Electrostatic field-induced tip-electrospray ionization mass spectrometry for direct analysis of raw food materials.

Rapid characterization of metabolites and risk compounds such as chemical residues and natural toxins in raw food materials such as vegetables, meats, and edible living plants and animals plays an important part in ensuing food quality and safety. To rapidly characterize the analytes in raw food materials, it is essential to develop in situ method for directly analyzing raw food materials. In this work, raw food materials including biological tissues and living samples were placed between an electrode and mass spectrometric (MS) inlet under a strong electrostatic field; analytes were rapidly induced to generate electrospray ionization (ESI) from the sample tip by adding a drop of solvent onto the sample. Therefore, the electrostatic field-induced tip-ESI-MS allows raw samples to avoid contacting high voltage, and thus this method has the advantage for in vivo analysis of food living plants and animals. Metabolite profiling, residues of pesticides and veterinary drugs, and natural toxins from raw food materials have been successfully detected. The analytical performances, including the linear ranges, sensitivity, and reproducibility, were investigated for direct sample analysis. The ionization mechanism of electrostatic field-induced tip-ESI was also discussed in this work.