The digestion of biogenic organic matter is an essential step of sample preparation within microplastic analyses. Organic residues hamper the separation of polymer particles especially within density separation or polymer identification via spectroscopic and staining methods. Therefore, a concise literature survey has been undertaken to identify the most commonly applied digestion protocols with a special focus on water and sediments samples. The selected protocols comprise different solutions, concentrations, and reaction temperatures. Within this study we tested acids (nitric acid and hydrochloric acid), bases (sodium hydroxide and potassium hydroxide), and oxidizing agents [hydrogen peroxide, sodium hypochlorite and Fenton's reagent (hydrogen peroxide 30% in combination with iron(II)sulfate 0.27%)] at different concentrations, temperature levels, and reaction times on their efficiency of biogenic organic matter destruction and the resistance of different synthetic polymers against the applied digestion protocols. Tests were carried out in three parallels on organic material (soft tissue—leaves, hard tissue—branches, and calcareous material—shells) and six polymers (low-density polyethylene, high-density polyethylene, polypropylene, polyamide, polystyrene, and polyethylene terephthalate) in two size categories. Before and after the application of different digestion protocols, the material was weighed in order to determine the degree of digestion efficiency and polymer resistance, respectively. The efficiency of organic matter destruction is highly variable. Calcareous shells showed no to very low reaction to oxidizing agents and bases, but were efficiently dissolved with both tested acids at all concentrations and at all temperatures. Soft and hard tissue were most efficiently destroyed by sodium hypochlorite. However, the other reagents can also have good effects, especially by increasing the temperature to 40–50°C. The additional temperature increase to 60–70°C showed a further but less effective improvement, compared to the initial temperature increase. The resistance of tested polymer types can be rated as good except for polyamide and polyethylene terephthalate. Increasing the concentrations and temperatures, however, results in accelerated degradation of all polymers. This is most evident for polyamide and polyethylene terephthalate, which show losses in weight between 15 and 100% when the digestion temperature is increased. This effect is most pronounced for polyamide in the presence of acids and for polyethylene terephthalate digested with bases. As a concluding recommendation the selection of the appropriate digestion method should be specifically tested within initial pre-tests to account for the specific composition of the sample matrix and the project objectives.

中文翻译：

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微塑料样品处理中的各种消化方案——评估不同合成聚合物的抵抗力和生物有机物破坏的效率

生物有机物的消化是微塑料分析中样品制备的重要步骤。有机残留物阻碍了聚合物颗粒的分离，尤其是在通过光谱和染色方法进行的密度分离或聚合物鉴定中。因此，进行了简明的文献调查，以确定最常用的消化方案，特别关注水和沉积物样品。所选方案包括不同的溶液、浓度和反应温度。在这项研究中，我们测试了酸（硝酸和盐酸）、碱（氢氧化钠和氢氧化钾）和氧化剂 [过氧化氢、次氯酸钠和芬顿试剂（30% 过氧化氢与 0.27% 硫酸铁（II）的组合） )] 在不同浓度下，温度水平、反应时间对生物有机物破坏效率和不同合成聚合物对应用消化方案的抵抗力。对有机材料（软组织——叶子、硬组织——树枝和钙质材料——壳）和六种聚合物（低密度聚乙烯、高密度聚乙烯、聚丙烯、聚酰胺、聚苯乙烯和聚对苯二甲酸乙二醇酯）进行了三个平行的测试) 分为两个尺寸类别。在应用不同的消化方案之前和之后，对材料进行称重以确定消化效率和聚合物电阻的程度。有机物破坏的效率变化很大。钙质壳对氧化剂和碱没有或非常低的反应，但在所有浓度和所有温度下都被两种测试酸有效溶解。次氯酸钠能最有效地破坏软组织和硬组织。然而，其他试剂也可以产生很好的效果，特别是通过将温度提高到 40-50°C。与初始温度升高相比，额外的温度升高到 60-70°C 显示出进一步但不太有效的改进。除聚酰胺和聚对苯二甲酸乙二醇酯外，被测聚合物类型的电阻可以评为良好。然而，增加浓度和温度会导致所有聚合物的降解加速。这对于聚酰胺和聚对苯二甲酸乙二醇酯最为明显，当消化温度升高时，它们的重量损失在 15% 到 100% 之间。这种效果对于存在酸的聚酰胺和用碱消化的聚对苯二甲酸乙二醇酯最为明显。作为结论性建议，应在初始预测试中对适当消解方法的选择进行具体测试，以考虑样品基质的特定组成和项目目标。