CN111175407B - Method for detecting residual quantity of organic solvent in leached oil crop meal - Google Patents
Method for detecting residual quantity of organic solvent in leached oil crop meal Download PDFInfo
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Abstract
A detection method for the residual quantity of organic solvent in leached oil crop meal comprises the following steps: (1) pretreatment of oil crop meal leaching: adding an extracting agent and leached oil crop meal into a headspace bottle, sealing and performing ultrasonic extraction; and (2) sample injection detection: heating and balancing the headspace bottle filled with the pretreatment sample obtained in the step (1), and then removing the upper layer gas of the headspace bottle for gas chromatography analysis to obtain the total peak area; (3) drawing a standard curve of the reference meal: adding different volumes of organic solvent standard solutions into the standard oil crop meal to prepare standard oil crop meal samples with different contents, respectively processing according to the steps (1) and (2), taking the content of the organic solvent of the standard oil crop meal samples as an abscissa, taking the measured total peak area as an ordinate, and drawing a standard curve; (4) calculating a result: according to the formula: x=ρ is calculated. The method has high sensitivity to the target object, low detection limit, high precision and accurate result.
Description
Technical Field
The invention relates to a method for detecting the residual quantity of an organic solvent, in particular to a method for detecting the residual quantity of the organic solvent in leached oil crop meal.
Background
The leached oil crop meal is a byproduct obtained after oil crop is extracted by a leaching method, and is a main raw material of livestock and poultry feed due to high protein content, the extraction solvent adopted in the leaching process is a No. six solvent, namely a low-boiling organic solvent such as methanol, ethanol, isopropanol and the like, wherein the No. six solvent is the most common grease extractant used by domestic grease enterprises at present, and the leaching process is an alkane mixed compound, and comprises the main components of: 2, 2-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane, methylcyclopentane, and cyclohexane. The residual quantity of the solvent in the meal is an important economic index for measuring the production process of enterprises, and because the main method for removing the organic solvent in the wet meal is evaporation, the solvent must be reused after all evaporation, condensation and recovery, so that the production can be economically and reasonably maintained. Therefore, the solvent in the wet meal is reduced as much as possible, so that the wet meal is not only beneficial to the storage and transportation of the meal, but also has guiding significance on the technical level of leaching technology, and therefore, the accurate detection of the residual quantity of the solvent in the meal is of great significance.
The national standard GB5009.262-2016 mainly aims at measuring the residual quantity of the solvents in edible vegetable oil and bean pulp in food, and if the method is adopted for measuring the residual quantity of the leached bean pulp, the result is lower. Thus, accurate quantification of residual solubility in leached oil crop meal is not suitable. However, many leaching equipment production companies adopt national standard GB5009.262-2016 to measure the residual leaching pulp solubility, which results in erroneous judgment of the technological level.
At present, although research on detecting the residual leaching amount of the leached meal is carried out early, the method has technical defects.
Xu Yingmei A test and research of distilled off dreg residual solvent is disclosed, and a direct solvent injection method is adopted after DMF extraction alone, but the target peaks in the spectrum are not separated and are difficult to distinguish, so that the sensitivity of the method is poor, and the measurement result is low (Xu Yingmei. Test and research of distilled off dreg residual solvent [ J ]. Grain and grease, 1996 (2): 35-38.).
Zhang Jing and Zhou Xiujin et al disclose a method for determining 6 solvent residues in soybean meal by an HS-GC-FID method, wherein the equilibrium temperature and time of a headspace method are optimized within a certain temperature range and time, but when preparing a reference soybean meal, the soybean meal with high residual solvent is difficult to prepare into a low-concentration reference soybean meal by an oven heating method alone, and the influence of the reference soybean meal on the determination of a low-concentration sample cannot be reduced; the method simply uses water with strong polarity as an extracting agent, can not effectively extract nonpolar organic solvents in the meal, and can not completely moisten the soybean meal by adding 1mL of water, so that the solvents in the soybean meal are unevenly volatilized, and the precision of the result is deteriorated (Zhang Jing, zhou Xiujin, shao Honghong, zhang Xiaoling, chaulmoogra source. HS-GC-FID method is used for measuring 6 solvent residues [ J ]. Instrument analysis, 2019 (1): 141-145.) in the soybean meal.
Gao Shuping and Mei Haijuan et al disclose a corn germ meal solvent residue determination practice employing the method of the old national standard GB/T5009.117-2003, which not only ignores the influence of the reference meal, but also does not reasonably establish a standard curve, which does not conform to the sample conditions, resulting in inaccurate results (Gao Shuping, mei Haijuan, shadow, tian Jing, li Shaoji. Corn germ meal solvent residue determination practice [ J ]. Modern salt chemical, 2017 (4): 29-30.).
Ma Lingfei and surrounding et al disclose a method for determining the residual amount of solvent No. six in sunflower seed meal by headspace-gas chromatography, first pulverizing the sample meal, which has resulted in volatilization of the solvent residues in the sample, which would result in lower results; secondly, when a standard curve is manufactured, the influence of the reference soybean meal is ignored; and the sample weighing amount in the headspace bottle of 20mL is only 1g, and a part of solvent is lost in the weighing process, so that the detection is lower, and the concentration of the target object is diluted in the limited upper-layer space of the headspace bottle, which is equivalent to the fact that the detection result precision is poor, because of adding 10mL of large-dose extractant MNF. The experiment shows that: the larger the MNF addition, the lower the response of the target (Ma Ling fly, surrounding, zhang Yahang, etc. the residual solvent content of sunflower seed meal [ J ] was measured by headspace-gas chromatography, food safety quality inspection journal 2015,6 (11): 160-165).
In view of the foregoing, it is highly desirable to find a method for detecting the residual amount of an organic solvent in oil crop meal, which has high sensitivity to a target object, low detection limit, high precision and accurate result.
Disclosure of Invention
The invention aims to solve the technical problems and overcome the defects in the prior art, and provides the detection method for the residual quantity of the organic solvent in the leached oil crop meal, which has the advantages of high sensitivity to the target object, low detection limit, high precision and accurate result.
The technical scheme adopted for solving the technical problems is as follows: a detection method for the residual quantity of organic solvent in leached oil crop meal comprises the following steps:
(1) Pretreatment of oil crop meal leaching:
adding an extracting agent and leached oil crop meal into a headspace bottle, sealing and performing ultrasonic extraction;
(2) And (3) sample injection detection:
heating and balancing the headspace bottle filled with the pretreatment sample obtained in the step (1), and then removing the upper layer gas of the headspace bottle for gas chromatography analysis to obtain the total peak area;
(3) Drawing a standard curve of the reference meal:
adding different volumes of organic solvent standard solutions into the standard oil crop meal to prepare standard oil crop meal samples with different contents, respectively processing according to the steps (1) and (2), taking the content of the organic solvent of the standard oil crop meal samples as an abscissa, taking the measured total peak area as an ordinate, and drawing a standard curve;
(4) And (3) calculating results:
according to the formula: x=ρ, where: x is the residual amount of the organic solvent in leached oil crop meal, mg/kg, rho is the content of the organic solvent corresponding to the total peak area obtained in the step (2) read from the standard curve obtained in the step (3), and mg/kg.
Preferably, in the step (1), the mass-to-volume ratio (g/mL) of the leached oil crop meal to the extractant is 1:1.0-1.5. Under the condition that the using amount of the extracting agent is excessive, the extracting agent can completely infiltrate and leach oil crop meal, and is sufficient for completely extracting the residual organic solvent in the meal, and if the using amount of the extracting agent is excessive, volatilization of a target object can be interfered, so that the precision of a result is reduced.
Preferably, in the step (1), the extracting agent is a mixed solution of the extracting agent and water in a volume ratio of 1:0.8-1.2. The extractant is the main extractant for leaching the residual organic solvent in the oil crop meal, and the addition of a proper amount of water can not only improve the sensitivity of the hydrogen flame ion detector to the organic solvent target, but also assist the extractant to fully extract the target. However, if the amount of water is too large, the amount of water vapor formed is also large, and the precision of the sample results is lowered; if the amount of water used is too small, the sensitivity of the hydrogen flame ion detector to the organic solvent target cannot be effectively improved, and the precision of the result is also reduced.
Preferably, in the step (1), the extractant is an aprotic highly polar organic solvent with a boiling point of 140-220 ℃. According to the similar principle of compatibility, a high-boiling aprotic strong polar solvent is selected as a main extractant for leaching low-boiling organic solvents in oil crop meal.
Preferably, in the step (1), the extractant is one or more of N, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide and the like. N, N-dimethylacetamide is more preferable as an extractant because of its low toxicity and low cost.
Preferably, in the step (1), the mass-volume ratio (g/mL) of the leached oil crop meal to the headspace bottle is 1.0-1.5:10. If the amount of the leached oil crop meal is too small, the sensitivity and the precision of the method can be reduced; if the amount of leached oil crop meal is too much, the headspace bottle is limited, which is unfavorable for the sufficient volatilization of the organic solvent and can reduce the precision of the result.
Preferably, in the step (1), the leached oil crop meal is one or more of soybean meal, rapeseed meal, sunflower seed meal, peanut meal and the like.
Preferably, in the step (1), the temperature of the ultrasonic extraction is 50-80 ℃, the frequency is 25-40 kHz, and the time is 20-40 min. The purpose of ultrasonic extraction is to make the extractant fully extract and leach residual organic solvent in oil crop meal, so as to raise extraction efficiency.
Preferably, in step (2), the temperature of the heating balance is 100 to 110 ℃ (more preferably 102 to 108 ℃), and the time is 40 to 80 minutes (more preferably 50 to 70 minutes). If the balance temperature is too high, the sealing gasket of the headspace bottle is deformed, so that the air tightness of the headspace bottle is poor, and the precision of a result is affected; if the equilibrium temperature is too low, the amount of steam formed is small and insufficient to improve the sensitivity of the ion flame detector to the target object, so that the precision of the measurement result of the residual solution of the low-content leached oil crop meal is poor. If the balancing time is too short, the organic solvent in the leached oil crop meal does not reach the balance yet; if the equilibration time is too long, the detection time is prolonged.
Preferably, in the step (2), the gas injection mode is headspace injection or manual injection.
Preferably, in step (2), the headspace sample injection mode is as follows: and (3) placing the headspace bottle with the pretreatment sample obtained in the step (1) on a headspace sample bottle rack for automatic sample injection.
Preferably, in step (2), specific parameters of the headspace sampling are: the temperature of the quantitative ring/valve is 110-120 ℃, the temperature of the transmission line is 120-130 ℃, the circulation time is 25-30 min, the sample injection time is 0.5-1.5 min, the pressure time is 0.5-1.5 min, and the sample injection volume is 1mL.
Preferably, in the step (2), the specific operation of the manual sample injection is: controlling the room temperature of the instrument to be more than or equal to 25 ℃, heating and balancing the sample injection needle and the headspace bottle with the pretreatment sample obtained in the step (1), then removing 1mL of upper layer gas of the headspace bottle by the sample injection needle, and rapidly injecting the gas chromatograph. And under the condition that a headspace instrument is not provided, manual sample injection is adopted.
Preferably, in step (2), the conditions of the gas chromatographic analysis are: column box programming temperature: the temperature is kept at 50-60 ℃ for 3-5 min, then the temperature is raised to 200-220 ℃ at the speed of 20-40 ℃/min, the temperature of a sample inlet is kept at 250-280 ℃, the temperature of a detector is kept at 250-300 ℃, the flow rate of carrier gas nitrogen is 0.8-1.0 mL/min, the flow rate of hydrogen is 20-40 mL/min, the flow rate of air is 280-320 mL/min, and the split ratio is 10-120:1.
Preferably, in the step (3), the preparation method of the reference oil crop meal comprises the following steps: adding eluent into the leached oil crop meal, heating and stirring, vacuum filtering while the oil crop meal is hot, cleaning with hot water, wetting with water, tiling and baking, cooling and sealing.
Preferably, the mass to volume ratio (g/mL) of the leached oil crop meal to the eluent is 1:8-20 (more preferably 1:10-15). The eluent can be used for fully extracting and leaching the organic solvent in the oil crop meal.
Preferably, the eluent is a mixed solution of extractant and water in a volume ratio of 1:2.0-4.0.
Preferably, the extractant is an aprotic strongly polar organic solvent having a boiling point of 140-220 ℃. According to the similar principle of compatibility, aprotic strong polar solvent is selected as the main extractant for leaching organic solvent in oil crop meal.
Preferably, the extractant is one or more of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and the like. N, N-dimethylacetamide is more preferable as an extractant because of its low toxicity and low cost.
Preferably, the temperature of the heating and stirring is 50-70 ℃ and the time is 20-40 min. Aims to make the extractant fully extract and leach the residual organic solvent in the oil crop meal to obtain the reference oil crop meal with low solvent residue.
Preferably, the vacuum degree of the vacuum suction filtration is 0.5-1.0 MPa.
Preferably, the temperature of the hot water is 60 to 100 ℃ (more preferably 80 to 90 ℃).
Preferably, the number of hot water washes is greater than or equal to 5.
Preferably, the volume to mass ratio (mL/g) of the amount of water per hot water wash to the leached oil crop meal is from 5 to 20:1 (more preferably from 5.5 to 10.0:1).
Preferably, the volume to mass ratio (mL/g) of the added water to the leached oil crop meal is from 4 to 20:1 (more preferably from 5 to 10:1).
Preferably, the baking temperature is 120-150 ℃ and the time is 2-5 h.
Preferably, in the step (3), the concentration of the organic solvent standard solution is 0.5-10.0 mg/mL. If the concentration of the standard sample is too low, the preparation is not easy to be accurate; if the concentration of the standard sample is too high, the precision requirement of the required removing device is high when preparing the standard samples with different contents.
Preferably, in the step (3), the different contents are not less than 5 contents in the range of 0-1000 mg of organic solvent/kg of standard oil crop meal.
Preferably, in the step (3), the preparation method of the organic solvent standard solution is as follows: firstly, adding an extractant into a volumetric flask, then adding an organic solvent standard substance, and fixing the volume by using the extractant. The extractant is added first to dissolve the added organic solvent standard sample into the extractant, so that the volatilization of the standard sample is reduced, and the accuracy of the result is improved.
Preferably, the amount of extractant added first is 0.4 to 0.8 times the volume of the fixed volume.
Preferably, the extractant is an aprotic strongly polar organic solvent having a boiling point of 140-220 ℃.
Preferably, the extractant is one or more of N, N-dimethylformamide, N-dimethylacetamide or dimethyl sulfoxide and the like.
Preferably, the organic solvent is one or more of a sixth solvent, methanol, ethanol, isopropanol and the like. The organic solvent is a common low-boiling point organic solvent for extracting grease, namely a residual organic solvent. In order to detect the content of the organic solvent more specifically, the organic solvent for preparing the standard solution is consistent with the leaching solvent for leaching the oil crop meal to be detected.
Before drawing a standard curve of the reference meal, 0.5-1.0 mL of organic solvent standard solution is taken and placed in a headspace bottle, and gas chromatography analysis is carried out according to the step (2) so as to qualify a target peak.
The weighing precision in the method is 0.001g, and the weighing temperature is less than 20 ℃. The weighing temperature is controlled to reduce volatilization of the organic solvent standard sample so as to improve accuracy of results.
The ultrapure water is used in the detection process.
The method has the beneficial effects that:
(1) The relative error between the detection result and the actual value is less than or equal to 4.5%, the standard deviation is less than or equal to 5% and the relative standard deviation is less than or equal to 100.7-104.8%, the detection limit is 1mg/kg, and the method has the advantages of high sensitivity to the target object, low detection limit, high precision and accurate result;
(2) Compared with national standard GB5009.262-2016, the method can more accurately reflect the actual residual dissolving amount of the soybean meal in the production of the leaching process, can more truly guide the production, and plays an important role in optimizing the process, saving energy and reducing emission and ensuring the quality safety of the product.
Drawings
FIG. 1 is a graph showing the peak characteristics of the organic solvent No. six in example 1 of the present invention;
FIG. 2 is a standard curve of different amounts of organic solvent No. six in the reference soybean meal of example 1 of the present invention;
FIG. 3 is a graph showing the peak characteristics of the sixth organic solvent in example 2 of the present invention;
FIG. 4 is a standard curve of the different contents of organic solvent No. six in the reference soybean meal in example 2 of the present invention;
FIG. 5 is a graph showing the peak characteristics of ethanol in example 3 of the present invention;
FIG. 6 is a standard curve of different ethanol contents in the reference soybean meal in example 3 of the present invention.
Detailed Description
The invention is further described below with reference to examples and figures.
The leached soybean meal 1 and the leached soybean meal 2 used in the reference example are both from a production workshop of the full-stock part company of the road; the content of the organic solvent in the leached soybean meal 1-5 to be detected used in the embodiment of the invention is about 550mg/kg, 850mg/kg, 200mg/kg, 500mg/kg and 900mg/kg respectively; the solvent standard No. six used in the examples of the present invention was purchased from helpful technologies, inc; the gas chromatograph used in the examples of the present invention was 7890B agilent gas chromatograph (FID equipped with hydrogen flame ion detector, 7597a agilent headspace injector); n, N-dimethylformamide (boiling point 153 ℃), N-dimethylacetamide (boiling point 165.1 ℃) and dimethyl sulfoxide (boiling point 189 ℃) used in the examples of the invention are analytically pure and purchased from Tianjin chemical industry Co., ltd; the ethanol standard (density 0.7893 g/mL) used in the embodiment of the invention is chromatographic purity and is purchased from Tianjin chemical reagent manufacturing limited company; the weighing precision in the reference example and the example is 0.001g, and the weighing temperature is less than 20 ℃; ultrapure water is used in the reference example and the embodiment of the invention; the raw materials, chemical reagents or instruments used in the reference examples and examples of the present invention, unless otherwise specified, were all obtained by conventional commercial means.
Reference example 1 for preparation method of reference soybean meal
Placing 18g of leached soybean meal 1 into a 150mL conical flask, adding 250mL of eluent (the volume ratio of N, N-dimethylacetamide to water is 1:3), heating and stirring for 30min at 55 ℃, vacuum-filtering while hot at 0.8MPa, washing the soybean meal 9 times with 100mL of hot water each time, wetting with 100mL of water again, tiling and baking for 2.5h at 140 ℃, cooling and sealing to obtain the standard soybean meal 1.
The detection of the method of the invention shows that the total peak area of the obtained standard soybean meal 1 is 8.5, which indicates that the preparation method of the standard soybean meal 1 can volatilize the organic solvent in the leached soybean meal 1 completely.
Reference example 2 for preparation method of reference soybean meal
Placing 25g of leached soybean meal 2 into a 150mL conical flask, adding 300mL of eluent (the volume ratio of N, N-dimethylformamide to water is 1:2.5), heating and stirring for 40min at 50 ℃, carrying out vacuum filtration while hot under 0.5MPa, washing the soybean meal with 150mL of hot water at 90 ℃ for 8 times each time, then adding 150mL of water for wetting, flatly laying and baking for 3.0h at 150 ℃, cooling, and sealing to obtain the standard soybean meal 2.
The detection of the method of the invention shows that the total peak area of the obtained standard soybean meal 2 is 12.8, which indicates that the preparation method of the standard soybean meal 2 can volatilize the organic solvent in the leached soybean meal 2 completely.
Reference example 3 for preparation method of reference soybean meal
Placing 20g of leached soybean meal 1 into a 150mL conical flask, adding 300mL of eluent (the volume ratio of dimethyl sulfoxide to water is 1:4), heating and stirring for 35min at 60 ℃, carrying out vacuum filtration while hot at 1.0MPa, washing the soybean meal 10 times each time with 120mL of hot water at 80 ℃, adding 100mL of water for wetting, tiling and baking for 3h at 140 ℃, cooling, and sealing to obtain the standard soybean meal 3.
The detection of the method of the invention shows that the total peak area of the obtained standard soybean meal 3 is 5.4, which indicates that the preparation method of the standard soybean meal 3 can volatilize the organic solvent in the leached soybean meal 1 completely.
Reference example 4 for preparation of No. six solvent Standard solution
15mL of N, N-dimethylacetamide was added to a 25mL volumetric flask, and 142mg of a No. six solvent standard was added, and the volume was fixed with N, N-dimethylacetamide to prepare No. six solvent standard solution 1 having a concentration of 5.68 mg/mL.
18mL of N, N-dimethylformamide is added into a 25mL volumetric flask, 232mg of No. six solvent standard substance is added, and N, N-dimethylformamide is used for fixing the volume to prepare No. six solvent standard solution 2 with the concentration of 9.28 mg/mL.
Reference example 5 for preparation of ethanol Standard solution
24mL of dimethyl sulfoxide is added into a 50mL volumetric flask, 50.7 mu L of ethanol standard substance is added, and the volume is fixed by using the dimethyl sulfoxide to prepare a standard solution with the ethanol concentration of 0.8 mg/mL.
Example 1
(1) Pretreatment of bean pulp leaching:
in 4 headspace bottles of 20mL, respectively adding 2mL of extractant (the volume ratio of N, N-dimethylacetamide to water is 1:1), respectively adding 2.000g of leached soybean meal 1-1 and 1-2 to be detected (2 parts of each leached soybean meal to be detected are used for parallel detection), sealing, and performing ultrasonic extraction for 20min at 70 ℃ and 40 kHz;
the preparation method of the leached soybean meal 1-1 and 1-2 to be detected comprises the following steps: weighing 2 parts of 2.000g of standard soybean meal 1, respectively adding 194 mu L and 299 mu L of No. six organic solvent standard solution 1 (the concentration is 5.68 mg/mL), placing into a rotary mixer, uniformly mixing for 10min at 1500r/min, keeping the soybean meal in contact with the inner cover film of a headspace bottle in the uniformly mixing process, placing at 0 ℃ and standing for 24h to obtain the soybean meal;
(2) And (3) sample injection detection:
placing the headspace bottle with the pretreatment sample obtained in the step (1) on a headspace sample bottle rack, heating and balancing for 60min at 105 ℃, automatically sampling and removing the upper layer gas thereof for gas chromatography sample injection analysis, and measuring the total peak area;
the specific parameters of the automatic sample injection are as follows: the dosing ring/valve temperature was 115 ℃; the temperature of the transmission line is 125 ℃, the circulation time is 28min, the sample injection time is 1.0min, the pressure time is 1.0min, and the sample injection volume is 1mL;
the conditions of the gas chromatographic analysis are as follows: column box programming temperature: firstly, keeping at 55 ℃ for 4min, then heating to 200 ℃ at a speed of 30 ℃/min, keeping for 2.0min, wherein the temperature of a sample inlet is 250 ℃, the temperature of a detector is 300 ℃, the flow rate of carrier gas nitrogen is 1.0mL/min, the flow rate of hydrogen is 25mL/min, the flow rate of air is 300mL/min, and the split ratio is 100:1;
(3) Drawing a standard curve of the reference meal:
placing 1.0mL of a No. six solvent standard solution 1 into a 20mL headspace bottle, and performing gas chromatographic analysis by automatic sample injection according to the step (2), as shown in FIG. 1;
transferring 0 muL, 17 muL, 34 muL, 68 muL, 102 muL, 170 muL and 340 muL of six-number organic solvent standard solution 1 (with the concentration of 5.68 mg/mL) into 2.000g of standard soybean meal 1 to prepare standard samples with the content of 0mg/kg, 48.28mg/kg, 96.56mg/kg, 193.12mg/kg, 289.68mg/kg, 482.8mg/kg and 965.6mg/kg respectively, processing according to the steps (1) and (2), taking the content of the six-number organic solvent as an abscissa, taking the total peak area measured as an ordinate, and drawing a standard curve, as shown in fig. 2;
(4) And (3) calculating results:
according to the formula: x=ρ, where: x is the residual quantity of the organic solvent in the leached soybean meal to be detected, mg/kg, rho is the content of the organic solvent corresponding to the total peak area obtained in the step (2) read from the standard curve obtained in the step (3), and the results are shown in table 1.
As shown in FIG. 1, the peak time of the No. six organic solvent component is 0 to 4.2min, and the peak time of the N, N-dimethylacetamide is 9.45min, which shows that the separation effect is good; the sum of all peak areas of the organic solvent component No. six in the period of time serves as the total peak area of the organic solvent No. six.
As shown in fig. 2, the standard curve equation of the standard curve fitting of the reference meal is: y= 21.548x-9.5299, the correlation coefficient r=0.9993, and it is explained that the content of the sixth organic solvent in the standard sample of the reference soybean meal has a good linear relation with the peak area.
For comparison, each 2.000g of leached soybean meal to be detected 1-1 and 1-2 (2 parts of each leached soybean meal to be detected are used for parallel detection), and national standard GB5009.262-2016 is adopted for detection to compare the difference of the results of the two methods, and the results are shown in Table 1.
Table 1 Table corresponds to the results of the method of the present invention and GB5009.262-2016 on the detection of residual amounts of organic solvents in leached soybean meal to be tested
As can be seen from Table 1, for the same sample, the detection result of the method is far higher than the detection result of national standard GB5009.262-2016, the relative error of the amount of the leached organic solvent from the actual soybean meal is only 0.82% and 0.64%, and the relative error of the amount of the actual leached organic solvent from the national standard GB5009.262-2016 is as high as 66.5% and 70.6%, which indicates that the method is more suitable for accurately and quantitatively determining the residual solvent amount of the No. six organic solvent in the leached soybean meal compared with the national standard GB 5009.262-2016. Therefore, the method can more accurately reflect the residue dissolving amount of the soybean meal in the leaching process, can be more truly used for guiding production, optimizing the process, saving energy and reducing emission, and ensuring the quality safety of products.
Example 2
(1) Pretreatment of bean pulp leaching:
adding 3mL of extracting agent (the volume ratio of N, N-dimethylformamide to water is 1:0.8) into 4 20mL headspace bottles, respectively adding 3.000g of leached soybean meal to be detected 2-1 and 2-2 (2 parts of each leached soybean meal to be detected are used for parallel detection), sealing, and performing ultrasonic extraction for 30min at 60 ℃ and 30 kHz;
the preparation method of the leached soybean meal 2-1 and 2-2 to be detected comprises the following steps: weighing 2 parts of 3.000g of standard soybean meal 2, respectively adding 178 mu L of standard solution 2 of a No. six organic solvent and 275 mu L of standard solution 2 of the No. six organic solvent (the concentration is 9.28 mg/mL), placing into a rotary mixer, uniformly mixing for 10min at 1500r/min, keeping the soybean meal from contacting with an inner cover film of a headspace bottle in the uniformly mixing process, placing at 0 ℃ and standing for 24h to obtain the soybean meal;
(2) And (3) sample injection detection:
heating and balancing the headspace bottle filled with the pretreatment sample obtained in the step (1), and manually sampling and removing the upper gas layer of the headspace bottle for gas chromatography sample injection analysis to obtain the total peak area;
the specific operation of the manual sample injection is as follows: controlling the room temperature of the instrument to be more than or equal to 25 ℃, placing the sample injection needle and the headspace bottle with the pretreatment sample obtained in the step (1) into an oven, heating and balancing for 60min at 105 ℃, then removing 1mL of upper layer gas of the headspace bottle by using the sample injection needle, and rapidly injecting into a gas chromatograph;
the conditions for the gas chromatography were the same as in example 1;
(3) Drawing a standard curve of the reference meal:
placing 0.5mL of the No. six solvent standard solution 2 into a 20mL headspace bottle, and manually injecting sample according to the step (2) to perform gas chromatography analysis, as shown in FIG. 3;
transferring 0 muL, 16 muL, 32 muL, 64 muL, 96 muL, 160 muL and 320 muL of six-number organic solvent standard solution 2 (with the concentration of 9.28 mg/mL) into 3.000g of standard soybean meal 2 to prepare standard samples with the content of 0mg/kg, 49.5mg/kg, 99.0mg/kg, 198.0mg/kg, 297.0mg/kg, 495.0mg/kg and 990mg/kg respectively, treating according to the steps (1) and (2), and drawing a standard curve by taking the content of the six-number organic solvent as an abscissa and the total peak area measured as an ordinate, wherein the standard curve is shown in FIG. 4;
(4) And (3) calculating results:
according to the formula: x=ρ, where: x is the residual quantity of the organic solvent in the leached soybean meal to be detected, mg/kg, rho is the content of the organic solvent corresponding to the total peak area obtained in the step (2) read from the standard curve obtained in the step (3), and the results are shown in Table 2.
As shown in FIG. 3, the peak time of the organic solvent component No. six is 0-4.2 min, and the peak time of N, N-dimethylformamide is 9.58 min, which shows that the separation effect is good; the sum of all peak areas of the organic solvent component No. six in the period of time serves as the total peak area of the organic solvent No. six.
As shown in fig. 4, the standard curve equation of the standard curve fitting of the reference meal is: y=21.367x+23.285, and the correlation coefficient r=0.9993, which indicates that the content of the sixth organic solvent in the standard sample of the reference soybean meal has a good linear relationship with the peak area.
For comparison, each 3.000g of leached soybean meal to be detected 2-1 and 2-2 (2 parts of each leached soybean meal to be detected are used for parallel detection) are subjected to a six-number organic solvent standard adding experiment, the standard adding amounts are respectively 50mg/kg, 100mg/kg, 200mg/kg, 300mg/kg and 500mg/kg, and the standard adding detection results are shown in Table 2.
Table 2 results of the method of the present invention and the labeled detection of residual amount of organic solvent in leached soybean meal to be tested
As shown in Table 2, the relative error between the average value of the detection result of the method and the actual content of the sample is 0.27-3.9%, and when the addition amount is 50-500 mg/kg, the addition recovery rate of the method is 100.3-101.0%, which proves that the method is accurate and reliable.
Example 3
(1) Pretreatment of bean pulp leaching:
adding 2mL of extracting agent (the volume ratio of dimethyl sulfoxide to water is 1:1.2) into 6 20mL headspace bottles, respectively adding 2.000g of leached soybean meal 3-1, 3-2 and 3-3 to be detected, sealing, and performing ultrasonic extraction at 50 ℃ and 40kHz for 40min;
the preparation method of the leached soybean meal 3-1, 3-2 and 3-3 to be detected comprises the following steps: weighing 3 parts of 2.000g of standard soybean meal 3, respectively adding 500 mu L, 1.25mL and 2.25mL of ethanol standard solution (with the concentration of 0.8 mg/mL) into the standard soybean meal, placing the standard soybean meal in a rotary mixer, uniformly mixing the standard soybean meal for 10min at 1500r/min, keeping the soybean meal in contact with an inner cover film of a headspace bottle in the uniformly mixing process, placing the soybean meal at the temperature of 0 ℃, and standing the soybean meal for 24h to obtain the soybean meal;
(2) And (3) sample injection detection:
placing the headspace bottle with the pretreatment sample obtained in the step (1) on a headspace sample bottle rack, heating and balancing for 70min at 107 ℃, automatically sampling and removing the upper layer gas thereof for gas chromatography sample injection analysis, and measuring the total peak area;
the conditions of the automatic sample injection are as follows: the quantitative ring/valve temperature is 118 ℃, the transmission line temperature is 129 ℃, the circulation time is 28min, the sample injection time is 1.0min, the pressure time is 1.0min, and the sample injection volume is 1mL;
the conditions for the gas chromatography were the same as in example 1;
(3) Drawing a standard curve of the reference meal:
placing 0.5mL of ethanol standard solution into a 20mL headspace bottle, and performing gas chromatography analysis by automatic sample injection according to the step (2), as shown in FIG. 5;
transferring 0 μL, 125 μL, 250 μL, 500 μL, 750 μL, 1250 μL and 2500 μL ethanol standard solution (with concentration of 0.8 mg/mL) into 2.000g standard soybean meal 3 to prepare standard samples of standard soybean meal with ethanol content of 0mg/kg, 50mg/kg, 100mg/kg, 200mg/kg, 300mg/kg, 500mg/kg and 1000mg/kg, respectively, processing according to steps (1) and (2), taking the content of ethanol as an abscissa, taking the total peak area measured as an ordinate, and drawing a standard curve as shown in fig. 6;
(4) And (3) calculating results:
according to the formula: x=ρ, where: x is the residual quantity of the organic solvent in the leached soybean meal to be detected, mg/kg, rho is the content of the organic solvent corresponding to the total peak area obtained in the step (2) read from the standard curve obtained in the step (3), and the results are shown in Table 3.
As shown in FIG. 5, the peak time of ethanol is 2.0-2.9 min, and the peak time of dimethyl sulfoxide is 7.86min, which shows that the separation effect is good; the sum of all peak areas of the ethanol component over the period of time serves as the total peak area of the leaching solvent.
As shown in fig. 6, standard curve equations of standard curve fitting of the reference meal are respectively: y= 22.066x-4.9498, correlation coefficient R 2 0.9998, respectively, which shows that the linear relation between the ethanol content and the peak area in the standard sample of the standard soybean meal is good.
Each 2.000g of leached soybean meal 3-1, 3-2 and 3-3 is subjected to ethanol standard adding experiments, the standard adding amount is respectively 50mg/kg, 100mg/kg and 200mg/kg, and the standard adding detection results are shown in table 3.
TABLE 3 results of the method of the invention and the labeled detection of residual amount of organic solvent in leached soybean meal to be detected
As shown in Table 3, the relative error between the detection result and the actual error is less than or equal to 4.5%, the sample labeling recovery rate of the method is 100.7-104.8%, and the detection result of the method is accurate, so that the production process can be effectively guided.
Claims (9)
1. The method for detecting the residual amount of the organic solvent in the leached oil crop meal is characterized by comprising the following steps of:
(1) Pretreatment of oil crop meal leaching:
adding an extracting agent and leached oil crop meal into a headspace bottle, sealing and performing ultrasonic extraction; the mass volume ratio of the leached oil crop meal to the extractant is 1:1.0-1.5; the extractant is mixed liquid with the volume ratio of the extractant to water of 1:0.8-1.2; the extractant is N, N-dimethylformamide, N-dimethylacetamide or dimethyl sulfoxide;
(2) And (3) sample injection detection:
heating and balancing the headspace bottle filled with the pretreatment sample obtained in the step (1), and then removing the upper layer gas of the headspace bottle for gas chromatography analysis to obtain the total peak area; the temperature of the heating balance is 100-110 ℃ and the time is 40-80 min; a hydrogen flame ion detector is arranged in the gas chromatograph;
(3) Drawing a standard curve of the reference meal:
adding different volumes of organic solvent standard solutions into the standard oil crop meal to prepare standard oil crop meal samples with different contents, respectively processing according to the steps (1) and (2), taking the content of the organic solvent of the standard oil crop meal samples as an abscissa, taking the measured total peak area as an ordinate, and drawing a standard curve; the preparation method of the benchmark oil crop meal comprises the following steps: adding eluent into the leached oil crop meal, heating and stirring, vacuum filtering while the oil crop meal is hot, cleaning with hot water, wetting with water, tiling and baking, cooling and sealing to obtain the oil crop meal; the mass volume ratio of the leached oil crop meal to the eluent is 1:8-20; the eluent is a mixed solution of an extractant and water in a volume ratio of 1:2.0-4.0; the temperature of the heating and stirring is 50-70 ℃ and the time is 20-40 min; the preparation method of the organic solvent standard solution comprises the following steps: firstly, adding an extractant into a volumetric flask, then adding an organic solvent standard substance, and fixing the volume by using the extractant to obtain the product; the extractant is N, N-dimethylformamide, N-dimethylacetamide or dimethyl sulfoxide;
(4) And (3) calculating results:
according to the formula: x=ρ, where: x is the residual quantity of the organic solvent in leached oil crop meal, mg/kg, rho is the content of the organic solvent corresponding to the total peak area obtained in the step (2) read from the standard curve obtained in the step (3), mg/kg; the organic solvent is solvent No. six, methanol, ethanol or isopropanol.
2. The method for detecting the residual amount of the organic solvent in the leached oil crop meal according to claim 1, wherein the method comprises the following steps: in the step (1), the mass-volume ratio of the leached oil crop meal to the headspace bottle is 1.0-1.5:10; the leached oil crop meal is one or more of soybean meal, rapeseed meal, sunflower seed meal or peanut meal; the temperature of the ultrasonic extraction is 50-80 ℃, the frequency is 25-40 kHz, and the time is 20-40 min.
3. The method for detecting the residual amount of an organic solvent in leached oil crop meal according to claim 1 or 2, wherein: in the step (2), the gas sample injection mode is headspace sample injection or manual sample injection; the headspace sample injection mode is as follows: placing the headspace bottle with the pretreatment sample obtained in the step (1) on a headspace sample bottle rack for automatic sample injection; the specific parameters of the headspace sample injection are as follows: the temperature of the quantitative ring/valve is 110-120 ℃, the temperature of the transmission line is 120-130 ℃, the circulation time is 25-30 min, the sample injection time is 0.5-1.5 min, the pressure time is 0.5-1.5 min, and the sample injection volume is 1mL; the specific operation of the manual sample injection is as follows: controlling the room temperature of the instrument to be more than or equal to 25 ℃, heating and balancing the sample injection needle and the headspace bottle with the pretreatment sample obtained in the step (1), then removing 1mL of upper layer gas of the headspace bottle by using the sample injection needle, and rapidly injecting the gas chromatograph; the conditions of the gas chromatographic analysis are as follows: column box programming temperature: the temperature is kept at 50-60 ℃ for 3-5 min, then the temperature is raised to 200-220 ℃ at the speed of 20-40 ℃/min, the temperature of a sample inlet is kept at 250-280 ℃, the temperature of a detector is kept at 250-300 ℃, the flow rate of carrier gas nitrogen is 0.8-1.0 mL/min, the flow rate of hydrogen is 20-40 mL/min, the flow rate of air is 280-320 mL/min, and the split ratio is 10-120:1.
4. The method for detecting the residual amount of an organic solvent in leached oil crop meal according to claim 1 or 2, wherein: in the step (3), the vacuum degree of the vacuum suction filtration is 0.5-1.0 MPa; the temperature of the hot water is 60-100 ℃; the number of times of hot water cleaning is more than or equal to 5; the volume-mass ratio of the water quantity of each hot water washing to the leached oil crop meal is 5-20:1; the volume-mass ratio of the water adding amount to the leached oil crop meal is 4-20:1; the baking temperature is 120-150 ℃ and the baking time is 2-5 h.
5. The method for detecting the residual amount of an organic solvent in leached oil crop meal according to claim 3, wherein the method comprises the steps of: in the step (3), the vacuum degree of the vacuum suction filtration is 0.5-1.0 MPa; the temperature of the hot water is 60-100 ℃; the number of times of hot water cleaning is more than or equal to 5; the volume-mass ratio of the water quantity of each hot water washing to the leached oil crop meal is 5-20:1; the volume-mass ratio of the water adding amount to the leached oil crop meal is 4-20:1; the baking temperature is 120-150 ℃ and the baking time is 2-5 h.
6. The method for detecting the residual amount of an organic solvent in leached oil crop meal according to claim 1 or 2, wherein: in the step (3), the concentration of the organic solvent standard solution is 0.5-10.0 mg/mL; the different contents are more than or equal to 5 contents in the range of 0-1000 mg of organic solvent/kg of standard oil crop meal; the amount of the extractant added is 0.4 to 0.8 times of the volume of the fixed volume.
7. The method for detecting the residual amount of an organic solvent in leached oil crop meal according to claim 3, wherein the method comprises the steps of: in the step (3), the concentration of the organic solvent standard solution is 0.5-10.0 mg/mL; the different contents are more than or equal to 5 contents in the range of 0-1000 mg of organic solvent/kg of standard oil crop meal; the amount of the extractant added is 0.4 to 0.8 times of the volume of the fixed volume.
8. The method for detecting the residual amount of an organic solvent in leached oil crop meal according to claim 4, wherein the method comprises the following steps: in the step (3), the concentration of the organic solvent standard solution is 0.5-10.0 mg/mL; the different contents are more than or equal to 5 contents in the range of 0-1000 mg of organic solvent/kg of standard oil crop meal; the amount of the extractant added is 0.4 to 0.8 times of the volume of the fixed volume.
9. The method for detecting the residual amount of the organic solvent in the leached oil crop meal according to claim 5, wherein the method comprises the following steps: in the step (3), the concentration of the organic solvent standard solution is 0.5-10.0 mg/mL; the different contents are more than or equal to 5 contents in the range of 0-1000 mg of organic solvent/kg of standard oil crop meal; the amount of the extractant added is 0.4 to 0.8 times of the volume of the fixed volume.
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