GB 23200.84-2016Food safety national standard -- Determination of Methanol -- DDT Residues in Meat by Gas Chromatography -- Mass Spectrometry (English PDF)

4.1 Reagents

4.1.1 Ethyl acetate (C4H8O2).

4.1.2 Cyclohexane (C6H12).

4.1.3 n-hexane (C6H14).

4.1.4 Anhydrous sodium sulfate (Na2SO4). analytical grade, used before the 650

C burning 4 h, stored in a dryer, cooling and standby.

4.2 Solution preparation

4.2.1 Ethyl acetate - cyclohexane solution (1 1, volume ratio). take.200 mL of ethyl acetate, add.200 mL of cyclohexane, shake the standby.

4.3 Standards

4.3.1 Methoxychloride, C16H15Cl3O2, relative molecular weight. 345.66, CAS. 72-43-5). pure

Degrees >= 99%.

4.4 Standard solution preparation

4.4.1 Methanol DDT standard stock solution. accurately weighed the appropriate amount of methanoxazole standard, with n-hexane prepared into 100 µg/mL Standard storage solution, dark in 0 oC ~ 4 oC preservation, shelf life of 6 months.

4.4.2 Methanol Drops Standard Working Solution. According to the testing requirements, absorb the appropriate amount of the above standard solution in the volumetric flask, Alkaline Dilute the standard working solution with appropriate mass concentration and keep it at 0 oC ~ 4 oC for 1 month.

6.1 Preparation of the sample

Remove some of the representative samples from the original sample, the sampling site according to GB 2763 Appendix A implementation, into the high-speed tissue crusher Broken evenly. Fully mixed, with a four-point split out of not less than 500 g as a sample. Into a clean container, marked with a mark after sealing.

6.2 Sample storage

The sample was stored at -18 ° C or lower.

During sample preparation and storage operations, the sample should be protected from contamination or changes in residue content.

7.1 Extraction

Weigh 10 g (accurate to 0.01 g) sample in a 100 mL stoppered centrifuge tube, add 20 g of anhydrous sodium sulfate, add ethyl acetate-Cyclohexane (1 1, volume ratio) 40 mL, homogeneous 2 min, 4000 r/min centrifugation 5 min, the supernatant through the anhydrous sodium sulfate with a funnel, Collected in 100 mL rotary vials, the residue and then add 20 mL of ethyl acetate - cyclohexane (1 1, volume ratio), according to the above steps to extract a the combined extracts were concentrated to near dryness by rotary evaporation at 40 ° C.

7.2 Purification

7.2.1 Gel Permeation Chromatographic Conditions

Gel permeation chromatography conditions are as follows.

A) Purification column..200 mm × 25 mm, containing Bio-Beads S-X3 packing;

B) mobile phase. ethyl acetate-cyclohexane mixed solvent (1 1, volume ratio);

C) Flow rate. 4.7 mL/min;

D) Injection volume. 5 mL;

E) Start collection time. 9.5 min;

F) End of collection time. 13 min.

7.2.2 Gel permeation chromatography purification

The residue was dissolved in 10 mL of ethyl acetate-cyclohexane (1 1, by volume) and washed, transferred into a gel permeation chromatography vial, Mix well. If there is a granular substance present, it is centrifuged or filtered. 5 mL of the sample was injected into a calibrated GPC tube and chromatographed by gel permeation System for purification. Eluting with ethyl acetate-cyclohexane solution (1 1, by volume) and the eluate was collected in 100 mL of pear-shaped flask. in 40 °C below the rotation of evaporation to near dry. It was dissolved with n-hexane (or other suitable solvent) and fixed to 1.0 mL.

7.3 Determination

7.3.1 Gas Chromatography - Mass Spectrometry Reference Conditions

A) Column. DB-35MS (30 m × 0.25 mm × 0.25 µm) quartz capillary column or equivalent.

B) Column temperature. 80 °C for 1 min, then 20 °C/min program temperature to 180 °C, keep 3 min, then 20 °C / Min program to 230 °C, keep 7 min, to 10 °C/min program temperature to 290 °C, keep 10 min.

C) Inlet temperature. 260 ° C.

D) Injection method. no split injection.

E) Injection volume. 1 µL.

F) Carrier gas. helium, purity >=99.999%, flow rate 1.0 mL/min;

G) electron bombardment source. 70 eV;

H) ion source temperature. 230 ° C;

I) GC-MS interface temperature. 280 ° C;

J) Select ion monitoring (SIM). Quantitative ion. 227; Qualitative ion. 344,274.

7.3.2 Qualitative determination

Respectively, the same volume into the standard working solution and sample solution in the gas chromatography - mass spectrometer, according to the above conditions for analysis, the peak time was 23.5 min. The chromatogram of the standard is shown in Appendix A, Figures A.1, A.2, A.3. When the sample is measured, if the color is detected the peak retention time is consistent with the retention time of the standard, and the abundance of the selected ions is greater than the abundance of the corresponding ions of the standard in the range permitted by Table 1, it is judged that there is methanoxazole in the sample.

Table 1 Maximum allowable error of relative ion abundance using gas chromatography-mass spectrometry

7.3.3 Quantitative determination

Quantitative use of a single ion quantitative, the preparation of a series of standard solution concentration, the peak area and the relationship between the concentration of external standard quantitative determination.

7.4 Blank experiment

Unless the sample is not weighed, according to the above steps.

10.1 Quantitation limits

The limit of quantification for methotrexate is 0.005 mg/kg.

Relative abundance (base) 50% 20% to 50% 10% to 20% <=10% Allowable relative deviation ± 20% ± 25% ± 30% ± 50%

10.2 Recovery rate

When the levels were 0.005 mg/kg, 0.01 mg/kg, 0.02 mg/kg, the recovery rates for methotrexate were given in Appendix D.

Appendix A

(Informative)

DNA of DDT pesticide, retention time and monitoring of ion abundance ratio A.1 Methoxy DDT pesticide CAS number, retention time and monitoring ion abundance ratio See Table A.1.

Table A.1 CAS Number, Retention Time and Monitoring Ion Abundance Ratio of Methanol DDT Pesticides

Pesticide Chinese

name

Pesticide English

name

CAS number Molecular formula Molecular retention time Min Monitor the ion abundance ratio

1 Ozone drops

Methoxychlor 72-43-5 C16H15Cl3O2 345.66 23.50 227 (100), 228 (18), 344 (1) Note. "*" mark ions as quantitative ions.

Appendix B

(Informative)

DNA - DDT pesticide standard substance total ion chromatogram

Figure B.1 Total ion chromatogram of the standard substance for methotrexate

Appendix C

(Informative)

Standard Test Method for Methanol - DDT Pesticide Standard

Figure C.1 Methanol DDT Pesticide Standard Quality Spectrum

Figure C.2 Ozone DDT pesticide standard selection ion mass spectrometry

Appendix D

(Informative)

Addition Recovery of Methanol DDT Pesticides in Different Substrates

Table D.1 Recovery of Methanol DDT Pesticides in Different Substrates

Sample Name Add Concentration/(µg/kg) Recovery% chicken 5 82.8-89.6 10 98.6-104.7 20 100.9-103.2 duck 5 97.4-102.8 10 99.6-103.1 20 101.9-102.7 beef 5 85.2-93.4 10 95.8-97.5 20 93.2-96.2 Appendix E (Normative appendix) Laboratory repeatability requirements

Table E.1 Laboratory repeatability requirements

Measured component content Mg/kg Precision <=0.001 36 > 0.01 > 1 14 Appendix F (Normative appendix) Inter-laboratory reproducibility requirements

Table F.1 Inter-laboratory reproducibility requirements

Measured component content Mg/kg Precision <=0.001 54 > 0.01 > 1 19