# Application of Sorbent-Based Extraction Techniques in Food Analysis
## 3 SPE in Food Analysis--Main Fields of Applications
### Environmental Contaminants in Food  
In addition to the mycotoxins and pesticide residues described above, food is exposed to more adverse factors such as environmental contaminants. This type of pollution could arise naturally (weathering of the earth's crust, combustion) or it can be introduced artificially by humans (industrial uses or as undesired side products of industrial processes, combustion). Climate change contributes to the increase in the occurrence of phenomena such as cyclones, droughts, floods, forest fires, landslides, and storms and consequently to the increase in environmental contaminants. Animals are able to accumulate environmental impurities, incorporating them into the food chain and ultimately also into food consumed by humans. Metals, especially heavy metals (cadmium, lead, mercury), arsenic, brominated flame retardants, dioxins, furans, polychlorinated biphenyls, and PAHs, create a group of environmental contaminants. These compounds have an undesirable effect on human health and they are capable of causing chronic diseases or damaging internal organs [60]. Cereal and cereal derivative products are an important element in the human diet; however, cereal-based foods are also carriers of arsenic, especially if it comes from a location where the natural concentration of this element is high or it is contaminated. Maize, rice and wheat crops are therefore exposed to arsenic; moreover, plants do not use this element and are capable of bioaccumulation, which can harm the potential consumers. The most toxic varieties of arsenic are arsenite (As(III)) and arsenate (As(V)); therefore, the qualitative and quantitative determinations are focused on them. Speciation analysis of this element is complicated as a result of its relatively low ionization ability, monoisotopic character, and polyatomic interferences. The sample preparation step before analysis using the SPE is extremely important because it greatly improves the analysis results of cereal-based products such as tortillas by reducing interferences from the matrix [61]. Antimony, chromium, cobalt, copper, nickel, selenium, silver and thallium are slightly less harmful to human health compared to arsenic. SPE is utilized to obtain satisfactory resolution and to concentrate analyte level [62]. To determine the content of metals in food samples (e.g., seafood, water, and vegetables), different varieties of SPE are applied (offline, online, d-SPE); however, nowadays, magnetic SPE is considered the most convenient to use. Currently, sorbents based on magnetic nanoparticles attract attention due to numerous advantages (omission of the centrifuging/filtering step, high resistance against harsh factors, e.g., pH, temperature, substantial versatility in shape, size and sorption properties). The use of magnetic nanoparticles results in a greater efficiency in enriching the sample in the analyte, and consequently lower LOD and satisfactory reproducibility [62]. Polybrominated diphenyl ethers and polychlorinated biphenyls can be transferred to food from the environment. These organic compounds have a high persistence and bioaccumulation ability, thus enriching the food chain with an increasing amount of undesirable impurities. Intake of edible fishery and aquaculture products is associated with an increased risk of taking polybrominated diphenyl ethers and polychlorinated biphenyls [57]. These pollutants cause many negative effects on human health, thus their control is required, especially for seafood. Analysis of animal tissues is a challenge due to trace amounts of the analyzed compounds, and the need to eliminate interferences caused mainly by lipids, which leads to a significant reduction in the sample volume. The efficient process of purifying samples of biological tissue origin after accelerated solvent extraction uses sequential SPE (d-SPE as well as tandem SPE). For this purpose, various sorbents, e.g., silica gel, alumina, and Florisil, with modification were applied [63].