The preparation of a new 3,5-dichlorophenylcarbamated cellulose-bonded stationary phase and its application for the enantioseparation and determination of chiral fungicides by LC-MS/MS

A new 3,5-dichlorophenylcarbamated cellulose-bonded silica gel stationary phase (CELCSP) was prepared by a “thiol-ene” addition reaction. The alkenyl group was first introduced onto the cellulose, and then the cellulose was completely isocyanated with 3,5-dichlorophenyl isocyanate. Finally, the alkenyl group was reacted with the 3-mercaptopropyl silica gel to obtain the cellulose-bonded stationary phase. The structures of the ligand and the stationary phase were characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy and elemental analysis. The newly prepared cellulose-bonded phase was successfully used for the enantio-resolution of six common chiral fungicides including triticonazole, hexaconazole, tebuconazole, triadimefon, metalaxyl and benalaxyl under reversed-phase mode, respectively. The resolution (Rs) and selectivity factor (α) of the above fungicide enantiomers on CELCSP could reach 3.46 and 1.27, respectiviely, by using the common 0.1% formic acid-acetonitrile as the mobile phase. Base on the CELCSP column, a new LC-MS/MS method for the quantitative determinations of all six chiral fungicide enantiomers in ten kinds of fruits and vegetables such as cucumber, grape, etc. was established within 30 min. After the sample pretreatment with Fe3O4 magnetic particles, the enantiomers were separated by LC and determined in positive ion multi-reaction monitoring (MRM) by mass spectrometry. The good linear relationship between the response and the concentration of the enantiomers were observed in a range from 0.10 μg/L to 100 μg/L with the relative standard deviation (RSDs, correlation coefficient (0.9965–0.9982)). The averaged recoveries from fruits and vegetables were between 65% and 110% (n = 3). The detection limit (LODs) and limit of quantitation (LOQs) for the enantiomers were 0.05–0.61 μg/kg and 0.18–2.01 μg/kg, respectively. The RSDs of the repeated determination in the samples were 1.2%–6.0% (intra-day, n = 5) and 2.5%–13.0% (inter-day, n = 10), respectively. The mild condition of the thiol-ene addition reaction was beneficial to maintain the order stereostructure of cellulose, while its high yield of the oriented synthesis could also provide sufficient binding amount of chiral ligand, which made the new stationary phase have good chiral chromatographic performance. The newly prepared stationary phase has strong solvent resistance, which is a guarantee for establishing a reliable food safety analysis method for monitoring pesticide enantiomer residues by LC-MS/MS.