A review of micro-solid-phase extraction techniques and devices applied in sample pretreatment coupled with chromatographic analysis

Sample pretreatment is one of the most crucial and error-prone steps of an analytical procedure; it consents to improve selectivity and sensitivity by sample clean-up and pre-concentration. Nowadays, the arousing interest in greener and sustainable analytical chemistry has increased the development of microextraction techniques as alternative sample preparation procedures. In this review, we aimed to show two different categorizations of the most used micro-solid-phase extraction (mu SPE) techniques. In essence, the first one concerns the solid-phase extraction (SPE) sorbent selection and structure: normal-phase, reversed-phase, ion-exchange, mixed-mode, molecular imprinted polymer, and special techniques (e.g., doped cartridges for specific analytes). The second is a grouping of the commercially available mu SPE products in categories and sub-categories. We present every device and technology into the classifications paying attention to their historical development and the actual state of the art. So, this study aims to provide the state-of-the-art of mu SPE techniques, highlighting their advantages, disadvantages, and possible future developments in sample pretreatment.