CN117630237A - Method for non-targeted screening of semi-volatile residual substances in composite membrane for infant milk powder and internal standard composition - Google Patents
Method for non-targeted screening of semi-volatile residual substances in composite membrane for infant milk powder and internal standard composition Download PDFInfo
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- CBFCDTFDPHXCNY-UHFFFAOYSA-N icosane Chemical compound CCCCCCCCCCCCCCCCCCCC CBFCDTFDPHXCNY-UHFFFAOYSA-N 0.000 claims abstract description 51
- 239000002904 solvent Substances 0.000 claims abstract description 31
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N30/06—Preparation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/72—Mass spectrometers
- G01N30/7206—Mass spectrometers interfaced to gas chromatograph
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/86—Signal analysis
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/86—Signal analysis
- G01N30/8675—Evaluation, i.e. decoding of the signal into analytical information
- G01N30/8679—Target compound analysis, i.e. whereby a limited number of peaks is analysed
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N2030/042—Standards
- G01N2030/045—Standards internal
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N30/06—Preparation
- G01N2030/062—Preparation extracting sample from raw material
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
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Abstract
The invention provides a method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder and an internal standard composition, wherein the method comprises the following steps: sample pretreatment: cutting infant milk powder with a composite film sample, taking a food contact surface as an inner surface, making a bag, injecting an extraction solvent added with an internal standard substance into the sample bag, sealing, and vibrating to obtain a sample to-be-detected liquid; detecting on the machine; analyzing and calculating the atlas; wherein the extraction solvent is dichloromethane, and the internal standard substance is a combination of 4,4' -difluorobiphenyl and n-eicosane. The invention has simple operation, adopts the bag making method to prepare the composite membrane for the infant milk powder, selects methylene dichloride as an extraction solvent, and can extract more substances to the maximum extent by oscillation extraction. The invention optimizes the best extraction method and internal standard after a large number of experiments, and the detection method has high accuracy and good recovery rate through multiple experimental verification.
Description
Technical Field
The invention belongs to the technical field of food safety detection, and particularly relates to a method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder and an internal standard composition.
Background
The development of High Resolution Mass Spectrometry (HRMS) has played a great impetus for the analysis of NIAS species. The use of a gas chromatograph-quadrupole-time-of-flight mass spectrometer (GC-QTOF) allows not only confirmation of the analysis results of GC-MS but also identification of more NIAS material than a conventional gas chromatograph-mass spectrometer (GC-MS). The composite membrane for the infant milk powder is formed by compounding PET, nylon, PE and other materials, and the extraction and analysis of residual substances are particularly difficult due to the complexity of the materials.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder and an internal standard composition.
In order to achieve the above purpose, the present invention provides a method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder, comprising the following steps:
sample pretreatment: cutting infant milk powder with a composite film sample, taking a food contact surface as an inner surface, making a bag, injecting an extraction solvent added with an internal standard substance into the sample bag, sealing, and vibrating to obtain a sample to-be-detected liquid;
and (3) detecting: respectively adding a sample to-be-detected liquid and a standard working solution prepared from an internal standard substance into a headspace bottle, and carrying out gas chromatography-four-level rod-time-of-flight high-resolution mass spectrometry to obtain a total ion flow chromatogram;
and (3) analyzing and calculating a map: carrying out qualitative analysis and semi-quantitative analysis on screened target substances according to the measurement result;
wherein the extraction solvent is dichloromethane, and the internal standard substance is a combination of 4,4' -difluorobiphenyl and n-eicosane.
The method adopts a bag making method to extract the semi-volatile residual substances in the composite film for the infant milk powder, and uses 4,4' -difluorobiphenyl standard substance (C 12 H 8 F 2 CAS 398-23-2) and n-eicosane standard (C 20 H 42 CAS 112-95-8) is an internal standard, and results are semi-quantitatively analyzed with good accuracy and reproducibility by means of a commercial NIST spectral library.
According to an embodiment of the present invention, preferably, the on-machine detection step further comprises adding a blank sample to the headspace bottle and performing the measurement.
According to a specific embodiment of the present invention, preferably, the mass ratio of 4,4' -difluorobiphenyl to n-eicosane in the internal standard is (0.5-1): 1.
According to a specific embodiment of the present invention, preferably, the solvent of the standard working fluid is dichloromethane.
According to a specific embodiment of the present invention, it is preferable that the sample bag is shaken at 20 to 30℃for 5 to 10 hours in the sample pretreatment.
According to a specific embodiment of the present invention, preferably, the ratio between the composite film sample for infant milk powder and the extraction solvent is (1-4) × (1-4) cm 2 /(10-30)ml。
According to a specific embodiment of the present invention, preferably, the concentration of the internal standard in the standard working fluid is the same as the concentration of the internal standard in the extraction solvent.
According to a specific embodiment of the present invention, preferably, the concentration of the 4,4' -difluorobiphenyl internal standard or the n-eicosane internal standard in the standard working fluid and the extraction solvent is 100-200mg/L.
According to a specific embodiment of the present invention, preferably, wherein the gas chromatography column is HP-5MS UI having a column length of 30m, an inner diameter of 0.25mm, and a film thickness of 0.5 μm; the temperature of the chromatographic column is 300-320 ℃.
According to a specific embodiment of the present invention, preferably, the other chromatographic conditions include:
chromatographic column temperature program: maintaining at 35-45deg.C for 1-3min, heating to 300-310 deg.C at a rate of 5-15deg.C/min for 10-20min, and operating at 310-320 deg.C for 4-6min;
carrier gas: helium with a flow rate of 1-3mL/min;
sample injection mode: split sample injection, split ratio (5-20): 1, a step of;
sample inlet temperature: 300-310 ℃;
auxiliary heater temperature: 300-310 ℃;
sample injection amount: 0.5-2. Mu.L.
According to a specific embodiment of the present invention, preferably, the mass spectrometry conditions include:
ion source: an electron bombardment ion source; ion source temperature: 220-250 ℃;
four-stage bar temperature: 130-170 ℃;
interface temperature: 180-220 ℃;
solvent delay: 3-5min;
scanning mode: a full scan mode; scanning interval: 33-900Da.
According to a specific embodiment of the present invention, preferably, in the qualitative analysis, chromatographic peaks satisfying the following conditions simultaneously are resolved:
a. the chromatographic peak area of the sample at the same retention time is more than 10 times of that of the blank sample;
b. the chromatographic peak of the sample is more than 1-2 times of the area of the internal standard peak with close retention time or similar structure.
According to a specific embodiment of the present invention, preferably, the analytical procedure of the chromatographic peak is as follows:
a. and (5) searching a spectrum library: carrying out spectrum library retrieval on a target substance spectrogram by using an NIST database, and carrying out qualitative analysis according to the matching degree, the correlation between a molecular structure and material information or the correlation between the molecular structure and common additives and oligomer structures, wherein the matching degree of the spectrum library is more than 70 percent, and the unknown substance can be judged as a spectrum library retrieval substance;
b. manual spectrum splitting: and carrying out qualitative analysis by utilizing knowledge of organic chemistry/analytical chemistry according to the material information, additives possibly existing in the processing process and processing material residues on the upstream of the production line and combining the mass-nuclear ratio information of the target material.
According to a specific embodiment of the present invention, preferably, the calculation method of the semi-quantitative analysis is: the concentration of the screened target is calculated by multiplying the ratio of the peak area of the screened target and the peak area of the internal standard by the known concentration of the internal standard.
According to a specific embodiment of the present invention, preferably the gas chromatograph-quadrupole-time-of-flight high resolution mass spectrometer used is Agilent 8890GC-7250QTOF.
According to a specific embodiment of the present invention, preferably, the raw material of the composite film for infant milk powder includes one or a combination of two or more of PET (polyethylene terephthalate), nylon, and PE (polyethylene).
According to a specific embodiment of the present invention, preferably, the method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder includes the following steps:
step one: preparing required reagents: analytically pure reagent dichloromethane; 4,4' -difluorobiphenyl standard (C) 12 H 8 F 2 398-23-2) with purity greater than or equal to 99.9%; normal eicosane standard (C) 20 H 42 112-95-8% of CAS), the purity is more than or equal to 98%;
step two: preparing an internal standard stock solution: the ratio of the mass of 4,4' -difluorobiphenyl (in g), the mass of n-eicosane (in g) to the volume of dichloromethane (in L) is 1:1:1-2, transferring into a volumetric flask to prepare an internal standard stock solution A with the concentration of 500-1000mg/L after dissolving in a beaker, and storing in a dark place at the temperature of 4-8 ℃;
step three: preparing an internal standard intermediate solution: diluting the internal standard stock solution A and dichloromethane according to the volume ratio of 1:2.5-1:10 to prepare an internal standard intermediate solution B with the concentration of 100-200mg/L, and storing the internal standard intermediate solution B in a dark place at the temperature of 4-8 ℃;
step four: preparation of a standard working solution: adding 10-30mL of dichloromethane and 50-100 mu L of internal standard intermediate liquid B into a headspace bottle, capping, oscillating for 5-10h at 20-30 ℃, and taking out to obtain standard working solution;
step five: pretreatment of the sample: cutting the sample into pieces of (1-4) × (1-4) cm 2 Taking the food contact surface as the inner surface to make a bag, injecting 10-30mL of dichloromethane into the bag, then removing redundant gas in the bag, adding 50-100 mu L of internal standard intermediate liquid B, sealing, oscillating for 5-10h at 20-30 ℃, and taking out to obtain a sample to-be-detected liquid;
step six: adding 10-30mL of dichloromethane into another headspace bottle, capping, oscillating for 5-10h at 20-30 ℃, and taking out to obtain a blank sample;
step seven: sequentially carrying out gas chromatography-four-stage rod-time-of-flight high-resolution mass spectrometry on a blank sample, a standard working solution and a sample to-be-detected solution to obtain a total ion flow chromatogram;
step eight: qualitative analysis: chromatographic peaks satisfying the following conditions were resolved:
(a) The chromatographic peak area of the sample at the same retention time is more than 10 times of that of the blank sample;
(b) The chromatographic peak of the sample is more than 1-2 times of the area of the internal standard peak with close retention time or similar structure;
step nine: semi-quantitative calculation:
A. the mass of the screened substances in the sample to be tested of the upper machine is converted according to the following formula:
M＝(A target object /A Internal standard )×M Internal standard
Wherein:
m, screening out the mass of a target object in the sample to be tested of the upper machine, wherein the unit is microgram (mug);
A target object Screening out the area of an extracted ion peak of a target object in the sample to be detected of the machine sample;
A internal standard The area of the extracted ion peak of the target in the sample to be detected of the machine sample corresponding to the internal standard;
M internal standard -the mass of the internal standard in the sample to be measured of the machine is expressed in micrograms (μg);
B. the mass of the screened material in the blank sample was converted according to the following formula:
M 0 ＝(A target 0 /A Internal standard 0 )×M Internal standard
M 0 Screening out the mass of the target in the blank sample, wherein the unit is micrograms (mug);
A target 0 Screening out the extracted ion peak area of the target object in the blank sample;
A internal standard 0 The peak area of the extracted ions of the internal standard corresponding to the target in the blank sample;
M internal standard -the mass of the internal standard in the blank sample in micrograms (μg);
C. the residual amount of the screened substance in the sample is converted as follows:
C＝(M-M 0 )/M weighing
C-sieving out the residual amount of the target in the sample in milligrams per kilogram (mg/kg)/microgram per square decimeter (μg/dm) 2 )；
M, screening out the mass of a target object in the sample to be tested of the upper machine, wherein the unit is microgram (mug);
M 0 screening out the mass of the target in the blank sample, wherein the unit is micrograms (mug);
M weighing The mass measured/area of the sample weighed on the machine is given in grams (g)/square decimeter (dm) 2 )。
The invention also provides an internal standard composition for non-targeted screening of semi-volatile residual substances in the composite membrane for infant milk powder, which is a combination of 4,4' -difluorobiphenyl and n-eicosane with the mass ratio of (0.5-1) to 1.
The invention also provides a kit for non-targeted screening of semi-volatile residue in the composite film for infant milk powder, which comprises the internal standard composition for non-targeted screening of semi-volatile residue in the composite film for infant milk powder.
According to a specific embodiment of the present invention, preferably, the kit for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder further comprises an extraction solvent, wherein the extraction solvent is dichloromethane. The extraction solvent is used for extracting semi-volatile residue.
The invention also provides application of the internal standard composition in detection of semi-volatile residual substances in the composite membrane for non-targeted screening of infant milk powder, wherein the internal standard composition is a combination of 4,4' -difluorobiphenyl and n-eicosane with the mass ratio of (0.5-1): 1.
The technical scheme provided by the invention has the following beneficial effects:
the invention has simple operation, adopts the bag making method to prepare the composite membrane for the infant milk powder, selects methylene dichloride as an extraction solvent, and can extract more substances to the maximum extent by oscillation extraction.
The invention optimizes the best extraction method and internal standard after a large number of experiments, and the experiment verification shows that the detection method has high accuracy and good recovery rate, can perform semi-quantitative analysis on semi-volatile residual substances in the composite film for the infant milk powder, and provides scientific basis for the safety detection of food contact materials, thereby providing risk monitoring and early warning for foods of food enterprises and food contact material production enterprises.
The method provided by the invention has the characteristics of simplicity and convenience in operation, high stability and the like, and can be used for semi-quantitative analysis through spectrum analysis. In some embodiments, when the composite membrane sample sampling area is 1dm 2 The detection limit is up to 10 mug/dm 2 The product can be comprehensively evaluated, the product quality is stabilized, and the safety of food contact materials and products is ensured.
Drawings
FIG. 1 is a total ion flow chromatogram of a hollow white sample of example 1 of the present invention;
FIG. 2 is a graph showing the total ion flow of the standard working fluid in example 1 of the present invention;
FIG. 3 is a graph showing the total ion flow of the sample solution to be measured in example 1 of the present invention;
fig. 4 is a graph showing the total ion flow chromatograms of the three solvents to be tested for acetonitrile, acetone, and methylene chloride in comparative example 1 of the present invention, wherein green is acetonitrile, blue is acetone, and red is methylene chloride.
Detailed Description
The technical solution of the present invention will be described in detail below for a clearer understanding of technical features, objects and advantageous effects of the present invention, but should not be construed as limiting the scope of the present invention.
The invention provides a method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder, which specifically comprises the following steps:
step one: preparing required reagents: analytically pure reagent dichloromethane; 4,4' -difluorobiphenyl standard (C) 12 H 8 F 2 398-23-2) with purity greater than or equal to 99.9%; normal eicosane standard (C) 20 H 42 112-95-8% of CAS), the purity is more than or equal to 98%;
step two: preparing an internal standard stock solution: the ratio of the mass of 4,4' -difluorobiphenyl (in mg), the mass of n-eicosane (in mg) to the volume of dichloromethane (in L) is 1:1:1-2, transferring into a volumetric flask to prepare an internal standard stock solution A with the concentration of 500-1000mg/L after dissolving in a beaker, and storing in a dark place at the temperature of 4-8 ℃;
step three: preparing an internal standard intermediate solution: diluting the internal standard stock solution A and dichloromethane according to the volume ratio of 1:2.5-1:10 to prepare an internal standard intermediate solution B with the concentration of 100-200mg/L, and storing the internal standard intermediate solution B in a dark place at the temperature of 4-8 ℃;
step four: pretreatment of standard working solution: adding 10-30mL of dichloromethane and 50-100 mu L of internal standard intermediate liquid B into a headspace bottle, capping, oscillating for 5-10h at 20-30 ℃, and taking out to obtain standard working solution;
step five: pretreatment of the sample: cutting a sample into squares with the length of 1.2cm multiplied by 1.2cm, taking a food contact surface as an inner surface for making a bag, injecting 10-30mL of methylene dichloride into the bag, removing redundant gas in the bag, adding 50-100 mu L of internal standard intermediate liquid B, oscillating for 5-10h at the temperature of 20-30 ℃, and taking out to obtain a sample to-be-detected liquid;
step six: pretreatment of blank samples: adding 10-30mL of dichloromethane into a headspace bottle, capping, oscillating for 5-10h at 20-30 ℃, and taking out to obtain a blank sample;
step seven: sequentially carrying out gas chromatography-four-stage rod-time-of-flight high-resolution mass spectrometry on a blank sample, a standard working solution and a sample to-be-detected solution to obtain a total ion flow chromatogram; wherein the chromatographic separation process is as follows: chromatographic column: HP-5MS UI, column length 30m, inner diameter 0.25mm, film thickness 0.5 μm; heating program: maintaining at 40 deg.C for 1-3min, heating to 300-310 deg.C at a rate of 5-15 deg.C/min for 10-20min, and operating at 310-320 deg.C for 4-6min; carrier gas: helium, 1-3mL/min; sample injection mode: split sample injection, split ratio 5:1, a step of; sample inlet temperature: 300-310 ℃; auxiliary heater temperature: 300-310 ℃; sample injection amount: 0.5-2. Mu.L. The mass spectrum detection process comprises the following steps: an electron bombardment ion source (EI) mode is adopted; the temperature of the ion source is 220-250 ℃; four-stage bar temperature: 130-170 ℃; interface temperature: 180-220 ℃; solvent delay: 3-5min; the mass spectrum scanning method is a full scanning mode (SCAN), and the scanning interval is as follows: 33-900Da; the gas chromatography-quaternary rod-time-of-flight high-resolution mass spectrometer adopted in the sample measurement is Agilent 8890GC-7250QTOF of Agilent and is provided with an EI ion source;
step eight: qualitative analysis: chromatographic peaks satisfying the following conditions were resolved:
a. the chromatographic peak area of the sample at the same retention time is more than 10 times of that of the blank sample;
b. the chromatographic peak of the sample is more than 1 time of the area of the internal standard peak with close retention time or similar structure.
Step nine: the analysis flow is as follows:
a. and (5) searching a spectrum library: carrying out spectrum library retrieval on a target substance spectrogram by using an NIST database, and carrying out qualitative analysis according to the matching degree, the correlation between a molecular structure and material information or the correlation between the molecular structure and common additives and oligomer structures (the matching degree of the spectrum library is more than 70 percent and unknown substances can be judged as spectrum library retrieval substances);
b. manual spectrum splitting: according to material information, possible additives in the processing process and processing material residues at the upstream of the production line, combining with the mass-to-nuclear ratio information of the target material, and performing qualitative analysis by utilizing knowledge of organic chemistry/analytical chemistry; when the structure of the substance cannot be determined by the analysis method, the substance is reported in the form of an unknown substance or a fitted molecular formula.
Step ten: quantitative calculation:
A. the mass of the screened substances in the sample to be tested of the upper machine is converted according to the following formula:
M＝(A target object /A Internal standard )×M Internal standard
Wherein:
m, screening out the mass of a target object in the sample to be tested of the upper machine, wherein the unit is microgram (mug);
A target object Screening out the area of an extracted ion peak of a target object in the sample to be detected of the machine sample;
A internal standard The area of the extracted ion peak of the target in the sample to be detected of the machine sample corresponding to the internal standard;
M internal standard -the mass of the internal standard in the sample to be measured of the machine is expressed in micrograms (μg);
B. the mass of the screened material in the blank sample was converted according to the following formula:
M 0 ＝(A target 0 /A Internal standard 0 )×M Internal standard
M 0 Screening out the mass of the target in the blank sample, wherein the unit is micrograms (mug);
A target 0 Screening out the extracted ion peak area of the target object in the blank sample;
A internal standard 0 The peak area of the extracted ions of the internal standard corresponding to the target in the blank sample;
M internal standard -the mass of the internal standard in the blank sample in micrograms (μg);
C. the residual amount of the screened substance in the sample is converted as follows:
C＝(M-M 0 )/M weighing
C-sieving out the residual amount of the target in the sample in milligrams per kilogram (mg/kg)/microgram per square decimeter (μg/dm) 2 )；
M, screening out the mass of a target object in the sample to be tested of the upper machine, wherein the unit is microgram (mug);
M 0 screening out the mass of the target in the blank sample, wherein the unit is micrograms (mug);
M weighing The mass measured/area of the sample weighed on the machine is given in grams (g)/square decimeter (dm) 2 )。
The measurement procedure of the present invention is further described by way of examples.
Example 1
The embodiment provides a method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder, which specifically comprises the following steps:
1. experimental part
1.1 experimental materials and instrumentation:
the infant milk powder of the experimental sample is packed by a composite film and purchased from the inner Mongolian illi real group Co., ltd; agilent 8890GC-7250QTOF gas chromatograph-quadrupole-time-of-flight high resolution mass spectrometer (equipped with EI source) of Agilent equipped with a chromatographic column HP-5MS UI, 30m length, 0.25mm inner diameter, 0.5 μm film thickness.
1.2 main reagents:
analytically pure reagent dichloromethane; 4,4' -difluorobiphenyl standard (C) 12 H 8 F 2 398-23-2) with purity greater than or equal to 99.9%; normal eicosane standard (C) 20 H 42 112-95-8% of CAS) and the purity is more than or equal to 98%.
1.3 preparation of internal standard stock solution:
accurately weighing 100mg of 4,4' -difluorobiphenyl and 100mg (accurate to 0.1 mg) of n-eicosane into a beaker, dissolving with 50mL of dichloromethane, transferring into a 100mL volumetric flask, washing the beaker for 2 times with a small amount of dichloromethane, merging the washing liquid into the volumetric flask, fixing the volume to a scale with dichloromethane, shaking uniformly, preparing into an internal standard stock solution A with the concentration of 1000mg/L, and storing in a dark place at the temperature of 4 ℃.
1.4 preparation of internal standard intermediate liquid:
accurately transferring the internal standard stock solution A into a volumetric flask with 1000 mu L to 10mL, fixing the volume to the scale with dichloromethane, shaking uniformly to prepare an internal standard intermediate solution B with the concentration of 100mg/L, and storing in a dark place at the temperature of 4 ℃.
1.5 preparation of standard working solution:
to a headspace bottle, 20mL of dichloromethane and 100 μl of internal standard intermediate solution B were added, and after capping, the mixture was shaken at 20 ℃ for 7h and taken out to obtain a standard working solution.
1.6 pretreatment of samples:
cutting a sample into squares of 1.2cm multiplied by 1.2cm, taking a food contact surface as an inner surface for making a bag, injecting 20mL of dichloromethane into the bag, removing redundant gas in the bag, adding 100 mu L of internal standard intermediate liquid B, oscillating for 7h at 20 ℃, and taking out to obtain a sample to-be-detected liquid.
1.7 preparation of blank samples:
taking a headspace bottle, adding 20mL of dichloromethane, capping, oscillating for 7h at 20 ℃, and taking out to obtain a blank sample.
2. Analysis part
2.1 chromatographic conditions:
chromatographic column: HP-5MS UI, column length 30m, inner diameter 0.25mm, film thickness 0.5 μm; heating program: maintaining at 40deg.C for 3min, heating to 300deg.C at 10deg.C/min, maintaining for 15min, and operating at 310 deg.C for 5min; carrier gas: helium, 1mL/min; sample injection mode: split sample injection, split ratio 5:1, a step of; sample inlet temperature: 300 ℃; auxiliary heater temperature: 300 ℃; sample injection amount: 1 mul.
2.2 Mass Spectrometry conditions:
an EI ion source; ion source temperature: 230 ℃; four-stage bar temperature: 150 ℃; solvent delay time: 3.5min; scanning mode: SCAN; scanning an ion interval: 33-900Da.
3. Results and discussion
3.1 semi-quantitative analysis:
and (3) sequentially sampling and measuring a blank sample, a standard working solution and a sample to-be-measured solution according to the chromatographic and mass spectrometry conditions. Fig. 1 and 2 are total ion flow diagrams of a blank sample and a standard working fluid, respectively, of the present invention. In contrast, it can be seen that the retention time of 4,4' -difluorobiphenyl was 14.971min and that of n-eicosane was 21.828min. Fig. 3 is a total ion flow diagram of a sample fluid under test.
Comparing fig. 3 with fig. 1 and fig. 2, selecting chromatographic peaks with peak areas similar to or larger than those of the internal standard substances to perform NIST library analysis, and calculating the content of the screened substances according to the similarity of the structures of the screened substances and the internal standard substances.
The specific results are shown in Table 1.
Table 1 screening out target information
| Detection limit | Substance name | CAS number | Test results | Possible sources of |
| 10μg/dm 2 | 6-aminocaproic acid glycol ester | / | 30.1μg/dm 2 | PET |
| 10μg/dm 2 | 2, 4-Di-tert-butylphenol | 96-76-4 | 29.3μg/dm 2 | Antioxidant |
| 10μg/dm 2 | Erucamide | 112-84-5 | 29μg/dm 2 | Slipping agent |
| 10μg/dm 2 | Antioxidant 168 | 31570-04-4 | 134μg/dm 2 | Antioxidant |
| 10μg/dm 2 | Antioxidant 1076 | 2082-79-3 | 51.1μg/dm 2 | Antioxidant |
| 10μg/dm 2 | Diethylene glycol adipate | / | 34.6μg/dm 2 | Monomer(s) |
| 10μg/dm 2 | Caprolactam | 105-60-2 | 11.9μg/dm 2 | Slipping agent |
Table 1 summarizes the content of semi-volatile substances in the composite film package for the infant milk powder, and detects that the slipping agent comprises erucamide and caprolactam, the antioxidant comprises antioxidant 168 and antioxidant 1076, and the monomers comprise diethylene glycol adipate and ethylene glycol 6-aminocaproate, so that the slipping agent can provide safety evaluation for food contact materials and products.
3.2 precision, recovery:
100 mu L of internal standard intermediate solution B is added into a packaging material, the GC-QTOF is measured after pretreatment, 6 parts of the internal standard intermediate solution B are prepared in parallel with the same standard concentration, and the recovery rate and the precision are calculated, and the result is shown in Table 2.
Table 2 precision and recovery experiments (n=6)
As can be seen from Table 2, the recovery rates of the internal standard substance addition are 64.5% and 96%, respectively, which shows that the accuracy of the method is high; the relative standard deviations were 10.4% and 15.0%, respectively, demonstrating the good reproducibility of the process of the invention.
Comparative example 1: selection of extraction solvent
The comparative example was examined by selecting as solvents acetone and acetonitrile which are miscible with water and most organic solvents, and methylene chloride which is capable of dissolving most substances, and the specific experimental procedure is as follows:
1. experimental part
1.1 experimental materials and instrumentation:
the infant milk powder of the experimental sample is packed by a composite film and purchased from the inner Mongolian illi real group Co., ltd; agilent 8890GC-7250QTOF gas chromatograph-quadrupole-time-of-flight high resolution mass spectrometer (equipped with EI source) of Agilent equipped with a chromatographic column HP-5MS UI, 30m length, 0.25mm inner diameter, 0.5 μm film thickness.
1.2 main reagents:
analytically pure reagents dichloromethane, acetone and acetonitrile; 4,4' -difluorobiphenyl standard (C) 12 H 8 F 2 398-23-2) with purity greater than or equal to 99.9%; normal eicosane standard (C) 20 H 42 112-95-8% of CAS) and the purity is more than or equal to 98%.
1.3 preparation of internal standard stock solution:
accurately weighing 100mg of 4,4' -difluorobiphenyl and 100mg (accurate to 0.1 mg) of n-eicosane into a beaker, dissolving with 50mL of dichloromethane, transferring into a 100mL volumetric flask, washing the beaker for 2 times with a small amount of dichloromethane, merging the washing liquid into the volumetric flask, fixing the volume to a scale with dichloromethane, shaking uniformly, preparing into an internal standard stock solution A with the concentration of 1000mg/L, and storing in a dark place at the temperature of 4 ℃.
1.4 preparation of internal standard intermediate liquid:
accurately transferring the internal standard stock solution A into a volumetric flask with 1000 mu L to 10mL, fixing the volume to the scale with dichloromethane, shaking uniformly to prepare an internal standard intermediate solution B with the concentration of 100mg/L, and storing in a dark place at the temperature of 4 ℃.
1.5 pretreatment of samples:
cutting three samples into squares of 1.2cm multiplied by 1.2cm respectively, taking a food contact surface as an inner surface for making bags, respectively injecting 20mL of dichloromethane, 20mL of acetone and 20mL of acetonitrile into the bags, then removing redundant gas in the bags, adding 100 mu L of internal standard intermediate liquid B, oscillating for 7 hours at 20 ℃, and taking out to obtain a sample to-be-detected liquid.
2. Analysis part
2.1 chromatographic conditions:
chromatographic column: HP-5MS UI, column length 30m, inner diameter 0.25mm, film thickness 0.5 μm; heating program: maintaining at 40deg.C for 3min, heating to 300deg.C at 10deg.C/min, maintaining for 15min, and operating at 310 deg.C for 5min; carrier gas: helium, 1mL/min; sample injection mode: split sample injection, split ratio 5:1, a step of; sample inlet temperature: 300 ℃; auxiliary heater temperature: 300 ℃; sample injection amount: 1 mul.
2.2 Mass Spectrometry conditions:
an EI ion source; ion source temperature: 230 ℃; four-stage bar temperature: 150 ℃; solvent delay time: 3.5min; scanning mode: SCAN; scanning an ion interval: 33-900Da.
3. Results and discussion
Fig. 4 shows the chromatographic superposition spectra of three extraction solvents of acetonitrile, acetone and dichloromethane, and it can be seen that the total ion flow diagram using dichloromethane as the extraction solvent has the largest chromatographic peak, the same chromatographic peak has the largest peak area, and the chromatographic response is the largest. The results show that dichloromethane is able to extract more residual material than acetonitrile and acetone.
Therefore, the dichloromethane extraction solvent has higher solubility to semi-volatile substances and higher permeability to sample materials, and has higher extraction effect on various residual substances in the sample. In addition, the dichloromethane solvent has moderate boiling point, good accessibility and safety.
Claims (12)
1. A method for non-targeted screening of semi-volatile residual materials in a composite membrane for infant milk powder, comprising the steps of:
sample pretreatment: cutting infant milk powder with a composite film sample, taking a food contact surface as an inner surface, making a bag, injecting an extraction solvent added with an internal standard substance into the sample bag, sealing, and vibrating to obtain a sample to-be-detected liquid;
and (3) detecting: respectively adding a sample to-be-detected liquid and a standard working solution prepared from an internal standard substance into a headspace bottle, and carrying out gas chromatography-four-level rod-time-of-flight high-resolution mass spectrometry to obtain a total ion flow chromatogram;
and (3) analyzing and calculating a map: carrying out qualitative analysis and semi-quantitative analysis on screened target substances according to the measurement result;
wherein the extraction solvent is dichloromethane, and the internal standard substance is a combination of 4,4' -difluorobiphenyl and n-eicosane;
preferably, the on-machine detection step further comprises adding a blank sample to the headspace bottle and performing the assay.
2. The method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder according to claim 1, wherein the mass ratio of 4,4' -difluorobiphenyl to n-eicosane in the internal standard is (0.5-1): 1.
3. The method for non-targeted screening of semi-volatile residual materials in a composite membrane for infant milk powder of claim 1, wherein the solvent of the standard working fluid is methylene chloride.
4. The method for non-targeted screening of semi-volatile residual materials in a composite membrane for infant milk powder according to claim 1, wherein the sample bag is subjected to sample pretreatment and is shaken at 20-30 ℃ for 5-10 hours;
preferably, the ratio of the composite film sample for infant milk powder to the extraction solvent is (1-4) x (1-4) cm 2 /(10-30)ml。
5. The method for non-targeted screening of semi-volatile residual materials in a composite membrane for infant milk powder according to claim 1, wherein the concentration of internal standard in the standard working fluid is the same as the concentration of internal standard in the extraction solvent;
preferably, the concentration of the 4,4' -difluorobiphenyl internal standard or the n-eicosane internal standard in the standard working solution and the extraction solvent is 100-200mg/L.
6. The method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder according to claim 1, wherein the gas chromatography column is HP-5MS UI having a column length of 30m, an inner diameter of 0.25mm, and a membrane thickness of 0.5 μm; the temperature of the chromatographic column is 300-320 ℃;
preferably, the other chromatographic conditions include:
chromatographic column temperature program: maintaining at 35-45deg.C for 1-3min, heating to 300-310 deg.C at a rate of 5-15deg.C/min for 10-20min, and operating at 310-320 deg.C for 4-6min;
carrier gas: helium with a flow rate of 1-3mL/min;
sample injection mode: split sample injection, split ratio (5-20): 1, a step of;
sample inlet temperature: 300-310 ℃;
auxiliary heater temperature: 300-310 ℃;
sample injection amount: 0.5-2. Mu.L.
7. The method for non-targeted screening of semi-volatile residual materials in a composite membrane for infant milk powder of claim 1, wherein the mass spectrometry conditions comprise:
ion source: an electron bombardment ion source; ion source temperature: 220-250 ℃;
four-stage bar temperature: 130-170 ℃;
interface temperature: 180-220 ℃;
solvent delay: 3-5min;
scanning mode: a full scan mode; scanning interval: 33-900Da.
8. The method for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder according to claim 1, wherein in the qualitative analysis chromatographic peaks satisfying simultaneously the following conditions are resolved:
a. the chromatographic peak area of the sample at the same retention time is more than 10 times of that of the blank sample;
b. the chromatographic peak of the sample is more than 1-2 times of the area of the internal standard peak with close retention time or similar structure;
preferably, the analytical procedure for the chromatographic peaks is as follows:
a. and (5) searching a spectrum library: carrying out spectrum library retrieval on a target substance spectrogram by using an NIST database, and carrying out qualitative analysis according to the matching degree, the correlation between a molecular structure and material information or the correlation between the molecular structure and common additives and oligomer structures, wherein the matching degree of the spectrum library is more than 70 percent, and the unknown substance can be judged as a spectrum library retrieval substance;
b. manual spectrum splitting: according to material information, possible additives in the processing process and processing material residues at the upstream of the production line, combining with the mass-to-nuclear ratio information of the target material, and performing qualitative analysis by utilizing knowledge of organic chemistry/analytical chemistry;
preferably, the calculation method of the semi-quantitative analysis is as follows: the concentration of the screened target is calculated by multiplying the ratio of the peak area of the screened target and the peak area of the internal standard by the known concentration of the internal standard.
9. A method of non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder according to any one of claims 1-8, comprising the steps of:
step one: preparing required reagents: analytically pure reagent dichloromethane; the purity of the 4,4' -difluorobiphenyl standard product is more than or equal to 99.9%; the purity of the normal eicosane standard substance is more than or equal to 98 percent;
step two: preparing an internal standard stock solution: according to the volume ratio of the mass of 4,4' -difluorobiphenyl, the mass of n-eicosane and dichloromethane of 1g:1g:1-2L, transferring into a volumetric flask to prepare internal standard stock solution with the concentration of 500-1000mg/L after dissolving in a beaker, and storing in a dark place at the temperature of 4-8 ℃;
step three: preparing an internal standard intermediate solution: diluting the internal standard stock solution and dichloromethane according to the volume ratio of 1:2.5-1:10 to prepare an internal standard intermediate solution with the concentration of 100-200mg/L, and storing in a dark place at the temperature of 4-8 ℃;
step four: preparing a standard working solution: adding 10-30mL of dichloromethane and 50-100 mu L of internal standard intermediate liquid into a headspace bottle, capping, oscillating for 5-10h at 20-30 ℃, and taking out to obtain standard working solution;
step five: pretreatment of the sample: cutting the sample into pieces of (1-4) × (1-4) cm 2 Taking the food contact surface as the inner surface to make a bag, injecting 10-30mL of dichloromethane into the bag, then removing redundant gas in the bag, adding 50-100 mu L of internal standard intermediate solution, sealing, oscillating for 5-10h at 20-30 ℃, and taking out to obtain a sample to-be-detected liquid;
step six: adding 10-30mL of dichloromethane into another headspace bottle, capping, oscillating for 5-10h at 20-30 ℃, and taking out to obtain a blank sample;
step seven: sequentially carrying out gas chromatography-four-stage rod-time-of-flight high-resolution mass spectrometry on a blank sample, a standard working solution and a sample to-be-detected solution to obtain a total ion flow chromatogram;
step eight: qualitative analysis: chromatographic peaks satisfying the following conditions were resolved:
a. the chromatographic peak area of the sample at the same retention time is more than 10 times of that of the blank sample;
b. the chromatographic peak of the sample is more than 1-2 times of the area of the internal standard peak with close retention time or similar structure;
step nine: semi-quantitative calculation:
A. the mass of the screened substances in the sample to be tested of the upper machine is converted according to the following formula:
M＝(A target object /A Internal standard )×M Internal standard
Wherein:
m, screening out the mass of a target object in the sample to be tested of the upper machine, wherein the unit is micrograms;
A target object Screening out the area of an extracted ion peak of a target object in the sample to be detected of the machine sample;
A internal standard The area of the extracted ion peak of the target in the sample to be detected of the machine sample corresponding to the internal standard;
M internal standard The mass of the internal standard in the sample to be measured of the machine is expressed in micrograms;
B. the mass of the screened material in the blank sample was converted according to the following formula:
M 0 ＝(A target 0 /A Internal standard 0 )×M Internal standard
M 0 Screening out the mass of the target in the blank sample, wherein the unit is micrograms;
A target 0 Screening out the extracted ion peak area of the target object in the blank sample;
A internal standard 0 The peak area of the extracted ions of the internal standard corresponding to the target in the blank sample;
M internal standard -the mass of the internal standard in the blank sample in micrograms;
C. the residual amount of the screened substance in the sample is converted as follows:
C＝(M-M 0 )/M weighing
Screening out the residual amount of the target in the sample, wherein the unit is milligrams per kilogram per microgram per square decimeter;
m, screening out the mass of a target object in the sample to be tested of the upper machine, wherein the unit is micrograms;
M 0 screening out the mass of the target in the blank sample, wherein the unit is micrograms;
M weighing The mass measured per area measured for the sample on machine is given in grams per square decimeter.
10. An internal standard composition for non-targeted screening of semi-volatile residual substances in a composite membrane for infant milk powder, wherein the internal standard composition is a combination of 4,4' -difluorobiphenyl and n-eicosane with the mass ratio of (0.5-1) to 1.
11. A kit for non-targeted screening of semi-volatile residue materials in a composite membrane for infant milk powder comprising the internal standard composition for non-targeted screening of semi-volatile residue materials in a composite membrane for infant milk powder of claim 10.
12. Use of an internal standard composition for detecting semi-volatile residual substances in a composite membrane for non-targeted screening of infant milk powder, wherein the internal standard composition is a combination of 4,4' -difluorobiphenyl and n-eicosane with a mass ratio of (0.5-1): 1.
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