National food safety standard―Determination of 500 pesticides and related chemicals residues in fruits and vegetables Gas chromatography-mass spectrometry
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This standard replaces GB/T 19648-2006 Method for determination of 500 pesticides and related chemicals residues in fruits and vegetables—GC-MS method.
The following main changes have been made with respect to GB/T 19648-2006:
—The standard text format has been changed to the text format of national food safety standard;
—The expression of “It may apply for other vegetables and fruits” has been added to the scope of the standard.
The previous edition of this standard is as follows:
—GB/T 19648-2006.
National food safety standards—
Determination of 500 pesticides and related chemicals residues in fruits and vegetables—
Gas chromatography-mass spectrometry
1 Scope
This standard specifies gas chromatography-mass spectrometry (GC-MS) method for determination of 500 pesticides and related chemicals (see Annex A) residues in apples, oranges, grapes, cabbages, celeries and tomatoes.
This standard is applicable to the determination of 500 pesticides and related chemicals residues in apples, oranges, grapes, cabbages, celeries and tomatoes. It may apply for other vegetables and fruits.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB 2763 National food safety standard—Maximum residue limits for pesticides in food
GB/T 6682 Water for analytical laboratory use—Specification and test methods
3 Principle
The sample is extracted with acetonitrile homogenate, salted out and centrifuged, and the supernatant is purified with solid phase extraction column. Pesticides and related chemicals are eluted with acetonitrile-toluene solution (3+1) and, after solvent exchange, tested by GC-MS.
4 Reagents and materials
4.1 Reagents
4.1.1 Acetonitrile (CH3CN, 75-05-8), chromatographic grade.
4.1.2 Sodium chloride (NaCl, 7647-14-5), guaranteed grade.
4.1.3 Anhydrous sodium sulfate (Na2SO4, 7757-82-6), analytical grade. Calcine it at 650°C for 4h, store it in a desiccator, and leave it to cool before use.
4.1.4 Toluene (C7H8,108-88-3), guaranteed grade.
4.1.5 Acetone (CH3COCH3, 67-64-1), analytical grade and redistilled.
4.1.6 Dichloromethane (CH2Cl2, 75-09-2), chromatographic grade.
4.1.7 n-hexane (C6H14, 110-54-3), analytical grade and redistilled.
4.2 Standards
Standards of pesticides and related chemicals: with a purity ≥95%, see Annex A.
4.3 Preparation of standard solutions
4.3.1 Standard stock solutions
Take an appropriate amount, accurate to 0.1mg, of various pesticide and related chemical standards and place them in 10mL volumetric flasks. Dissolve them with appropriate solvents such as toluene, toluene + acetone mixture and dichloromethane, depending on the solubility of the standards (see Annex A for solvent selection), and make up to the mark. Keep the standard solution away from light at 4°C throughout the storage life of one year.
4.3.2 Mixed standard solutions (mixture of standard solutions A, B, C, D and E)
According to the properties and retention time of pesticides and related chemicals, the 500 pesticides and related chemicals are divided into five groups, namely, A, B, C, D and E, and the concentration of each pesticide and related chemical in the mixed standard solution is determined according to the individual response sensitivity of the instrument. See Annex A for the grouping of 500 pesticides and related chemicals and the individual concentrations in their mixed standard solutions for the purposes of this standard.
According to the group number of each pesticide and related chemical, the concentration in the mixed standard solution and the concentration in the standard stock solution, transfer a certain amount of standard stock solution of single pesticide and related chemical into a 100mL volumetric flask, and make up to the mark with toluene. The mixed standard solution shall be stored at 4°C away from light throughout the storage life of one month.
4.3.3 Internal standard solutions
Accurately take 3.5mg of heptachlor-epoxide and place it in a 100mL volumetric flask, and make up to the mark with toluene.
4.3.4 Substrate-mixed standard working solution
The substrate-mixed standard working solutions of pesticides and related chemicals in groups A, B, C, D and E are prepared as follows: Add 40μL of internal standard solution (4.3.3) and 50μL of mixed standard solution (4.3.2) respectively to 1.0mL of sample blank substrate extract, and mix them well to obtain the substrate-mixed standard working solutions A, B, C, D and E. Substrate-mixed standard working solutions shall be prepared immediately before use.
4.4 Materials
4.4.1 Envi-18 column ): 12 mL, 2.0g or equivalent.
4.4.2 Envi-Carb1) activated carbon column: 6mL, 0.5g or equivalent.
4.4.3 Sep-Pak ) NH2 solid phase extraction column: 3mL, 0.5g or equivalent.
5 Apparatus
5.1 Gas chromatography-mass spectrometer: with electron impact (EI) source.
5.2 Analytical balance, with a sensitivity of 0.01g and 0.0001g.
5.3 Homogenizer: with the rotating speed not less than 20000r/min.
5.4 Pear-shaped flask: 200mL.
5.5 Pipette: 1mL.
5.6 Nitrogen blow dryer.
6 Sample preparation
The sampling position for fruits and vegetables shall comply with Annex A of GB 2763. Cut the sample into pieces, and mix and homogenize them well to obtain a homogenate. Divide the prepared homogenate into two even portions, pack them separately into clean containers, and seal and identify the containers appropriately. The samples are stored as frozen at-18°C.
7 Analysis procedure
7.1 Extraction
Take 20g of sample, accurate to 0.01g, and place it into a 80mL centrifuge tube; add 40mL of acetonitrile, homogenize and extract for 1min with homogenizer at 15000r/min; add 5g of sodium chloride, further homogenize and extract for 1min; put centrifuge tube in place, centrifuge at 3000r/min for 5min; take 20mL of the resultant supernatant (equivalent to 10g of sample) for purification.
7.2 Purification
7.2.1 Secure the Envi-18 column with holder. Before the sample is applied, wash the column with 10mL of acetonitrile; apply the pear-shaped flask to the bottom of the column; pipette the said 20mL supernatant to the column and wash the column with 15mL of acetonitrile; subject the collected supernatant and washing liquid to water bath at 40°C for rotating concentration until about 1mL is left before use.
7.2.2 Add about 2cm-high anhydrous sodium sulfate into the Envi-Carb column; apply the column to the top of Sep-Pak aminopropyl column; connect the pear-shaped flask to the bottom of the column tandem, and secure the tandem with a holder. Before the sample is applied, wash the column with 4mL acetonitrile-toluene solution (3+1). As the liquid level reaches the top of sodium sulfate, quickly transfer the sample concentrate (7.2.1) to the purification column, then wash the sample bottle three times with 2mL acetonitrile-toluene solution (3+1) each time, and transfer the washing liquid into the column. Apply a 50mL receiver to the top of the column tandem; wash the tandem with 25mL of acetonitrile-toluene solution (3+1); collect all effluent into a pear-shaped flask, and subject the flask to water bath at 40°C for rotating concentration until about 0.5mL is left. Add 5mL of n-hexane every time during the rotating evaporation in the water bath at 40°C, and exchange solvents twice so as to make the volume of sample solution about 1mL; add 40μL of internal standard solution and mix well before use for GC-MS determination.
7.3 Determination
7.3.1 Reference GC-MS conditions
a) Chromatographic column: DB-1701 (30×0.25mm×0.25μm) quartz capillary column or equivalent;
b) Chromatographic column thermal program: hold at 40°C for 1min, then increase to 130°C at 30°C/min, to 250°C at 5°C/min, and to 300°C at 10°C/min in sequence and hold for 5min;
c) Carrier gas: helium, purity ≥99.999%, flow rate of 1.2 ml/min;
d) Temperature at injection port: 290°C;
e) Injection volume: 1 unit °C;
f) Injection mode: Inject without split and, after 1.5min, open the split valve and septum purge valve;
g) Electron impact source: 70eV;
h) Ion source temperature: 230°C;
i) GC-MS interface temperature: 280°C;
j) Selected ion monitoring: One quantitative ion and two to three qualitative ions are selected for each compound. All the ions to be tested in each group are determined in different time periods according to the peak order. See Annex B for retention times quantitative ion, qualitative ions and abundance ratio of quantitative ion to qualitative ions of each compound. See Annex C for the starting time and residence time of each group of ions under test.
7.3.2 Qualitative determination
For the purpose of sample determination, if the retention time of the tested chromatographic peak is consistent with that of the standard sample, and the selected ions all appear in the mass spectrogram of the sample after background subtraction, and the selected ion abundance ratio is consistent with that of the standard sample (for relative abundance > 50%, tolerance of ±10% applies; for relative abundance > 20 % – 50 %, tolerance of ±15% applies; for relative abundance > 10 % – 20 %, tolerance of ±20% applies; for relative abundance ≤10%, tolerance of ±50% applies), presence of the pesticide or related chemical in the sample can be concluded. If it cannot be confirmed, the sample shall be re-injected, scanning (with sufficient sensitivity), use of other confirming ions or other analytical instruments with higher sensitivity shall be considered for confirmation purposes.
Foreword i
1 Scope
2 Normative references
3 Principle
4 Reagents and materials
5 Apparatus
6 Sample preparation
7 Analysis procedure
8 Calculation and expression of results
9 Precision
10 Quantitative limit and recovery rate
Annex A (Informative) Quantitative limits, grouping, selected solvents and concentrations of mixed standard solutions of 500 pesticides and related chemicals
Annex B (Informative) Retention times, quantitative ions, qualitative ions and ratios of quantitative ion to qualitative ions of 500 pesticides and related chemicals, and internal standard compounds
Annex C (Informative) Selected ion monitoring groups of the pesticides and related chemicals by Groups A, B, C, D and E under GC-MS determination
Annex D (Informative) GC-MS diagrams of selected ion monitoring of the standards in apple substrate
Annex E (Normative) Repeatability in laboratory
Annex F (Normative) Interlaboratory reproducibility requirements
Annex G (Informative) Experimental data of adding concentration and recovery rate of samples
