The ultrasonic technology was applied to optimize the processing parameters of extraction of flavonoids from litchi seed using the response surface methodology. The Box–Behnken design was used to analyze the effect of independent variables including extraction temperature (X1), methanol concentration (X2) and extraction time (X3) on the yield of total flavonoids as the dependent variable(Y). The analysis of variance (ANOVA) indicated that three independent variables, their quadratic terms and interaction terms showed a significant effect on yield of total flavonoids (YTF) except the interaction between X1and X2. A mathematical model with high determination coefficient was constructed, according to which the optimal extraction conditions were determined as follows: extraction temperature 70°C, methanol concentration 68%, extraction time 70 min. Under the above-mentioned condition, the experimental value of YTF was 3.55 g catechin equivalent per 100 g of dry (g CE/100 g ), which agreed with the predicted value perfectly, demonstrating the response surface model was suitable in optimizing the extraction of flavonoids from litchi seed.
A method was developed for the simultaneous determination of six strobilurin fungicide (-metominostrobin, azoxystrobin, kresoxim-methyl, picoxystrobin, pyraclostrobin and trifloxystrobin) residues in orange, banana, apple and pineapple samples by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The fragmentation routes of all the compounds were explained by the aid of a fragment predicting software ACD Lab/MS Fragmenter. The samples were extracted by acetonitrile, then cleaned up by amino solid phase extraction cartridges (SupelClean LC-NH). The extracts were separated on a ACQUITY UPLC BEH C column (50 mm×2.1 mm, 1.7 μm) with gradient elution. Acetonitrile containing 0.1% (v/v) formic acid and 10 mmol/L ammonium acetate containing 0.1% (v/v) formic acid were used as mobile phases. The samples were detected by electrospray ionization (ESI)-MS/MS in positive ion and multiple reaction monitoring (MRM) mode, quantified by external standard method. Good linearities were obtained in the range of 5-100 μg/L (for pyraclostrobin, 1-20 μg/L) with correlation coefficients () greater than 0.999. The recoveries ranged from 60.4% to 120% with the relative standard deviations between 2.15% and 15.1% (=6). The developed method can meet the inspection of the six strobilurin residues in the orange, banana, apple and pineapple samples.
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