Jin-Zhong Xu

Analysis of tetracycline residues in royal jelly by liquid chromatography-tandem mass spectrometry

A confirmatory method coupling liquid chromatography with tandem mass spectrometry (LC/MS/MS) was developed to determine the concentration of oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC) and doxycycline (DC), which make up the tetracycline (TC) groups present in royal jelly. Sample preparation included deproteination, control of pH, extraction and clean-up on a solid-phase extraction (SPE) cartridge. The analyses were achieved by LC/MS/MS in selected reaction monitoring mode (SRM). The overall recovery of fortified royal jelly at the levels of 5.0, 10.0 and 40.0 microg/kg ranged from 62% to 115%, and the coefficients of variation ranged from 3.4% to 16.3% (n=6). The detection limits for TCs were under 1.0 microg/kg. The transformation between the TCs and its epimers (EpiTCs) was studied in standard solution and during the sample preparation process. This method can be used for the detection of tetracycline residues in royal jelly.

Determination of methylene blue residues in aquatic products by liquid chromatography-tandem mass spectrometry.

A method for the determination and confirmation of methylene blue (MB) in aquatic products was developed. Residues of MB were extracted from homogenized tissues with acetonitrile/sodium acetate buffer solution, and simply cleaned up with dichloromethane liquid/liquid extraction. After concentration and dissolution, the sample solutions were cleaned up by the neutral alumina and weak cation-exchange solid phase extraction (SPE) cartridge, prior to LC-MS/MS analysis. MB was determined at 1.0-20 microg/kg in eel, toasted eel and shrimp, with a limit of quantification of 0.5 microg/kg. Recovery for MB was between 73.0% and 108.3%. This method is fast, exact and sensitive. It can be applied to determine MB in aquatic products.

Determination of amitraz and 2,4-dimethylaniline residues in honey by using LC with UV detection and MS/MS.

A method for the determination and confirmation of amitraz and its degradation product 2,4-dimethylaniline (2,4-DMA) in honey is reported. Determination of the two compounds was based on HPLC with UV detection and MS/MS (LC-MS/MS) after a liquid-liquid extraction with hexane and isopropyl alcohol. Chromatographic separation was achieved by using a C18 column with a gradient mobile phase consisting of 0.02 M ammonium acetate and ACN. Recoveries for fortified honey ranged from 83.4 to 103.4% for amitraz and from 89.2 to 104.7% for 2,4-DMA with RSD values lower than 11.6% for HPLC and LC-MS/MS methods. LOD was 6 microg/kg for amitraz and 8 microg/kg for 2,4-DMA, while LOQ was 20 microg/kg for amitraz and 25 microg/kg for 2,4-DMA in HPLC method. LOD was 1 microg/kg for amitraz and 2 microg/kg for 2,4-DMA, while LOQ was 5 microg/kg for amitraz and 10 microg/kg for 2,4-DMA in LC-MS/MS method.

A novel method to detect seven microcystins in hard clam and corbicula fluminea by liquid chromatography-tandem mass spectrometry.

A simple and reliable method to detect seven microcystins in hard clam and corbicula fluminea, based on liquid chromatography with electrospray ionization and tandem mass spectrometry (LC-ESI-MS/MS), was developed and validated. The sample preparation procedure includes extraction of tissue by methanol, followed by cleanup on a reversed-phase solid phase extraction (SPE) cartridge. With the optimized method, recoveries were between 43.7% and 92.3% for hard clam, 54.3% and 93.8% for corbicula fluminea, the relative standard deviations (RSD) were less than or equal to 16.2% and 15.7% in hard clam and corbicula fluminea at spiking levels of 1 microg/kg, 2 microg/kg and 5 microg/kg for MC-RR, MC-YR, MC-LR, and MC-LY, and 2 microg/kg, 5 microg/kg and 10 microg/kg for MC-LA, MC-LW and MC-LF, respectively, the limits of quantitation (LOQ) of this method were ranged from 0.7 microg/kg to 2.0 microg/kg.

SIMULTANEOUS DETERMINATION OF 14 QUINOLONES IN ROYAL JELLY BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY USING ANION-EXCHANGE SOLID-PHASE EXTRACTION

A new method based on liquid chromatography-tandem mass spectrometry has been developed for simultaneous determination of 14 quinolones (QNs) residues, including ciprofloxacin, danofloxacin, difloxacin, enoxacin, enrofloxacin, flumequine, lomefloxacin, marbofloxacin, norfloxacin, orbifloxacin, ofloxacin, pipemidic acid, pefloxacin, and sarafloxacin in royal jelly. The proposed analytical procedure involves extraction of the QNs from samples by 0.1 M sodium hydroxide aqueous solution, a step for clean-up and preconcentration of the analytes by anion-exchange solid-phase extraction (SPE) and liquid chromatographic separation with mass spectrometric detection. Internal standard calibration was applied with norfloxacin-D5 as internal standard (I.S.). Satisfactory recovery (from 64% to 113%), excellent repeatability precision (relative standard deviations, RSDs below 6%), reproducibility precision (RSDs below 10%), and low limits of quantifications (LOQs from 0.3 to 2.5 µg kg−1) were evaluated from spiked royal jelly samples at 2.5, 5.0, and 10.0 µg kg−1 three concentration levels. This protocol has been validated by five authoritative laboratories and successfully used for analysis of a large number of import–export samples (n > 2000). Norfloxacin and ciprofloxacin were found to be the most common contamination in royal jelly in the ranges of 3.5–30 µg kg−1 and 4.5–20 µg kg−1, respectively.