UHPLC combined with mass spectrometric study of as-synthesized carbon dots samples

A fast and green approach to synthesize carbon dots (C-dots) by microwave-assisted pyrolysis of precursor chitosan as the carbon source and glacial acetic acid as the condensation agent has been developed. Ultra-high performance liquid chromatography (UHPLC) has been applied to study C-dots samples prepared with various synthetic conditions including amount of chitosan, concentration of acetic acid and reaction time. All the as-prepared C-dots samples are complex mixtures of C-dots species which can be separated by UHPLC within 16 min. All the separated C-dots peaks display a distinctive absorption bands at 261-271 nm corresponding to the n→π* transition of C=O bond. The obtained chromatograms indicate the composition and complexity of an as-synthesized C-dots sample which is commonly neglected. In addition, high-performance liquid chromatography is employed to fractionate the C-dots sample. The separated C-dots fractions are collected and characterized by photoluminescence (PL) spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The PL spectra of the fractions display emission peaks at 427-446 nm upon excitation at 340 nm. The C-dots fractions are fully anatomized by MALDI-TOF MS, displaying their fragmentation mass ion features and indicating the surface functionalities of C-dots. The findings highlight the virtues of UHPLC to separate and reveal the unique characteristics of individual C-dots product which may have potential applications in the fields of bioanalysis, bioimaging, catalysis, chemosensing, energy storage, and optoelectronics device.