English Abstract
ABSTRACT :
B-Cyclodextrin (BCD) has been immobilized on silica and Amberlite XAD resin bases and evaluated as selective materials for use in solid phase extraction (SPE). This work focuses on the synthesis, characterization and applications of the SPE materials in the determination of pesticide residues.
A number of synthetic methods were employed for bonding ẞCD to silica and XAD-4 resin. ẞCD, methylated ẞCD and the mixed functionality of diol and ẞCD phases were prepared on a silica base using (3-isocyanatopropyl)triethoxysilane as a linker. ẞCD was also immobilized by adsorption onto Amberlite XAD-4 resin or by chemical linking onto silica-modified XAD-4.
The loadings of BCD on the modified silicas and XAD resins were qualitatively and quantitatively determined. Molish's test and a diphenylamine-aniline test confirmed the presence of BCD bonded on the solid phases. The ẞCD contents were colorimetrically determined using a newly developed phenol-sulphuric acid method. Silicas modified with BCD and the mixed functionality Diol-ẞCD showed little difference between their BCD loadings (17.4µmol and 16.7µmol ẞCD/g, respectively). Adsorption of ẞCD onto XAD resulted in material having a lower loading of ẞCD than the materials synthesised on a silica base. Infrared and Raman spectroscopy showed the presence of ẞCD on the silica surfaces. Elemental (CHN), gravimetric and thermogravimetric (TGA) analyses were together used to demonstrate the presence of organic material on the silica surface. The ẞCD loadings calculated from TGA and CHN data were in agreement with data obtained by the phenol-sulphuric acid colorimetric method. The ability of ẞCD to form inclusion complexes with a number of pesticides was assessed by TLC (thin layer chromatography), UV (ultraviolet spectrophotometry), TGA and DSC (differential scanning calorimetry). TLC showed that for many pesticide the formation of such complexes is either kinetically very slow or that it may not occur. The addition of ẞCD to dichlobenil and triallate enhanced their UV absorption spectra, suggesting possible complex formation. The TGA and DSC characteristics of the atrazine-ẞCD "complex" were assigned to weak associations between ẞCD and atrazine rather than the presence of a true inclusion complex.
The retention of pesticides by the SPE materials was evaluated using organo-chlorine, nitrogen and phosphorus pesticides. Using ẞCD-modified silica and XAD materials the extraction of pesticides from water was very good (81-100%), and the overall recoveries
ranged from 58 to 100%. The ẞCD-modified silica efficiently retained most of the pesticides from orange juice and skimmed milk samples (78-100%). The overall recoveries of most of the pesticides from juice were good (68-91%) but generally poor from milk (7-61%). The application of the technique to water from the Itchen estuary showed the presence of dichlobenil (12-14ppb), propachlor (8ppb), diazinon (13-16ppb) and disulfoton (12-15ppb).
