GB 23200.44-2016Food safety national standard -- Determination of carbon disulfide, carbon tetrachloride and dibromoethane residues in grain (English PDF)

4.1 Reagents

4.1.1 distilled water. boiled before use for 20min, cooling standby. Take 300 ml of distilled water in a flask of a distillation extractor (see figure below) Add 15 ml of isooctane, according to the extraction step (7.1) operation. Under the specified chromatographic conditions, 1 l of the isooctane extract was chromatographed, should be the same as the octane other than the chromatographic peaks.

4.1.2 Isooctane (C8H18). analytical grade, in the same chromatographic conditions with the determination of injection 1ul for chromatography, should be no octane Other than the peaks.

Note. Isooctane purification. 1000ml flask by adding 500ml isooctane, and then add metal sodium tablets 5-10g, connected to the grinding of the condenser, reflux 6-8h, and then use the whole glass distiller was distilled to collect fractions between 97.5 and 99.5 ° C.

4.1.3 anhydrous sodium sulfate (Na2SO4). analysis of pure, 650 °C burning 4h, after cooling stored in a closed container.

4.1.4 concentrated sulfuric acid (H2SO4). analytical grade.

4.1.5 sulfuric acid aqueous solution. 10% (V/V).

4.1.6 Carbon disulfide (CS2). Analytical pure (d

1.263)

4.1.7 Carbon tetrachloride (CCl4). Analytical purity (d

1.594)

4.1.8 Dibromoethane (C2H4Br2). Analytical pure (d

2.177)

4.2 Standard solution preparation

4.2.1 Standard stock solution. accurately measure the appropriate volume of carbon disulfide, carbon tetrachloride, dibromoethane, and weigh the weight Calculate, with isooctane, respectively, with the concentration of 1.00mg/ml of the standard stock solution.

4.2.2 Standard working solution

If necessary, standard stock solutions are diluted with isooctane to form a mixed standard working solution at the following concentrations (Table 1).

6.1 Preparation of the sample

The samples taken, the sampling site according to GB 2763 Appendix A implementation, with a sub-sampling device or quadruple to 1kg, all grinding and through 20 Mesh sieve, mix, are divided into two, immediately into the clean container, sealed, marked mark.

6.2 Sample storage

Store the sample below 0 ° C.

Note. (1) shrink the sample, the operation should be as fast as possible to prevent the loss of fumigant.

During the operation of the sample preparation, it is necessary to prevent the sample from being contaminated or the change in the content of the residue.

7.1 Extraction

A sulfuric acid aqueous solution (10%, V/V) was added to the return port from the receiving tube of the distillation extractor and the gas inlet. even Connect the condenser and gas absorption wells, add 5 mL of isooctane from the mouth of the condenser to the gas absorption trap. Access to cooling water. Quickly take the mix 50.0 g (accurate to 0.1 g) of the sample was placed in a flask to connect the flask and extractor. Add 12 mL of isooctane from the flotation port of the flask 300 m1 sulfuric acid aqueous solution (10%, V/V). Close the dosing port and seal the dosing with a small amount of sulfuric acid solution (10%, V/V). Will be used to heat sets the flask was heated and the isooctane extract was slowly distilled off until the isooctane extract was completely distilled off and heated for about 5 minutes. stop Heat the flask to cool. The aqueous layer in the receiving tube was released from the lower mouth and then the isooctane extract was passed through an anhydrous sodium sulfate column and collected 25 mL volumetric flask. From the upper surface of the condenser, rinse the condenser, gas absorption trap, receiver tube and anhydrous sulfur with about 7 mL of isooctane Sodium sulphate column, lotion into the volumetric flask, with isooctane capacity, gas chromatographic determination.

7.2 Determination

7.2.1 Gas Chromatographic Reference Conditions

A) Column. glass column, 1.6 m X3.2 m m (inner diameter), filler 25% (m/m) DC-200 applied to Chromosorb W AW-DMCS (60-80 mesh).

B) Column temperature. 75 ° C.

C) Inlet temperature. 150 ° C.

D) Detector temperature. 150 ° C.

E) helium, purity >=99.99%, 25m L/min.

7.2.2 Chromatographic determination

According to the sample solution of carbon disulfide, carbon tetrachloride, dibromoethane content, selected peak height similar to the standard working solution. Standard working solution and carbon tetrachloride, carbon tetrachloride and dibromoethane in the sample solution should be within the linear range of the instrument. On the standard working solution and sample solution Measurement of volume injection. Under the above chromatographic conditions, the retention times of carbon disulfide, carbon tetrachloride and dibromoethane were 1.7 m in, 3.5 Min, 8.1 min.

7.3 Blank experiment

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

10.1 Quantitation limits

The quantification limit of this method is. carbon disulfide. 0.02 mg/kg; carbon tetrachloride. 0.004 mg/kg; dibromoethane. 0.005 mg/kg.

10.2 Recovery rate

The recovery of this method is shown in Table 2.

Appendix A

(Normative appendix) Laboratory repeatability requirements

Table A.1 Laboratory repeatability requirements

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

Table B.1 Inter-laboratory reproducibility requirements

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