GB/T 34270-2017Determination of polychorinated biphenyls and hexachlorobenzene in feeds—Gas chromatography (English PDF)

Foreword

This standard was drafted in accordance with the rules given in GB/T 1.1-2009.

1 Scope

This standard specifies the gas chromatography method for the determination of indicative polychlorinated biphenyls and hexachlorobenzene in feed.

This standard is applicable to the determination of single or multiple contents of indicator polychlorinated biphenyls (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, PCB180) and hexachlorobenzene (HCB) in compound feed, concentrated feed, additive premix, feed raw materials (except oils and fats) and feed additive copper sulfate.

The detection limits of indicative polychlorinated biphenyls and hexachlorobenzene in this standard are both 0.5 µg/kg, and the quantification limits are both 2 µg/kg.

2 Normative references

The following documents are essential to the application of this document. For referenced documents with dates, only the versions corresponding to the dates are applicable to this document; for referenced documents without dates, the latest versions (including all amendments) are applicable to this document.

GB/T 603 Chemical reagent - Preparations of reagent solutions for use in test methods

GB/T 6682 Water for analytical laboratory use - Specification and test methods

GB/T 14699.1 Feed - Sampling

GB/T 20195 Animal feed - Preparation of test samples

3 Principle

The indicative polychlorinated biphenyls and hexachlorobenzene in the sample are extracted with n-hexane acetone solution and sulfonated with concentrated sulfuric acid, then determined by gas chromatography-electron capture detector (ECD) and quantified by external standard method.

4 Reagents and materials

Unless otherwise specified, all reagents are analytically pure and conform to the secondary water specified in GB/T 6682. The preparations used in the test shall be prepared in accordance with the provisions of GB/T 603. In the analysis, high-purity reagents of pesticide residue grade are used, and blank tests are performed.

Polychlorinated biphenyls and hexachlorobenzene shall not be detected when the organic reagents are concentrated 10,000 times.

4.1 N-Hexane: Pesticide residue grade.

4.2 Acetone: pesticide residue grade.

4.3 Anhydrous sodium sulfate: It shall be baked at 660 °C for at least 6 hours, stored in a sealed container in a desiccator, and used within one month.

4.4 Saturated sodium sulfate solution.

4.5 Concentrated sulfuric acid: a guaranteed reagent.

4.6 N-Hexane acetone solution: 1+1. Take 500 mL of n-hexane and 500 mL of acetone and mix them evenly.

4.7 Indicative polychlorinated biphenyls (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, PCB180) and hexachlorobenzene standards: with a purity of >=98.0%. The Chinese names, English names, molecular formulas and CAS numbers of the substances are shown in Table A.1.

4.8 Standard stock solution: Weigh the hexachlorobenzene standard and prepare a 100 µg/mL standard stock solution with n-hexane. Polychlorinated biphenyls are liquid standards and are diluted with n-hexane to 100 µg/mL standard stock solutions. Store at -20 °C, valid for 6 months.

4.9 Mixed standard stock solution: Take appropriate amounts of hexachlorobenzene and indicative polychlorinated biphenyl standard stock solutions (4.8) respectively, and dilute with n-hexane to a mixed standard stock solution with a concentration of 1 µg/mL; store at -20 °C, valid for 3 months.

4.10 Diatomaceous earth.

5 Instruments and equipment

5.1 Gas chromatograph: It is equipped with an electron capture detector (ECD).

5.2 Analytical balance: The sensitivities are 0.1 mg and 0.01 mg.

5.3 Soxhlet extractor.

5.4 Accelerated solvent extraction (ASE) system: It is equipped with a 34 mL extraction cell.

5.5 Mortar.

5.6 Centrifuge: The speed is >10000 r/min.

5.7 Termovap Sample Concentrator.

5.8 Vortex mixer.

5.9 Ultrasonic cleaner.

5.10 Rotary evaporator.

6 Sampling and specimen preparation

Take a representative sample according to GB/T 14699.1 and reduce the sample by quartering. Prepare the specimen according to GB/T 20195; grind it, pass it through a 0.45 mm mesh sieve, mix it, put it into a sealed container, and store it at a low temperature away from light for later use.

7 Analysis steps

8 Result calculation

The content Xi of indicative PCBs and hexachlorobenzene in the specimen is expressed as a mass fraction, in mg/kg, and is calculated according to formula (1) for the single-point calibration method and formula (2) for the multi-point calibration method:

Single-point calibration method: where: m -- Mass of the specimen, in grams (g);

Ai -- Peak area of indicative polychlorinated biphenyls or hexachlorobenzene to be detected in the specimen;

Asi -- Peak area of indicative polychlorinated biphenyls or hexachlorobenzene in the standard working solution; ci -- Concentration of indicative polychlorinated biphenyls or hexachlorobenzene in the standard working solution, in micrograms per milliliter (µg/mL); V -- The metered volume before injection, in milliliters (mL).

The determination result is expressed as the arithmetic mean of parallel determinations, and the result is rounded to three significant figures. Multi-point calibration method: […]