Microdroplet extraction assisted ultrasensitive Raman detection in complex oil.

Because of the complicated component and suppression in spectrum, the Raman detection of trace substances in complex oil is still the great challenge at present. In this work, a simple and robust approach based on microdroplet liquid–liquid extraction for real-time Raman spectroscopy monitoring of trace substances in complex oil is reported. Based on unbalanced chemical potentials between the water and oil in a microfluidic chip, target trace molecule is extracted from complex mineral oil to water microdroplet. Benefiting real-time fluorescence intensities of fluorescein in water microdroplet, the extraction performance is investigated and optimized. The optimal water microdroplet is implemented to Raman detection of furfural in complex mineral oil, a typical trace performance marker in electric power equipment, which exhibit excellent sensitivity with limit of detection (LOD) at 26ppb. Compared to traditional most sensitive technology (high performance liquid chromatography, HPLC, LOD at 50ppb for furfural), microdroplet extraction assisted Raman detection of trace substance in complex oil not only simplify the detection process with low cost and much high sensitivity but also shows a portable real-time online monitoring potential, which has great application prospect in quality inspection of complex oil, e.g electric insulating oil and mechanic lubrication oil.