GB 23200.87-2016Food safety national standard -- Determination of thiabendazole residues in milk and dairy products -- Fluorescence spectrophotometric method (English PDF)

4.1 Reagents

4.1.1 Potassium hydroxide (KOH).

4.1.2 Hydrochloric acid (HCl).

4.1.3 Ethyl acetate (CH3COOH).

4.2 Solution preparation

4.2.1 50% (m/V) potassium hydroxide solution. accurately weighed 50 g of potassium hydroxide solid, dissolved in water, cooled to 100 mL, Shaking back.

4.2.2 0.05% (m/V) potassium hydroxide solution. accurate removal of 50% potassium hydroxide solution (4.2.1) 1mL in 1000 mL volumetric flask, Water volume, shake back spare.

4.2.3 0.1 mol/L hydrochloric acid solution. accurate removal of 0.83 mL concentrated hydrochloric acid in a 100 mL volumetric flask, the volume of water, shake back.

4.3 Standards

4.3.1 Thiabendazole standard. purity >= 99%.

4.4 Standard solution preparation

4.4.1 Thiabendazole standard stock solution. accurately weighed the appropriate amount of thiabendazole standard, with hydrochloric acid solution dubbed the concentration of 0.100 mg/mL Standard stock solution. According to the need to use hydrochloric acid solution diluted to the appropriate concentration of standard working solution. Store in 4 °C refrigerator.

6.1 Preparation of the sample

The retrieved vials were thoroughly mixed and about 250 mL was taken as a sample. Into a clean container, sealed, marked mark.

Note. The above sample sampling site according to GB 2763 Appendix A implementation.

6.2 Sample storage

Store the sample below -5 ° C.

Note. During sampling and sample preparation, it is necessary to prevent contamination of the sample or change in the content of the residue.

7.1 Saponification

Weigh the sample 10 g (accurate to 0.1 g) in the conical flask, add 7 mL of potassium hydroxide solution, connected to the condenser, in the boiling water bath Reflux saponification 40 min, remove, fully cooled.

7.2 Extraction

The saponified solution was transferred to a separatory funnel and the Erlenmeyer flask was washed with 10 mL of water and the lotion was incorporated into the same separatory funnel. Add 15 mL of ethyl acetate Ester, gently shake 0.5 min, static stratification. The aqueous layer was transferred to another separatory funnel, extracted again with 15 mL of ethyl acetate, shaken vigorously for 1 min, Static stratification. The ethyl acetate extracts were combined.

7.3 Purification

The ethyl acetate extract was washed with 20 mL of potassium hydroxide solution, shaken vigorously for 1 min, and the layers were discarded and the aqueous layer was discarded. Add another 20 mL the potassium hydroxide solution was washed gently and the water was discarded. The ethyl acetate layer was extracted with 2 x 5 mL hydrochloric acid solution. The combined hydrochloric acid extract was added at 10 mL Volumetric flask, and with hydrochloric acid solution volume. Determination by fluorescence spectrophotometry.

7.4 Determination

7.4.1 Fluorescence spectrophotometric determination of the reference conditions

Excitation wavelength. 307 nm; emission wavelength. 359 nm. Different models of equipment, according to the actual situation to adjust to get the best excitation wave Long and emission wavelengths.

7.4.2 Drawing of standard curves

Respectively, draw 0.2, 0.5, 1.0, 5.0 and 10.0 mL standard stock solution to a group of 10 mL volumetric flask, with hydrochloric acid solution volume, the fluorescence absorbance was measured on a fluorescence spectrophotometer and the standard curve was plotted against the concentration of thiabendazole by fluorescence absorbance. The fluorescence of the standard light the scan of the scale is shown in Figure A1 in Appendix A.

7.4.3 Determination of sample solution

The fluorescence intensity of the sample solution was measured on a fluorescence spectrophotometer. From the standard curve on the sample solution of thiophene Bacteria concentration.

7.5 Blank experiment

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

10.1 Quantitation limits

The limit of this method is 0.02 mg/kg.

10.2 Recovery rate

The recovery of thiabendazole is given in Appendix B.

Appendix A

Standard Fluorescence Absorbance Scanning Chart

Figure A1 Thiabendazole standard Fluorescence absorbance scan

Appendix B

(Informative)

Thiabendazole added levels and added recovery rates

Table B.1 Thiabendazole added levels and added recovery rates

Add level

(Mg/kg)

Recovery rate

0.02 102

0.10 96.5

0.50 99.6

Appendix C

(Normative appendix) Laboratory repeatability requirements

Table C.1 Laboratory repeatability requirements

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

Table D.1 Inter-laboratory reproducibility requirements

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