Application of MIP Sensors to the Determination of Preservatives in Nonalcoholic Drinks

The piezoelectric sensors modified with a molecularly imprinted polymer (MIP) with potassium sorbate (MIP-E202) and sodium benzoate (MIP-E211) imprints are tested and implemented in the determination of preservatives in soft drinks. Molecularly imprinted polymers were synthesized by noncovalent imprinting on the base of copolymer of 1,2,4,5-benzene tetracarboxylic acid dianhydride and 4,4'-diaminodiphenyl oxide in N,N-dimethylformamide (DMF) in the presence of templates. Piezoelectric sensors based on MIP and non-imprinted polymer (polyimide) were compared. High values of the imprinting factor (IF) and selectivity coefficient (k) obtained for MIP-E202 (IF = 5.4) and MIP-E211 (IF = 6.0) sensors indicated better selectivity and ability of MIP-based sensors to recognize target molecules than piezoelectric sensors modified with a reference polymer. The detectable concentrations range within 5–500 mg/L; the detection limits for potassium sorbate and sodium benzoate are 1.6 and 2.0 mg/L, respectively. The correctness of the determination of preservatives in model solutions was verified using the spike test. MIP-based sensors appeared sensitive to the determination of preservatives and insensitive to interfering substances. The matrix composition of the nonalcoholic drinks did not affect the value of the analytical signal of the piezoelectric sensor. High performance liquid chromatography (HPLC) was used as a reference method. The results of potassium sorbate and sodium benzoate determination in nonalcoholic drinks using piezoelectric sensors match the HPLC data rather well, their content in the studied soft drinks being 130–176 and 129–146 mg/L, respectively.