Optosensor and Sample Preparation Techniques for the Determination of Veterinary Drugs and Pesticides

Abstract

This thesis aimed to develop new analytical techniques for the determination of trace veterinary drugs and pesticides in environment and food samples. It consist of two-part including the optosensor and sample preparation techniques. The first part focused on the development of novel fluorescence probe using molecularly imprinted polymer composited with quantum dots nanoparticles. The facile method for coating a molecularly imprinted polymer onto quantum dots (MIP-QDs) which are CdTe QDs and graphene quantum dots (GQDs) were successfully formulated and used for the first time as a highly selective and sensitive fluorescence probes for the determination of trace amoxicillin, salbutamol, ceftriaxone and cephalexin. The nanocomposite MIP-QDs fluorescence probes were prepared via a sol-gel process with 3-aminopropyl-ethoxysilane as a functional monomer, tetraethoxysilane as a cross- linker and the target analyte as a template molecule. After removal of the template molecules from the polymer layer, MIP-QDs containing cavities specific to the target analyte were obtained. The obtained cavities of MIP-QDs were specific to target analyte (amoxicillin, salbutamol, ceftriaxone and cephalexin) by size, shape and functional group. The fluorescence intensity of MIP-QDs was more strongly quenched by target analytes by comparing with the non- imprinted polymer (NIP-QDs) with high imprinting factor of 43.6 for amoxicillin, 7.14 for salbutamol, 30.0 for ceftriaxone and 26.5 for cephalexin, respectively. The synthesized nanocomposite MIP-QDs showed a high sensitivity and good selectivity toward to amoxicillin in the concentration range of 0.20 - 50.0 μg L-1 with a low detection limit of 0. 14 μg L-1 and 0.10 - 25.0 μg L-1 with a low detection limit of 0.03 μg L-1 for salbutamol detection. The dual nanocomposite fluorescence probe showed a good linearity from 0.10 to 50.0 μg L-1 with a low detection limit of 0.06 and 1.00 μg L-1 for cephalexin and ceftriaxone, respectively. The developed nanocomposite MIP-QDs was successfully applied toward the determination of amoxicillin in milk, eggs and honey with a good recovery of 85 - 102% and the relative standard deviation of less than 6% being achieved. The hybrid MIP- QDs fluorescence probe was effectively applied for the determination of salbutamol in animal feed and meat samples with a satisfactory recovery of 85 to 98 % (RSD < 8). The developed dual nanocomposite MIP-QDs fluorescence probes were applied for the detection of ceftriaxone and cephalexin in the milk sample with a satisfactory recovery of 83 - 99% and RSD lower than 8%. Furthermore, the accuracy of the developed nanocomposite MIP-QDs fluorescence probes were investigated by comparing with HPLC method with the results obtained using the two methods agreeing well with each other. It demonstrated that the developed method is reliable and can be applied for real sample analysis. The advantages of the developed optosensor are simplicity, rapidity, cost-effectiveness, high sensitivity and good selectivity. The second part focused on the development of sample preparation techniques for the determination of veterinary drugs and pesticides using chromatography analysis. Two sub-project were carried out. The first one is a hybrid monolith sorbent of polypyrrole coated graphene oxide incorporated into a polyvinyl alcohol cryogel. It was successfully synthesized and used as a sorbent in solid-phase extraction technique for extraction and preconcentration of trace sulfonamides. The large surface areas with many adsorption sites of polypyrrole (PPY) and graphene oxide (GO) facilitated the high adsorption ability of sulfonamides via hydrogen bonding, л-л and hydrophobic interaction. The high porosity of the polyvinyl alcohol (PVA) cryogel helped to reduce the backpressure that occurs in a conventional packed SPE cartridge. Under the optimum conditions, the developed method provided a wide linear range from 0.20 to 100 μg L-1 with a low detection limit of 0.20 μg L-1 for sulfadiazine, sulfathiazole and sulfamerazine and from 0.10 to 100 μg L-1 with a low detection of 0.10 μg L ̈1 for sulfamethazine, sulfamonomethoxine and sulfadimethoxine. The developed hybrid monolith polypyrrole-coated graphene oxide embedded in the polyvinyl alcohol cryogel sorbent provided good recoveries in the range of 85.5 -99.0% with RSD less than 5%. The sorbent offered a good reproducibility and can be reused at least 10 times. It was successfully applied for the extraction and preconcentration of trace amount sulfonamides in the environmental water samples. The last project is an application of bubble-in-single drop microextraction (BI-SDME) for the extraction and analysis of eight carbamate pesticides from the environmental water sample. The increasing of the extraction solvent surface area when encapsulated air bubble in the microdroplet caused the greater extraction efficiency with still less volume of extraction solvent. Under the optimal conditions, the developed method showed a wide linearity in the range of 0.05 to 20.0 μg L-1 with the low limit of detection in the range of 0.02 to 0.04 μg L-1. This method was successfully applied for the determination of carbamate pesticides in the environmental water samples with good recoveries of 82-99% and RSD less than 9%. The advantages of this method is solventless, environmentally friendly, low cost and simple to operate. In conclusion, the optosensor and sample preparation techniques were successfully developed and applied for determination of trace veterinary drugs and pesticides in real sample with a satisfactory performance. There are many advantages such as simple to prepare, cost-effective, rapid, high sensitivity and good selectivity. It provided good accuracy and precision. These developed method can be used as an alternative method for the determination of other organic compounds in a various samples.