Chang-Ying Guo

Fast determination of multi-mycotoxins in corn by dispersive solid-phase extraction coupled with ultra-performance liquid chromatography with tandem quadrupole time-of-flight mass spectrometry

Abstract A fast analytical method for the simultaneous determination of 9 mycotoxins, including aflatoxins (B1, B2, G1, and G2), fumonisins (B1, B2 and B3), zearalenone, and deoxynivalenol in corn using dispersive solid-phase extraction method and ultra-performance liquid chromatography coupled to tandem quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) was developed and validated. Samples were extracted with acetonitrile-water (84:16, v:v, containing 1% acetic acid) using ultrasonic extraction. The extracts were purified with a dispersive SPE method using C18 as a cleaning agent. The final clear extracts were dried by nitrogen blowing and subsequently redissolved in methanol-water (5:5, v:v). The samples were then analyzed by UPLC-Q-TOF-MS with 0.1% formic acid in ammonium acetate-methanol as mobile phase. The mean recoveries were ranged from 68.0 to 120.0%, and the relative standard deviation (RSD) ranged from 0.18 to 6.29%. Limits of detections ranged from 0.05 to 50 μg kg−1, and limits of quantification ranged from 0.1 to 200 μg kg−1, which were below the legal limits set by the European Union for the legislated mycotoxins. The developed method was applied to 130 corn samples. Among the mycotoxins studied, aflatoxins B1 and fumonisins B1, B2 and B3 were the most predominant mycotoxins, and their concentrations were 0–593.12, 0–2.01×104, 0–6.94×103 and 0–3.05×103 μg kg−1, respectively.

Photoluminescence properties of a new orange-red-emitting Sm(3+)-La3SbO7 phosphor.

The antimonate compound La3SbO7 has high chemical stability, lattice stiffness and thermal stability. Orange-red-emitting antimonate-based phosphors La3SbO7:xSm(3+) (x = 0.02, 0.05, 0.08, 0.10, 0.15, 0.20 and 0.25) were synthesized. The phase structure and photoluminescence properties of these phosphors were investigated. The emission spectrum obtained on excitation at 407 nm contained exclusively the characteristic emissions of Sm(3+) at 568, 608, 654 and 716 nm, which correspond to the transitions from (4)G5/2 to (6)H5/2, (6)H7/2, (6)H9/2 and (6)H11/2 of Sm(3+), respectively. The strongest emission was located at 608 nm due to the (4)G5/2→(6)H7/2 transition of Sm(3+), generating bright orange-red light. The critical quenching concentration of Sm(3+) in La3SbO7:Sm(3+) phosphor was determined as 10% and the energy transfer between Sm(3+) was found to be through an exchange interaction. The International Commission on Illumination chromaticity coordinates of the La3SbO7:0.10Sm(3+) phosphors are located in the orange-red region. The La3SbO7:Sm(3+) phosphors may be potentially used as red phosphors for white light-emitting diodes.

Determination of Mesotrione and Its Metabolite Residues in Maize by Ultra Performance Liquid Chromatography Coupled with Tandem Mass Spectrometry

A novel method was developed for the simultaneous determination of mesotrione and its metabolite(4-methylsulfonyl-2-nitrobenzoic acid,MNBA) in maize by ultra performance liquid chromatography coupled with tandem mass spectrometry(UPLC-MS/MS).The samples were extracted with acetonitrile-water(50 ∶ 50,V/V) solutions and an aliquot of the extract was acidified to pH 2 with formic acid and then cleaned-up by Oasis HLB cartridge.The residues were eluted from cartridge with methanol-diethyl ether(70 ∶ 30,V/V).The elutions were evaporated to appropriately dry under a stream of nitrogen,dissolved in 2 mL acetonitrile-1 mmol/L ammonium acetate(75 ∶ 25,V/V).The residues were analyzed by mass spectrometry with negative ion mode using multiple-reaction monitoring(MRM) and quantification was achieved by matrix calibration.The method had a good linear correlation(correlation coefficient was above 0.99) in the range of 1-200 μg/L.The average recoveries of mesotrione and MNBA were 83.8%-101.1% at spiked level between 5 μg/kg and 50 μg/kg with the relative standard deviation(RSD) between 5.3% and 12.8%.The limits of quantification for mesotrione and MNBA were 1.0 and 2.0 μg/kg,respectively.

Dynamics of Oxine-Copper in Pears and Soil by High-Performance Liquid Chromatography

ABSTRACT Oxine-copper, which is used as a disinfectant for vegetables, was determined by high-pressure liquid chromatography (HPLC) with an ultraviolet detector. The calibration relationship was linear from 0.025 µg mL−1 to 20 µg mL−1 and good precision was obtained. The recovery was between 72.8 and 113.8%. The limits of quantification were 0.1 mg kg−1 in soil and 0.05 mg kg−1 in pears. The half-lives of oxine-copper in pears in 2011 and 2012 were 7.1 days and 7.8 days in Hebei, 10.1 days and 10.4 days in Shandong, and 4 days and 8.9 days in Henan. The half-lives of oxine-copper in soil in 2011 and 2012 were 8.1 days and 9.1 days in Hebei, 6.8 days and 8.6 days in Shandong, and 9.7 days and 8.9 days in Henan. The maximum residue of oxine-copper in pears was 1.64 mg kg−1.