| L-carnitine is a very important "nutrition", for the milk industry, especially for the infant formula milk powder industry, L-carnitine plays a major role of nutrition and health care. The baby cannot synthesized carnitine himself, mainly supplying by the breast milk, which contains higher carnitine. But with the development of society, many mothers not breastfeeding the baby owing to work or other reasons, often use the infant formula milk powder to feed their babies. So L-carnitine as a kind of nutritional supplementadded to the infant milk powder. L-carnitine as a nutrient composition marking in the nutritional label, the content must be detected. And L-carnitine in the infant formula milk powder has free type and combination type such two kinds of form, the bound L-carnitineaccounted for about 30% of the total carnitine content, and its physiological function is as the same as the free L-carnitine. Therefore, it is very important to establish a method for the simultaneousdetermination of free L-carnitine and total carnitinein the infant formula milk powder on monitoring its content.This study demonstrated a hydrophilic ultra performance Liquid chromatography-mass spectrometry method for simultaneous determination of free L-carnitine and total carnitine in infant formula milk powder. Specific research results are as follows:(1)This study demonstrated a hydrophilic ultra performance Liquid chromatography-mass spectrometry(UPLC-MS/MS)method for the free L-carnitinein the infant formula milk powder. The sampleswere dissolved with ultra pure water, the dilutionwas precipitated the protein with acetonitrile, filtering through 0.22 μm filter membrane, then separating by waters Acquity UPLC BEH HILIC column(1.7μm,2.1mm×50mm). The column temperature is 25 °C. The flow rate is 0.3 m L/ min, the injection volume is 5 μL, 6 min a testing period, using gradient elution conditions.Applying the retention time and multiple reaction ion monitoring(MRM) to make qualitative and quantitative analysis, isotope internal calibration. The linear ranger of L-carnitine was 3.75~90.0 ng/m L withsquare of the correlation coefficient above 0.9997.The average recoveries of free L-carnitine were 97.35%~100.07% and the relative standard deviations ranged from 0.20% to 0.57%.The limit of detection was0.023 mg/100 g and the limit of quantification was0.075mg/100 g.(2)This study demonstrated a UPLC-MS/MS method for the total L-carnitinein the infant formula milk powder.The sampleswere dissolved with 40 m L of ultra pure water, added 6m L of 2mol/L KOH and hydrolyzed in 100°C for 1.5 hours. Then dilute to volume with ultra pure water.The dilutionwas precipitated the protein with acetonitrile, filtering through 0.22 μm filter membrane to analyze by UPLC-MS/MS. The conditions of UPLC-MS/MS are as below.The linear ranger of L-carnitine was 3.75~90.0 ng/m L with square ofcorrelation coefficient above 0.9997.The average recoveries of total L-carnitine were 97.35%~101.76% and the relative standard deviations ranged from 0.09% to 0.77%.The limit of detection was0.023 mg/100 g and the limit of quantification was0.075 mg/100 g. |
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