| Vitamin A and vitamin E are the nutritional elements labeled in the nutritional label of infant formula milk powder.The content of vitamin A and vitamin E must be tested.The relevant regulations also stipulate the content of vitamin A and vitamin E.Therefore,it is great significance to establish a method for the determination of the content of vitamin A and vitamin E in infant formula milk powder.In this thesis,the determination of vitamin A and E in infant formula milk powder was studied as follows:1.A rapid pretreatment method for vitamin A and E in infant formula milk powder was established.The method is as follows: weight 5 g sample into 150 mL grinding triangular flask,dissolve it with 10 mL warm water,add 15 mL 0.1% BHT pyrophenol ethanol solution and 9 mL 10 mol/L sodium hydroxide solution,mix well,protect it by nitrogen.Saponify it with water bath at 70℃ for 30 minutes,after 30 minutes,take out the samples from water bath and cool it to room temperature,and then add 6 mL 0.5% glacial acetic acid solution and 25 mL hexane,extract it 10 minutes with the reciprocating shaking bed at 200 r/min,and wash the organic layer with about 35 mL milli-Q water,after standing for 15 minutes,absorb the upper organic liquid filter by 0.45 μm filterhead,and then put into the HPLC for determination.2.A method for the determination of vitamin A and E in infant formula milk powder by normal phase high performance liquid chromatography was established.Select silica gel column(Agilent Zorbax RX-SIL,3 μm,4.6×150 mm)for Separation,the column temperature is 35℃,the flow rate is 2.0 mL/min,the mobile phase is hexane: THF =90:10,detected them by UV detector,determined vitamin A at 325 nm,and determined four isomers of vitamin E at 294 nm,quantified by External standard method.The detection limit of vitamin A is 0.49 μg/100 g,the quantitative limit of vitamin A is 1.64 μg/100g;the detection limit of vitamin E is 19.8~23.6 μg/100 g,and the quantitative limit of vitamin E is 65.9~78.7 μg/100 g.The linearity of vitamin A and vitamin E is good in the range of curve concentration.The correlation coefficient is more than 0.99.The recovery rate of vitamin A is 93.5%~103.5%,RSD% is 0.41%~2.13%;the recovery rate of vitamin E is 92.5%~98.9%,RSD% is 0.40%~2.98%.3.The stability of vitamin A and vitamin E curves during preparation and storage was studied.The formulation of vitamin A was improved as follows: weigh 25.0 mg vitamin A standard,dissolv it with 0.1% BHT ethanol solution,and transfer into 50 mL volumetric bottle,constant volume with 0.1%BHT ethanol solution.The concentration of the solution was about 0.500 mg/mL.transfer the standard solution of vitamin A into a brown reagent bottle,seale it with a sealing film,and store it in at –20℃ refrigerator for one month.Before use,rewarm the standard solution to 20℃ first and correct the concentration by UV.The standard solution of vitamin A is relatively stable after adding BHT for protection,and BHT is hardly absorbed at 325 nm of UV,which will not cause deviation in the concentration correction of vitamin A.The standard reserve solution of 4 kinds of vitamin E isomers was investigated.It was found that 4 kinds of vitamin E isomers were stable and did not need to be protected by BHT.The vitamin A and vitamin E standard working solution protected by BHT were studied for 15 days stored at –20℃ refrigerator.It was found that the response values of each concentration point had little change within 15 days and could be used for quantification accurately.4.Analyze the sources of uncertainty in the measurement of vitamin A and vitamin E in milk powder: 1.Uncertainty caused by the repeated measurement experiment;2.Uncertainty caused by the introduction of reference materials: uncertainty caused by the standard stock solution and dilution;3.Uncertainty in the sample preparation process: including the uncertainty of balance and recovery rate;4.Uncertainty caused by instrument.The uncertainty of vitamin A and vitamin E was 7.9% and 7.7%. |
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