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4.
Safety reminder
(1 ) Aflatoxin is a highly active carcinogenic toxin, so the entire operation should be particularly cautious
.
During operation, please wear protective masks, gloves, glasses, isolation suits or disposable test suits, and prepare a rag soaked with 5% sodium hypochlorite solution for use
(2) The utensils used in the test need to be soaked in 5% sodium hypochlorite solution overnight, and then cleaned with acetone for 1 to 2 times, and then cleaned as ordinary utensils
.
(3) The waste liquid after the test should be treated with 5% sodium hypochlorite solution before being poured into the designated place
.
(4) The thin layer expansion should be carried out in a fume hood
.
(5) The standard solution of aflatoxin is recommended to be diluted and quantified with a standard solution prepared by commercial acetonitrile , and it is not recommended to purchase a solid standard to prepare it by yourself
.
5.
Operation steps
(1) Extraction Weigh 10.
00g of soy sauce sample into a small beaker.
To prevent emulsification during extraction, add 0.
4g of sodium chloride and transfer it to a separatory funnel.
Wash the beaker with 15mL of chloroform , and add the lotion to the separator.
In the liquid funnel, shake for 2 minutes and stand for stratification (if emulsification occurs, methanol can be added dropwise to promote stratification)
.
Release the chloroform layer, filter it in a 50mL evaporating dish with a quantitative slow filter paper containing about 10g of anhydrous sodium sulfate pre- moistened with chloroform , add 5mL of chloroform to the separatory funnel, and repeat the extraction by shaking , The chloroform layer is filtered in an evaporating dish, and finally a small amount of chloroform is used to wash the filter, the washing liquid is combined in the evaporating dish, and the evaporating dish is placed in a fume hood and ventilated on a 65℃ water bath.
Or weigh 10.
00g sample, place it in a separatory funnel, and add 12mL methanol (the volume of soy sauce is used instead of water, so the volume ratio of methanol to water is still about 55+45)
.
Extract with 20 mL of chloroform , and operate according to the above-mentioned starting from "shaking for 2 minutes and standing for stratification"
(2) Measurement (one-way expansion method)
①Preparation of thin layer plate: Weigh about 3g of silica gel G, add water equivalent to about 2 to 3 times the amount of silica gel, and grind vigorously for 1 to 2 minutes until it becomes a paste, then pour it into the spreader and push it into 5cm×20cm , Three thin-layer boards with a thickness of about 0.
25mm
.
After drying in the air for about 15 minutes, activate it at 100°C for 2 hours, take it out, and store in a desiccator
Note: Finished silica gel plates (5cm×20cm, thickness 0.
25mm) can be purchased
.
②Sampling: Scrape the adsorbent attached to the edge of the thin-layer plate, and drip the sample solution on the baseline 3 cm from the lower end of the thin-layer plate with a micro syringe or hemoglobin pipette
.
One board can drop 4 dots.
The first point: 10uL aflatoxin B1 standard use solution (0.
04ug/mL)
.
The second point: 20uL sample solution
.
The third point: 20uL sample solution + 10uL 0.
04ug/mL aflatoxin B1 standard use solution
.
The fourth point: 20uL.
sample solution + 10uL 0.
2ug/mL aflatoxin B1 standard use solution
.
③Expansion and observation: Add 10mL of anhydrous ether to the expansion tank, pre-expand it for 12cm, take it out and evaporate it to dry
.
Then add 10 mL of acetone-trichloromethane (8+92) into another expansion tank, expand 10-12cm, and take it out
a.
Since a drop of aflatoxin B1 standard use liquid is added to the sample solution point, the aflatoxin B1 standard spot can be overlapped with the aflatoxin B1 fluorescence spot in the sample solution
.
If the sample solution is negative, the aflatoxin B1 in the third point on the thin-layer plate is 0.
b.
