Droplet-based microextraction — when to go with the flow?

Over the last few decades, droplets have been used for enrichment of target compounds from various types of samples including water, body fluids, soils, and food. Leveraging the high surface area-to-volume ratio, droplets are excellent means of rapidly concentrating the target compounds. The droplet-based microextraction technologies reported so far can be categorized as static and continuous. For a static method, droplets are exposed to a given amount of sample while for a continuous method the sample is continuously fed by a flow and the droplets can either remain static or move with the sample flow. Both the extraction performance and types of analyses that can be used depend on whether the method is static or continuous microextraction. This review classifies various droplet-based microextraction techniques as either a static or continuous method and discusses the advantages and drawbacks of each.