Investigation of the molecular extraction process in single subpicoliter droplets using a near-infrared laser Raman trapping system

The near-infrared (NIR) laser Raman trapping system was applied to study liquid-liquid extraction in a single droplet in a subpicoliter range. The system trapped a single subpicoliter toluene droplet in water using the NIR laser beam and provided time-dependent optical images of the droplet during liquid-liquid extraction. The size of the trapped droplet gradually increased after p-nonylphenol solution was added in water. The Raman spectra of the droplet prove that the increase of the droplet size was caused by the absorption of p-nonylphenol from the water. The distribution coefficient of p-nonylphenol in the subpicoliter droplet was much higher than that in bulk solution.