Latest trends, green aspects, and innovations in liquid-phase based microextraction techniques: a review

Liquid-phase microextraction (LPME) methods including single-drop microextraction (SDME), hollow-fiber LPME (HF-LPME), and dispersive liquid-liquid microextraction (DLLME) have in the very short time since their invention grabbed the attention of scientists. Up to now, LPME methods have shown important innovations for the extraction and preconcentration of both inorganic and organic trace analytes from different matrices. These LPME methods offer unique advantages such as high preconcentration factor for target analytes in a single step, low cost, simplicity, excellent preconcentration capability, sample cleanup and integration of steps, and combined use with almost every analytical measurement technique. We describe the milestones and the combined use of different types of LPME methods as well as the green aspects and advantages and shortcomings of known LPME protocols. In addition, we discuss the main results and innovations of different types of LPME published in the period 2010-2016 and we compare the performance of these techniques to that of other recent techniques.