A confirmatory method was developed for the rapid determination of abamectin, ivermectin, doramectin and eprinomectin residues in various food products of animal origin, such as pork muscle, pork liver, fish and milk. Samples were homogenized, extracted and de-proteinized by acetonitrile, cleaned via two-step cleaning procedure using Bond Elut C(18) SPE columns and then alumina-N cartridges. All the four avermectin residues in different animal-food products were simultaneously separated and determined by ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) within 3.5 min. Data acquisition under positive ESI-MS/MS was performed by applying multiple reaction monitoring (MRM) for both identification and quantification, and mass spectrometric conditions were optimized to increase selectivity and sensitivity. The matrix-matched calibration curves for different matrices, such as pork muscle, pork liver, fish and milk, were constructed and the interference effect of different sample matrices on the ionization was effectively eliminated. The UPLC-MS/MS method was validated with satisfactory linearity, recovery, precision and stability. Matrix-matched calibration curves of abamectin, ivermectin, doramectin and eprinomectin in four different matrices were linear (r(2)( )≥ 0.990, goodness-of-fit coefficients ≤12.8%) in the range 2.5-200 µg kg(-1). The limits of detection and quantification for the four avermectins were in the range 0.05-0.68 and 0.17-2.27 µg kg(-1), respectively. Recoveries were 62.4-104.5% with good intra- and inter-day precision. The method was rapid, sensitive and reliable, and can be applied to the quantitative analysis of avermectin residues in different animal-food products.
A method of ultra-performance liquid chromatography-linear ion trap/orbitrap high resolution mass spectrometry (UPLC-LTQ/Orbitrap MS) was used to screen and confirm 24 banned aromatic amines and their 14 isomers at the same time. The main factors influencing the separation including the column, and the nature of make-up solvent were optimized. Under the optimized experimental conditions, the analytes were reduced to banned aromatic amine with sodium dithionite, extracted by methyl tert-butyl ether and loaded onto a ZORBAX SB-C18 column (150 mm x 2.1 mm, 5 μm) with a gradient elution of methanol and 0.1% formic acid aqueous solution, and finally detected by LTQ/Orbitrap MS. The screening and quantitative analysis were carried out by the accurate mass of quasi-molecular ion and the peak in extracted chromatogram with accurate mass. The correlation coefficients were higher than 0.99 and the limits of detection were in the range of 0.5-5 μg/kg. The method could screen and confirm the 24 banned aromatic amines and their 14 isomers at the same time. The results were 1.56 mg/kg of 4-chloroaniline, 0.34 mg/kg of o-toluidine, and 0.81 mg/kg of 2,6-toluylenediamine with the relative standard deviations ranging from 0.27% to 1.32% in actual samples. The results indicate that the developed method is simple, efficient and precise, and can be a reliable technique for the separation of the 24 banned aromatic amines and their 14 isomers in textile samples.
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