (Niu Fan, Huang Jiantong, He Sen, et al. Analysis and classification of blue ballpoint pen ink by gas chromatography-mass spectrometry and thin layer chromatography [J]. Physical and Chemical Testing (Chemical Section). 2017, 53(01): 22-27.), and the Technical Specification for Forensic Identification SF / Z JD0203004-2018 reported that the composition of solvents in signature pen ink was analyzed by gas chromatography, gas chromatography-mass spectrometry and other methods, but no quantitative research was conducted. Li et al. (LiB, Xie P, Guo Y, et al. GC Analysis of Black Gel Pen Ink Stored under Different Conditions[J]. Journal of Forensic Sciences. 2014, 59(2): 543-549.), Ni et al. (Ni Y, HeN, LüY, et al. Study of ink aging: Targeting triethylene glycol in carbon-based black gel ink strokes on paper[J]. Forensic Science International. 2020, 311: 110296.) reported that the writing time could be judged by the residual amount of ink solvent in the handwriting of a signature pen. They studied the relationship between the residual amount of ethylene glycol, diethylene glycol, propylene glycol, 1,2-propylene glycol, and triethylene glycol in the handwriting and the writing time, but only determined the ratio of each solvent component to the internal standard, and other researchers were unable to know the absolute content. However, the initial content of solvent components in different pens varies greatly, and the relative content reflects less effective information. Determining its absolute content is of great reference value for interpreting the identification results of the ink writing time.

[0006] Only a few literatures have conducted absolute quantitative analysis on the content of solvents in ink, but they all have certain defects: (1) There are limitations in the determination of different types of handwriting, such as Koenig et al. (Koenig A, Magnolon S, Weyermann C. A comparative study of ballpoint ink ageing parameters using GC / MS [J]. Forensic Science International. 2015, 252: 93-106.), Li Shuangping et al. (Li Shuangping, Yang Xu, Sun Qiran. Quantitative analysis of benzyl alcohol and phenoxyethanol in ballpoint pen ink by GC / MS [J]. China Judicial Appraisal. 2020 (03): 41-45.) conducted quantitative determination of the solvent components of ballpoint pen ink, but their methods can only be applied to the determination of solvent components in ballpoint pen ink and cannot be used for other types of pens; (2) The solvent components analyzed are The types are not comprehensive enough. For example, Guo Dongdong et al. (Guo Dongdong, Lv Yinni, Zhang Haipeng. Analysis of the formation time of black ink by solvent extraction-working curve method [J]. Journal of China Criminal Police College. 2015(02):76-78.) analyzed the solvent content of ethylene glycol and propylene glycol in neutral pen and water-based pen inks with different formation times, but did not analyze other common solvent components such as diethylene glycol, triethylene glycol, and 2-phenoxyethanol; (3) The analysis and detection takes a long time, usually about 30 minutes.

[0007] Therefore, it is necessary to provide a method for detecting solvent components in ink, which has high accuracy, high precision, and short time consumption, and can detect multiple solvent components at the same time. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects in the prior art and provide a method for detecting solvent components in ink. A gas chromatograph equipped with a FID detector is used to detect multiple inks. The method has high sensitivity, high accuracy, high precision, and short time consumption, and can detect multiple solvent components at the same time.

[0009] To achieve the above object, the present invention adopts the following technical solution:

[0010] A method for detecting solvent components in ink, comprising the following steps:

[0011] S1. Prepare mixed standard solution:

[0012] Mixed standard solutions of different concentrations were prepared using internal standards and standards of target compounds;

[0013] The internal standard is 1,3-butanediol or 1,4-butanediol; the target compound is ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol and diethylene glycol ethyl ether;

[0014] S2. Prepare sample solution:

[0015] Use a sampler to sample the sample to be tested, immerse the sample in an extractant containing an internal standard, centrifuge after extraction, and take the supernatant as the sample solution;

[0016] S3. Gas chromatography analysis:

[0017] The mixed standard solution and the sample solution are subjected to gas chromatography analysis, and the solvent components in the ink are qualitatively or quantitatively detected by gas chromatography.

[0018] In the detection method of the present invention, in order to eliminate the errors caused by the injection volume and instrument instability, an internal standard method is used in conjunction with gas chromatography analysis to perform qualitative or quantitative analysis and detection on samples written with ink.

[0019] The present invention uses 1,3-butanediol or 1,4-butanediol as an internal standard and adopts the internal standard method for quantitative analysis. Both 1,3-butanediol and 1,4-butanediol are not commonly used as ink solvents, and as internal standards, they can be completely separated from the target compound to be detected. In addition, the internal standard used in the present invention has similar physical and chemical properties to the target compound, and in the gas chromatography method of the present invention, the chromatographic peak position of the internal standard is close to the position of the chromatographic peak of the target compound, thereby achieving good qualitative and quantitative detection of the solvent components in the ink.

[0020] The internal standards commonly used in the prior art for measuring polyols include 1,3-butylene glycol, 1,4-butylene glycol, ethyl benzoate, etc. The inventors have found that the chemical structure of ethyl benzoate is quite different from that of most target substances such as ethylene glycol, glycerol, triethylene glycol, etc. in the present invention, and the response of ethyl benzoate of the same mass concentration on the FID detector is several times higher than that of other target substances. In addition, ethyl benzoate is extremely volatile and easily causes cross contamination of other reagents. Therefore, ethyl benzoate is difficult to use as an internal standard in the detection method of the present invention.

[0021] Preferably, the internal standard is 1,3-butanediol.

[0022] Under the gas chromatography analysis conditions of the present invention, the elution time of 1,4-butanediol is between diethylene glycol ethyl ether and diethylene glycol, and the chromatogram of the mixed standard is slightly crowded in the middle; while the elution time of 1,3-butanediol is appropriate, the ten compounds are evenly distributed on the chromatogram, and the separation degree of each compound is relatively maximum. Therefore, using 1,3-butanediol as the internal standard can achieve better detection results.

[0023] By using the detection method of the present invention, the internal standard is reasonably selected, the sample solution is prepared, and suitable gas chromatography analysis conditions are set, the detection time of a single sample is only about 12 minutes, of which the signal acquisition time is only about 8.8 minutes, which greatly shortens the detection time and greatly improves the detection efficiency. In addition, compared with the conventional gas chromatography-mass spectrometry method, the method of the present invention only uses a gas chromatograph for detection and analysis, without the need for mass spectrometer detection, and achieves a high-accuracy and high-precision detection effect while reducing operating costs and reducing the use of instruments.

[0024] Preferably, step S1 includes the following steps:

[0025] The internal standard substance is mixed with the extractant to obtain an internal standard working solution; the standard substance of the target compound is weighed, added to the internal standard working solution, and diluted to obtain mixed standard solutions of different concentrations.

[0026] More preferably, step S1 includes the following steps:

[0027] Weigh the internal standard standard, prepare an internal standard stock solution with a concentration of 10 mg / mL using the extractant, and then dilute it to a fixed volume with the extractant to obtain an internal standard working solution with a concentration of 50 μg / mL;

[0028] Weigh the standard of each target compound separately, prepare a 10 mg / mL mixed standard solution with the internal standard working solution, and then dilute it with the internal standard working solution to prepare 7 levels of 1, 5, 10, 50, 100, 200, and 300 μg / mL mixed standard solutions of 9 target compounds containing 50 μg / mL internal standard.

[0029] Optionally, the extractant is at least one of methanol, acetonitrile, ethanol, chloroform, and N,N-dimethylformamide.

[0030] Preferably, the extractant is methanol.

[0031] In the present invention, the use of a sampler to sample the sample to be tested refers to: using a puncher to punch holes in the sample to be tested that is written with ink to take samples.

[0032] Preferably, the hole punched by the punch has a diameter of 0.1 to 1 mm.

[0033] More preferably, the punching diameter of the punch is 0.5 mm.

[0034] The sample to be tested is punched with a puncher to obtain a disc of a certain diameter as the sample, and then subsequent extraction is performed.

[0035] Optionally, the extraction method may be at least one of static, mechanical oscillation, and ultrasound.

[0036] Through extraction, the solvent contained in the ink of the sample to be tested is gradually dissolved into the extractant containing the internal standard, and then centrifuged to take the supernatant to obtain a sample solution in which the target compound is extracted.

[0037] Preferably, in step S2, the extraction is performed by standing at 10-50° C. for 5-60 min.

[0038] More preferably, in step S2, the extraction is performed by standing at 25°C for 40 minutes.

[0039] Using methanol as the extraction agent, the inventors studied the extraction temperature and time and found that the extraction rate of most solvent components was the highest when the sample was left to stand for extraction at 25°C for 40 minutes.

[0040] Preferably, in step S3, the gas chromatography analysis conditions are:

[0041] Chromatographic column: DB-ALC2 chromatographic column, specification is 30m×0.32mm×1.2μm;

[0042] Carrier gas: nitrogen, purity 99.999%;

[0043] Column flow rate: constant flow mode 1~3mL / min;

[0044] Inlet temperature 230-290°C, splitless injection, purge time 0.3-1.0 min, purge flow 30-70 mL / min;

[0045] Column temperature program:

[0046] Initial temperature 40-85℃, maintain for 0.5-5min, heat up to 110-135℃ at 15-130℃ / min, maintain for 2-4min, heat up to 150-190℃ at 15-130℃ / min, maintain for 1-4min, heat up to 220-260℃ at 15-130℃ / min, maintain for 2-15min, post-operation: maintain at 220-260℃ for 2-15min;

[0047] Or: the initial temperature is 40-85°C and maintained for 0.5-5 min, then the temperature is increased to 110-135°C at a rate of 15-130°C / min and maintained for 2-4 min, then the temperature is increased to 220-260°C at a rate of 15-130°C / min and maintained for 4-15 min;

[0048] Detector temperature: 250~300℃.

[0049] The chromatographic column selected in the present invention is a DB-ALC2 chromatographic column, the specification of which is 30m×0.32mm×1.2μm.

[0050] The selection of the chromatographic column should achieve the effect of high separation degree and high column efficiency of the target object. The inventors found through a large number of creative experimental studies that the DB-ALC2 chromatographic column produced by Agilent J&W can completely separate 9 target compounds and internal standards under the gas chromatography analysis conditions of the present invention, with high column efficiency, sharp and symmetrical peaks, and the entire gas phase circulation time including the post-operation is only 12 minutes.

[0051] Other conventional chromatographic columns for alcohol analysis have defects to varying degrees. For example, the HP-5ms (30m×0.25mm×0.25μm) chromatographic column is used to analyze solvent components such as benzyl alcohol, phenoxyethanol, and diethylene glycol ether in inks with high viscosity such as ballpoint pens and medium oil pens, and achieves good results. However, the inventors have found through experiments that the chromatographic column will cause serious tailing when used to analyze strong polar solvent components such as ethylene glycol, 1,2-propylene glycol, and 1,3-propylene glycol in inks with low viscosity such as neutral pens and water-based pens. Glycerol has no peak shape at all on the chromatographic column; when gas chromatography analysis was performed on a strong polar column with polyethylene glycol (PEG) as the stationary phase (DB-FFAP column (30m×0.25mm×0.25μm), HP-INNOWax (30m×0.32mm×0.25μm), etc.) at a heating rate of 10℃ / min, the maximum separation degree between glycerol and triethylene glycol was only 1.17. Due to the low separation degree (gas chromatograph analysis requires the separation degree between compounds to reach 1.5 or above for accurate quantification), accurate quantification could not be achieved.

[0052] As for the injection method, the present invention adopts non-divided flow injection. Since the solvent component in the writing ink is a trace component, especially when doing the identification research of the writing time, the higher the detection sensitivity, the more accurate the judgment of the inflection point. The inventors have found that split injection will reduce the detection sensitivity to a certain extent, so the non-divided flow injection method is adopted to achieve improved sensitivity and reduce the detection limit and quantitative limit.

[0053] Optionally, the column temperature rising program is:

[0054] The initial temperature is 40-65℃, maintained for 0.5-3min, then heated to 110-135℃ at 40-130℃ / min, maintained for 2-4min, then heated to 150-190℃ at 40-130℃ / min, maintained for 1-4min, then heated to 220-260℃ at 40-130℃ / min, maintained for 2-15min, then maintained at 240-260℃ for 2-5min;

[0055] Alternatively: the initial temperature is 40-65°C, maintained for 0.5-3 min, then heated to 110-135°C at a rate of 40-130°C / min and maintained for 2-4 min, then heated to 220-260°C at a rate of 30-60°C / min and maintained for 4-15 min.

[0056] Optionally, the column temperature rising program is:

[0057] The initial temperature is 45-55℃, maintained for 0.5-1.5min, then heated to 120-130℃ at 80-120℃ / min, maintained for 2-3min, then heated to 160-180℃ at 80-120℃ / min, maintained for 1-2min, then heated to 220-240℃ at 80-130℃ / min, maintained for 2-4min, then maintained at 240-250℃ for 2-3min;

[0058] Alternatively: the initial temperature is 45-55°C, maintained for 0.5-1.5 min, then heated to 120-130°C at a rate of 80-120°C / min and maintained for 2-4 min, then heated to 230-250°C at a rate of 35-45°C / min and maintained for 4-10 min.

[0059] More preferably, in step S3, the gas chromatography analysis conditions are:

[0060] Column flow rate: constant flow mode 2mL / min;

[0061] The injection port temperature was 240 °C, splitless injection, injection volume was 1 μL, purge time was 0.5 min, and purge flow rate was 60 mL / min;

[0062] Column temperature program: initial temperature 50 °C for 1 min, heating to 125 °C at 100 °C / min for 2 min, heating to 170 °C at 100 °C / min for 1 min, heating to 230 °C at 100 °C / min for 3 min, post-run: heating to 240 °C at 100 °C / min for 3 min;

[0063] Detector temperature: 290°C.

[0064] The inventors have found that, unlike the traditional temperature rise program that directly connects the first and last isothermal holding stages at a slower uniform temperature rise rate of 5 to 15°C / min, the above-mentioned column temperature rise program innovatively adds two isothermal holding stages of 125°C and 170°C between the first and last isothermal holding stages of 50°C and 230°C, and the isothermal stages are connected at a high temperature rise rate of 100°C / min. This innovation greatly speeds up the analysis speed while ensuring the separation degree, and has a better detection effect.

[0065] In addition, in the case of non-split injection, the solvent effect will cause the peaks of early eluting compounds such as ethylene glycol, 1,2-propylene glycol, and 1,3-propylene glycol to become wider and the column efficiency to decrease. The inventors found that when the initial column temperature is 50°C, the peak width, symmetry factor, separation, column efficiency, analysis speed and other parameters of the chromatographic peak are relatively optimal when comprehensively considered.

[0066] Preferably, in the gas chromatography analysis, the gas chromatograph is a 7890B gas chromatograph (Agilent Technologies, USA) equipped with a flame ionization detector (FID); and data acquisition and processing are performed using an OpenLAB CDS ChemStation workstation.

[0067] Preferably, in step S3, the qualitative detection method is: using the retention time of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample solution as a qualitative basis to determine the presence of the target compound in the sample to be tested.

[0068] In this method, the retention time of the target compound is compared with the retention time of the standard for qualitative analysis. If the relative error between the two is within ±2%, it is determined that the sample to be tested contains the target sample. The standard can also be added to the sample extract and then subjected to chromatographic analysis. The increase in the integrated area of ​​each peak can be used to determine whether the target compound is present.

[0069] Preferably, in step S3, the quantitative detection method is: according to the peak area ratio of each target substance such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, diethylene glycol ethyl ether in the sample solution to the internal standard, the content of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample to be tested is calculated according to their respective standard working curves.

[0070] The internal standard method was used for quantitative analysis. After the working curve was established, the ChemStation workstation integrated and calculated the mass concentration of the target compound in the sample solution. i The content of the target compound in the sample to be tested C i It is expressed as the mass of the target compound contained in the handwriting per unit length, and the calculation method is as shown in formula (1):

[0071]

[0072] Where C i is the content of the target compound in the sample to be tested, in ng / cm;

[0073] ρ iTo measure the mass concentration of the target compound in the sample solution, the unit is μg / mL;

[0074] ρ 0 To measure the mass concentration of the target compound in the blank paper sample extract, the unit is μg / mL;

[0075] v is the volume of the sample solution, in μL;

[0076] l is the length of the handwriting obtained by punching, in cm.

[0077] The same sample is injected twice, and the average value of the result is calculated. The result is valid when the relative standard deviation is within the acceptable range according to the concentration range of the result. When the result is lower than the detection limit, it is reported as not detected (-); when the result is higher than the detection limit and lower than the quantification limit, it is reported as not detected (NQ); when the result is higher than the quantification limit, the result value is reported.

[0078] Compared with the prior art, the present invention has the following beneficial effects:

[0079] The present invention has developed a method for detecting solvent components in ink. Through the detection method of the present invention, the internal standard is reasonably selected, the sample solution is prepared, and the appropriate gas chromatography analysis conditions are set. The detection time of a single sample is only about 12 minutes, of which the signal acquisition time is only about 8.8 minutes, which greatly shortens the detection time and greatly improves the detection efficiency. In addition, compared with the conventional gas chromatography-mass spectrometry method, the method of the present invention only uses gas chromatography for detection and analysis, and does not need to be combined with a mass spectrometer for detection. While reducing operating costs and reducing the use of instruments, it achieves a high-sensitivity, high-accuracy, and high-precision detection effect, and can simultaneously perform qualitative and quantitative analysis of 9 kinds of ink solvent components in a single detection process. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 Schematic diagram of the sampling method of Example 1;

[0081] Figure 2 This is the gas chromatogram of the HP-5ms (30m×0.25mm×0.25μm) chromatographic column used in Example 3;

[0082] Figure 3 This is the gas chromatogram of the DB-FFAP column (30m×0.25mm×0.25μm) used in Example 3;

[0083] Figure 4 This is the gas chromatogram of the HP-INNOWax (30m×0.32mm×0.25μm) chromatographic column used in Example 3;

[0084] Figure 5 This is the gas chromatogram of the DB-ALC2 (30m×0.32mm×1.2μm) chromatographic column used in Example 3;

[0085] Figure 6 The gas chromatograms of 1,2-propylene glycol at different initial temperatures (50°C, 60°C, 80°C) in Example 4;

[0086] Figure 7 The gas chromatogram of the sample N3 in Example 6;

[0087] Figure 8 This is a gas chromatogram of separating nine target compounds using 1,4-butanediol as an internal standard in Example 7;

[0088] Fig. 9 This is a gas chromatogram of separating nine target compounds using a three-step isothermal temperature program in Example 8.

[0089] exist Figure 2 to Figure 5 , Figure 7 to Figure 9 In the figure, the corresponding relationship between the chromatographic peak numbers and the compounds is as follows: 1, ethylene glycol, 2, 1,2-propylene glycol, 3, 1,3-propylene glycol, 4, 1,3-butylene glycol (internal standard), 5, diethylene glycol ethyl ether, 6, diethylene glycol, 7, benzyl alcohol, 8, glycerol, 9, phenoxyethanol, 10, triethylene glycol, 11, 1,4-butylene glycol (internal standard). DETAILED DESCRIPTION

[0090] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings, but the embodiments do not limit the present invention in any form.

[0091] The selection of the instruments and reagents of the present invention is as follows:

[0092] Gas chromatograph: 7890B gas chromatograph (Agilent, USA), equipped with flame ionization detector (FID); data acquisition and processing were completed using OpenLAB CDS ChemStation workstation;

[0093] Chromatographic column: DB-ALC2 chromatographic column (30m×0.32mm×1.2μm);

[0094] Analytical balance: sensitivity 0.0001g;

[0095] Solvent: methanol (HPLC grade);

[0096] Internal standard: 1,3-butanediol (GC standard);

[0097] Target compound standards: ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, diethylene glycol ethyl ether (GC standard)

[0098] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the present invention are commercially available.

[0099] Example 1

[0100] This embodiment provides a method for detecting solvent components in ink, comprising the following steps:

[0101] S1. Prepare mixed standard solution:

[0102] Use an analytical balance to accurately weigh the 1,3-butanediol standard, use methanol to prepare an internal standard stock solution with a concentration of 10 mg / mL, and then dilute it to a fixed volume with methanol to obtain an internal standard working solution with a 1,3-butanediol concentration of 50 μg / mL;

[0103] Use an analytical balance to accurately weigh the standard samples of the target compounds, prepare a 10 mg / mL mixed standard solution with the internal standard working solution, and then dilute with the internal standard working solution to prepare 7 levels of 1, 5, 10, 50, 100, 200, and 300 μg / mL mixed standard solutions of the target compounds containing 50 μg / mL internal standard.

[0104] S2. Prepare sample solution:

[0105] Use a 0.5 mm punch to punch 40 discs on the ink-written sample to be tested, such as Figure 1 As shown, a handwriting sample with a total length of 2 cm was taken and placed in a 0.2 mL centrifuge tube. 20 μL of internal standard working solution was added to immerse and mix. The centrifuge tube was placed in a 25°C water bath for 40 min and the supernatant was taken as the sample solution after centrifugation.

[0106] S3. Gas chromatography analysis:

[0107] Performing gas chromatography analysis on the mixed standard solution and the sample solution to perform qualitative and quantitative detection;

[0108] The gas chromatography analysis conditions are:

[0109] Chromatographic column: DB-ALC2 chromatographic column, specification is 30m×0.32mm×1.2μm;

[0110] Carrier gas: nitrogen, purity 99.999%;

[0111] Column flow rate: constant flow mode 2mL / min;

[0112] The injection port temperature was 240 °C, splitless injection, injection volume was 1 μL, purge time was 0.5 min, and purge flow rate was 60 mL / min;

[0113] Column temperature program: initial temperature 50 °C for 1 min, heating to 125 °C at 100 °C / min for 2 min, heating to 170 °C at 100 °C / min for 1 min, heating to 230 °C at 100 °C / min for 3 min, and then heating to 240 °C at 100 °C / min for 3 min.

[0114] Detector temperature: 290°C.

[0115] In step S3, the qualitative detection method is: using the retention time of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample solution as a qualitative basis to determine the presence of the target compound in the sample to be tested.

[0116] In this method, the retention time of the target compound is compared with the retention time of the standard for qualitative analysis. If the relative error between the two is within ±2%, it is determined that the sample to be tested contains the target sample. The standard can also be added to the sample extract and then subjected to chromatographic analysis. The increase in the integrated area of ​​each peak can be used to determine whether the target compound is present.

[0117] In step S3, the quantitative detection method is: according to the peak area ratio of each target substance such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample solution to the internal standard, the content of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample to be tested is calculated according to their respective standard working curves.

[0118] The internal standard method was used for quantitative analysis. After the working curve was established, the ChemStation workstation integrated and calculated the mass concentration of the target compound in the sample solution. i The content of the target compound in the sample to be tested C i It is expressed as the mass of the target compound contained in the handwriting per unit length, and the calculation method is as shown in formula (1):

[0119]

[0120] Where C i is the content of the target compound in the sample to be tested, in ng / cm;

[0121] ρ iTo measure the mass concentration of the target compound in the sample solution, the unit is μg / mL;

[0122] ρ 0 To measure the mass concentration of the target compound in the blank paper sample extract, the unit is μg / mL;

[0123] v is the volume of the sample solution, in μL;

[0124] l is the length of the cut handwriting, in cm, and in this embodiment, l=2.

[0125] The same sample is injected twice, and the average value of the calculated results is taken. The results are valid when the relative standard deviation is within the acceptable range according to the concentration range of the results. When the result is lower than the detection limit, report not detected (-); when the result is higher than the detection limit and lower than the quantification limit, report not detected (NQ); when the result is higher than the quantification limit, report the result value. The relationship between the content of the components to be tested in the sample and the acceptable range of precision can be found in the Pharmacopoeia of the People's Republic of China (2020 Edition), Part IV: 9101 Guiding Principles for Validation of Analytical Methods.

[0126] Example 2

[0127] In order to study the influence of extraction conditions on the extraction effect, this example uses methanol as the extractant and uses the uniform design method to conduct an experimental design of two factors and seven levels consisting of extraction temperature (10, 20, 25, 30, 35, 40, 50°C) and extraction time (5, 10, 15, 20, 25, 30, 40 min). The uniform design table, combined with its usage table, constitutes seven experimental schemes, see Table 1.

[0128] Table 1 Uniform design scheme for extraction temperature and time factors

[0129] Experimental protocol number Temperature / (℃) Time / (min) 1 10 25 2 20 10 3 25 40 4 30 20 5 35 5 6 40 30 7 50 15

[0130] Samples prepared by the same signing pen at the same time were extracted according to the conditions in Table 1. Except for the change in the extraction method in step S2, the other steps and conditions of the seven experimental schemes were the same as those in Example 1.

[0131] Two parallel samples were prepared for each experimental scheme, and each sample was measured twice, and the results were averaged. The experimental results are shown in Table 2. From the data in the table, it can be seen that the extraction rate of most components was the highest when the sample was extracted using experimental scheme No. 3 (25°C, 40min), so the optimal conditions for extracting the sample were determined to be: using methanol as the extraction agent and standing in a 25°C water bath for 40min.

[0132] Table 2 Effect of different extraction temperatures and times on the extraction amount of solvent components in samples

[0133]

[0134] Example 3

[0135] In order to study the influence of the chromatographic column on the gas chromatography analysis effect, this embodiment uses HP-5ms (30m×0.25mm×0.25μm) chromatographic column, DB-FFAP column (30m×0.25mm×0.25μm), HP-INNOWax (30m×0.32mm×0.25μm), DB-ALC2 chromatographic column (30m×0.32mm×1.2μm) to perform gas chromatography analysis on the sample solution; a mixed standard solution of 9 target substances and internal standards is used as the test sample. Except for the gas chromatography analysis conditions of step S3, other steps and conditions are the same as those of Example 1. The test results are shown in Figure 2 to Figure 5 The comparison of each target compound with the chromatographic peak is as follows: 1. ethylene glycol, 2. 1,2-propylene glycol, 3. 1,3-propylene glycol, 4. 1,3-butylene glycol (internal standard), 5. diethylene glycol ethyl ether, 6. diethylene glycol, 7. benzyl alcohol, 8. glycerol, 9. phenoxyethanol, 10. triethylene glycol.

[0136] The GC test results using the HP-5ms (30m×0.25mm×0.25μm) column are as follows Figure 2 As shown in the figure, it can be seen that the strong polar solvent components ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, etc. in the inks with low viscosity such as neutral pens and water-based pens will have serious tailing, and glycerol, which is widely present in various inks, does not form a peak shape at all on this chromatographic column. The GC detection results using the DB-FFAP column (30m×0.25mm×0.25μm) are shown in the figure. Figure 3 The GC detection results using the HP-INNOWax (30m×0.32mm×0.25μm) column are shown in Figure 4 As shown in the figure, it can be seen that the separation degree of glycerol and triethylene glycol of these two chromatographic columns is very poor. The HP-INNOWax with slightly better separation effect only reaches 1.17. The gas chromatograph analysis requires the separation degree between the target compounds to reach 1.5 or more for accurate quantification. In addition, glycerol and triethylene glycol are often contained in the ink of the signature pen. Therefore, the above-mentioned polyethylene glycol chromatographic columns are not suitable for quantitative analysis of the solvent components in the writing ink by gas chromatography. The GC detection results using the DB-ALC2 chromatographic column (30m×0.32mm×1.2μm) are shown in Figure 5 As shown. Under the gas chromatography analysis conditions of the present invention, the DB-ALC2 chromatographic column can completely separate the 9 target compounds from the internal standard, with high column efficiency, sharp and symmetrical peaks, and the entire gas phase cycle time including the post-run is only 12 minutes. Figure 5 and Figure 3 , Figure 4 It can be seen from the comparison that for the DB-ALC2 chromatographic column used in this method, all target compounds have completed peak emission within 7.5 min, while at this time, the chromatographic column used in the traditional method has not yet started to emit peaks.

[0137] The retention times of the 9 target compounds and internal standards separated by DB-ALC2 column are shown in Table 3.

[0138] Table 3 Retention times of 9 target compounds and internal standards on DB-ALC2 column

[0139] Chromatographic peak number Target compound Retention time / (min) 1 Ethylene glycol 3.909 2 1,2-Propanediol 4.101 3 1,3-Propanediol 4.801 4 1,3-Butanediol 4.986 5 Diethylene glycol ethyl ether 5.440 6 Diethylene glycol 5.756 7 Benzyl alcohol 5.935 8 Glycerol 6.196 9 2-Phenoxyethanol 6.990 10 Triethylene glycol 7.249

[0140] Example 4

[0141] In order to study the effect of the initial temperature of the column temperature on the gas chromatography analysis effect, this example studies the peak shape of 1,2-propylene glycol at different initial temperatures (45, 50, 55, 60, 65, 80°C) under non-split injection, among which the peak shapes at 50°C, 60°C, and 80°C are as follows: Figure 6 shown.

[0142] The study found that when the initial column temperature is below 50°C, the peak width, symmetry factor, separation, column efficiency and other parameters of the chromatographic peak are good. When it is above 55°C, the parameters of the chromatographic peak begin to deteriorate. At 80°C, the peak width is very wide and the tailing is serious, affecting quantification. Therefore, 50°C is selected as the preferred initial temperature of the heating program.

[0143] Example 5

[0144] This example provides a methodological verification of the above-mentioned method for detecting solvent components in ink.

[0145] (1) Establishment of working curve and determination of detection limit and quantification limit

[0146] A mixed standard solution was prepared according to the method of Example 1 and analyzed by gas chromatography, and quantitative calculation was performed using the internal standard method. The peak area ratio (y) of each target compound to the internal standard was used for linear regression analysis of the concentration ratio (x) of each target compound to the internal standard using the least squares method to obtain the linear equation and correlation coefficient of the standard working curve of each target compound.

[0147] A 1 μg / mL mixed standard solution was added to the blank sample and injected 12 times. The standard deviation of the determination results of each target compound was calculated. The detection limit and quantification limit were calculated according to the following formula (2). Then, the detection limit and quantification limit of the sample to be tested were converted to the detection limit and quantification limit of the sample to be tested using formula (1);

[0148]

[0149] Where C L is the detection limit / quantification limit;

[0150] k is the confidence factor, which is 3 when calculating the detection limit and 10 when calculating the quantification limit;

[0151] s i is the standard deviation of the sample measurement results;

[0152] c is the theoretical content of the target compound to be measured;

[0153] It is the average value of the sample measurement results.

[0154] The analysis results are shown in Table 4. It can be seen that the Pearson correlation coefficients r of the working curves of the nine target compounds are all greater than 0.999 in the concentration range of 1 to 300 μg / mL, and the linear relationship is good. The linear range converted to sample content is 10 to 3000 ng / cm; the detection limit of the sample is 0.3 to 4.7 ng / cm, and the quantification limit is 1.0 to 14.1 ng / cm.

[0155] Table 4

[0156]

[0157]

[0158] (2) Accuracy and precision

[0159] The blank spike method was used to calculate the spike recovery. A blank sample was prepared using blank paper according to the sample preparation method described above. Nine target analyte standards were added at low, medium and high concentration levels and chromatographic analysis was performed. Each level was repeated 6 times. The recoveries of the nine target compounds were calculated based on the spiked amount of the blank sample and the measured amount after spike addition. The results are shown in Table 5. It can be seen that the spiked recoveries of the nine target compounds are between 98.1% and 105.1%, and the relative standard deviations are between 0.2% and 2.1%. The recoveries of the samples added at each level meet the requirements in the concentration range to which they belong, indicating that the method has high accuracy and good repeatability.

[0160] Table 5

[0161]

[0162]

[0163] Example 6

[0164] This example is to detect the solvent components in the ink of 30 kinds of commercially available gel pens, water-based pens, and ballpoint pens. Using the method of Example 1, 10 kinds of gel pens (respectively recorded as N1 to N10), 10 kinds of water-based pens (direct liquid ballpoint pens) (respectively recorded as W1 to W10), and 10 kinds of ballpoint pens (respectively recorded as B1 to B10) purchased on the market were analyzed. The 30 pen samples are all products of different brands. The test results are shown in Table 6. The chromatogram of the N3 sample test is shown in Table 6. Figure 7 .

[0165] Table 6

[0166]

[0167]

[0168] *.-, not detected; NQ, not quantified; The samples were diluted once before measurement to keep the glycerol content within the linear range.

[0169] Example 7

[0170] This embodiment provides a method for detecting solvent components in ink, which is different from Embodiment 1 in that:

[0171] In step S1, the internal standard used is 1,4-butanediol.

[0172] According to this method, the chromatographic separation of the 9 target compounds is shown in Figure 8 , it can be seen from the figure that the peak of 1,4-butanediol is between diethylene glycol ethyl ether and diethylene glycol. The resolution between 1,4-butanediol and the two is 5.00 and 5.99 respectively. When 1,3-butanediol is used as the internal standard, there is no internal standard between diethylene glycol ethyl ether and diethylene glycol, and the resolution between the two reaches 10.79. It can be seen that using 1,4-butanediol as the internal standard will reduce the resolution between diethylene glycol ethyl ether and diethylene glycol.

[0173] Therefore, under the gas chromatography analysis conditions of the present invention, using 1,4-butanediol as the internal standard can achieve good results in most cases, but the separation index of diethylene glycol ethyl ether and diethylene glycol is not as good as the embodiment using 1,3-butanediol as the internal standard.

[0174] Example 8

[0175] This embodiment provides a method for detecting solvent components in ink, which is different from Embodiment 1 in that:

[0176] In step S3, the gas chromatography analysis conditions are:

[0177] Column temperature program: initial temperature 45 °C for 1 min, then increase the temperature to 125 °C at a rate of 100 °C / min and hold for 2.5 min, then increase the temperature to 230 °C at a rate of 40 °C / min and hold for 3 min, post-operation: increase the temperature to 240 °C at a rate of 100 °C / min and hold for 3 min.

[0178] According to this method, the chromatographic separation effect of each target compound is shown in Fig. 9 It can be seen from the figure that the separation effect of each target compound is good, but the time required is slightly longer than that of Example 1. The temperature adjustment of each isothermal stage in Example 1 of the present invention requires corresponding adjustment of the holding time of each stage. It can be seen that removing the isothermal stage at 170°C in this example has a slight adverse effect on the efficiency of the entire analysis process.

[0179] Comparative Example 1

[0180] This comparative example provides a method for detecting solvent components in ink, which differs from Example 1 in that:

[0181] In step S3, the gas chromatography analysis conditions are:

[0182] Column temperature program: initial temperature 50 °C, maintained for 1 min, increased at 10 °C / min to 230 °C, maintained for 5 min.

[0183] According to this method, although the target compounds can be completely separated, since the column temperature heating program adopts the traditional uniform heating method, the entire gas phase circulation time is 24 minutes, which is much longer than the 12 minutes in Example 1 of the present invention.

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for detecting solvent components in ink, It is characterized in that The steps include: S1. Prepare mixed standard solution: Mixed standard solutions of different concentrations were prepared using internal standards and standards of target compounds; The internal standard is 1,3-butanediol or 1,4-butanediol; the target compound is ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol and diethylene glycol ethyl ether; S2. Prepare sample solution: Use a sampler to sample the sample to be tested, immerse the sample in an extractant containing an internal standard, centrifuge after extraction, and take the supernatant as the sample solution; S3. Gas chromatography analysis: Performing gas chromatography analysis on the mixed standard solution and the sample solution, and using gas chromatography to perform qualitative or quantitative detection on the solvent components in the ink; The conditions of the gas chromatography analysis are: Chromatographic column: DB-ALC2 chromatographic column, specification is 30m×0.32mm×1.2μm; Carrier gas: nitrogen, purity 99.999%; Column flow rate: constant flow mode 1~3mL / min; Inlet temperature 230-290°C, splitless injection, purge time 0.3-1.0 min, purge flow 30-70 mL / min; Column temperature program: initial temperature 45-55℃, hold for 0.5-1.5min, heat to 120-130℃ at 80-120℃ / min, hold for 2-3min, heat to 160-180℃ at 80-120℃ / min, hold for 1-2min, heat to 220-240℃ at 80-130℃ / min, hold for 2-4min, and then run at 240-250℃, hold for 2-3min; Or: the initial temperature is 45-55°C and maintained for 0.5-1.5 min, then the temperature is increased to 120-130°C at a rate of 80-120°C / min and maintained for 2-4 min, then the temperature is increased to 230-250°C at a rate of 35-45°C / min and maintained for 4-10 min; The gas chromatographic analysis was performed using a gas chromatograph equipped with a flame ionization (FID) detector.

2. The detection method according to claim 1, It is characterized in that Step S1 includes the following steps: The internal standard substance is mixed with the extractant to obtain an internal standard working solution; the standard substance of the target compound is weighed, added to the internal standard working solution, and diluted to obtain mixed standard solutions of different concentrations.

3. The detection method according to claim 2, It is characterized in that Step S1 includes the following steps: weighing a standard of an internal standard substance, preparing an internal standard stock solution with a concentration of 10 mg / mL using an extractant, and then diluting the solution with the extractant to obtain an internal standard working solution with a concentration of 50 μg / mL; Weigh the standard of each target compound separately, prepare a 10 mg / mL mixed standard solution with the internal standard working solution, and then dilute it with the internal standard working solution to prepare 7 levels of 1, 5, 10, 50, 100, 200, and 300 μg / mL mixed standard solutions of 9 target compounds containing 50 μg / mL internal standard.

4. The detection method according to claim 1, It is characterized in that The extractant is at least one of methanol, acetonitrile, ethanol, chloroform and N,N-dimethylformamide.

5. The detection method according to claim 1, It is characterized in that In step S2, the diameter of the hole punched by the puncher is 0.1-1 mm.

6. The detection method according to claim 1, It is characterized in that In step S2, the extraction is performed by standing at 10-50° C. for 5-60 minutes.

7. The detection method according to claim 1, It is characterized in that In step S3, the method of qualitative detection is: comparing the retention time of the target compound in the sample solution with the retention time of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether standards as a qualitative basis to determine the presence of the target compound in the sample to be tested.

8. The detection method according to claim 1, It is characterized in that In step S3, the quantitative detection method is: according to the peak area ratio of each target substance of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample solution to the internal standard, the content of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, glycerol, benzyl alcohol, 2-phenoxyethanol, and diethylene glycol ethyl ether in the sample to be tested is calculated according to their respective standard working curves.

Images