Molecularly-imprinted microspheres for selective extraction and determination of melamine in milk and feed using gas chromatography-mass spectrometry

Molecularly-imprinted polymers in the form of microspheres were synthesized using the dispersion polymerization protocol; cyromazine was used as dummy template, while methacrylic acid, ethylene glycol dimethacrylate and acetonitrile (MeCN) were used as functional monomer, cross-linker, and porogen, respectively. When compared with the non-imprinted polymer, the molecularly-imprinted polymers (MIPs) showed outstanding affinity toward melamine in MeCN with a maximum binding concentration (B_max) of 53.20nmolmg^-1 MIPs, imprinting effect of 4.6, and a dissociation constant (K_d) of 90.45μM. After optimization of the molecularly-imprinted solid-phase extraction conditions, a new method was developed to determine the melamine in milk and feed with gas chromatography-mass spectrometry. The performance of this method has been evaluated in the tainted milk and feed in terms of recovery, precision, linearity, the limit of detection (LOD) and limit of quantitation (LOQ). Recovery ranged in samples from 93.1 to 101.3% with intra-day and inter-day relative standard deviation values below 5.34%. The LOD and LOQ of melamine in milk and feed were 0.01μgmL^-1 (μgg^-1) and 0.05μgmL^-1 (μgg^-1), respectively.