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Determination of Polychlorinated Biphenyls in Marine Products by Gas Chromatography

Abstract: Polychlorinated biphenyls (PCBs) are carcinogenic and easily accumulate in adipose tissue, causing diseases in the brain, skin and internal organs, and affecting the nervous, reproductive and immune systems.

1 Principle Polychlorinated biphenyl residues in seafood, extracted with hexane (or petroleum ether). The extract is purified, separated by silica gel column, and concentrated. The total content was determined by gas chromatography using an electron capture detector.

2 Reagent 2.1 Hexane: Analytically pure, re-steamed in a full glass distiller.

2.2 petroleum ether: analytically pure. 2.3 concentrated sulfuric acid: excellent grade pure.

2.4 anhydrous sodium sulfate: excellent grade pure, burned at 550 ° C high temperature, stored in a desiccator.

2.5 silica gel: chromatography, 60 ~ 100 mesh silica gel, heat treatment at 360 ° C for 10 ~ 12h, after cooling, add 3.0% water, shake for 2h, stored in a desiccator.

2.6 Polychlorinated biphenyl standard solution: Accurately weigh 10.0mg PCB3 and PCB5 in two 100ml volumetric flasks, dilute to the mark with n-hexane, and mix. The solution concentration was 100 μg/ml. Dilute to standard application solution with n-hexane before use. This application solution contains 0.20 μg each of PCB3 and PCB5.

3 Instrument 3.1100ml with a triangular flask.

3.2 Scale with a centrifuge tube.

3.310 × 150mm stoppered glass chromatography column.

3.4 Centrifugal sedimentation machine.

3.5 constant temperature water bath.

3.6K-D concentrator.

3.7 Gas chromatograph ECDNI63.

4 Analysis step 4.1 Chromatographic conditions 4.1.1 The column is a glass column with an inner diameter of 3 mm and a length of 2 m.

4.1.2 Fixed phase 4.1.2.1 ChromosorbWAWDMCS 80 ~ 100 mesh. 2.8% OV-210 + 0.23% OV-17.

4.1.2.23% OV-101 ChromosorbWAWDMCS 80 ~ 100 mesh.

4.1.3 Temperature: column temperature 210 ° C; detector 250 ° C; vaporization chamber 230 ° C.

4.1.4 Carrier gas: high purity nitrogen (99.99%).

4.2 Sample preparation and extraction Take 5g of edible part of the fish, add about 20g of anhydrous sodium sulfate to grind into sand, place it in a flask, shake it with 40ml of hexane for 0.5h or soak overnight, filter, residue The mixture was rinsed twice with 10 ml of hexane each time, and the filtrate was combined in a graduated centrifuge tube, concentrated to 5 ml, concentrated with 5 ml of sulfuric acid, shaken, centrifuged at 3000 r/min for 15 min, and the hexane extract was taken out.

4.3 Purification of the extract 1 ml of hexane extract was placed in a 2 g silica gel column (wet packed column). The upper and lower layers of the silica gel were each filled with 1 cm high anhydrous sodium sulfate and rinsed with 7 ml of hexane. It is preferred to drip (about 30 drops/min) and the eluent is concentrated to 1.0 ml, which is available for chromatography.

4.4 Quantification 4.4.1 Take the same volume of sample extract and PCB standard application solution, enter the chromatograph under the same chromatographic operating conditions, and quantify the sum of the peak heights of the main peaks of PCB3 and PCB5. PCB3 uses at least one main peak. PCB5 calculates the basis weight using at least the sum of the three main peaks. See the peaks 1, 2, 3, and 4 in the figure below.

4.4.2 Calculation formula: X——the content of polychlorinated biphenyls in the sample, mg/kg; H1——the sum of the peak heights of polychlorinated biphenyls in the sample, mm; H2——the polychlorinated biphenyls in the standard application liquid The sum of the peak heights, mm; C - the concentration of polychlorinated biphenyls in the standard application liquid, ? g / ml; M - the injection volume (? l) is equivalent to the mass of the sample, g.

Note: The variety of silica gel, the number of meshes and the time of storage after deactivation have a certain effect on the adsorption effect. The amount of eluent should be tested with a standard PCB on the column before use. The amount of silica gel depends on the level of organic chlorine in the seafood sample to eliminate the interference of organochlorine pesticide DDT.

(Source: China Chemical Instrument Network)

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