On-site separation and identification of polycyclic aromatic hydrocarbons from edible oil by TLC-SERS on diatomite photonic biosilica plate

The accumulated polycyclic aromatic hydrocarbons (PAHs) in edible oil can bring serious health concerns because of their carcinogenic features. PAHs could accumulate in edible oil from contaminated environment or food stuff. In this study, the combination uses of on-site thin layer chromatography and surface enhanced Raman scattering (SERS) spectroscopy has been successfully displayed to identify PAHs from edible oil samples. Diatomite which is a kind of porous biosilica was used to construct stationary phase on TLC plate, the photonic crystal feature of diatomite is beneficial for SERS enhancement. The highly-porous stationary phase composed of porous diatomite with void shell structure could promote mobile phase interaction with the stationary phase, which leading to improved mass transfer, uniformity and analyte resolution compare with the conventional silica gel plate. The edible oil (1 µL) was directly applied to the diatomite plate without pretreatment, and subjected to TLC separation. The polarity of target analytes was calculated for eluent optimization, on which four compounds of PAHs(benzo[a]pyrene, pyrene, anthracene and indeno[1,2,3-cd] pyrene) were successfully separated by using hexane/chloroform (15/1, v/v) as eluent, including compounds with similar polarity(benzo[a]pyrene 0.0477, indeno[1,2,3-cd] pyrene 0.6545, pyrene and anthracene are 0). 2 µL of Au colloid at 2.4 × 10 −7  M were transferred onto the diatomite plate for the SERS measurement. The limit of detection was found to be nearly at 1 ppm. The obtained results can easily identify the four compounds of PAHs in edible oil by their own characteristic Raman peaks. This proposed method provides a simple, instant and effective strategy for on-site identification PAHs from food samples.