填充吸附剂微萃取技术及其在微小体积样品萃取应用中的研究进展

微萃取技术是分析化学领域发展迅速,且已经得到广泛应用的样品前处理技术。填充吸附剂微萃取(MEPS)是一种微量固相萃取技术,使用微量的吸附剂填充于微量注射器,通过反复抽推方式使样品多次流经吸附剂以完成样品吸附萃取过程,萃取后的样品可直接用于色谱分析。典型的MEPS萃取设备包括MEPS注射器和MEPS吸附床(BIN)。MEPS优化的主要因素为MEPS处理过程的参数,包括样品流速、样品量与样品萃取循环次数,吸附剂及淋洗、洗脱溶剂的种类和体积,还需要考虑样品基质对MEPS性能的影响和样品残留和重复使用问题。MEPS中最重要的部分是吸附剂,主要有商品化的MEPS吸附剂,包括硅基的Silica、C18、C8等,碳材料的Hypercarb和聚苯乙烯聚合物类的SDVB、HDVB吸附剂等。研究用的吸附剂包括分子印迹材料、限进分子印迹材料、碳基材料、导电聚合物类材料、改性硅基材料及共价-有机骨架材料等。MEPS结合多种分析仪器已经成功应用于从不同基质中提取单一或多种分析物,所涵盖基质包括生物样品(尿液、唾液、血浆或血液)、河流水体或生活污水以及几种食品和饮料。MEPS处理复杂生物基质样品时,通常需要稀释样品、除蛋白质等预处理。MEPS具有需要样品体积小、操作快速等特点,在生物基质样品分析中有望得到更广泛的使用。在环境样品中,该技术可与现场便携仪器联用,未来将有望在现场进行快速检测,并于易分解样品等方面发挥作用。

Research progress of microextraction by packed sorbent and its application in microvolume sample extraction

Microextraction is a rapidly developing sample preparation technology in the field of analytical chemistry, which is seeing widespread application. Accurate sample preparation can not only save time but also improve the efficiency of analysis, determination, and data quality. At present, sample pretreatment methods must be rapid, allow for miniaturization, automation, and convenient online connection with analytical instruments. To meet the requirements of green analytical methods and improve the extraction efficiency, microextraction techniques have been introduced as suitable replacements to conventional sample preparation and extraction methods. Microextraction using a packed sorbent (MEPS) is a new type of sample preparation technology. The MEPS equipment was prepared using microsyringe with a volume of 50-500 μL, including MEPS syringes and MEPS adsorption beds (barrel insert and needle, BIN), which is essentially similar to a miniaturized solid phase extraction device. The BIN contains the adsorbent and is built into the syringe needle. A typical MEPS extraction procedure involves repeatedly pumping the sample solution in two directions (up and down) through the adsorbent multiple times in the MEPS syringe. The specific operation course of MEPS includes conditioning, loading, washing, elution, and introduction into the analysis instrument. The conditioning process is adopted to infiltrate the dry sorbent and remove bubbles between the filler particles. The adsorption process is accomplished by pulling the liquid plunger of the syringe so that the sample flows through the adsorbent in both directions multiple times. The washing process involves rinsing the sorbent to remove unwanted components after the analyte is retained. The elution process involves the use of an eluent to ensure that the sample flows through the adsorbent in both directions multiple times, so that elution can be realized by the pumping-pushing action. The target analyte is eluted with the eluent, which can be directly used for chromatographic analysis. However, when processing complex biological matrix samples by MEPS, pretreatment steps such as dilution of the sample and removal of proteins are commonly required. At present, the operation modes of the MEPS equipment are classified into three types: manual, semi-automated, and fully automated. This increase in the degree of automation is highly conducive to processing extremely low or extremely high sample volumes. Critical factors affecting the MEPS performance have been investigated in this study. The conditions for MEPS optimization are the operating process parameters, including sample flow rate, sample volume, number of sample extraction cycles, type and volume of the adsorbent, and elution solvents. It is also necessary to consider the effect of the sample matrix on the performance of MEPS. The MEPS sorbent should be cleaned by a solvent to eliminate carryover and reuse. The sorbent is a core aspect of MEPS. Several types of commercial and non-commercial sorbents have been used in MEPS. Commercial sorbents include silica-based sorbents such as unmodified silica (SIL), C2, C8, and C18. Unmodified silicon-based silica is a normal phase adsorption material, which is highly polar and can be used to retain polar analytes. C18, C8, and C2 materials are suitable for reversed-phase adsorption, while SCX, SAX, APS, and M1 (C8+SCX) adsorbents are suitable for the mixed-mode and ion-exchange modes. Noncommercial sorbents include molecularly imprinted materials, restricted-access molecularly imprinted materials, graphitized carbon, conductive polymer materials, modified silicon materials, and covalent-organic framework materials. The performance of MEPS has recently been illustrated by online with LC-MS and GC-MS assays for the analysis of biological matrices, environmental samples, and food samples. Pretreatment in MEPS protocols includes dilution, protein precipitation, and centrifugation in biological fluid matrices. Because of the small sample size, fast operation, etc., MEPS is expected to be more widely used in the analysis of bio-matrix samples. MEPS devices could also play an important role in field pretreatment and analysis.