To improve selectivity during sample pretreatment, various selective tools inducing a molecular recognition mechanism during the extraction procedure have been developed, such as sorbents constituted of immobilized antibodies, i.e., immunosorbents, or molecularly imprinted polymers. More recently, as an alternative to both previous approaches, aptamers immobilized onto a solid support, i.e., oligosorbents, were proposed. Thanks to the high affinity and high selectivity of the interaction that some aptamers offer toward some target analytes, they also provide powerful techniques that make selective extraction and the concentration of a target analyte from liquid matrices in one step or sample purification of extracts from solid matrices possible. This review describes the development and the properties of these oligosorbents developed for different types of targets-pharmaceuticals, mycotoxins, proteins, cells, etc. After describing the immobilization procedures, we discuss different parameters characterizing the potential of aptamer-based supports as extraction sorbents. Close relations exist between extraction recoveries and the affinity and amounts of aptamers immobilized on the extraction device. In addition, analyte-aptamer interactions may be affected by matrix components and by additives in the samples. This may also lower extraction recoveries and affect the stability and the possible reusability of the aptamer-based sorbent. All these points are discussed and illustrated. Numerous examples of applications of these sorbents to the treatment of complex samples such as food samples, environmental samples, and biological fluids are also reported. Their association with analytical devices, from conventional to miniaturized analytical systems, is also discussed.

A complete characterization of a novel target-specific DNA aptamer-based miniaturized solid phase extraction (SPE)-sorbent coupled on-line to nanoLC is presented. A miniaturized oligosorbent (mOS) was prepared via the in situ sol-gel synthesis of a hybrid organic-inorganic monolith in 100 μm i.d. capillary columns using tetraethoxysilane and 3-aminopropyltriethoxysilane as precursors, followed by covalent binding of a 5'-amino-modified DNA aptamer with a C12 spacer arm specific for a molecule of small molecular weight. Ochratoxin A (OTA), one of the most abundant naturally occurring mycotoxins, was chosen as model analyte to demonstrate the principle of such an approach. The mOS was coupled on-line to RP-nanoLC-LIF. Selective extraction of OTA on several mOSs was demonstrated with an average extraction recovery above 80 % when percolating spiked binding buffer and a low recovery on control monoliths grafted with a non-specific aptamer. Reproducibility of mOSs preparation was highlighted by comparing extraction yields. Otherwise, the mOSs demonstrated no cross-reactivity towards an OTA structural analogue, i.e., ochratoxin B. Due to the high specific surface area of the hybrid silica-based monolith, the coverage density of DNA aptamers covalently immobilized in the capillaries was very high and reached 6.27 nmol μL(-1), thus leading to a capacity above 5 ng of OTA. This miniaturized device was then applied to the selective extraction of OTA from beer samples. It revealed to be effective in isolating OTA from this complex matrix, thus improving the reliability of its analysis at the trace level.

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The active ingredients in antiperspirant products are aluminum chlorohydrates (ACHs) that, when interacting with proteins present in sweat and sweat duct walls, lead to the obstruction of the sweat ducts and thus reduce delivery of sweat at the skin surface. This study is aimed at developing a methodology based on affinity capillary electrophoresis (ACE) to obtain a quantitative ranking of the interaction between ACHs and proteins under experimental conditions close to those of industrial applications. Usually, in ACE, the metal ligand is introduced at typically μM to mM concentrations in a background electrolyte (BGE) containing a buffering agent that sets the pH and ionic strength. In this work, ACE was implemented in a range of ACH (ligand) concentrations up to 50 g/L (0.2 M in Al(H 2 O) 6 •3Cl) in the absence of other buffering agents, to mimic as much as possible the conditions encountered in the production of antiperspirant products. Under such electrophoretic conditions, the challenge is to extract quantitative information about the interaction from the electrophoretic mobility of the protein, knowing that many effects (including Joule heating, viscosity, pH, ionic strength of the BGE, and distribution of the ligands) vary with the concentration of ACH. With relevant corrections on the effective mobility, it has been possible to observe and quantify a much stronger interaction of ACH components with bovine serum albumin compared to lysozyme.

Amphiphilic hyaluronic acid (HA), synthesised by modifying HA to varying extents with acrylate groups, was successfully separated according to degree of substitution (DS) using solvent gradient high performance liquid chromatography (HPLC). Two HPLC methods based on the amphiphilic structure of the HA were developed. In the first approach, normal phase gradient HPLC was explored, and separation was based on the interactions of HA's polar hydroxyl groups with a polar cyano stationary phase. In the second approach, separation was based on the interaction of the hydrophobic acrylate moieties with a non-polar C8 stationary phase (reversed phase gradient HPLC). The separation was optimised by using an electrolyte in the sample solvent to suppress non-covalent interactions and improve the selectivity of the developed method. The photolytic stability of the modified and unmodified HA was also investigated in order to optimise the sample preparation procedure. Furthermore, an alternative method to NMR spectroscopy was developed for determining the DS of HA. Graphical abstract ᅟ.

Aluminum chlorohydrates (ACH) are used in numerous applications and commercial products on a global scale including water treatment, catalysis or antiperspirants. They are complex mixtures of water soluble aluminum polycations of different degrees of polymerization, that are difficult to separate and quantify due to their susceptibility to depolymerize in solution when placed out of equilibrium, which is inherent to any separation process. We recently achieved the first capillary electrophoresis separation and characterization of ACH oligomers using 4-morpholineethanesulfonic acid (MES) as background electrolyte counter-ion. MES stabilizes the separated ACH oligomers during the electrophoretic process leading to highly repeatable and fast separations. In this work, the separation of ACH oligomers was further studied and perfected by varying the ionic strength, MES concentration and pH of the background electrolyte. Complex electrophoretic behavior is reported for the separation of Al, Al and Na ions according to these experimental parameters. The transformation of the electropherograms in effective mobility scale and the use of the slope-plot approach are used to better understand the observed changes in selectivity/resolution. Optimal conditions (700 mM MES at 25 mM ionic strength containing 0.1 mM didodecyldimethylammonium bromide for dynamic capillary coating, pH 4.8) obtained for the separation of ACH oligomers are used for the baseline separation of samples difficult to analyze with other methods, including different molecular, aggregated and colloidal forms of aluminum from the Al, Al and Na mixture, validating the rationale of the approach.