Lund University, Department of Chemistry, Centre for Analysis and Synthesis, P.O. Box 124, SE-22100 Lund, Sweden.
Lund University, Department of Chemistry, Division of Biotechnology, P.O. Box 124, SE-22100 Lund, Sweden.
J Chromatogr A. 2023 Sep 13;1706:464267. doi: 10.1016/j.chroma.2023.464267. Epub 2023 Aug 2.
It is well-known that an ideal extraction method enabling quantitative analysis should give complete extraction of the target analytes as well as minimal co-extraction of unwanted matrix substances. If the extraction method is part of a nontarget screening protocol, the desired analytes can differ widely in terms of chemical properties. In chromatography, terminologies such as recovery, selectivity, and comprehensiveness are well-established and can easily be determined. However, in extraction, these concepts are much less developed. Hence, the aim of our research is to develop and scrutinize theory in extraction with respect to numerical descriptors for extractability, selectivity, and comprehensiveness. Our approach is based on experiments determining the extractability of target analytes and selected interferences. As a case study, we use a pooled sample of three species of seaweed (Alaria esculenta, Laminaria digitata and Ascophyllum nodosum). Target analytes are β-carotene, fucoxanthin, δ-tocopherol, and phloroglucinol; and selected interferences are carbohydrates, proteins, ash, arsenic, and chlorophyll a. As a "green and clean" extraction technique, supercritical fluid extraction (SFE) using mixtures of CO, ethanol and water were explored using a design of experiment. The temperature was varied between 40-80°C, and the pressure was held constant at 300 bar. Obtained results clearly demonstrate that highest relative selectivity was achieved with CO containing only 5 vol% of ethanol and no water, which primarily enabled high extractability of β-carotene, and yielding an extract free of carbohydrates, proteins, and toxic metals such as arsenic. Best methods for highest extractability of the other target analytes varied quite widely. Analytes requiring the highest water content (fucoxanthin and phloroglucinol), also resulted in the lowest relative selectivity. Maximum relative comprehensiveness was achieved using CO/ethanol/water (40/55/5, v/v/v) at 70°C and 300 bar. Our study demonstrates the feasibility of using relative quantitative descriptors for extractability, selectivity, and comprehensiveness, in optimization strategies for analytical extractions.
众所周知，一种理想的萃取方法应能定量分析，既要完全萃取目标分析物，又要尽量减少不需要的基质物质共萃取。如果萃取方法是非目标筛选方案的一部分，那么所需的分析物在化学性质上可能有很大差异。在色谱法中，回收率、选择性和全面性等术语已经得到很好的确立，可以很容易地确定。然而，在萃取中，这些概念的发展要少得多。因此，我们的研究目的是针对可提取性、选择性和全面性的数值描述符来开发和研究萃取理论。我们的方法基于实验，确定目标分析物和选定干扰物的可提取性。作为一个案例研究，我们使用三种海藻（海人草、海带和裙带菜）的混合样本。目标分析物为β-胡萝卜素、岩藻黄质、δ-生育酚和间苯三酚；选定的干扰物为碳水化合物、蛋白质、灰分、砷和叶绿素 a。作为一种“绿色清洁”的萃取技术，我们使用 CO、乙醇和水的混合物，通过实验设计探索了超临界流体萃取（SFE）。温度在 40-80°C 之间变化，压力保持在 300 巴。得到的结果清楚地表明，在仅含有 5 体积%乙醇和不含水的 CO 中，相对选择性最高，这主要实现了β-胡萝卜素的高可提取性，并得到了不含碳水化合物、蛋白质和砷等有毒金属的提取物。对于其他目标分析物，获得最高提取率的最佳方法差异很大。需要最高含水量的分析物（岩藻黄质和间苯三酚），也导致相对选择性最低。在 70°C 和 300 巴下，使用 CO/乙醇/水（40/55/5，v/v/v）可获得最大的相对全面性。我们的研究表明，在分析萃取的优化策略中，使用相对定量描述符来描述可提取性、选择性和全面性是可行的。
