Determination of fatty acid content in food by gas chromatography

1. principle

Gas chromatography uses a carrier and a fixed liquid to be filled into the chromatographic column, and a carrier gas is used to bring the mixture to be analyzed into the chromatographic column. Under certain temperature and pressure conditions, the distribution coefficients of each gas component in the gas-liquid two-phase phase of the carrier gas and the fixed liquid film are different. As the carrier gas flows forward, the components of the sample are repeatedly distributed in the gas and liquid phases, making the movement speeds of each fatty acid component faster and slower, so that each component can be separated. Then perform separate measurements.

2. scope of application

This method is suitable for the analysis of fatty acids in food.

3. instrument

gas chromatograph

hydrogen flame ionization detector

Nitrogen, hydrogen, compressed air

the microprocessor

The chromatographic column 2m × 4mm or 3m × 4mm is filled with 80--100 mesh ChromosorbW and coated with 8% or 10% W/W diethylene glycol succinate DEGS

gas chromatographic conditions

Column temperature:210℃

Injector temperature: 280℃

Detector temperature: 280℃

Nitrogen flow rate: 40ml/cm2

4. reagent

All reagents, if the specifications are not specified, are referred to as excellent purity, and all experimental water is distilled water.

1 Petroleum ether boiling range 30~60℃ Analytical pure

2 benzene

3 Anhydrous methanol

40.4mol/L potassium hydroxide-methanol solution: Weigh 2.24g potassium hydroxide and dissolve it in a little methanol, and then dilute it to 10ml with methanol.

5 Fatty acid standard SIGMA

6 Fatty acid mixing standards

CHAIN %BYWT

6:0 1.0

8:0 5.0

10:0 4.0

12:0 27.0

14:0 10.0

16:0 10.0

18:0 2.0

18:1 15.0

18:2 25.0

18:3 1.0

5. operation steps

Weigh 30--100mg of about 2 -6 drops of oil, place it into a 10ml volumetric flask, add 1-2ml of a mixed solvent of petroleum ether and benzene at a boiling range of 30 - 60℃ and 1:1, and gently shake to dissolve the oil. Add 1-2ml of 0.4 mol/L potassium hydroxide-methanol solution and mix well. After standing at room temperature for 5 to 10 minutes, add distilled water to raise all the petroleum ether benzyl ester solution to the upper part of the bottleneck, and let it be clarified. If the supernatant fluid is turbid and urgently needed for analysis, drop a few drops of absolute ethanol and it will be clarified within 1-2 minutes. Suction the supernatant, blow in nitrogen at room temperature to concentrate, and the resulting concentrate can be used for gas layer analysis.

6. result calculation

In the case of a microprocessor, the peak area and the percentage of