GB 23200.27-2016Food safety national standard -- Determination of 4,6-dinitro-o-cresol Residue in Fruits by Gas Chromatography -- Mass Spectrometry (English PDF)

4.1 Reagents

4.1.1 dichloromethane (CH2Cl2). excellent grade pure.

4.1.2 acetonitrile (CH3CN). pure chromatography.

4.1.3 anhydrous sodium sulfate (Na2SO4). 650 °C burning 4 h, placed in the dryer in the spare.

4.1.4 Derivative reagent N- (tert-butyldimethylsilyl) -N-methyltrifluoroethylphthalide (MTBSTFA). 99% purity.

4.2 Standards

4.2.1 4,6-dinitro-o-cresol standard (C7H6N2O5, CAS No .. 534-52-1). purity 99%.

4.3 Standard solution preparation

4.3.1 4,6-dinitro-o-cresol standard stock solution. accurately weighed 10 mg 6,6-dinitro-o-cresol standard, dissolved in acetonitrile and prepared Into the concentration of 100 rng/L of the standard stock solution, can be stored in the refrigerator 0 °C ~ 4 °C for 3 months.

4.3.2 4,6-dinitro-o-cresol standard working solution. according to the need for acetonitrile will be 4,6-dinitro-o-cresol standard stock solution diluted to the appropriate concentration Degree of standard working fluid, can be stored in the refrigerator 0 °C ~ 4 °C for 1 month.

6.1 Preparation of the sample

Replace the sample of about 500 g, the sampling site according to GB 2763 Appendix A implementation, (not available washing) chopped, with a crusher will sample the product is processed into a slurry, mixed, packed into a clean container, sealed and marked.

6.2 Sample storage

Samples stored at -5 ° C in the dark. During sample preparation, the sample should be protected from contamination or changes in the residue content.

7.1 Extraction

Weigh 1 g (accurate to 0.01 g) of the prepared homogeneous sample in a 15 mL centrifuge tube, add 3 g of anhydrous sodium sulfate and 5 mL of dichloromethane, Mix thoroughly for 3 min on a vortex mixer and centrifuge at 2 000 r/min for 5 min. Transfer the dichloromethane to another 15 mL centrifuge tube, with 5 mL of methylene chloride repeated extraction time, combined extract, 50 °C nitrogen blowing concentrated to near dry.

7.2 Derivatization

After drying in nitrogen, add 0.4 mL of acetonitrile to the centrifuge tube and add 100 µL of MTBSTFA, sealed at 80 ° C Derived 1 h. Standard working fluid also added 100 µL MTBSTFA, sealed, under the above conditions for derivatization. After derivatization 0.22 µm microporous membrane was determined by gas chromatography-mass spectrometry.

7.3 Determination

7.3.1 Gas Chromatography - Mass Spectrometry Reference Conditions

A) Column. HP-5MS quartz capillary column. 30 m × 0.25 mm (inner diameter) × 0.25 µm film thickness, or equivalent.

B) Column temperature. 100 ° C (1 min) 30 ° C/min 180 ° C (1 min) 50 ° C/min 205 ° C 10 ° C/min 260 ° C (20 min).

C) Inlet temperature. 210 ° C.

D) Transmission line temperature. 250 ° C.

E) Carrier gas. helium, purity 99.999%, flow rate 1.0 mL/min.

F) Injection volume. 1 µL.

G) Injection method. no split injection, 1 min, open the diverter valve, split ratio of 20. 1.

H) ionization mode. EI.

I) Ionization energy. 70 eV.

J) Measurement method. Select the ion monitoring mode (SIM).

K) monitoring of ions. m/z 255,209,239,179, quantitative ion m/z 255.

L) solvent delay. 5 min.

7.3.2 Determination and confirmation of chromatography

According to the content of 4,6-dinitro-o-cresol in the sample, the standard working solution with similar concentration of sample peak area was selected. Derivatized the response values of the 4,6-dinitro-o-cresol derivative in the standard working solution and the sample should be within the linear range of the instrument. Derivative After the standard working solution and sample volume to participate in the measurement. The retention time of the 4,6-dinitro-o-cresol derivative under the above chromatographic conditions About 9.31 min. Under the same experimental conditions, the chromatographic retention time of the test substance in the sample was the same as that of the standard working solution and after subtracting the background of the selected ions in the sample mass chromatogram, the abundance of the selected ions is compared to the abundance ratio of the corresponding ions of the standard, Within the allowable range (see Table 1) allows you to determine the corresponding sample in the sample. Standard SIM chromatograms and full scan spectra See Appendix A, Figure A.1, Figure A.2.

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

7.4 Blank experiment

In addition to the sample, according to the above determination steps.

10.1 Quantitation limits

The quantitation limit of this method 4, 6-dinitro-o-cresol is 0.01 mg/kg.

10.2 Recovery rate

The recoveries of 4, 6 - dinitro - o - cresol were between 74.0% and 105.0% at the concentration of 0.01 mg/kg.

The recoveries of 4, 6 - dinitro - o - cresol were between 72.0% and 101.0% at the concentration of 0.05 mg/kg.

The recoveries of 4, 6 - dinitro - o - cresol were between 81.1% and 105.0% at the concentration of 0.10 mg/kg.

Appendix A

(Informative)

4, 6-dinitro-o-cresol standard-MTBSTFA derivative gas chromatography-mass spectrometry

Figure A.2 SIM spectra of 4, 6-dinitro-o-cresol-MTBSTFA derivatives

Figure A.1 SIM chromatogram of 0.5 mg/L 4,6-dinitro-o-cresol-MTBSTFA derivative

Appendix B

(Normative appendix) Laboratory repeatability requirements

Table B.1 Laboratory repeatability requirements

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

Table C.1 Inter-laboratory reproducibility requirements

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