HPLC-MS/MS method for determining aflatoxin and homologue thereof in infant auxiliary food
阅读说明：本技术 一种测定婴幼儿辅助食品中黄曲霉毒素及其同系物的hplc-ms/ms方法 (HPLC-MS/MS method for determining aflatoxin and homologue thereof in infant auxiliary food ) 是由 张艾青 刘希凤 徐衍胜 高金明 杨艳 任伟伟 于 2019-12-23 设计创作，主要内容包括：本发明提出了一种测定婴幼儿辅助食品中黄曲霉毒素及其同系物的HPLC-MS/MS方法,包括如下步骤:配制标准品工作液；婴幼儿辅助食品样品的处理；将标准品工作液和婴幼儿辅助食品待测样品分别用HPLC-MS/MS进行检测,分别得到色谱图和质谱图；对得到的色谱图和质谱图进行处理,对八种黄曲霉毒素及其同系物进行定性、定量检测,分别得到婴幼儿辅助食品待测样品的中八种黄曲霉毒素及其同系物质量浓度,然后计算得到婴幼儿辅助食品待测样品中八种黄曲霉毒素及其同系物的含量。本发明适用全面,灵敏度高,简便快速,只需流程化浓缩净化即可对婴幼儿食品中的八种黄曲霉毒素及其同系物同时定性定量分析。(The invention provides an HPLC-MS/MS method for measuring aflatoxin and homologues thereof in infant auxiliary food, which comprises the following steps of preparing standard substance working solution; processing an infant auxiliary food sample; respectively detecting the standard substance working solution and the infant auxiliary food to-be-detected sample by using HPLC-MS/MS to respectively obtain a chromatogram and a mass spectrum; and processing the obtained chromatogram and mass spectrogram, performing qualitative and quantitative detection on the eight aflatoxins and homologues thereof to respectively obtain the mass concentrations of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected, and then calculating to obtain the content of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected. The method is comprehensive in application, high in sensitivity, simple, convenient and quick, and can be used for simultaneously, qualitatively and quantitatively analyzing the eight aflatoxins and homologues thereof in the infant food only by means of flow concentration and purification.)
1. An HPLC-MS/MS method for determining aflatoxin and homologues thereof in infant and young child auxiliary food is characterized by comprising the following steps:
s1, preparing a standard working solution;
respectively weighing appropriate amount of AFB by using a balance1、AFB2、AFG1、AFG2And MST and ST standard substances are subjected to constant volume to 50 mL (100mg/L) by using acetonitrile to obtain standard substance stock solution: storing at-20 deg.C; separately taking AFB1、AFB2、AFG1、AFG2、MST、ST、AFM1、AFM2Respectively adding 1mL of the stock solutions of the standard products into volumetric flasks, diluting the stock solutions to 100mL (1 mg/L) with acetonitrile, and storing at 4 ℃ to obtain intermediate solutions of the standard products; diluting the mixed intermediate solution of the standard substance with a mixed solution of methanol and water (45: 55, V: V) to obtain a working solution of the standard substance;
s2, processing the infant auxiliary food sample;
crushing the sample by using a grinder, uniformly mixing, and accurately weighing 6 +/-0.01 g of sample in a 50 mL centrifugal tube with a plug; adding 20mL of acetonitrile-water-acetic acid, performing vortex mixing and oscillation for 2 min, wherein the volume ratio of the acetonitrile-water-acetic acid is 89:10:1, freezing at 4 ℃, centrifuging at 5000 rpm for 10 min, transferring 10 mL of supernate of each centrifuge tube into a 20mL clean glass tube, and drying by using nitrogen; adding 50 mg ODS, 30mg PSA and 30mg NH2, dissolving with 1mL of initial mobile phase solution, vortex oscillating for 1min, standing for layering, sucking with an injector, and filtering with a 0.22 μm filter membrane to obtain sample of infant supplementary food to be tested;
s3, detecting the standard working solution obtained in the step S1 and the infant auxiliary food to-be-detected sample obtained in the step S2 by using HPLC-MS/MS respectively to obtain a chromatogram and a mass spectrogram respectively; wherein:
the chromatographic conditions are as follows:
a chromatographic column: shimadzu AQ-C18, HP: 2.1 mm × 100 mm, 3.0 μm;
temperature of the column oven: 35 ℃;
mobile phase A: water-formic acid (999: 1) +5 mmol/L ammonium acetate;
mobile phase B: methanol;
elution procedure: 0-3.0 min, 45-95% B; 3.0-3.1 min, 95% B; 3.1-5.0 min, 95% -45% B; 5.0-6.5 min, 45% B;
flow rate: 0.4 mL/min; sample introduction volume: 5 mu L of the solution;
the mass spectrum conditions are as follows:
MRM scanning mode: positive ion scanning mode (ESI)+）；
Collision gas: argon gas; heating gas: air; drying gas: nitrogen gas; atomizing: nitrogen gas; flow rate of drying gas: 10L/min; flow rate of atomizing gas: 3L/min; heating air flow: 10L/min; temperature of the heating block: 400 ℃; DL temperature: 250 ℃; interface temperature: 300 ℃; the interface voltage is 4 kv;
Q1and Q3The resolution is unit;
maximum scanning speed: 30000 u/sec;
and S4, processing the chromatogram and the mass spectrogram obtained in the step S3, performing qualitative and quantitative detection on the eight aflatoxins and the homologues thereof to respectively obtain the mass concentrations of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected, and then calculating to obtain the content of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected.
2. The HPLC-MS/MS method for determining aflatoxin and its homologues in infant and pre-school children' S auxiliary food according to claim 1, wherein in step S3, the optimization method of mass spectrum conditions comprises: firstly, determining the product ion ranges of eight aflatoxins and homologues thereof, respectively putting 1 mg/L of respective toxin standard substance into a sample injection bottle, replacing a chromatographic column with two passes, carrying out isocratic elution on a mobile phase, wherein the volume ratio of methanol to water is 1:1, and carrying out sample injection by using an automatic sample injector of 1 mu L; firstly finding precursor ions of each target compound through precursor ion scanning under positive ion mode scanning, and further scanning to determine two product ions with the highest response values of each target compound; the voltage is optimized in a multi-reaction monitoring mode through the precursor ions and the product ions determined by respective target objects, the voltage of the highest-abundance sub-ions in the chromatogram is selected as the optimum voltage along with the continuous increase of the set voltage from low to high, the highest-abundance sub-ions are respectively determined as the quantitative ions and the qualitative ions according to the highest abundance of the product ions, the precursor ions and the product ions are continuously optimized on the basis of the determined voltage, and the optimal precursor ions/product ions and the optimal voltage are established through two rounds of optimization.
3. The HPLC-MS/MS method for determining aflatoxins and homologs thereof in infant and young child' S helper food according to claim 1, wherein in step S3, the mass spectrometric conditions of the eight aflatoxins and homologs thereof are shown in the following Table:
。
Technical Field
The invention relates to the technical field of mycotoxin determination, in particular to an HPLC-MS/MS method for determining aflatoxin and homologues thereof in infant auxiliary food.
Background
The aflatoxin is a compound containing dihydrofurocoumarin with similar chemical structure, belongs to mycotoxin, and is a secondary metabolite produced by aspergillus parasiticus, aspergillus flavus, aspergillus trichomonad and the like in special environment. The parasitic aspergillus and aspergillus flavus exist widely in nature and crops, and can easily grow to generate aflatoxin under dark and humid conditions, and the article reports that 20 aflatoxins are found, wherein AFB (aflatoxin B) is1AFM, the most carcinogenic of a known chemical substance1Is AFB1The hydroxylated metabolite exists in polluted milk, milk powder and even breast milk, has slightly lower toxicity than the former, but still 40 times as much as arsenic and 5 times as much as potassium cyanide. Standard GB 2761-plus 2017 Fungin Limit in national Standard food for food safety, AFB in infant supplementary food1And AFM1Should not exceed 0.5. mu.g/kg-1. As long as aflatoxin analogues with dihydrofurocoumarin chemical structures are toxic, China mainly monitors AFB in food at present1And AFM1Then the hazard of aflatoxins cannot be comprehensively evaluated, while other aflatoxins AFB2、AFG1、AFG2、AFB2Metabolite AFM2And precursors MST and ST synthesized by aflatoxin have similar structures and are extremely strong in toxicity and carcinogenicity to human beings, for example, ST belongs to 2B carcinogenic substances and is closely related to liver cancer and lung cancer. The main raw materials of the infant auxiliary food are rice flour, low-gluten flour, corn starch, milk powder, egg white, milk, butter, a small amount of fruits, pigments and the like, and if the raw materials are polluted by aflatoxin, the raw materials are stable in chemical properties and not easy to decompose, the toxin can be polluted in the infant auxiliary food. 141 parts of infant nutrition rice flour sold in the market are collected in 2015-2016, 9 parts of aflatoxin B1 is detected, the detection rate is 6.4%, and the content range is 0.11-0.25 mu g/kg. 2017, organization of the State general administration of food and drugThe sample of the 412 batches of the 6-class food is sampled, wherein the detection value of aflatoxin B1 in one infant cereal auxiliary food is 0.8 mu g/kg, which is 60 percent higher than the standard (not more than 0.5 mu g/k g), and the sample fully indicates that AFB is polluted1Also present risks of toxins ST and MST in crops or food products. Infants belong to special sensitive groups, and food polluted by aflatoxin can cause irreversible damage, so that a comprehensive aflatoxin detection method is necessary to be established, so that the risk of eating aflatoxin and homologues thereof is really reduced for the infants, and a safer infant food environment is created.
At present, enzyme-linked immunosorbent assay and high performance liquid chromatography are commonly adopted for detecting food in the prior art, the enzyme-linked immunosorbent assay belongs to a rapid screening detection method, the pretreatment method is simple, the detection result can be obtained within half an hour, false positive can be easily caused by matrix interference, and the method is immature for simultaneously detecting various toxins. The accuracy and stability of the high performance liquid chromatography are superior to those of an enzyme-linked immunosorbent assay, but the high performance liquid chromatography is difficult to analyze when similar compounds with similar properties are detected, misjudgment is easily caused to the compounds with similar retention time, and meanwhile, the processing flux is limited and the sensitivity is low.
Disclosure of Invention
The invention provides an HPLC-MS/MS method for measuring aflatoxin and homologues thereof in infant auxiliary food, which is comprehensive in application, high in sensitivity, simple, convenient and quick, can be used for simultaneously qualitatively and quantitatively analyzing the eight aflatoxins and the homologues thereof in the infant food only by flow concentration and purification, and is particularly suitable for infant auxiliary food production enterprises and government related supervision departments.
The technical scheme of the invention is realized as follows: an HPLC-MS/MS method for determining aflatoxin and homologues thereof in infant and young children auxiliary food comprises the following steps:
s1, preparing a standard working solution;
respectively weighing appropriate amount of AFB by using a balance1、AFB2、AFG1、AFG2And MST and ST standard substances are subjected to constant volume to 50 mL (100mg/L) by using acetonitrile to obtain standard substance stock solution: storing at-20 deg.C; separately taking AFB1、AFB2、AFG1、AFG2、MST、ST、AFM1、AFM2Respectively adding 1mL of the stock solutions of the standard products into volumetric flasks, diluting the stock solutions to 100mL (1 mg/L) with acetonitrile, and storing at 4 ℃ to obtain intermediate solutions of the standard products; diluting the mixed intermediate solution of the standard substance with a mixed solution of methanol and water (45: 55, V: V) to obtain a working solution of the standard substance;
s2, processing the infant auxiliary food sample;
crushing the sample by using a grinder, uniformly mixing, and accurately weighing 6 +/-0.01 g of sample in a 50 mL centrifugal tube with a plug; adding 20mL of acetonitrile-water-acetic acid, performing vortex mixing and oscillation for 2 min, wherein the volume ratio of the acetonitrile-water-acetic acid is 89:10:1, freezing at 4 ℃, centrifuging at 5000 rpm for 10 min, transferring 10 mL of supernate of each centrifuge tube into a 20mL clean glass tube, and drying by using nitrogen; adding 50 mg ODS, 30mg PSA and 30mg NH2, dissolving with 1mL of initial mobile phase solution, vortex oscillating for 1min, standing for layering, sucking with an injector, and filtering with a 0.22 μm filter membrane to obtain sample of infant supplementary food to be tested;
s3, detecting the standard working solution obtained in the step S1 and the infant auxiliary food to-be-detected sample obtained in the step S2 by using HPLC-MS/MS respectively to obtain a chromatogram and a mass spectrogram respectively; wherein:
the chromatographic conditions are as follows:
a chromatographic column: shimadzu AQ-C18, HP: 2.1 mm × 100 mm, 3.0 μm;
temperature of the column oven: 35 ℃;
mobile phase A: water-formic acid (999: 1) +5 mmol/L ammonium acetate;
mobile phase B: methanol;
elution procedure: 0-3.0 min, 45-95% B; 3.0-3.1 min, 95% B; 3.1-5.0 min, 95% -45% B; 5.0-6.5 min, 45% B;
flow rate: 0.4 mL/min; sample introduction volume: 5 mu L of the solution;
the mass spectrum conditions are as follows:
MRM scanning mode: positive ion scanning mode (ESI)+）；
Collision gas: argon gas; heating gas: air; drying gas: nitrogen gas; atomizing: nitrogen gas; flow rate of drying gas: 10L/min; flow rate of atomizing gas: 3L/min; heating air flow: 10L/min; temperature of the heating block: 400 ℃; DL temperature: 250 ℃; interface temperature: 300 ℃; the interface voltage is 4 kv;
Q1and Q3The resolution is unit;
maximum scanning speed: 30000 u/sec;
and S4, processing the chromatogram and the mass spectrogram obtained in the step S3, performing qualitative and quantitative detection on the eight aflatoxins and the homologues thereof to respectively obtain the mass concentrations of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected, and then calculating to obtain the content of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected.
As a preferred technical solution, in step S3, the method for optimizing the mass spectrometry conditions includes: firstly, determining the product ion ranges of eight aflatoxins and homologues thereof, respectively putting 1 mg/L of respective toxin standard substance into a sample injection bottle, replacing a chromatographic column with two passes, carrying out isocratic elution on a mobile phase, wherein the volume ratio of methanol to water is 1:1, and carrying out sample injection by using an automatic sample injector of 1 mu L; firstly finding precursor ions of each target compound through precursor ion scanning under positive ion mode scanning, and further scanning to determine two product ions with the highest response values of each target compound; the voltage is optimized in a multi-reaction monitoring mode through the precursor ions and the product ions determined by respective target objects, the voltage of the highest-abundance sub-ions in the chromatogram is selected as the optimum voltage along with the continuous increase of the set voltage from low to high, the highest-abundance sub-ions are respectively determined as the quantitative ions and the qualitative ions according to the highest abundance of the product ions, the precursor ions and the product ions are continuously optimized on the basis of the determined voltage, and the optimal precursor ions/product ions and the optimal voltage are established through two rounds of optimization.
As a preferred embodiment, in step S3, the mass spectrum conditions of the eight aflatoxins and their homologues are shown in the following table:
No.
compound (I)
Precursor ion (m/z)
Product ion (m/z)
Retention time (min)
Voltage (eV)
1
AFB1
313.0
241.0*, 285.0
2.89
-38, -24
2
AFB2
315.0
259.0*, 287.0
3.15
-30, -27
3
AFG1
329.0
243.0*, 283.0
3.12
-29, -25
4
AFG2
331.0
245.0*, 257.0
2.73
-31, -31
5
MST
339.1
306.1*, 295.1
3.36
-29, -31
6
ST
325.0
310.1*, 281.1
2.59
-25, -36
7
AFM1
329.0
273.0*, 229.0
2.18
-25, -43
8
AFM2
331.0
259.0*, 273.0
1.21
-26, -25
By adopting the technical scheme, the invention has the beneficial effects that:the invention establishes a brand new HPLC-MS/MS method for measuring aflatoxin and homologues thereof in infant auxiliary food, wherein the infant auxiliary food is extracted and purified by acetonitrile-water-acetic acid (89: 10: 1), is subjected to gradient dilution by taking methanol, formic acid-water (1: 999, V/V) +5 mmol/L ammonium acetate solution as a mobile phase, is separated by AQ-C18 and HP (2.1 mm multiplied by 100 mm, 3.0 mu m), and is subjected to Multistage Reaction Monitoring (MRM) and positive ion mode scanning analysis. The result shows that the standard curve of the eight aflatoxins and the homologous compounds thereof is 0.15-50 mu g.L-1The linearity is good within the range, and the correlation coefficients are all larger than 0.996. The average recovery rate of the eight toxins of the sample under the condition of three standard adding concentrations of lower limit, two times and ten times of the sample is 76.3-95.9%, and the Relative Standard Deviation (RSD) is 3.1-11.5%. The determination method has the advantages of rapidness, economy, high sensitivity, strong practicability and the like, can simultaneously realize qualitative and quantitative detection of eight toxins, and can be used for detection and analysis of aflatoxin and homologs thereof in infant supplementary food.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a superimposed chromatogram of a mixed standard solution of eight aflatoxins and homologs thereof.
FIG. 2 is a graph showing the effect of the extraction reagent of the present invention on the recovery of eight aflatoxins and their homologs.
FIG. 3 is a graph showing the effect of different ratios of acetonitrile-water on recovery according to the present invention.
FIG. 4 is a scanning image of mass spectra of samples of the present invention before (a) and after (b) pre-treatment and decontamination.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An HPLC-MS/MS method for determining aflatoxin and homologues thereof in infant and young children auxiliary food comprises the following steps:
step one, preparing a standard substance working solution;
respectively weighing appropriate amount of AFB by using a balance1、AFB2、AFG1、AFG2And MST and ST standard substances are subjected to constant volume to 50 mL (100mg/L) by using acetonitrile to obtain standard substance stock solution: storing at-20 deg.C; separately taking AFB1、AFB2、AFG1、AFG2、MST、ST、AFM1、AFM2Respectively adding 1mL of the stock solutions of the standard products into volumetric flasks, diluting the stock solutions to 100mL (1 mg/L) with acetonitrile, and storing at 4 ℃ to obtain intermediate solutions of the standard products; and (3) diluting the mixed intermediate solution of the standard substance with a mixed solution of methanol and water (45: 55, V: V) in series to obtain the working solution of the standard substance.
Step two, processing the infant auxiliary food sample;
crushing the sample by using a grinder, uniformly mixing, and accurately weighing 6 +/-0.01 g of sample in a 50 mL centrifugal tube with a plug; adding 20mL of acetonitrile-water-acetic acid, performing vortex mixing and oscillation for 2 min, wherein the volume ratio of the acetonitrile-water-acetic acid is 89:10:1, freezing at 4 ℃, centrifuging at 5000 rpm for 10 min, transferring 10 mL of supernate of each centrifuge tube into a 20mL clean glass tube, and drying by using nitrogen; adding 50 mg ODS, 30mg PSA and 30mg NH2, dissolving with 1mL of initial mobile phase solution, vortex oscillating for 1min, standing for layering, sucking with a syringe, and filtering with a 0.22 μm filter membrane to obtain sample for infant supplementary food.
And step three, respectively detecting the standard substance working solution obtained in the step S1 and the infant auxiliary food to-be-detected sample obtained in the step S2 by using HPLC-MS/MS to respectively obtain a chromatogram and a mass spectrum.
And step four, processing the chromatogram and the mass spectrogram obtained in the step S3, performing qualitative and quantitative detection on the eight aflatoxins and the homologues thereof to respectively obtain the mass concentrations of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected, and then calculating to obtain the content of the eight aflatoxins and the homologues thereof in the infant auxiliary food sample to be detected.
As a preferred technical solution, in step S3, the method for optimizing the mass spectrometry conditions includes: firstly, determining the product ion ranges of eight aflatoxins and homologues thereof, respectively putting 1 mg/L of respective toxin standard substance into a sample injection bottle, replacing a chromatographic column with two passes, carrying out isocratic elution on a mobile phase, wherein the volume ratio of methanol to water is 1:1, and carrying out sample injection by using an automatic sample injector of 1 mu L; firstly finding precursor ions of each target compound through precursor ion scanning under positive ion mode scanning, and further scanning to determine two product ions with the highest response values of each target compound; the voltage is optimized in a multi-reaction monitoring mode through the precursor ions and the product ions determined by respective target objects, the voltage of the highest-abundance sub-ions in the chromatogram is selected as the optimum voltage along with the continuous increase of the set voltage from low to high, the highest-abundance sub-ions are respectively determined as the quantitative ions and the qualitative ions according to the highest abundance of the product ions, the precursor ions and the product ions are continuously optimized on the basis of the determined voltage, and the optimal precursor ions/product ions and the optimal voltage are established through two rounds of optimization.
The following experiment was conducted for the present measurement method.
1.1 instruments and reagents
High performance liquid chromatography mass spectrometer: LCMS-8045 (Shimadzu, Japan), electrospray ion source (ESI); KH19A type centrifuge (kaida scientific instruments, han, hu); ZX-DC Nitrogen blowing apparatus (Beijing Zhongjia apparatus science and technology company); Milli-Q water purification machines (Millipore, USA); KQ3200DA ultrasonic cleaner (baidian instruments, shanghai); GM300 mill (leys, germany); MS3 vortex mixer (aka germany); ML-T analytical balance (Mettler, Switzerland).
Aflatoxin B1(AFB1) Aflatoxins B2(AFB2) Aflatoxin G1(AFG1)、Aflatoxin G2(AFG2) All purchased from Beijing Tan ink quality testing technology. Aflatoxin M1(AFM1100. mu.g/mL), aflatoxin M2(AFM2100. mu.g/mL), O-Methyltricin (MST), and tricin (ST) were purchased from Sigma, USA. Neutral Alumina (Alumina-N) was purchased from Shanghai Aladdin Biotechnology, C18(ODS), PSA powder, graphite carbon black powder (GCB) and aminopropyl powder (NH)2) Available from Agilent, USA; methanol, acetonitrile, ethyl acetate and formic acid were all chromatographically pure and available from merck, usa; the experimental water was ultrapure water.
Standard stock solutions: respectively weighing appropriate amount of AFB by using a balance1、AFB2、AFG1、AFG2MST and ST standard substance, adding acetonitrile to 50 mL (100mg/L), and storing at 20 deg.C.
Mixing standard intermediate liquid: separately taking AFB1、AFB2、AFG1、AFG2、MST、ST、AFM1、AFM2Each stock solution of the standard substance was taken in a volumetric flask with 1mL volume to 100mL (1 mg/L) with acetonitrile and stored at 4 ℃.
Mixing standard working solution: diluting the mixed intermediate solution of the standard substance with mixed solution of methanol and water (45: 55, V: V) in series, and preparing the intermediate solution as it is.
Chromatographic conditions
A chromatographic column: shimadzu AQ-C18, HP (2.1 mm. times.100 mm, 3.0 μm); temperature of the column oven: 35 ℃; mobile phase A: water-formic acid (999: 1) +5 mmol/L ammonium acetate; mobile phase B: methanol; elution procedure: 0-3.0 min, 45-95% B; 3.0-3.1 min, 95% B; 3.1-5.0 min, 95% -45% B; 5.0-6.5 min, 45% B; flow rate: 0.4 mL/min; sample introduction volume: 5 μ L.
Conditions of Mass Spectrometry
MRM scanning mode: positive ion scanning mode (ESI)+) (ii) a Collision gas: argon gas; heating gas: air; drying gas: nitrogen gas; an atomizer: nitrogen gas; flow rate of drying gas: 10L/min; flow rate of atomizing gas: 3L/min; heating air flow: 10L/min; temperature of the heating block: 400 ℃; DL temperature: 250 ℃; interface temperature: 300 ℃; the interface voltage is 4 kv; q1And Q3The resolution is unit; maximum scanning speed: 30000 u/sec. Mass spectrum conditions of the eight aflatoxins and homologs thereof are shown in Table 1.
TABLE 1 Mass Spectrometry conditions for eight aflatoxins and their homologs
No.
Compound (I)
Precursor ion (m/z)
Product ion (m/z)
Retention time (min)
Collision energy (eV)
1
AFB1
313.0
241.0*, 285.0
2.89
-38, -24
2
AFB2
315.0
259.0*, 287.0
3.15
-30, -27
3
AFG1
329.0
243.0*, 283.0
3.12
-29, -25
4
AFG2
331.0
245.0*, 257.0
2.73
-31, -31
5
MST
339.1
306.1*, 295.1
3.36
-29, -31
6
ST
325.0
310.1*, 281.1
2.59
-25, -36
7
AFM1
329.0
273.0*, 229.0
2.18
-25, -43
8
AFM2
331.0
259.0*, 273.0
1.21
-26, -25
1.4 sample treatment
Pulverizing the sample with a grinder, mixing, accurately weighing 6 + -0.01 g of sample in 50 mL centrifuge tube with plug, adding 20mL acetonitrile-water-acetic acid (89: 10:1, V/V/V), vortex mixing and shaking for 2 min, freezing at 5000 rpm (4 deg.C), centrifuging for 10 min, transferring the supernatant of each centrifuge tube 10 mL into 20mL clean glass tube, blowing with nitrogen, adding 50 mg ODS, 30mg PSA and 30mg NH2Dissolving with 1mL of initial mobile phase solution, vortex and shake for 1min, standing for layering, sucking with a syringe, filtering with 0.22 μm filter membrane, and detecting and analyzing by HPLC-MS/MS.
Selection of chromatography columns
For the simultaneous detection of various aflatoxin homologues, the compounds have similar structural formulas and chemical properties, such as AFG1And AFM1Is an isomer, the precursor ion is the same, AFG2And AFM2Same precursor ion same, AFB1、AFB2、AFG1、AFG2The four precursor ions are closer to the product ions, which puts higher demands on the resolution, and therefore the choice of the column is very critical. The chromatographic column with the particle size of 5 mu m and the length of 250 mm belongs to a normal-pressure chromatographic column, if the mobile phase needs to be shunted after the chromatographic column is used in mass spectrometry detection, only part of the mobile phase enters a mass spectrum, otherwise, too much liquid enters the mass spectrum equipment, and the mass spectrum equipment is damaged; the detection period is long, the aflatoxin and the homologues thereof have high toxicity but low content in the nature, and an over-high sample loading amount of a chromatographic column is not required, so that the column efficiency can be further improved by selecting a small inner diameter. Considering that the larger the particle size of the chromatographic column is, the smaller the relative pressure is, the stronger the noise resistance to the complex matrix is, the longer the service life is, and finally selectingAn AQ-C18 HP chromatographic column is used for separation.
Optimization of mass spectrometry conditions
The product ion ranges of eight aflatoxins and homologues thereof are determined, the respective toxin standards (1 mg/L)) are put into a sample injection bottle, a chromatographic column is replaced by two-way, mobile phase is eluted at equal degrees (methanol: water =1:1, V: V), and an automatic sample injector is used for injecting 1 muL. The precursor ions of each target compound are firstly found through precursor ion scanning under positive ion mode scanning, and the two fragment ions (product ions) with the highest response value of each target compound are further determined through scanning. The method comprises the steps of selecting multiple reaction monitoring mode optimized voltage (collision energy) through precursor ion and product ion pairs determined by respective target objects, continuously increasing the set voltage from low to high, selecting the voltage of the highest abundance sub-ion in a chromatogram as the optimal voltage, respectively determining the highest abundance of the product ion as a quantitative ion and a qualitative ion, continuously optimizing the precursor ion and the product ion on the basis of the determined voltage, and establishing the optimal precursor ion/product ion pair and the optimal voltage through two rounds of optimization. Through the operations of the step 2.1 and the step 2.2, the aflatoxin and the homologues thereof in the step 8 can be well separated in a chromatographic column, the response value of the instrument is high, the specific parameters are shown in a table 1, and the flow chromatogram of the extracted particles of the mixed standard solution (0.50 mu g/L) is shown in the table 1. Wherein:
1. AFM2; 2. AFM1; 3. ST; 4. AFG2; 5. AFB1; 6. AFG1; 7. AFB2; 8. MST。
optimization of chromatographic conditions
Due to the fact that the mass-to-charge ratios of the eight toxins are 313-339, the chromatographic column factors are eliminated, the separation degree and the response value of the target can be improved by changing the conditions and the proportion of the mobile phase and the temperature of a column incubator in the test, and meanwhile the ionization efficiency and the peak pattern of the mass spectrum of the target can be improved by adding formic acid, ammonium formate, ammonium acetate and the like into the mobile phase. Firstly, the separation effect and chromatographic response intensity of eight toxins in two mobile phase systems of methanol-water and acetonitrile-water are tested, and the tests show that the separation degree of a methanol-water mobile phase system is better than that of an acetonitrile-water system target object, and the overall response intensity of a chromatographic peak is 40 percent higher. The influence of adding formic acid, ammonium formate and ammonium acetate to the response values of the eight toxins in the mobile phase water phase is further tested, the test shows that the response value of a target analyte can be obviously improved by adding the formic acid in the water phase, the ionization efficiency of the eight aflatoxins and homologs thereof in a slightly acidic environment is higher under the mass spectrum positive ion monitoring mode, the influence of the ammonium formate and the ammonium acetate on the signal intensity of the target analyte is small, and the peak pattern of a chromatographic peak is improved. The stability of ammonium acetate in the matrix detection is better than that of ammonium formate through the sample labeling detection, different combination verification is carried out on the addition ratio of formic acid to ammonium acetate, and multiple tests finally determine that methanol, water-formic acid (999: 1) +5 mmol/L ammonium acetate in 1.2 serves as a mobile phase, so that the method has stable baseline, high response value of each target analyte and good peak shape.
Selection of extraction solution
At present, the extraction solution of aflatoxin in food is mainly methanol, acetonitrile or a mixed solution of methanol, acetonitrile and water in different proportions. The extraction solution is a key factor of high and low recovery rate, the influence of four extraction reagents of methanol, methanol-water (8: 2, v/v), acetonitrile and acetonitrile-water (8: 2, v/v) on the recovery rate of eight aflatoxins is firstly compared in a mode of adding the eight aflatoxins and homologue thereof mixed standard (10 mu g/kg) in the infant auxiliary food, and the result shows that the recovery rate of the eight aflatoxins and homologue thereof is between 50% and 75% by using the acetonitrile-water as the extraction solution, the recovery rate is the best, and the result is shown in figure 2. After determining acetonitrile-water as an extraction solution, testing the influence of four mixing ratios of acetonitrile-water (8: 1, v/v), acetonitrile-water (8: 2, v/v), acetonitrile-water (8: 3, v/v) and acetonitrile-water (8: 4, v/v) on the recovery rate, and finding out that the recovery rate of acetonitrile-water (8: 1, v/v) is the highest, wherein analysis shows that the addition of a small amount of water is favorable for infiltration and dissolution of acetonitrile and a sample, but more water is unfavorable for extraction and separation of toxins in the sample, more importantly, the nitrogen blowing concentration time is prolonged due to the overlarge ratio of water in acetonitrile-water, and the method is not easy to blow and dry. The aflatoxin is easy to decompose under the alkaline condition, the experiment further investigates the influence of adding 0%, 1%, 2% and 3% acetic acid in the extraction solution on the recovery rates of the eight toxins, the data shows that the addition of the acetic acid remarkably improves the recovery rate of each toxin, the yields of the eight aflatoxins and homologues thereof reach more than 80%, but the influence of the addition of the 1%, 2% and 3% acetic acid on the recovery rates is not significant, and finally the extraction solution is determined to be acetonitrile-water-acetic acid (89: 10: 1).
Selection of purification mode
The infant supplementary food is rich in nutrition, high in protein, amino acid and saccharide content, and also added with natural or artificial pigments and the like, and the matrix is complex, so that the trace analysis of eight target analytes can be interfered, and the sensitivity of a detection method is influenced. In this example, 5 kinds of purification powders of aluminum-N, GCB, ODS, PSA, NH were simultaneously tested2The adsorption recovery rate of the eight toxins and homologues thereof in the acetonitrile extraction solution is shown in table 2. The experiments show that ODS, PSA, NH2The adsorption effect on the eight aflatoxins and homologues thereof is small, and the recovery rate is over 90.4 percent. The method has the advantages that the aluminum-N can adsorb eight toxins to a certain extent, the GCB can adsorb the eight toxins seriously, reagent researches show that the aluminum-N and GCB powder have strong adsorption capacity on nitrogen, phosphorus and sulfur-containing heterocyclic substances, aromatic hydrocarbons and other compounds, the eight toxins are heterocyclic compounds, and therefore the aim of improving the recovery rate is in conflict with the aim of improving the recovery rate in the experiment, and the two purifiers cannot be used. ODS has good effect of adsorbing nonpolar interferents such as fat and esters; PSA can adsorb various organic acids, pigments and partial fatty acids and saccharides; similar to GCB, can also absorb and remove steroids, chlorophyll and the like, and the effect is better when the molecular weight is smaller; NH (NH)2The steroid, the chlorophyll and the like can be adsorbed and removed, the interference of a matrix in the infant auxiliary food can be well reduced by the combined use of the steroid, the chlorophyll and the like, the purification addition proportion in the step 1.4 is finally determined through a further combination experiment, the detection cost is saved, the optimal purification effect is achieved, and the effect graphs before and after the blank sample of the infant auxiliary food is purified by the method are shown in a figure 4.
TABLE 2 ODS, aluminum-N, GCB, PSA, NH2Recovery (%), of the eight aflatoxins and their homologues after adsorption
No.
Compound (I)
ODS
Alumina-N
GCB
PSA
NH2
1
AFB1
95.7
62.0
3.4
92.7
100.1
2
AFB2
99.2
58.7
2.9
94.4
94.8
3
AFG1
102.3
62.5
1.1
83.2
95.2
4
AFG2
104.0
71.2
10.7
100.6
99.7
5
MST
101.2
45.9
11.3
94.9
99.7
6
ST
99.7
59.6
7.2
98.7
96.5
7
AFM1
95.4
45.3
12.3
106.2
90.4
8
AFM2
97.5
42.1
10.6
101.5
91.9
2.6 Linear relationship, detection Limit and quantitative lower Limit
Taking mixed standard intermediate solution of eight aflatoxins and homologues thereof, diluting with blank infant biscuit extraction matrix, detecting and determining by mass spectrometry, taking peak area average value (Y) of each toxin response value as ordinate, and mass concentration (X, μ g kg. corresponding to each toxin-1) Making standard curve for abscissa, the linear range of the eight aflatoxins and their homologues is 0.15-50 μ g.L-1The correlation coefficients (r) are all larger than 0.996. Adding a mixed standard substance series into the infant auxiliary food substrate, determining a method detection Limit (LOD) by using a signal-to-noise ratio (S/N) which is 3 times, determining a quantitative lower Limit (LOQ) by using a signal-to-noise ratio (S/N) which is 10 times, wherein the LOD range of the eight aflatoxins and homologs thereof is 0.05-0.10 mu g-kg-1Between 0.15 and 0.30 mu g/kg of LOQ-1The regression equation, r-value, linear range, LOD and LOQ specific results are shown in Table 3.
TABLE 3 regression equation, r-value, linear range, detection limit and lower limit of quantitation for eight aflatoxins and their homologs (n = 6)
2.7 accuracy and precision
Adding mixed standard substance solutions of eight aflatoxins and homologues thereof with lower quantitative limit, lower double quantitative limit and lower ten quantitative limit of 3 levels into a blank sample of the infant biscuit, and performing a labeling recovery experiment to verify the effectiveness of the method according to the pretreatment step of 1.4 samples. The accuracy of the method is expressed in recovery and the precision in Relative Standard Deviation (RSD), 6 replicates of each sample are taken and averaged. The result shows that the average recovery rate of the eight aflatoxins and homologues thereof at 3 standard adding levels is 76.3% -95.9%, the Relative Standard Deviation (RSD) is 3.1% -11.5%, the requirements of recovery rate and precision in GB/T27404-.
TABLE 4 average recovery and precision of eight aflatoxins and their homologues in the sample (n = 6)
2.8 sample determination
After 20 parts of infant supplementary food are purchased from the market, eight aflatoxins and homologue residues thereof are detected by the method established in the embodiment, and AFB is detected in 1 part of biscuit bar (milk flavor) sample1MST and ST, wherein AFB1The detection content is 0.55 mug/kg-1The ST content is 1.46 mu g/kg-1The MST content is 3.10 mug.kg-1And the detection result is as follows: AFB1Exceeds the limit requirement of national standard GB2761-2017 (0.5 mug. kg)-1）。
The invention can realize qualitative and quantitative detection of eight toxins simultaneously. The detection method has the advantages of rapidness, economy, high sensitivity, strong practicability and the like, can completely meet the detection requirements on the residues of the eight aflatoxins and the homologues thereof in the infant auxiliary food, and has profound significance on the safety detection of the infant auxiliary food.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.