Open-tubular capillary electrochromatography using capillary columns chemically bonded with the new host molecules calix[6]crown, calix[6]arene

Separation performance of p-tert-butyl(tetradecyloxy)calix[6]arene as a stationary phase for capillary gas chromatography

This work presents the first example of the utilization of p-tert-butyl(tetradecyloxy)calix[6]arene (C6A-C10) as a stationary phase for capillary gas chromatographic (GC) separation.

Analysis of nitrites and nitrates in hams and sausages by open-tubular capillary electrochromatography with a nanolatex-coated capillary column

In this work, a new open-tubular capillary electrochromatography (OT-CEC) method with the nanolatex-coated column was proposed for the determination of nitrites and nitrates in foodstuffs. The method was simple and repeatable as a result of avoiding the introduction of an electroosmotic flow reverse additive (such as cetyltrimethylammonium chloride) in electrophoretic buffer. The limits of quantitation were 0.89 and 1.05 mg kg⁻¹ for nitrate and nitrite, respectively, whereas the overall recoveries ranged from 94 to 103%. The developed OT-CEC method was successfully applied for 12 samples, and the residue profiles of nitrites and nitrates in hams and sausages were obtained and evaluated.

A novel PEG coating immobilized onto capillary through polydopamine coating for separation of proteins in CE

The antifouling PEG-immobilized capillary was introduced for the protein separation in CE through mussel adhesive protein inspired polydopamine coating for the first time. The polydopamine, formed by spontaneous oxidative polymerization of dopamine at alkaline in the inner surface of capillary, was exploited to immobilize amine-functionalized PEG onto the capillary surface. During the process, polydopamine-graft-PEG copolymer was formed via Michael addition or Schiff base reactions. The polymer coating was observed using X-ray photoelectron spectroscopy and SEM. And both of them indicated the formation of the polymer coating. A comparative study of EOF showed that the novel coating could provide effective suppression of EOF and minimized adsorption of proteins. As a consequence, fast and efficient separations of three proteins such as lysozyme, cytochrome c, and ribonuclease A were obtained within a broad pH range. Furthermore, the long-term stability of polydopamine-graft-PEG coating in consecutive protein separation runs and the high separation efficiency proved that this novel coating was capable of minimizing protein adsorption during the capillary separation. The successful capillary performance also was demonstrated in the separation of protein mixture and milk powder samples at acidic pH.

Poly(N,N-dimethylacrylamide-co-4-(ethyl)-morpholine methacrylamide) copolymer as coating for CE

In this work, a new physically adsorbed coating for CE is presented. This coating is based on a poly(N,N-dimethylacrylamide-co-4-(ethyl)-morpholine methacrylamide) (DMA/MAEM) copolymer synthesized in our laboratory. It is demonstrated that the direction and magnitude of the EOF in CE can be modulated by varying the composition of the DMA/MAEM copolymer and the type and pH of the BGE. Moreover, the DMA/MAEM coating provides %RSD(n) = 5 values for migration times lower than 0.9% for the same capillary and day, whereas the %RSD(n) = 25 obtained for the interday assay was lower than 2.9%. The stability of the coating procedure is also tested between capillaries obtaining %RSD(n) = 15 values lower than 2.9%, demonstrating that this physically adsorbed copolymer gives rise to a stable and reproducible coating in CE. Finally, the usefulness of this new cationic copolymer as CE coating is demonstrated through different applications. Namely, it is demonstrated that the CE separation of basic proteins, nucleotides and organic acids is achieved in a fast and easy way by using the DMA/MAEM coated capillary. The use of fused bare silica capillaries did not allow the separation of these compounds under the same analytical conditions. These results demonstrate that this type of coating in CE provides the option of using BGEs that are useless when utilized together with bare silica capillaries making wider the application and possibilities of this analytical technique.

A novel sol-gel calix[4]arene-modified capillary column for open-tubular capillary electrochromatography

A novel open-tubular CEC (OT-CEC) column was prepared by immobilized 5,11,17,23-tetra-tert-butyl-25,27-diethoxy-26,28-dihydroxy-calix[4]arene (Calix[4]) on fused-silica capillary column with sol-gel technology. Calix[4] was initially reacted with gamma-glycidoxypropyltrimethoxysilane (KH-560) to form a new sol-gel precursor (calix[4]-KH-560), and then mixed with another precursor, namely tetraethoxysilane (TEOS). After hydrolysis and condensation, a sol-gel matrix was obtained, in which calix[4] was incorporated. Successful calix[4]-modified sol-gel coating was suggested by infrared (IR) spectra and greatly decreased EOF. In comparison with OT columns prepared by the sol-gel method with TEOS and KH-560 only, the calix[4]-modified sol-gel column showed greatly improved separation of isomeric toluidines, nitrophenols, picolines and neurotransmitters with structural similarity. Migration time and theoretical plate number reproducibility were satisfactory with RSDs less than 1 and 6% each for within column runs and not more than 3 and 7% each for column-to-column measurements, using toluidine and nitrophenol isomers as test solutes on this column. High separation efficiencies (96,000-300,000 plates/m) for basic toluidine isomers were obtained. This column was also successfully employed to combine extraction procedure for the determination of dopamine (DA) and norepinephrine (NE) in Portulaca oleracea L. The recoveries of DA and NE were 93.3 and 94.2%, respectively.

High extraction efficiency fiber coated with calix[4] open-chain crown ether for solid-phase microextraction of polar aromatic and aliphatic compounds

The calix[4] open-chain crown ether, 5,11,17,23-tetra-tert-butyl-25,27-di(2-allyloxyethoxyl)-26,28-dihydroxycalix[4]arene was synthesized and used for preparation of solid-phase microextraction (SPME) fibers of enhanced extraction efficiency. The new SPME coating made from calix[4] open-chain crown ether and hydroxyl-terminated silicone oil was developed with the aid of vinyltriethoxylsilane as bridge using sol-gel method and cross-linking technology. The efficiency of the novel fiber in the extraction of polar aromatic and aliphatic compounds, such as phenols, alcohols, and volatile fatty acids, was also investigated. Due to the introduction of the polar open-chain crown ether in calix[4]arene molecules, the calix[4] open-chain crown ether fiber showed much better selectivity and sensitivity to these polar compounds in comparison with calix[4]arene fiber. It also had superior extraction efficiency when compared to commercial poly(dimethylsiloxane)-divinylbenzene and polyacrylate fibers. Parts per billion to parts per trillion level detection limits were achieved for most of the analytes through SPME in conjunction with GC and flame ionization detector. The linear ranges were two to four orders of magnitude, and the RSD values were below 7% for all analytes. The novel fiber was applied to determine volatile alcohols and fatty acids in wine samples. The volatile-free wine prepared in this work was used to assure similar chemical environment for analytes in both calibration solutions and in real wine samples, thus compensating for possible matrix interferences. The established internal standard method using 4-methyl-2-pentanol as internal standard showed satisfactory accuracy and precision.

p-tert-Butylcalix[4]arene-1,3-bis(allyloxyethoxy)ether Coated Capillaries for Open-Tubular Electrochromatography

The preparation and characterization of p-tert-butylcalix[4]arene-1,3-bis(allyloxyethoxy)ether (CA[4]-BAE) chemically coated capillaries via a free-radical reaction with vinyltriethoxysilane (VTES) that was attached onto the inner wall previously were carried out. IR spectra and decreased electroosmotic flow (EOF) suggested that the capillary was successfully coated with CA[4]-BAE. A slight slope of EOF versus pH at 5 < pH < 9 would help to make the separation reproducible. The CA[4]-BAE-coated capillary showed improved separations of toluidine isomers, naphthol isomers and polycyclic aromatic hydrocarbons (PAHs) compared with an uncoated capillary. The special selectivity indicates that there is a certain extent of host-guest interactions between the solutes and the CA[4]-BAE coating.

Recent highlights in stationary phase design for open-tubular capillary electrochromatography

This review examines the most recent innovations made to achieve high performance in open-tubular capillary electrochromatography (OT-CEC) separations, focusing on the ingenious chemical and physical solutions made to increase the surface area and equip the stationary phase with exploitable selectivity. Among the approaches taken are chemically bonded ligands, etching with chemical bonding, sol-gels, molecularly imprinted polymers, porous layers, physically attached or adsorbed phases, and nanoparticle coatings. Particularly noteworthy are modern developments with macrocyclic receptor ligands, nanoparticles and open channel electrochromatography on-chip.

Preparation and characteristics of sol–gel-coated calix[4]arene fiber for solid-phase microextraction

5,11,17,23-Tetra-tert-butyl-25,27-diethoxy-26,28-dihydroxycalix[4]arene/hydroxy-terminated silicone oil coated fiber was first prepared and applied for solid-phase microextraction (SPME) with sol-gel technology. The possible sol-gel mechanism was discussed and confirmed by IR spectra. It showed wonderful selectivity and sensitivity to polar (aromatic amines), nonpolar (benzene derivatives, polycyclic aromatic hydrocarbons) and high boiling point compounds (phthalates) and the extraction equilibria were reached quite fast. The coating has high thermal stability (380 degrees C) and solvent stability (organic and inorganic), thus its lifetime is longer than conventional fibers. In addition, it has surprising fiber-to-fiber and batch-to-batch reproducibility. The detection limits were quite low and the linear ranges were pretty broad for all analytes.