Determination of carbamates from samples by molecularly imprinted polymers

Abstract

In this work, new clean sorbent that has greater selectivity was used in the determination of pesticides residues in complex matrices at the desired limits of quantification. This work is divided into 3 papers focusing on molecularly imprinted polymers. Paper I is a review on challenges in elution of the template from molecularly imprinted polymers (MIPs). MIPs are materials that exhibit selective recognition towards the desired template. It possesses advantages of high selectivity, low-cost and low limit of detection. It is a promising alternative for natural antibodies that suffer from poor stability and high cost. However, the MIP has challenges of expensive templates, and the template might not get removed even after extensive washing or the MIP may get damaged during the removal process and this step often requires lengthy optimization which can alter the accuracy of the results. The review summarises the effective ways of washing off the template molecules, paying attention to the effect of washing techniques, pairing agents, and the number of elution cycles applied to achieve satisfactory template removal. It also reviews the use of dummy template and computational chemistry to select appropriate solvent and functional monomer. Finally, challenges and prospects in template bleeding are discussed. In Paper II, carbaryl was used to synthesize dummy template molecularly imprinted polymers (DMIPs) for the determination of carbofuran in grapes. The sorbent was used to selectively extract carbofuran from other closely related compounds. Carbofuran is one of the most toxic carbamate pesticides, and it is banned in most countries. Carbofuran was determined by carbaryl dummy templated molecularly imprinted polymer from grapes. FTIR characterization showed the C=O stretching absorbance in the region of 1714-1730 cm-1 between unwashed MIP, NIP, and washed MIP with different intensities. Various parameters affecting the extraction efficiency of the imprinted polymers were evaluated to optimize the selective pre-concentration of carbamates in grape samples. Under optimal condition, the enrichment factors of up to 215 were obtained. This method was successfully applied to quantitively detect carbamates residue in grape sample. The results during application showed that all the grape samples were found to contain no carbamates. In Paper III, pirimicarb is a carbamate pesticide used for controlling pests on vegetables and is used in gardens and household. Pirimicarb was determined using molecularly imprinted polymer from oranges. The MIP material was characterised with FTIR where all the peaks were similar except their intensities. The MIP and NIP were optimised using different parameters and enrichment factor of 19 was obtained. The linear range was 0.25-2.5 mg L-1 and percentage recoveries of three carbamates ranges were 69.43 -84.67%. The limit of detection and limit of quantification 0.41-0.61 and 1.24-1.86 mgL-1. The method indicated repeatability as the RSD ranged from 1.37-9.23. The potential of the developed MIP-SPE method for the selective sample clean-up were investigated in the analysis of oranges. It was found that none of the analytes were detected in the orange samples.