GB 31656.17-2022National Food Safety Standard - Determination of Dithiocyanomethane Residues in Aquatic Products by Gas Chromatography (English PDF)

5.1 Reagents

5.1.1 Acetonitrile (CH3CN). chromatographically pure.

5.1.2 Methanol (CH3OH). chromatographically pure.

5.1.3 n-Hexane (C6H14). chromatographically pure.

5.1.4 Dichloromethane (CH2Cl2). chromatographically pure.

5.1.5 Acetone (CH3COCH3). chromatographically pure.

5.1.6 Anhydrous sodium sulfate (Na2SO4).

5.2 Solution preparation

Dichloromethane-n-hexane (1.1, V/V). take 250mL of dichloromethane and n-hexane respectively, and mix well.

5.3 Standards

Methylenebisthiocyanate (Methylenebisthiocyanate, C3H2N2S2, CAS number. 6317-18-6), content >=99%.

5.4 Preparation of standard solution

5.4.1 Standard stock solution. Accurately weigh 10mg of dithiocyanomethane standard substance, dissolve it with an appropriate amount of acetonitrile and dilute to 50mL brown

The volumetric flask was prepared into a standard stock solution with a concentration of.200 µg/mL. Stored below -18°C, the validity period was 3 months.

5.4.2 Standard working solution. Accurately measure an appropriate amount of dithiocyanomethane standard stock solution, dilute it with dichloromethane, and prepare a concentration of

0.05µg/mL, 0.1µg/mL, 0.5µg/mL, 1.0µg/mL, 2.0µg/mL, 5.0µg/mL and 10.0µg/mL series standards

Working fluid. Ready to use.

5.5 Materials

Neutral alumina solid phase extraction column, packing 60mg/3mL, or equivalent.

6.1 Gas chromatograph equipped with pulsed flame photometric (PFPD) detector.

6.2 Homogenizer.

6.3 Rotary evaporator.

6.4 Centrifuge.

6.5 Vortex mixer.

6.6 Analytical balance. Sensitivity 0.00001g and 0.01g.

6.7 Nitrogen blowing instrument.

7.1 Preparation of samples

Prepare samples according to the requirements of Appendix B of GB/T 30891-2014.

a) Take the homogenized test sample as the test material;

b) Take the homogenized blank sample as the blank sample;

c) Take the homogenized blank sample, add the standard working solution of appropriate concentration, and add the sample as the blank.

7.2 Storage of samples

Store frozen below -18°C.

8.1 Extraction

Take 5g of the sample (accurate to +/-0.05g), put it in a 50mL stoppered glass centrifuge tube, add dichloromethane-n-hexane (1.1, V/V)

15 mL, immediately vortexed for 1 min, ultrasonically extracted for 10 min, centrifuged at 4000 r/min for 5 min, and the supernatant was taken into a chicken heart bottle with a glass dropper.

Repeat the extraction once, combine the supernatants of the two times, mix well, and blow nitrogen at 40°C to 0.5mL-1.0mL, and set aside.

8.2 Purification and concentration

Take a neutral alumina solid-phase extraction column, add 1.0 g of anhydrous sodium sulfate to the upper layer, pass the spare liquid through the column and collect it, and use dichloromethane-n-hexane

(1.1, V/V) 2.0 mL washes 8.1 chicken heart bottles containing the extract, passes through the column, and collects them in 15 mL glass test tubes, and then washes them with dichloromethane.

8mL eluted small column, and collected in the same glass test tube, dried with nitrogen at 40°C, added dichloromethane-n-hexane (1.1, V/V) 1.0mL, vortexed

8.3 Preparation of standard curve

Precisely measure the appropriate amount of standard working solution for gas chromatography determination. Take the measured peak area as the ordinate, and the corresponding standard solution concentration as the abscissa

Coordinates, draw a standard curve. Find the regression equation and correlation coefficient.

8.4 Determination

8.4.1 Chromatographic conditions

a) Chromatographic column. HP-5MS quartz capillary column (30mx0.32mm, particle size 0.25µm), or equivalent;

b) Injection method. splitless injection;

c) Carrier gas. nitrogen, purity 99.999%;

d) Column flow rate. 1.0mL/min;

e) The inlet temperature is 230°C, and the detector temperature is 310°C;

f) Column temperature program. the initial column temperature is 50°C, keep for 1min, raise the temperature to 180°C at 25°C/min, and keep for 2min;

g) Injection volume. 1.0 µL.

8.4.2 Determination method

Take the sample solution and the corresponding standard solution for single-point or multi-point calibration, and calculate the peak area according to the external standard method. The standard solution and the sample solution

The response value of dithiocyanatomethane in the liquid should be within the linear range of the instrument detection. Under the above chromatographic conditions, the gas chromatogram of the standard solution is shown in the attached

Record A.

8.4.3 Blank test

Take the blank sample, except that no drug is added, the same measurement steps are used for parallel operation.

10.1 Sensitivity

The detection limit of this method was 5 µg/kg, and the quantification limit was 10 µg/kg.

10.2 Accuracy

The recovery rate of this method was 60%-110% at the spiked concentration level of 10 µg/kg-500 µg/kg.

10.3 Precision

In this method, the relative standard deviation within the batch was <=20%, and the relative standard deviation between batches was <=20%.