Method for improving detection accuracy of naphthalene content in absorber oil

Abstract

The invention discloses a method for improving the detection accuracy of the content of naphthalene in absorber oil. The method mainly comprises the following steps: step 1, determining a detection principle; 2, detecting instruments and equipment; step 3, determination of chromatographic conditions; 4, selecting an internal standard substance; 5, quantifying an internal standard substance; step 6, measuring a correction factor; step 7, detecting the sample; and step 8, a calculation process. According to the method disclosed by the invention, the accuracy of detection data is improved by adopting a correction factor, a sampling mode, an internal standard substance addition amount and other methods, the accuracy and the detection speed of the detection data of the naphthalene content in the absorber oil are effectively improved, and the method has a positive promotion effect on tar deep processing industry and coal chemical industry production; meanwhile, a reference method is provided for detecting the content of naphthalene in the complex organic matter mixture, and progress and development of the detection technology in the coal chemical industry are promoted.

Description

Technical Field

[0001] This invention belongs to the field of coking by-product wash oil detection technology, and particularly relates to a method for improving the accuracy of naphthalene content detection in wash oil. Background Technology

[0002] Wash oil is an important product in the coal tar processing process. It is not only an important production purification medium for washing and absorbing benzene in coal gas purification processes, but also an important raw material for valuable chemical raw materials such as methylnaphthalene, indole, acenaphthene, fluorene, and oxyfluorene, which has extremely high economic benefits and considerable profit margins.

[0003] The naphthalene content in wash oil is a crucial parameter characterizing its quality, playing a vital role in the stable operation and quality assurance of wash oil production and coal tar processing. It also has a significant impact on the benzene absorption process in coal gas purification. Currently, the naphthalene content in wash oil is determined according to the standard GB / T24208-2009, which uses an Apison L packed column for qualitative separation and a single-point external standard method for quantification. This method suffers from poor separation of wash oil samples and large precision deviations in the determination results, failing to effectively guide production. Therefore, developing a faster, less affected, and more precise method for determining the naphthalene content in wash oil is particularly important and urgent for deep coal tar processing and coal gas purification. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this invention is to provide a method for improving the accuracy of naphthalene content detection in wash oil.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for improving the accuracy of naphthalene content detection in wash oil, which mainly includes the following steps:

[0007] Step 1, Detection Principle

[0008] After the sample is dissolved in solvent and diluted to a certain volume, it is determined by gas chromatograph equipped with a flame ionization detector. The content of naphthalene in the wash oil is calculated based on the retention time of the chromatographic peaks for qualitative analysis and the internal standard method for quantitative analysis.

[0009] Step 2, Testing Instruments and Equipment

[0010] A gas chromatograph with a flame hydrogen detector, programmed temperature rise function, interface for installing capillary columns, and split / splitless flow control, with a sensitivity of Mt≤5×10-11g / s; using a 100% polydimethylsiloxane quartz elastic capillary column, 50.00m×0.25mm×0.25μm, or a similar capillary column that can meet the separation requirements;

[0011] Step 3, Determination of chromatographic conditions

[0012] The core process of detection and analysis is the control of chromatographic separation conditions. The optimization of gas chromatography separation is to achieve rapid separation while ensuring resolution and sensitivity. By continuously testing, studying and adjusting various parameters of the gas chromatograph, reasonable chromatographic separation conditions are finally determined to ensure that the sample components can be completely separated with a resolution R≥1.5, and that the separated components can be quantified using appropriate and accurate methods.

[0013] The wash oil components are relatively complex. To ensure better separation of the test sample and shorten the detection time, the chromatographic column temperature was programmed using a temperature ramp method. The initial temperature was 120℃, held for 2 min; the temperature was ramped to 140℃ at a rate of 30℃ / min, held for 6 min; then ramped to 200℃ at a rate of 40℃ / min, held for 3 min; and finally ramped to 260℃ at a rate of 40℃ / min, held for 10 min.

[0014] Information regarding other chromatographic conditions is shown in Table 1;

[0015] Table 1 Typical chromatographic operating conditions

[0016] Chromatographic control parameters Chromatographic control parameter control values vaporization temperature 280℃ Temperature detection 290℃ <![CDATA[Column flow rate (N2)]]> 1.56 mL / min <![CDATA[Pre-column pressure (N2)]]> 0.09MPa <![CDATA[Hydrogen (H2)]]> 35mL / min Air 380mL / min Flow split ratio 60：1 <![CDATA[Tail gas purge (N2)]]> 30mL / min Injection volume 1μL Minimum peak area <![CDATA[1000mm 2 ]]>

[0017] Step 4, Selection of internal standard

[0018] n-Dodecane was selected as the internal standard for naphthalene content analysis in wash oil;

[0019] Step 5, quantification of internal standard

[0020] The amount of internal standard added is an important parameter for quantitative detection using the internal standard method in chromatographic detection, directly determining the accuracy of the detection results. Three naphthalene standard solutions with contents of 1%, 5%, and 10% were prepared and subjected to chromatographic analysis to determine that the internal standard was 0.5g.

[0021] Step 6, Determination of correction factor

[0022] Prepare a standard solution containing naphthalene, perform chromatographic analysis, and calculate the correction factor;

[0023] The relative correction factor of naphthalene relative to the n-dodecane internal standard was calculated according to formula (1);

[0024]

[0025] In the formula:

[0026] fi—Relative correction factor

[0027] AS – Peak area of ​​n-dodecane, in square millimeters (mm) 2 ;

[0028] Ai – Peak area of ​​naphthalene, in square millimeters (mm). 2 ;

[0029] mi – mass of naphthalene, in grams (g);

[0030] ms — the mass of n-dodecane, in grams (g);

[0031] Step 7, Sample Testing

[0032] Measure 10 mL of the wash oil sample using a pipette and place it in a pre-weighed 25 mL volumetric flask. Weigh the sample mass, and then accurately weigh 0.5 g of n-dodecane into the volumetric flask, ensuring the weighing is accurate to 0.0002 g. Add o-, m-, or p-xylene to the mark on the volumetric flask, make up to volume, and shake well before use. Adjust the chromatogram to the optimal analytical state according to the specified chromatographic conditions, and inject 1 μL of the prepared sample using a microsyringe or autosampler to analyze the sample.

[0033] Step 8, Calculation process

[0034] The mass fraction of naphthalene content in the wash oil is expressed as X%, with the value expressed as %, and is calculated according to the following formula (2):

[0035]

[0036] Where: X_analyte — the mass fraction of naphthalene in the wash oil (X%);

[0037] Ai — Average peak area of ​​naphthalene in the sample, in square millimeters (mm). 2 ;

[0038] As — the average peak area of ​​naphthalene in the standard sample, in square millimeters (mm). 2 ;

[0039] mi — the mass of the sample, in grams (g);

[0040] ms — the mass of n-dodecane, in grams (g);

[0041] fi—the relative correction factor for naphthalene;

[0042] M ad —Moisture content of the sample.

[0043] Furthermore, the gas chromatograph should be adjusted according to the column temperature and the chromatographic conditions specified in Table 1 for chromatographic detection and analysis. Considering the large differences in gas chromatograph models and brands, based on general chromatographic principles, appropriate adjustments can be made according to the actual situation based on the different performance of the chromatograph, chromatographic workstation or data processing machine used. However, it is necessary to ensure that the resolution R between naphthalene and other components is ≥1.5, and the sensitivity of the detection instrument should be controlled within the linear response range of naphthalene and n-dodecane.

[0044] Further, the configuration of the standard samples:

[0045] According to the variation range of naphthalene content in wash oil, a series of standard solutions containing internal standards for naphthalene were prepared; 0.1g, 0.2g, 0.4g, 0.6g, 0.8g, and 1.0g of naphthalene were accurately weighed and placed in 25mL volumetric flasks respectively, and 0.5g of n-dodecane was accurately weighed and placed in a volumetric flask. The solutions were then diluted to volume with ortho-, meta-, or p-xylene and mixed thoroughly for later use; these standards were naphthalene contents of 0.004g / mL, 0.008g / mL, 0.016g / mL, 0.024g / mL, 0.032g / mL, and 0.04g / mL.

[0046] Further, the calculation of the correction factor:

[0047] Adjust the chromatograph to the optimal analytical state according to the chromatographic conditions, inject 1 μL of standard sample using a microsyringe or autosampler, and measure each standard sample in parallel 3-5 times. Measure the peak areas of naphthalene and the internal standard n-dodecane using a chromatographic workstation or chromatographic data processor, and take the average value after removing discrete values ​​according to data statistical theory.

[0048] Furthermore, the calibration curve is calibrated every 6 months to ensure the accuracy of quantification; however, if the chromatographic conditions change, the calibration factor must be re-validated.

[0049] Furthermore, each sample was measured three times, and the peak areas of naphthalene and the internal standard n-dodecane were determined by a chromatography workstation or chromatography data processor. The average value was taken after removing discrete values ​​according to data statistical theory.

[0050] Furthermore, the peak areas of the analyte and internal standard in the sample should be kept appropriately balanced by adjusting the sampling amounts of the sample and internal standard, as well as the injection volume. After adjusting the parameters, the results should be verified using a standard sample.

[0051] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0052] This invention utilizes gas chromatography with capillary column component separation and programmed temperature rise internal standard method for the detection of naphthalene content in coal wash oil. It offers advantages such as rapid detection and high accuracy. The accuracy of the detection data is further improved by employing correction factors, sampling methods, and internal standard dosage. This effectively enhances the accuracy and speed of naphthalene content detection in coal wash oil, positively impacting the deep processing of coal tar and coal chemical production. It also provides a valuable method for detecting naphthalene content in complex organic mixtures, promoting the advancement and development of detection technology in the coal chemical industry. This invention positively promotes the deep processing and trade of coal tar, particularly providing a technical detection method for the coke oven gas benzene washing process and the three-stage distillation of coal tar, laying a solid foundation for stable and smooth production, and is of great significance for the extension and optimization of the coking industry chain. Attached Figure Description

[0053] The present invention will be further described below with reference to the accompanying drawings.

[0054] Figure 1 This is a chromatogram showing the analysis with dodecane as an internal standard;

[0055] Figure 2 This is a chromatogram showing the analysis with n-dodecane as an internal standard;

[0056] Figure 3 This is a chromatogram showing the analysis with hexadecane as an internal standard;

[0057] Figure 4 The chromatogram of wash oil;

[0058] Figure 5 This is a typical chromatogram of a standard sample for washing oil containing naphthalene using the internal standard method;

[0059] Figure 6 This is a chromatogram for the detection of naphthalene content in wash oil. Detailed Implementation

[0060] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0061] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0062] This invention discloses a method for improving the accuracy of naphthalene content detection in wash oil, which mainly includes the following steps:

[0063] Step 1, Detection Principle

[0064] After the sample is dissolved in solvent and diluted to a certain volume, it is measured by a gas chromatograph equipped with a flame ionization detector. The qualitative analysis is based on the retention time of the chromatographic peak, and the quantitative analysis is based on the internal standard method. The content of naphthalene in the wash oil is then calculated.

[0065] Step 2, Testing Instruments and Equipment

[0066] A gas chromatograph with a flame ionization detector (FID), temperature programmed operation, an interface for installing capillary columns, and split / splitless flow control, with a sensitivity of Mt≤5×10⁻¹¹ g / s (n-hexadecane). A 100% polydimethylsiloxane quartz flexible capillary column (50.00 m × 0.25 mm × 0.25 μm) or a similar capillary column capable of achieving the required separation is used.

[0067] Step 3, Determination of chromatographic conditions

[0068] The core process of detection and analysis is the control of chromatographic separation conditions. The optimization of gas chromatography separation aims to achieve rapid separation while ensuring resolution and sensitivity. By continuously testing, researching, and adjusting various parameters of the gas chromatograph, reasonable chromatographic separation conditions are ultimately determined to ensure that the sample components can be completely separated, with a resolution R≥1.5, and that the separated components can be quantified using appropriate and accurate methods.

[0069] The wash oil components are relatively complex. In order to ensure better separation of the test sample and shorten the detection time, the chromatographic column temperature adopts the temperature program method. The initial temperature is 120℃, held for 2 min; the temperature is increased to 140℃ at a rate of 30℃ / min, held for 6 min; then the temperature is increased to 200℃ at a rate of 40℃ / min, held for 3 min; and then the temperature is increased to 260℃ at a rate of 40℃ / min, held for 10 min.

[0070] Information on other chromatographic conditions is shown in Table 2.

[0071] Table 2 Typical chromatographic operating conditions

[0072] Chromatographic control parameters Chromatographic control parameter control values vaporization temperature 280℃ Temperature detection 290℃ <![CDATA[Column flow rate (N2)]]> 1.56 mL / min <![CDATA[Pre-column pressure (N2)]]> 0.09MPa <![CDATA[Hydrogen (H2)]]> 35mL / min Air 380mL / min Flow split ratio 60：1 <![CDATA[Tail gas purge (N2)]]> 30mL / min Injection volume 1μL Minimum peak area <![CDATA[1000mm 2 ]]>

[0073] Furthermore, the gas chromatograph should be adjusted according to the column temperature and the chromatographic conditions specified in Table 1 for chromatographic detection and analysis. Considering the large differences in gas chromatograph models and brands, based on general chromatographic principles, appropriate adjustments can be made according to the actual situation based on the different performance of the chromatograph, chromatographic workstation or data processing machine used. However, it is necessary to ensure that the resolution R between naphthalene and other components is ≥1.5, and the sensitivity of the detection instrument should be controlled within the linear response range of naphthalene and n-dodecane.

[0074] Step 4, Selection of internal standard

[0075] In gas chromatography with internal standard method, the selection of the internal standard is crucial. The internal standard should be a pure substance not present in the original sample. Its properties should be as similar as possible to the predicted component, it should not chemically react with the analyte, and it should be completely soluble in the analyte. The peak of the internal standard should be as close as possible to the peak of the analyte, or located in the middle of several analyte peaks, but it must not overlap with any peaks in the sample; that is, it must be completely separated. The selection range for internal standards is long-chain alkanes. An experiment is set up to optimize and determine the internal standard from dodecane, n-dodecane, and hexadecane.

[0076] Take three portions of m-xylene, add a certain amount of naphthalene, and then add dodecane, n-dodecane, and hexadecane respectively; weigh a certain amount of wash oil sample and dissolve it in xylene; perform gas chromatography analysis on each, and the chromatograms are shown below. Figure 1 , Figure 2 Figure 3 and Figure 4 As shown.

[0077] The following conclusions can be drawn from the chromatographic analysis: (1) When dodecane is used as an internal standard, there are many impurity peaks before and after it, which has a significant impact on the quantification of the internal standard and the separation is poor. However, there are no obvious impurity peaks near the positions of hexadecane and n-dodecane, and the separation is good. Therefore, dodecane is excluded as an internal standard. (2) Through the chromatograms of hexadecane and n-dodecane as internal standards, the retention time of n-dodecane is 8.609 min and the retention time of hexadecane is 14.008 min. Referring to the chromatogram of the wash oil, it is found that there are many impurities in the wash oil after 12 min. The retention time overlaps with that of hexadecane, which has a significant impact on the quantitative calculation of the naphthalene content in the wash oil using hexadecane as an internal standard. Therefore, hexadecane is excluded as an internal standard. (3) Finally, n-dodecane is selected as the internal standard for the analysis of naphthalene in the wash oil.

[0078] Step 5, quantification of internal standard

[0079] The amount of internal standard added is a crucial parameter for quantitative analysis using the internal standard method in chromatographic detection, directly determining the accuracy of the results. Three naphthalene standard solutions with concentrations of 1%, 5%, and 10% were prepared and analyzed by chromatography to determine the optimal internal standard as 0.5 g.

[0080] Based on the range of naphthalene content in the wash oil, three naphthalene standard solutions with contents of 1%, 5%, and 10% were designed and prepared for chromatographic analysis. The peak areas of naphthalene obtained from the detection of the three naphthalene standard solutions with different contents are shown in Table 3 below.

[0081] Table 3 Peak areas of standard solutions with different naphthalene contents

[0082]

[0083] The naphthalene content was chosen as the median index value as the reference sample; that is, a naphthalene content of 5% corresponds to a peak area of ​​8000 mm². 2 Therefore, the peak area of ​​the selected amount of n-dodecane should also be around 8000 mm. 2 Nearby; the peak areas of n-dodecane are shown in Table 4 below when 0.1 g, 0.5 g, and 1.0 g of n-dodecane are added.

[0084] Table 4 Peak areas of standard solutions with different naphthalene contents

[0085]

[0086]

[0087] When the amount of internal standard n-dodecane added was 0.5 g, the peak area was 7500 mm². 2 The peak area is similar to that of naphthalene in a 5% naphthalene standard solution, so the amount of n-dodecane added as the internal standard was determined to be 0.5g.

[0088] Step 6, Determination of correction factor

[0089] Prepare a standard solution containing naphthalene, perform chromatographic analysis, and calculate the correction factor.

[0090] Furthermore, the configuration of the standard samples.

[0091] According to the variation range of naphthalene content in wash oil, a series of standard solutions containing internal standards for naphthalene were prepared. Accurately weigh 0.1 g, 0.2 g, 0.4 g, 0.6 g, 0.8 g, and 1.0 g (accurate to 0.0002 g) of naphthalene (5.2), and place them in separate 25 mL volumetric flasks. Then accurately weigh 0.5 g (accurate to 0.0002 g) of n-dodecane (5.5) and place it in a volumetric flask. Dilute to volume with o-(m-, para-)xylene (5.4), mix thoroughly, and set aside. These standards are naphthalene contents of 0.004 g / mL, 0.008 g / mL, 0.016 g / mL, 0.024 g / mL, 0.032 g / mL, and 0.04 g / mL.

[0092] Furthermore, the calculation of the correction factor.

[0093] Adjust the chromatograph to the optimal analytical state according to the chromatographic conditions, inject 1 μL of standard sample using a microsyringe or autosampler, and perform parallel determinations of each standard sample 3-5 times. Measure the peak areas of naphthalene and the internal standard n-dodecane using a chromatographic workstation (or chromatographic data processor), and take the average value after removing discrete values ​​according to data statistical theory.

[0094] The relative correction factor of naphthalene relative to the n-dodecane internal standard was calculated according to equation (1).

[0095] In the formula:

[0096] fi—Relative correction factor

[0097] AS – Peak area of ​​n-dodecane, in square millimeters (mm) 2 );

[0098] Ai – Peak area of ​​naphthalene, in square millimeters (mm) 2 );

[0099] mi – the mass of naphthalene, expressed in grams (g);

[0100] ms — the mass of n-dodecane, in grams (g).

[0101] Furthermore, under normal circumstances, the calibration curve is calibrated every 6 months to ensure the accuracy of quantification. However, if the chromatographic conditions change, the calibration factor must be re-validated.

[0102] Step 7, Sample Testing

[0103] To fully consider the impact of the volatility of xylene, wash oil, and n-dodecane on the accuracy of experimental results, and to eliminate repeated sampling during the weighing process and improve sample representativeness, the sample method involves directly taking approximately 10 mL of wash oil sample, weighing 0.5 g of n-dodecane, and then quickly adjusting the volume to shorten the sample preparation time, reduce volatilization, and maximize the accuracy of detection from all aspects. The sample volume should not be too small; otherwise, the low naphthalene content in the wash oil will lead to poor separation and increased relative error, thus affecting the scientific validity and reliability of the experimental data. The principle for sample dissolution should be a low concentration that ensures the normal detection of the minimum content component and guarantees the scientific validity and reliability of the data. This ensures effective detection of the minimum component content in the test sample while preventing injection errors and reagent waste caused by excessive sample concentration. Extensive experimental verification has shown that a sample volume of approximately 10 mL for general wash oil components and approximately 15 mL of solvent are sufficient to meet the detection requirements.

[0104] Measure approximately 10 mL of the wash oil sample using a pipette and place it in a pre-weighed 25 mL volumetric flask. Weigh the sample. Then, accurately weigh 0.5 g of n-dodecane into the volumetric flask, ensuring the weighing is accurate to 0.0002 g. Add o-(m-, para-)xylene to the mark on the volumetric flask, make up to volume, and shake well. Adjust the chromatograph to its optimal analytical state according to the specified chromatographic conditions. Inject 1 μL of the prepared sample using a microsyringe or autosampler to analyze the sample.

[0105] Furthermore, each sample was measured three times, and the peak areas of naphthalene and the internal standard n-dodecane were determined by a chromatography workstation (or chromatography data processor). The average value was taken after removing discrete values ​​according to data statistical theory.

[0106] Furthermore, the peak areas of the analyte and internal standard in the sample should be kept appropriately balanced by adjusting the sampling amounts of the sample and internal standard, as well as the injection volume. After adjusting the parameters, the results should be verified using a standard sample.

[0107] Step 8, Calculation of test results

[0108] The mass fraction of naphthalene content in the wash oil is expressed as X (%), and the value is expressed as % and calculated according to the following formula 4:

[0109]

[0110] Where: X (analyte) – the mass fraction of naphthalene content in the wash oil, expressed as X (%);

[0111] Ai — The average value of the naphthalene peak apex area of ​​the sample, in square millimeters (mm). 2 );

[0112] As — the average peak area of ​​naphthalene in the standard sample, in square millimeters (mm). 2 );

[0113] mi — the mass of the sample, in grams (g);

[0114] ms — the mass of n-dodecane, in grams (g);

[0115] fi—the relative correction factor for naphthalene;

[0116] Mad—Moisture content of the sample.

[0117] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0118] A method for improving the accuracy of naphthalene content detection in coal wash oil is disclosed. This method utilizes capillary column chromatography with component separation and programmed temperature rise internal standard quantitative gas chromatography to detect naphthalene content in coal wash oil, offering advantages such as rapid detection and high accuracy. The accuracy of the detection data is further enhanced by employing correction factors, sampling methods, and internal standard dosage. This effectively improves the accuracy and speed of naphthalene content detection in coal wash oil, positively impacting the deep processing of coal tar and coal chemical production. It also provides a valuable method for detecting naphthalene content in complex organic mixtures, promoting the advancement and development of detection technology in the coal chemical industry. This invention positively promotes the deep processing and trade of coal tar, particularly providing a technical detection method for the operation of coke oven gas benzene washing process and the processing of three-stage coal tar distillation fractions, laying a solid foundation for stable and smooth production, and is of great significance for the extension and optimization of the coking industry chain. Specific Implementation Example 2

[0120] To further elaborate on this invention patent and to provide a detailed explanation of the inventive concept and implementation process, this method was used to detect the naphthalene content in wash oil produced by a coking plant.

[0121] The company uses a gas chromatograph (GC) of an international brand, assembled domestically. This GC features a flame ionization detector (FID), programmed temperature control, an interface for installing capillary columns, and split / splitless flow control. Its sensitivity is Mt≤5×10⁻¹¹ g / s (n-hexadecane). A 100% polydimethylsiloxane quartz flexible capillary column (50.00 m × 0.25 mm × 0.25 μm) is used.

[0122] The column temperature was programmed using a temperature ramp method: the initial temperature was 120℃ and held for 2 min; the temperature was ramped up to 140℃ at a rate of 30℃ / min and held for 6 min; the temperature was then ramped up to 200℃ at a rate of 40℃ / min and held for 3 min; and finally the temperature was ramped up to 260℃ at a rate of 40℃ / min and held for 10 min.

[0123] Information on other chromatographic conditions is shown in Table 5.

[0124] Table 5 Typical chromatographic operating conditions

[0125]

[0126]

[0127] Chromatographic analysis identified n-dodecane as the internal standard. The amount of internal standard to be added was determined through a specific experimental method. The amount of internal standard added is a crucial parameter in chromatographic internal standard method for quantitative detection, directly determining the accuracy of the results. Since the national standard requires that the naphthalene content in wash oil be ≤10%, three naphthalene standard solutions with contents of 1%, 5%, and 10% were prepared for chromatographic analysis. The peak areas of naphthalene obtained from the three different naphthalene standard solutions are shown in Table 6 below.

[0128] Table 6 Peak areas of standard solutions with different naphthalene contents

[0129]

[0130] Considering the naphthalene content as the median index value as the reference sample, that is, a naphthalene content of 5% corresponds to a peak area of ​​8000 mm². 2 Therefore, the peak area of ​​the selected amount of n-dodecane should also be around 8000 mm. 2 Nearby; the peak areas of n-dodecane when 0.1g, 0.5g, and 1.0g of n-dodecane were added are shown in Table 7 below.

[0131] Table 7 Peak areas of standard solutions with different naphthalene contents

[0132]

[0133]

[0134] Analysis of the above data shows that when the amount of internal standard n-dodecane added is 0.5 g, the peak area is 7500 mm². 2 The peak area is similar to that of naphthalene in a 5% naphthalene standard solution, so the amount of n-dodecane added as the internal standard was determined to be 0.5g.

[0135] To further verify the internal standard and its dosage, naphthalene standard solutions with contents of 1.00%, 4.97%, and 9.79% were prepared, and 0.5 g of the internal standard n-dodecane was added to each solution. The verification data are shown in Table 8 below.

[0136] Table 8. Statistical Table of Accuracy Verification Data

[0137] Parallel measurements 1.00% Naphthalene Content Standard Solution 4.97% naphthalene content standard solution 9.79% naphthalene content standard solution 1 0.99％ 4.91％ 9.68％ 2 0.97％ 5.05％ 9.65％ 3 0.99％ 4.84％ 9.79％ 4 0.94％ 4.83％ 9.70％ 5 0.97％ 4.82％ 9.72％ 6 0.93％ 5.05％ 9.63％ 7 0.94％ 5.03％ 9.56％ average value 0.96％ 4.94％ 9.68％ average deviation 0.03％ 0.03％ 0.11％ Range 0.06％ 0.23％ 0.23％

[0138] Data verification showed that when the amount of internal standard added was 0.5g, the accuracy of the verification results of naphthalene standard solutions with contents of 1.00%, 4.97%, and 9.79% all met the precision requirements. Therefore, it is further proven that the amount of internal standard added can be determined to be 0.5g.

[0139] Determine the correction factor

[0140] According to the variation range of naphthalene content in wash oil, a series of standard solutions containing internal standards for naphthalene were prepared. Accurately weigh 0.1 g, 0.2 g, 0.4 g, 0.6 g, 0.8 g, and 1.0 g (accurate to 0.0002 g) of naphthalene (5.2), and place them in separate 25 mL volumetric flasks. Then accurately weigh 0.5 g (accurate to 0.0002 g) of n-dodecane (5.5) and place it in a volumetric flask. Dilute to volume with o-(m-, para-)xylene (5.4), mix thoroughly, and set aside. These standards are naphthalene contents of 0.004 g / mL, 0.008 g / mL, 0.016 g / mL, 0.024 g / mL, 0.032 g / mL, and 0.04 g / mL.

[0141] Adjust the chromatograph to the optimal analytical state according to the specified chromatographic conditions, inject 1 μL of standard sample using a microsyringe or autosampler, and perform parallel determinations of each standard sample 3-5 times. Measure the peak areas of naphthalene and the internal standard n-dodecane using a chromatographic workstation (or chromatographic data processor), and take the average value after removing discrete values ​​according to data statistical theory.

[0142] The relative correction factor of naphthalene relative to the n-dodecane internal standard was calculated according to equation (5).

[0143] In the formula:

[0144] fi—Relative correction factor

[0145] AS – Peak area of ​​n-dodecane, in square millimeters (mm) 2 );

[0146] Ai – Peak area of ​​naphthalene, in square millimeters (mm) 2 );

[0147] mi – the mass of naphthalene, expressed in grams (g);

[0148] ms — the mass of n-dodecane, in grams (g).

[0149] Under normal circumstances, the calibration curve is calibrated every 6 months to ensure the accuracy of quantification. However, if the chromatographic conditions change, the calibration factor must be re-validated.

[0150] Multiple representative standard samples were prepared, and the correction factors were determined. Standard tests with concentrations of 1.00%, 4.97%, and 9.79% were prepared, and the correction factors were determined. The test values ​​are shown in Tables 9, 10, and 11.

[0151] Table 9 Correction Factors for Standard Samples with Naphthalene Content of 1.00%

[0152]

[0153] Table 10 Correction Factors for Standard Samples with Naphthalene Content of 4.97%

[0154]

[0155]

[0156] Table 11 Correction Factors for Standard Samples with Naphthalene Content of 9.79%

[0157]

[0158] Test of the sample

[0159] Measure approximately 10 mL of the wash oil sample using a pipette and place it in a pre-weighed 25 mL volumetric flask. Weigh the sample. Then, accurately weigh 0.5 g of n-dodecane into the volumetric flask, rounding to 0.0002 g. Add o-(m-, para-)xylene to the mark on the volumetric flask, dilute to volume, and mix well. Adjust the chromatogram to optimal analytical conditions according to the specified chromatographic parameters. Inject 1 μL of the prepared sample using a microsyringe or autosampler and analyze the sample. The chromatogram is shown below. Figure 5 and Figure 6 As shown.

[0160] Calculation formula

[0161] The mass fraction of naphthalene content in the wash oil is expressed as X (%), and the value is expressed as % and calculated according to the following formula 6:

[0162]

[0163] Where: X (analyte) – the mass fraction of naphthalene content in the wash oil, expressed as X (%);

[0164] Ai — The average value of the naphthalene peak apex area of ​​the sample, in square millimeters (mm). 2 );

[0165] As — the average peak area of ​​naphthalene in the standard sample, in square millimeters (mm). 2 );

[0166] mi — the mass of the sample, in grams (g);

[0167] ms — the mass of n-dodecane, in grams (g);

[0168] fi—the relative correction factor for naphthalene;

[0169] The calculated test data are shown in Table 12.

[0170] Table 12 Detection data from the examples

[0171] Sample Parallel detection 1 Parallel detection 2 Parallel detection 3 average value,% Wash oil sample 1 4.75 4.79 4.82 4.79

[0172] To better utilize and illustrate this patented method, multiple wash oil samples were tested according to the patented method, and the test analysis data are shown in Table 13.

[0173] Table 13 Data from multiple tests of different wash oil samples

[0174]

[0175]

[0176] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the accuracy of naphthalene content detection in wash oil, characterized in that: The main steps include the following: Step 1, Detection Principle After the sample is dissolved in solvent and diluted to a certain volume, it is determined by gas chromatograph equipped with a flame ionization detector. The content of naphthalene in the wash oil is calculated based on the retention time of the chromatographic peaks for qualitative analysis and the internal standard method for quantitative analysis. Step 2, Testing Instruments and Equipment A gas chromatograph with a flame hydrogen detector, programmed temperature rise function, interface for installing capillary columns, and split / splitless flow control, with a sensitivity of Mt≤5×10-11g / s; using a 100% polydimethylsiloxane quartz elastic capillary column, 50.00m×0.25mm×0.25μm, or a similar capillary column that can meet the separation requirements; Step 3, Determination of chromatographic conditions The core process of detection and analysis is the control of chromatographic separation conditions. The optimization of gas chromatography separation is to achieve rapid separation while ensuring resolution and sensitivity. By continuously testing, studying and adjusting various parameters of the gas chromatograph, reasonable chromatographic separation conditions are finally determined to ensure that the sample components can be completely separated with a resolution R≥1.5, and that the separated components can be quantified using appropriate and accurate methods. The wash oil components are relatively complex. To ensure better separation of the test sample and shorten the detection time, the chromatographic column temperature was programmed using a temperature ramp method. The initial temperature was 120℃, held for 2 min; the temperature was ramped to 140℃ at a rate of 30℃ / min, held for 6 min; then ramped to 200℃ at a rate of 40℃ / min, held for 3 min; and finally ramped to 260℃ at a rate of 40℃ / min, held for 10 min. Step 4, Selection of internal standard n-Dodecane was selected as the internal standard for naphthalene content analysis in wash oil; Step 5, quantification of internal standard The amount of internal standard added is an important parameter for quantitative detection using the internal standard method in chromatographic detection, directly determining the accuracy of the detection results. Three naphthalene standard solutions with contents of 1%, 5%, and 10% were prepared and subjected to chromatographic analysis to determine that the internal standard was 0.5g. Step 6, Determination of correction factor Prepare a standard solution containing naphthalene, perform chromatographic analysis, and calculate the correction factor; The relative correction factor of naphthalene relative to the n-dodecane internal standard was calculated according to formula (1); In the formula: fi—Relative correction factor AS – Peak area of ​​n-dodecane, in square millimeters (mm) 2 ; Ai – Peak area of ​​naphthalene, in square millimeters (mm). 2 ; mi – mass of naphthalene, in grams (g); ms — the mass of n-dodecane, in grams (g); Step 7, Sample Testing Measure 10 mL of the wash oil sample using a pipette and place it in a pre-weighed 25 mL volumetric flask. Weigh the sample mass, and then accurately weigh 0.5 g of n-dodecane into the volumetric flask, ensuring the weighing is accurate to 0.0002 g. Add o-, m-, or p-xylene to the mark on the volumetric flask, make up to volume, and shake well before use. Adjust the chromatogram to the optimal analytical state according to the specified chromatographic conditions, and inject 1 μL of the prepared sample using a microsyringe or autosampler to analyze the sample. Step 8, Calculation process The mass fraction of naphthalene content in the wash oil is expressed as X%, with the value expressed as %, and is calculated according to the following formula (2): Where: X_analyte — the mass fraction of naphthalene in the wash oil (X%); Ai — Average peak area of ​​naphthalene in the sample, in square millimeters (mm). 2 ; As — the average peak area of ​​naphthalene in the standard sample, in square millimeters (mm). 2 ; mi — the mass of the sample, in grams (g); ms — the mass of n-dodecane, in grams (g); fi—the relative correction factor for naphthalene; M ad —Moisture content of the sample.

2. The method for improving the accuracy of naphthalene content detection in wash oil according to claim 1, characterized in that: Considering the significant differences between gas chromatograph models and brands, and based on general chromatographic principles, appropriate adjustments can be made according to the actual situation, depending on the performance of the chromatograph, chromatographic workstation, or data processing machine used. However, it is necessary to ensure that the resolution R between naphthalene and other components is ≥1.5, and the sensitivity of the detection instrument should be controlled within the linear response range of naphthalene and n-dodecane.

3. The method for improving the accuracy of naphthalene content detection in wash oil according to claim 1, characterized in that: Standard sample configuration: According to the variation range of naphthalene content in wash oil, a series of standard solutions containing internal standards for naphthalene were prepared; 0.1g, 0.2g, 0.4g, 0.6g, 0.8g, and 1.0g of naphthalene were accurately weighed and placed in 25mL volumetric flasks respectively, and 0.5g of n-dodecane was accurately weighed and placed in a volumetric flask. The solutions were then diluted to volume with ortho-, meta-, or p-xylene and mixed thoroughly for later use; these standards were naphthalene contents of 0.004g / mL, 0.008g / mL, 0.016g / mL, 0.024g / mL, 0.032g / mL, and 0.04g / mL.

4. The method for improving the accuracy of naphthalene content detection in wash oil according to claim 1, characterized in that: Calculation of correction factor: Adjust the chromatograph to the optimal analytical state according to the chromatographic conditions, inject 1 μL of standard sample using a microsyringe or autosampler, and measure each standard sample in parallel 3-5 times. Measure the peak areas of naphthalene and the internal standard n-dodecane using a chromatographic workstation or chromatographic data processor, and take the average value after removing discrete values ​​according to data statistical theory.

5. The method for improving the accuracy of naphthalene content detection in wash oil according to claim 1, characterized in that: The calibration curve is calibrated every 6 months to ensure the accuracy of quantification; however, if the chromatographic conditions change, the calibration factor must be re-validated.

6. The method for improving the accuracy of naphthalene content detection in wash oil according to claim 1, characterized in that: Each sample was measured three times. The peak areas of naphthalene and the internal standard n-dodecane were determined by a chromatography workstation or chromatography data processor. The average value was taken after removing discrete values ​​according to data statistical theory.

7. The method for improving the accuracy of naphthalene content detection in wash oil according to claim 1, characterized in that: The peak areas of the analyte and internal standard in the sample should be kept appropriately balanced by adjusting the sampling amounts of the sample and internal standard, as well as the injection volume. After adjusting the parameters, the results should be verified using a standard sample.

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