3.3.2. MPs Analytical Methods

Contributed keywords can be found in cluster yellow in Figure 4 and cluster purple in Figure 5, including identification, density separation, elutriation, sediment, spectroscopy, FT-IR, Raman, etc.

MPs analytical methods were developed to meet different purposes in MPs surveys, and can be divided into three steps: (1) sampling; (2) pretreatment for MPs extraction; and (3) qualitative and quantitative analysis. For sediment samples, high density solutions were commonly used to extract MPs, based on density separation [47]. In addition, elutriation columns proved to be useful tools with high extraction efficiency [48]. For seawater or water samples, selective sampling [49,50] and bulk sampling [51] methods were used in different studies, as were different pretreatment methods, such as enzyme digestion with subsequent filtration [49], and the sieve method [50]. For biota samples, the sampling methods always depended on the organisms being studied. For example, plankton trawls and nets were used to study the accumulation of MPs in plankton [52], whereas the dissection of different organs [53] was used for other target species. Digestion pretreatment methods for MPs extraction from biota samples have received a lot of attention, and many studies compared different digestion pretreatment methods, in pursuit of higher extraction efficiency [54]. For qualitative and quantitative analysis, MPs were usually measured and classified by shape, size, color, and chemical components. Most commonly, the extracted MPs were visually sorted under a microscope, and in some cases, the chemical components of MPs were determined by Raman spectroscopy [49], FT-IR micro-spectroscopy [51], and FT-IR [53]. It is notable that MPs analytical methods are now still debatable and have yet to be standardized.
