Recent advances of online coupling of sample preparation techniques with ultra high performance liquid chromatography and supercritical fluid chromatography

Ultra high performance liquid chromatography and supercritical fluid chromatography techniques are favored because of their high efficiency and fast analysis speed. Although many sample preparation techniques have been coupled with common liquid chromatography online, the online coupling of sample preparation with the two popular chromatography techniques have gained increasing attention owing to the increasing requirements of efficiency and sensitivity. In this review, we have discussed and summarized the recent advances of the online coupling of sample preparation with ultra high performance liquid chromatography and supercritical fluid chromatography techniques. The main sample preparation techniques that have been coupled with ultra high performance liquid chromatography online are solid‐phase extraction and in‐tube solid‐phase microextraction, while solid‐phase extraction and supercritical fluid extraction are the main techniques that have been coupled with supercritical fluid chromatography online. Especially, the strategies for online coupling of sample preparation with chromatography techniques were summarized. Typical applications and growing trends of the online coupling techniques were also discussed in detail. With the increasing demands of improving the efficiency, throughput, and analytical capability toward complex samples of the analysis methods, online coupling of sample preparation with chromatography techniques will acquire further development.     

共价-有机骨架材料在色谱及样品预处理中的应用

共价-有机骨架（COFs）材料具有比表面积大、热和化学稳定性好、结构和功能多样等优点,目前已广泛用于气体储存、催化、吸附和分离等领域。近年来,以COFs为固定相和吸附剂的色谱分离和样品预处理研究引起了人们的极大兴趣。该文综述了近年来COFs的色谱和样品预处理应用研究进展,并对这一领域进行了展望。     

Electrodialytic sample treatment coupled on-line with high-performance liquid chromatography

Summary An electrodialytic sample treatment method coupled on-line with high-performance liquid chromatography (EDIST-HPLC) is discussed in this paper. The performance of EDIST as a function of the donor-phase (sample solution) flow rate, the voltage applied over the electrodialysis block, and the time of dialysis has been studied using the basic drug ephedrine as a model compound. Enrichment of the analyte by a factor of 10–20 was possible. The determination of human plasma spiked with ephedrine is briefly discussed.     

Automated sample preparation using supported liquid membranes for liquid chromatographic determination of sulfonylurea herbicides

Summary Sample preparation for determination of sulfonylurea herbicides in aqueous samples is investigated. The technique studied utilizes extraction and back extraction in an automated flow system and is coupled on-line to a liquid chromatographic system. The extraction unit consists of an immobilized liquid membrane, separating two aqueous phases. From the acidified donor phase the analytes are extracted into the organic solvent of the membrane. After traversing the membrane they are back extracted into an alkaline/neutral aqueous acceptor phase. They are trapped in the acceptor by dissociation, making them insoluble in the membrane.Studies of the sample preparation system concern factors like channel length of separators, distribution coefficients of analytes and use of a precolumn instead of loop for chromatographic injections. Effects of the internal diameter of the analytical column as well as the detection of the sulfonylurcas are investigated.     

Theoretical models for electrodialytic sample treatment in trace analysis by liquid chromatography

Summary Basic considerations for analyte enrichment and recovery obtainable by electrodialysis as a sample treatment method are given. Equations are derived which describe the dependence of the concentration profiles of ionic compounds on the electric field strength in a set-up with stagnant donor and acceptor solutions. It is shown that analyte recovery increases when less ion-selective membranes are used in the electrodialysis cell. Computer models are used to estimate the analyte enrichment for a flowing donor (sample) and a stagnant acceptor phase. About 10-fold enrichment can be obtained in an electrodialytic sample treatment system within 20 min under maximum current conditions. A compromise has to be found between analyte recovery and the donor (sample) flow rate.     

分子印迹整体柱富集-高效液相色谱法测定植物中的痕量细胞分裂素

采用分子印迹整体柱富集-高效液相色谱法选择性分离分析了植物样品中痕量细胞分裂素的含量。结果表明,以激动素为模板分子,甲基丙烯酸(MAA)为功能单体,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,甲苯与十二醇为致孔剂,可在不锈钢柱管中原位聚合制备激动素分子印迹整体柱;与非分子印迹整体柱对比,该分子印迹整体柱能选择性富集4种细胞分裂素,具有较好的重复性和高的萃取效率;在优化的实验条件下,激动素(K)、激动素核苷(KR)、反式-玉米素(tZ)和meta-topolin(mT)的平均加标回收率分别为91.9%、80.0%、87.5%和50.2%,相对标准偏差均小于11.8%。本方法已成功地用于不同植物样品中4种细胞分裂素的分离和分析。     

Review of online coupling of sample preparation techniques with liquid chromatography

Sample preparation is still considered as the bottleneck of the whole analytical procedure, and efforts has been conducted towards the automation, improvement of sensitivity and accuracy, and low comsuption of organic solvents. Development of online sample preparation techniques (SP) coupled with liquid chromatography (LC) is a promising way to achieve these goals, which has attracted great attention. This article reviews the recent advances on the online SP-LC techniques. Various online SP techniques have been described and summarized, including solid-phase-based extraction, liquid-phase-based extraction assisted with membrane, microwave assisted extraction, ultrasonic assisted extraction, accelerated solvent extraction and supercritical fluids extraction. Specially, the coupling approaches of online SP-LC systems and the corresponding interfaces have been discussed and reviewed in detail, such as online injector, autosampler combined with transport unit, desorption chamber and column switching. Typical applications of the online SP-LC techniques have been summarized. Then the problems and expected trends in this field are attempted to be discussed and proposed in order to encourage the further development of online SP-LC techniques.     

Rapid determination of aflatoxin B1 by an automated immunomagnetic bead purification sample pretreatment method combined with high‐performance liquid chromatography

We aimed to establish an automated versatile sample preconcentration method based on the modified immunomagnetic beads, which was utilized to enrich for aflatoxin B1 from the matrices. The critical main parameters affecting the extraction efficiency, such as usage amount of immunomagnetic beads, reaction time, elution time, and blending way were investigated. Under the optimized conditions, the content of aflatoxin B1 was analyzed by high‐performance liquid chromatography, the mobile phase consists of water–acetonitrile–methanol (42:18:10, v/v/v), and fluorescence detection was performed with excitation and emission wavelengths at 360 and 440 nm, respectively. Moreover, the performance of preconcentration method was compared with the conventional method based on the immunoaffinity column. The accuracy of two clean‐up methods was within the error range. In addition, the stability and recyclability of the immunomagnetic beads was studied by recycling them five times. The results for the respective analysis in various samples demonstrated that the developed extraction platform provides a promising approach that is simple, rapid, sensitive, and easy to use.     

Automation and Standardization—A Coupled Approach towards Reproducible Sample Preparation Protocols for Nanomaterial Analysis

Whereas the characterization of nanomaterials using different analytical techniques is often highly automated and standardized, the sample preparation that precedes it causes a bottleneck in nanomaterial analysis as it is performed manually. Usually, this pretreatment depends on the skills and experience of the analysts. Furthermore, adequate reporting of the sample preparation is often missing. In this overview, some solutions for techniques widely used in nano-analytics to overcome this problem are discussed. Two examples of sample preparation optimization by automation are presented, which demonstrate that this approach is leading to increased analytical confidence. Our first example is motivated by the need to exclude human bias and focuses on the development of automation in sample introduction. To this end, a robotic system has been developed, which can prepare stable and homogeneous nanomaterial suspensions amenable to a variety of well-established analytical methods, such as dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), field-flow fractionation (FFF) or single-particle inductively coupled mass spectrometry (sp-ICP-MS). Our second example addresses biological samples, such as cells exposed to nanomaterials, which are still challenging for reliable analysis. An air–liquid interface has been developed for the exposure of biological samples to nanomaterial-containing aerosols. The system exposes transmission electron microscopy (TEM) grids under reproducible conditions, whilst also allowing characterization of aerosol composition with mass spectrometry. Such an approach enables correlative measurements combining biological with physicochemical analysis. These case studies demonstrate that standardization and automation of sample preparation setups, combined with appropriate measurement processes and data reduction are crucial steps towards more reliable and reproducible data.     

Hyphenation of optimized microfluidic sample preparation with nano liquid chromatography for faster and greener alkaloid analysis

A glass liquid–liquid extraction (LLE) microchip with three parallel 3.5 cm long and 100 μm wide interconnecting channels was optimized in terms of more environmentally friendly (greener) solvents and extraction efficiency. In addition, the optimized chip was successfully hyphenated with nano-liquid chromatography with ultraviolet and mass spectrometric detection (nanoLC–UV–MS) for on-line analysis. In this system, sample pretreatment, separation and detection are integrated, which significantly shortens the analysis time, saves labor and drastically reduces solvent consumption. Strychnine was used as model analyte to determine the extraction efficiency of the optimized 3-phase chip. Influence of organic solvent, pH of feed phase, type of alkaloid, and flow rates were investigated. The results demonstrated that the 3-phase chip nanoLC–UV/MS hyphenation combines rapid (∼25 s) and efficient (extraction efficiency >90%) sample prep, with automated alkaloid analyses. The method was applied to real samples including Strychnos nux-vomica seeds, Cephaelis ipecacuanha roots, Atropa belladonna leaves, and Vinca minor leaves.     

Advances in sample preparation in chromatography for organic environmental pollutants analyses

Many pollutants are present at trace level in our environment, which are beyond the scope of the detection by advance instruments too. Therefore, there is urgent need to develop advance sample preparation methods to determine the concentrations of the pollutants even at trace levels. Keeping this into consideration, many extraction techniques have been developed and applied for the analysis of organic pollutants in environmental samples. This review presents the sate-of-the-art of sample preparation methods in environmental samples. The extraction techniques discussed are headspace, liquid based extraction, supported liquid, homogeneous liquid–liquid, homogeneous liquid–liquid, single drop micro-extraction, membrane assisted solvent, solid-phase, molecularly imprinted solid-phase, monolithic spin column, matrix solid-phase, dispersive solid-phase, disposable pipette, magnetic solid-phase, solid-phase micro-extraction, micro-extraction by packed sorbent and stir bar sorptive. The article will be highly useful for environmental chromatographers.     

Size exclusion chromatography sample pretreatment for GC-AED analysis of metalloporphyrins in crude oils

Size exclusion chromatography (SEC) has been demonstrated to be an effective and reproducible sample pretreatment procedure for removal of heavy oil matrices prior to GC-AED analysis of metalloporphyrins, and for the resolution of volatile metal species into clean and defined fractions. This paper also discusses the results obtained by SEC for determination of the distribution of metallopor-phyrins in crude oils and the correlation between total metal, metal-loporphyrin, and total distillable metal content.     

高效液相色谱分析样品处理技术进展

综述高效液相色谱样品处理技术.液–液萃取在常温常压下开展,处理能力强,回收率高;固相萃取所需样品量少,耗费溶剂少,操作简单,重复性好;固相微萃取在固相萃取的基础上,简化样品制备与分析过程;微波辅助萃取则利用高频电磁波的穿透和电磁场作用缩短萃取时间,提高萃取效率;超临界流体萃取凭借超临界流体萃取剂的惰性、低毒、纯净、无残...     

样品前处理技术在气相色谱分析中的应用进展

气相色谱法是当前应用最广泛的分析技术之一。使用气相色谱对复杂基体进行分析时的样品前处理步骤往往繁琐耗时,易引起误差,已成为制约分析效率和准确度提升的关键环节。本文综述了2009-2013年几种主要的样品前处理技术,包括吹扫捕集、固相萃取、固相微萃取、液相微萃取技术以及微波辅助萃取、超声波辅助萃取等场辅助萃取技术在气相色谱分析中的应用研究进展。     

Theoretical considerations for zone electrophoretic sample treatment in liquid chromatography

Summary In this paper a concept is proposed for the selective isolation of ionogenic, low-molecular weight compounds from biological samples prior to a determination by liquid chromatography. The basis for this sample treatment method is free zone electrophoresis in a system of capillaries connected by switching valves. The influence of various parameters (the geometry of the capillaries, the conductivity of the sample and the buffers used, protein binding) on the selectivity of the method is discussed. A strategy to study reversible protein binding of ionogenic compounds is indicated. Calculations have been performed to estimate the temperature increase of the solutions during the electrophoretic process. It is shown that for a given amount of sample to be introduced and a maximum time allowed for the procedure, the temperature increase is the smallest when wide capillaries are used. Equations are given describing the zone broadening caused by diffusion, by differences in temperature and by unequal migration path lengths in bent capillaries. It is shown that in this respect the use of narrow capillaries is usually preferable. A compromise has to be found starting from the boundary conditions on loadability and speed imposed by the chromatographic determination.     

Comprehensive two-dimensional liquid chromatography

Having nearly exhausted the possibilities for generating peak capacity through improvements in column technology, chromatographers are increasingly looking to alternative ways of maximising chromatographic separation. In recent years there has been increasing activity in the field of comprehensive multidimensional separations to meet analysis demands. Comprehensive two-dimensional liquid chromatography (LC×LC) approaches offer high peak capacity which leads to significantly improved analytical performance over single-column liquid chromatography. There are several closely related avenues available for achieving an LC×LC separation and this review pays special attention to the different valve-based interfaces that have been used to comprehensively couple the first and second dimension columns in LC×LC systems. A brief discussion of column choices for selected applications and the conditions employed is also presented.