Selective SPE of derivates of p-hydroxybenzoic acid (pHBA) from plant extract of Melissa officinalis is presented using a molecularly imprinted polymer (MIP) made with protocatechuic acid (PA) as template molecule. MIP was prepared with acrylamide as functional monomer, ethylene glycol dimethacrylate as crosslinking monomer and ACN as porogen. MIP was evaluated towards six phenolic acids: PA, gallic acid, pHBA, vanillic acid (VA), gentisic acid (GeA) and syringic acid (SyrA), and then steps of molecularly imprinted SPE (MISPE) procedure were optimized. The best specific binding capacity of MIP was obtained for PA in ACN (34.7 microg/g of MIP). Other tested acids were also bound on MIP if they were dissolved in this solvent. ACN was chosen as solvent for sample application. M. officinalis was extracted into methanol/water (4:1, v/v), the extract was then evaporated to dryness and dissolved in ACN before application on MIP. Water and ACN were used as washing solvents and elution of benzoic acids was performed by means of a mixture methanol/acetic acid (9:1, v/v). pHBA, GA, PA and VA were extracted with recoveries of 56.3-82.1% using this MISPE method. GeA was not determined in plant extract.
Nylon-6 was used as a molecularly imprinted polymer (MIP). For imprinting L-theanine (5-N-ethylglutamine) in the polymer, 2.0 g of Nylon-6, 0.8 g (MIP 1), and 1.2 g (MIP 2), respectively, of L-theanine templates and 7.2 g of formic acid was used for the phase inversion process in water. The resulting polymers, including the template molecule, were washed with acetic acid solution to extract the template from the polymers. The polymers were investigated as solid phase extraction (SPE) sorbents for the cleanup of water extracts of green tea. Various amounts of the template in the polymerization mixture had no influence on sorptive properties of MIPs in the range under study. Water was found as a suitable solvent for sample loading. The selective binding capacity of MIPs was 3.49 mg/1 g MIP. Water with addition of acetic acid (2% by volume) was used as an elution solvent. The recovery of the MISPE procedure was 87.8% + 5.5%.
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