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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.

In this paper, a method based on HPLC coupled with ESI-TOF/MS and on-line to a stable free radical scavenging detection system has been developed to rapidly screen and identify the major antioxidants in the water extract of Hippocampus japonicus Kaup, a kind of marine medicinal organism. The developed on-line stable free radical scavenging detection method of water extract from H. japonicus Kaup revealed the presence of three radical scavenging compounds, which were simultaneously identified as hypoxanthine, phenylalanine and tryptophane by high-resolution TOF-MS. To the best of our knowledge, it is original to demonstrate the rapid and successful use of HPLC-ESI-TOF/MS and on-line 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt free radical scavenging assay to directly and simultaneously screen and identify the antioxidants in the water extracts of H. japonicus Kaup without any purification. The present method provides a useful improvement on the reducing of workload and a powerful tool for rapid screening and identification of free radical scavenging compounds in complex natural products.

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