Determination of synthetic colorants in food (2)

(4) Operation steps

①Sample handling: Weigh 500g of the sample with more grease, 1000g for the sample with less grease, and then take two-quarters or two-sixths with a diagonal line, or take a representative according to the condition of the sample The test sample is ground in a glass emulsion, mixed evenly, and stored in a wide-mouth bottle in the refrigerator
.

② Fat extraction
.

a.
Samples with high fat content (such as peach crisps, etc.
): Weigh 50g, mix well, put it in a 250mL conical flask with a stopper, add 50mL petroleum ether (boiling range 30-60℃), leave it overnight, and use After rapid filter paper filtration, the solvent is recovered under reduced pressure, and the residual fat is used for later use
.

b.
Samples with medium fat content (such as cakes, rice noodles, etc.
): Weigh about 100g, mix well, put in a 500mL conical flask with stopper, add 100~200mL petroleum ether (boiling range 30~60℃) , Stand overnight, filter with quick filter paper, recover the solvent under reduced pressure, and use residual fat for later use
.

c.
Samples with low oil content (such as bread, biscuits, etc.
): weigh 250～300g and mix well, add appropriate amount of petroleum ether to soak the sample in a 500mL conical flask with stopper , leave it overnight, and filter with quick filter paper , Recover the residual fat of the solvent under reduced pressure for later use
.

③ Preparation of samples for analysis
.

a.
Preparation of the chromatography column: add a small amount of glass wool and a small amount of anhydrous sodium sulfate to the bottom of the chromatography column , and mix 10g of silica gel-florisil (6+4) with petroleum ether wet method to pack the column.
Add a small amount of anhydrous sodium sulfate to the top
.

b.
Sample preparation: Weigh 0.
50～1.
00g of the fat prepared in ②, dissolve it with 25mL petroleum ether and transfer it to the chromatographic column of ③a, and then wash with 100mL dichloromethane for 5 times, combine the eluents, and depressurize When the concentration is nearly dry, dilute the volume to 2.
0 mL with carbon disulfide .
This solution is the solution to be tested
.

c.
Preparation of vegetable oil sample: Weigh 2.
00 g of a well-mixed sample into a 50 mL beaker, add 30 mL of petroleum ether to dissolve, transfer to the chromatographic column ③a, and then wash it into the beaker several times with 10 mL of petroleum ether , and Transfer to a chromatography column, rinse with 100 mL of dichloromethane five times, combine the eluates, concentrate under reduced pressure to near dryness, and dilute to 2 mL with carbon disulfide .
This solution is the test solution
.

④ Determination
.

a.
Reference conditions of gas chromatography:

Chromatographic column: a glass column with a length of 1.
5m and an inner diameter of 3mm, with QF-1Gas Chrom Q (80-100 mesh) coated with a mass fraction of 10%
.

Temperature: detection room 200℃, sample inlet 200℃, column temperature 140℃
.

Carrier gas flow: nitrogen 70mL/min, hydrogen 50mL/min, air 500mL/min
.

b.
Chromatographic analysis: Inject 3.
0uL standard liquid for gas chromatography, draw a chromatogram, measure the peak height or area of ​​each component, and enter 3.
0uL sample solution to be tested (depending on the content of the sample), and draw the chromatogram , Measure the peak height or area respectively, and calculate the content by comparing with the standard peak height or area
.

c.
Chromatogram: The gas chromatograms of BHA and BHT are shown in Figure 5-2
.

(5) Calculate the mass of BHA (or BHT) of the solution to be tested by the following formula:

Where m ₁ ——the mass of BHA (or BHT) of the solution to be tested, mg

h _i ——the peak height or area of ​​BHA (or BHT) injected into the chromatographic sample

h _s ——The peak height or area of ​​BHA (or BHT) in the standard solution

V _i ——The volume of injected chromatographic sample solution, mL

V _m ——The constant volume volume of the sample to be tested, mL

V _s ——the volume of standard liquid used in the injection chromatogram, mL

p _s ——concentration of standard liquid, mg/mL

The content of BHA (or BHT) in fat in food is calculated as follows:

Where x-the content of BHA (or BHT) in the food as fat, g/kg

m ₁ ——The mass of BHA (or BHT) in the solution to be tested, mg

m ₂ ——the mass of fat (or fat in food), g

Figure 5-2 Gas chromatogram of BHA and BHT

The calculation result retains three significant figures
.

(6) The main points remind the detection limit of this method: when the detection amount is 2ug, when the oil sampling amount is 0.

Related links: Determination of synthetic colorants in food (1)