Rosario T. Fuertes | Benilda S. Ebarvia | Derrick Ethelbhert C. Yu
Labelling of trans fatty acid (TFA) content in foods is mandatory in many countries and being considered in several countries because of the deleterious effect of trans fatty in health and nutrition of the individual. The impact of legislation restricting use of TFA in food products and requiring TFA content on food labels prompts analytical laboratories to address outstanding issues on trans fatty acid analysis. In this work, a molecularly imprinted polymer (MIP) using trans oleic fatty acid methyl ester as template has been prepared by precipitation polymerization method using methacrylic acid as functional monomer, trimethylolpropane methacrylate (TRIM) as cross-linking agent, 2,2-azobis (isobutyronitrile) as the radical initiator and dichloromethane as porogen. This trans-MIP was used as sorbent for the solid-phase extraction of trans oleic fatty acid before injection to the gas chromatograph for quantification. A nonimprinted polymer (NIP) was also prepared using the same procedure but without the addition of the template, trans oleic fame. Template removal was done by soxhlet extraction using methanol-acetic acid (9:1 v/v) as the extraction solvent. The binding properties of trans oleic fame imprinted polymers were evaluated in different solvent system by equilibrium experiments. A higher difference between the affinity of trans oleic fame to MIP and NIP in heptane and dichloromethane was observed. Scatchard plot’s analysis revealed that there were two classes of binding sites populated in the imprinted polymers which indicated that the polymer possesses a heterogeneous binding sites distribution. The stronger affinity binding type exhibits dissociation constant (Kd) 10 times smaller than that of the weaker type with binding capacity of 48.04 ug trans oleic fame/mg MIP. The resulting Freundlich isotherm further demonstrated the heterogeneity of the binding sites of the MIP, with heterogeneity index “a” equal 0.4758 which is less than 1. The imprinting effect of the MIP was assessed by its performance as sorbent in SPE experiment by varying the solvent type, time, amount of sorbent and amount of trans oleic fame to obtain acceptable recoveries in each step of the solid-phase extraction. Recoveries in trans-MIP was higher (79.9-87.4%) using methanolacetic acid as the eluting solvent compared to NIP (55.8-68.7%). Polymer characterization was done by scanning electron microscopy and particle size analyzer for its morphology and particle size distribution, respectively. Elemental and FTIR analysis of the synthesized MIP was also done and results showed that the polymerization method was successful.
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