Key words: milk powder; vanillin; ethyl vanillin; GC-FID
Key words: milk powder; Vanillin; Ethyl vanillin; GC-FID
Summary
The vanillin and ethyl vanillin in milk powder were extracted with methylene chloride as solvent. After purification by dispersive solid phase extraction, the sample was determined by Trace1310 gas chromatograph. The external standard method was used for quantitative determination, linearity, recovery and reproducibility. Sexuality meets analytical requirements.
introduction
Vanillin, also known as vanillin, scientific name 3-methoxy-4-hydroxybenzaldehyde; ethyl vanillin, scientific name 3-ethoxy-4-hydroxybenzaldehyde. Both are white or slightly yellow crystalline powder, slightly soluble in water, with vanilla aroma and rich milky aroma, are important food additives, widely used as flavoring agents for food, beverages and daily chemicals. However, the use of perfumes such as vanillin in large doses can be detrimental to health. According to the National Food Safety Standards for the Use of Food Additives GB2760-2011, no edible flavors should be added to infant formulas covering 0 to 6 months. In July 2012, it was reported that the milk powder of Phase I of several major ocean brands was detected and added with the prohibition of vanillin in the country. Therefore, it is necessary to establish a related test method to detect vanillin in milk powder.
At present, the determination methods of vanillin and ethyl vanillin mainly include spectrophotometry, electrochemical method, high performance liquid chromatography, gas chromatography and gas chromatography-mass spectrometry. Because the HPLC method does not require high degree of sample purification, the sample is not required. There are few studies on pretreatment. The method adopts dichloromethane extraction, dispersive solid phase extraction and purification, and establishes a gas chromatography method for simultaneously determining the content of vanillin and ethyl vanillin in infant formula.
Experimental part
Main equipment and reagents
Instrument: Gas Chromatograph, Trace 1310, ThermoFisher, USA.
Reagents: dichloromethane, chromatographically pure; sodium chloride, analytically pure; Cleanert C18 solid adsorbent; vanillin and ethyl vanillin standards.
Sample preparation method
Weigh 5 g of milk powder (accurate to 0.01 g) in a 100 mL volumetric flask, add 20 mL of water, shake to make a uniform milk, add water to volume, and shake well. Pipette 5 mL of milk into a 15 mL centrifuge tube, add 2 g of NaCl, 5 mL of dichloromethane, cover the lid and shake for 5 min, let stand for 2 min, then centrifuge at 10,000 rpm for 5 min. The lower organic layer was removed. After passing through anhydrous sodium sulfate, the volume was adjusted to 5 mL. 150 mg of C18 adsorbent was added and vortexed for 1 min. After standing, the supernatant was aspirated through a 0.2 μm filter and determined by gas chromatography.
Sample determination
The sample solution obtained above is directly injected, detected by a gas chromatograph, and quantified by an external standard method. Instrument parameter settings are shown in Table 1.
Results and discussion
Chromatogram and linearity of standard samples
The chromatograms of vanillin and ethyl vanillin in the standard samples are shown in Figure 1. Prepare a standard working solution with a concentration of 1 μg/mL, 2.5 μg/mL, 10 μg/mL, 35 μg/mL, 50 μg/mL using standard samples, inject 1 μL, and then measure as described above. Methods The GC-FID was determined by taking the concentration of the standard substance as the abscissa and the peak area of ​​each standard substance as the ordinate. The standard curve was drawn to obtain the standard working curve of vanillin and ethyl vanillin. The correlation coefficients of vanillin and ethyl vanillin were 0.9980 and 0.9991, respectively.
Method precision and recovery
Three spiked samples of 1 μg/mL, 2 μg/mL, and 10 μg/mL of vanillin and ethyl vanillin were measured three times. The average recovery and relative standard deviation are listed in Table 2. . The chromatogram of the sample spike is shown in Figure 3. The standard solution of 1 μg/mL was selected, and the detection limits of vanillin and ethyl vanillin in this method were 0.33 μg/mL and 0.25 μg/mL, respectively, based on 3 times noise.
Determination of vanillin and ethyl vanillin in 4 commercially available milk powder samples
The content of vanillin and ethyl vanillin in the four milk powder samples was determined according to the above pretreatment method, and the sample 1 was the milk powder of the first stage, which was prohibited from adding vanillin and ethyl vanillin. Samples 2, 3, and 4 are stage III milk powders, which can be added with vanillin and ethyl vanillin, and the allowable amount is 5 mg/100 mL, which is 50 μg/mL. Among them, 100 mL is calculated as ready-to-eat food, that is, the prepared milk is prepared. According to the milk powder, 14 g of milk powder is generally added per 100 mL of water. The content of vanillin and ethyl vanillin in the sample was quantified by external standard method, and a series of standard working solutions were prepared. The concentration was plotted on the abscissa and the peak area was plotted on the ordinate. The quantitative results were converted according to formula (1). The content in the milk is listed in Table 3.
in conclusion
A gas chromatographic method for the determination of vanillin and ethyl vanillin in infant formula was established. The method has the advantages of simple and rapid steps, high precision, good separation degree, less impurity interference, accurate and reliable measurement result and high sensitivity, and is a better method for determining vanillin and ethyl vanillin in infant formula. method.
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