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This standard replaces GB/T 19649-2006 Determination of 475 Pesticides and Related Chemicals Residues in Grains - Gas Chromatography-mass Spectrometry.
The following changes have been made with respect to GB/T 19649-2006:
——Text format of this standard is revised as that of national food safety standard;
——“other food may also refer to the provisions of this standard” is added in standard scope.
The previous edition of the standard replaced by this standard is as follows:
——GB/T 19649-2006.
National Food Safety Standards - Determination of 475 Pesticides and Related Chemicals Residues in Grains - Gas Chromatography-Mass Spectrometry
1 Scope
This standard specifies gas chromatography-mass spectrometry (hereinafter referred to GC-MS) for determination of 475 pesticides and related chemicals (see Annex A) residues in barley, wheat, oat, rice and corn.
This standard is applicable to determination of 475 pesticides and related chemicals residues in barley, wheat, oat, rice and corn. Other grains and foods may also refer to the provisions of this standard.
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
Extract the sample with acetonitrile in accelerated solvent extractor, then elute pesticides and related chemicals with acetonitrile-toluene solution (3+1) after the extracting solution is purified through solid-phase extraction column, and detect it with GC-MS.
4 Reagents and Materials
Unless otherwise specified, all reagents are analytical reagents and water shall be Grade 1 water complying with GB/T 6682.
4.1.3 Anhydrous sodium sulfate (Na2SO4, 7757-82-6): analytical reagent. Prior to use, burn it at 650℃ for 4h, then store it in dryer and cool it for standby.
Standard materials of pesticides and related chemicals: with purity≥95%, see Annex A.
4.3 Preparation of standard solution
4.3.1 Standard stock solution
Exactly weigh 5mg~10mg (to the nearest 0.1mg) of each standard material of pesticides and related chemicals, put them into 10mL volumetric flasks respectively; dissolve them with appropriate solvents such as toluene, mixed solution of toluene-acetone, and dichloromethane, depending on the solubility of the standard materials and determination purpose, and bring their volume to the scale (see Annex A for solvent selection).
4.3.2 Mixed standard solution (mixed standard solutions A~E).
Based on the property and retention time of pesticides and related chemicals, divide 475 pesticides and related chemicals into five groups (A~E); based on response sensitivity of each pesticide and related chemical on apparatus, determine its concentration in mixed standard solution. See Annex A for grouping of 475 pesticides and related chemicals and concentration of their mixed standard solution.
Transfer a certain amount of standard stock solution (4.3.1) of single pesticide and related chemical to a 100mL-volumetric flask according to grouping No. of each pesticide and related chemical, as well as concentration of mixed standard solution and that of its standard stock solution, and bring the volume with toluene to the scale. Mixed standard solution is preserved at 4℃ in a dark place for a month.
4.3.3 Internal standard solution
Exactly weigh 3.5mg of heptachlor epoxide in a 100mL-volumetric flask, and bring the volume with toluene to the scale.
4.3.4 Matrix-mixed standard working solution
For preparing groups A~E matrix-mixed standard working solutions for pesticides and related chemicals: add 40μL of internal standard solution (4.3.3) and certain amount of mixed standard solution to 1.0mL of blank sample matrix extracting solution respectively and mix well to obtain matrix-mixed standard working solutions A~E. Matrix-mixed standard working solution shall be prepared immediately before use.
4.4 Materials
4.5.1 Envi-18 column ): 12mL, 2g or equivalent.
4.5.2 Envi-Carb column1): 6mL, 0.5g or equivalent.
4.5.3 Sep-Pak NH2 column ): 3mL, 0.5g or equivalent.
5 Apparatuses
5.1 Gas chromatograph-mass spectrometer: equipped with electronic ignition (EI).
5.2 Analytical balance: with sensibility of 0.01g and 0.0001g.
5.3 Accelerated solvent extractor: equipped with 34mL extraction pool.
5.4 Nitrogen evaporator.
5.5 Pear-shaped flask: 200mL.s
5.6 Pipette: 1mL.
6 Sample Preparation and Preservation
6.1 Sample preparation
After grain samples taken according to GB 5491 are pulverized via grinder, they are sieved with 425μm standard mesh sieve and mixed uniformly; the prepared samples are divided into two equal parts and put in clean sample containers, sealed and indicated with labels.
7 Analytical Procedures
7.1 Extraction
Mix 10g of sample (to the nearest 0.01g) with 10g of diatomite and then transfer them into 34-mL extraction pool of accelerated solvent extractor. Under 10.34MPa-pressure and 80℃, heat them for 5min, extract for 3min with static acetonitrile in two cycles, and then rinse extraction pool with acetonitrile (20.4mL) which accounts 60% of pool body and purge with nitrogen for 100s. After extraction, uniformly mix the extraction solution; for sample with less oil, take half (equivalent to 5g sample) of the extraction solution; for that with more oil, take a quarter (equivalent to 2.5g sample) of the extraction solution, purify afterwards.
7.2 Purification
7.2.1 Prewash Envi-18 column with 10mL of acetonitrile, place the column on fixing frame down-connected with pear-shaped flask, transfer it into the above-mentioned extraction solution; wash Envi-18 column with 15mL of acetonitrile, collect extraction solution and detergent, and concentrate the solution collected on rotary evaporator to about 1mL for standby.
7.2.2 Add about 2cm-high anhydrous sodium sulfate into Envi-Carb column which is connected to the top of Sep-PakNH2 column, prewash columns in series that are down-connected with pear-shaped flask with 4mL of acetonitrile-toluene solution (3+1) and put the pear-shaped flask on fixing frame. Transfer the above sample concentration solution into columns in series, wash sample solution flask with 3×2mL acetonitrile-toluene and transfer the detergent into the columns; install a 50mL liquid reservoir on columns in series, wash the columns with 25mL acetonitrile-toluene, collect all of the above effluents into pear-shaped flask, and concentrate in rotation to about 0.5mL in 40℃ water bath. Add into 2×5mL n-hexane, exchange solvent twice to make the volume of sample solution reach about 1mL, add 40μL of internal standard solution, mix uniformly for GC-MS determination.
Foreword i 1 Scope 2 Normative References 3 Principle 4 Reagents and Materials 5 Apparatuses 6 Sample Preparation and Preservation 7 Analytical Procedures 8 Result Calculation and Expression 9 Precision 10 Limit of Quantitation and Recovery Rate Annex A (Informative) Limit of Quantitation, Grouping, Solvent Selection and Concentration of Mixed Standard Solution for 475 Pesticides and Related Chemicals Annex B (Informative) Retention Time, Quantitative Ion, Qualitative Ion and Abundance Ratio of Quantitative Ion to Quantitative Ion for 475 Pesticides and Related Chemicals as well as Internal Standard Compounds Annex C (Informative) Grouping Table Regarding Selected Ion Monitoring of Five Groups (A~E) of Pesticides and Related Chemicals Annex D (Informative) GC-MS Figure for Selected Ion Monitoring of Standard Substances in Wheat Matrix Annex E (Informative) Repeatability Requirements in Laboratory Annex F (Informative) Repeatability Requirements between Laboratories Annex G (Informative) Test Data for the Addition Concentration and Recovery Rate of Sample
Cs 基质标准工作溶液中被测物的浓度，单位为微克每毫升（µg/mL）； A 试样溶液中被测物的色谱峰面积； As 基质标准工作溶液中被测物的色谱峰面积； Ci 试样溶液中内标物的浓度，单位为微克每毫升（µg/mL）； Csi 基质标准工作溶液中内标物的浓度，单位为微克每毫升（µg/mL）； Asi 基质标准工作溶液中内标物的色谱峰面积； Ai 试样溶液中内标物的色谱峰面积； V 样液最终定容体积，单位为毫升（mL）； m 试样溶液所代表试样的质量，单位为克（g）。
计算结果应扣除空白值，测定结果用平行测定的算术平均值表示，保留两位有效数字。
9 精密度
9.1 在重复性条件下获得的两次独立测定结果的绝对差值与其算术平均值的比值（百分率），应符合附 录 D 的要求。 9.2 在再现性条件下获得的两次独立测定结果的绝对差值与其算术平均值的比值（百分率），应符合附 录 E 的要求。
