Enantiomeric Discrimination and Quantification of the Chiral Organophosphorus Pesticide Fenamiphos in Aqueous Samples by a Novel and Selective 31P Nuclear Magnetic Resonance Spectroscopic Method Using Cyclodextrins as Chiral Selector

A rapid, selective, and accurate quantitative P-31 nuclear magnetic resonance (P-31 NMR) spectroscopy method was used for the chiral recognition of the racemic organophosphorus pesticide fenamiphos using chiral solvating agents (CSAs). Six neutral cyclodextrins (CDs) (alpha-CD, beta-CD, methyl-beta-CD, hydroxyethyl-beta-CD, hydroxypropyl-beta-CD, and hydroxypropyl-gamma-CD) and two anionic CDs (carboxymethyl-beta-CD and carboxyethyl-beta-CD) were selected for these experiments. The shift displacement values (Delta delta), after addition of each of the eight CDs in the highest possible molar ratio to a guest, were recorded. The results showed that beta-CD and hydroxypropyl-beta-CD were the best chiral solvating agents for the enantiomeric discrimination of fenamiphos. Two-dimension rotating frame nuclear Overhauser spectroscopy (ROESY) was used to investigate the structure of the beta-CD-fenamiphos inclusion complex in aqueous solution. To determine the fenamiphos enantiomers, a calibration curve was drawn for two enantiomers over the range of 0.05-0.25 mg mL(-1). The limits of detection (S/N = 3) were obtained as 0.0068 and 0.0060 mg mL(-1) for fenamiphos enantiomers. The recovery studies were performed on aqueous real samples ranging from 94 to 107% with coefficients of variation of <= 9%.