Shi-Lu Da

In-tube solid phase microextraction using a β-cyclodextrin coated capillary coupled to high performance liquid chromatography for determination of non-steroidal anti-inflammatory drugs in urine samples

A configuration of in-tube solid-phase microextraction (SPME) coupled to HPLC was constructed by using a pump and a six-port valve combined with a PEEK tube as the pre-extraction segment. The extraction capillary was fixed directly on the HPLC six-port valve to substitute for the sample loop. The whole system could be handled easily to perform accurate on-line extraction, and the possible inaccurate quantification caused by sample/mobile phase mixing when using an autosampler could be eliminated. A beta-cyclodextrin coated capillary, prepared by sol-gel method, was used as the extraction capillary for in-tube SPME. Three non-steroidal anti-inflammatory drugs, ketoprofen, fenbufen and ibuprofen, were employed to evaluate the extraction performance of the capillary. After optimizing the extraction conditions, satisfactory extraction efficiency was obtained and detection limits for ketoprofen, fenbufen and ibuprofen in diluted urine samples were 38, 18 and 28ng/mL, respectively. The extraction reproducibility was evaluated with intra-day and inter-day precision, and the R.S.D.s obtained were lower than 4.9 and 6.9%, respectively. The capillary was proved to be reusable and the extraction efficiency did not decrease after 250 extractions.

Synthesis of a carbon monolith with trimodal pores

Mesoporous carbons are of great importance in a variety necessary to fabricate them in macroscopic shapes. Carbon of fields such as catalysis, separation, energy storage, and monoliths with mesopores have been synthesized by Zhao electrode materials because they have a high specific et al. [14] and Sayari et al. [15]. However, shrinkage or surface area, large pore volume, good mechanical stability cleft was usually observed for their resulting products, and chemical inertness. Therefore, synthesis of mesoporprobably due to the lack of mechanical stability of the ous carbons with a narrow pore size distribution is template and the big capillary pressure [16]. Furthermore, currently receiving considerable attention. A templating no textural pores exist in the products, which severely method using appropriate materials has been successfully restrict their application in separation, purification etc. employed for the purposes [1–4]. Ryoo and co-workers A silica monolith, which was prepared by Nakanishi et [4–7] first reported the synthesis of ordered mesoporous al. [17] via the combination of phase separation and carbons of the CMK family using ordered mesoporous sol–gel processes, exhibits both co-continuous structure silica particles as templates. Pinnavaia et al. [8] have and mesoporosity; the co-continuous structure results from prepared a hexagonal mesostructured carbon molecular the interconnected silica skeletons and the interconnected sieve (C-MSU-H) using a silica with meso-ordered structextural pores with their size in the micrometer range, ture (MSU-H) as a hard template. In addition to these while the mesopores exist in the silica skeleton surface ordered mesoporous carbons, some worm-like or disorwith the pore size in the nanometer scale. Furthermore, the dered porous carbons were also reported. Hyeon and coshape and macropore /mesopore size of the silica monolith workers [9,10] demonstrated that mesoporous carbons is easily controlled by the adjustment of the preparation could be prepared using silica sols as templates. However, conditions. The unique property of the silica monolith due to the dispersion character of silica sols, the mesopores itself presents an attracting template for carbon replica. in the final carbons were discrete, which severely limited Here, we report the synthesis of a carbon monolith with their applications [9,10]. Recently, mesocellar silica foam co-continuous structure and trimodal pores by a templating (MCF) and very large pore hexagonal and cellular foammethod using a novel silica monolith as the template. The like molecular sieve silica with well cross-linked frameresultant carbon monolith is characterized by high surface work walls (MSU-F) were adopted by the same group for area, micropores, uniform mesopores and macroporosity, carbon replicas [11,12]. The resulting carbons, named which facilitate its usage in adsorption, separation and MCF-carbon and C-nano-MSU-F, respectively, featured purification etc. uniform mesocells interconnected through uniform winThe silica monolith was synthesized by means of phase dows. The pore connectivity facilitated the diffusion of large molecules within these materials, thereby rendering them more effective for applications. Hyeon et al. [13] also reported the fabrication of carbons with bimodal pores, designated as Meso-nano-C, using a corresponding silica template. The structure of the Meso-nano-C was comparable with those of MCF-carbon and C-nano-MSU-F. Therefore, it could provide similar effectiveness. Though various structured mesoporous carbons have been synthesized, most of them are in the form of powder. For the development of their actual applications, it is

Preparation and characterization ofp-tert-butyl-calix[6]arene-bonded silica gel stationary phase for high-performance liquid chromatography

SummaryFor the first time calix[6]arene has been chemically combined with silica gel via a longer spacer to prepare calix[6]arene-bonded silica gel stationary phase for high-performance liquid chromatography (HPLC). The separation of positional isomers and polycyclic aromatic hydrocarbons on the calix[6]arene-bonded phase was achieved with methanol-water as mobile phase. Some nucleosides were also separated on the bonded phase. The reversed-phase chromatographic performance of the bonded phase was studied. The results showed that the calix[6]arene-bonded phase was highly hydrophobic. A possible separation mechanism has been proposed.

Preparation and evaluation of zirconia-coated silica monolith for capillary electrochromatography.

Silica monoliths were fabricated inside fused-silica capillaries. Then the monolithic columns were coated with membrane-like zirconia. The zirconia-coated silica monoliths exhibited different EOF behavior comparing with that of bare silica monoliths. The magnitude and direction could be manipulated by changing the running buffers. Due to the amphoteric characteristic of zirconia, the silica monoliths with zirconia surface facilitate the separation of basic compounds. Aromatic amines and alkaloids were separated without obvious peak tailing. The zirconia surface was easily modified with octadecylphosphonic acid for the separation of neutral compounds. Column efficiency as high as 90,000 and 80,000m(-1) was obtained for beberine and naphthalene, respectively. Furthermore, the zirconia coating increased the stability of the monolithic columns. Even after being exposed to severe condition, there was no apparently efficiency decrease for the test samples.

Preparation and characterization of an L-tyrosine-derivatized β-cyclodextrin-bonded silica stationary phase for liquid chromatography

An L-tyrosine-derivatized β-cyclodextrin (CD)-bonded silica stationary phase (TCDS) for liquid chromatography (LC) was prepared by bonding L-tyrosine to β-CD which had been grafted to the silica surface via a longer spacer. The new stationary phase was characterized using elemental analysis, and Fourier transform infrared (FT-IR) and solid state NMR spectroscopy. The separation of positional isomers, phenylpropionic acids and some dansyl amino acids was achieved on the new stationary phase. Their retention behavior was compared with that on the native β-CD-bonded silica gel stationary phase. The results show that the introduction of L-tyrosine to β-CD leads to enhancement of the retention of solutes such as p-nitrophenol and dansyl amino acids.

High performance liquid chromatography with cyclodextrin and calixarene macrocycle bonded silica stationary phases for separation of steroids

Beta-cyclodextrin, p-tert-butyl-calix[8]arene and chloropropyl bonded silica stationary phases have been prepared and were applied at the same time to develop a chromatographic procedure to separate steroids. In order to select the best type of stationary phase for the analysis, similar preparation processes of the two kinds of macrocycle stationary phases with the same spacer were adopted respectively. The chromatographic behaviors and retention mechanisms of the two kinds of macrocycle stationary phases for steroids were systematically studied and compared with those of chloropropyl bonded silica and ODS. The effect of mobile phase variables, such as methanol content, pH value of buffer, ionic strength and buffer composition on chromatographic behaviors was investigated. The results showed that the retention mechanisms of the four stationary phases for steroids were obviously different, and excellent separation was achieved on beta-cyclodextrin bonded silica stationary phase (beta-CD-BS), as a consequence of the structure and the properties of the stationary phase. The retention process on beta-CD-BS exhibited inclusion complexation, hydrogen-bonding and weak hydrophobic interaction, while for p-tert-butyl-calix[8]arene bonded silica stationary phase (CBS), pi-pi and hydrogen-bonding besides hydrophobic interaction played an important role.

Characterization and Evaluation of Magnesia-Zirconia Supports for Normal-Phase Liquid Chromatography

SummaryA new packing based on a magnesia-zirconia composite was synthesized as rigid microparticles (4–6 μm) by a sol-gel process. The magnesia-zirconia composite exhibits a larger specific surface area, larger specific pore volume, better pore connectivity and more uniform pore size distribution than pure zirconia prepared under the same conditions. The chromatographic performance of magnesia-zirconia and zirconia packings in normalphase HPLC was evaluated using binary mobile phases (dichloromethane/cyclohexane, chloroform/cyclohexane and isopropanol/cyclohexane) and acidic, neutral and basic compounds as solutes. The efficiency of columns packed with the magnesia-zirconia composite was higher than that of zirconia.

Study on the chromatographic behavior of water-soluble vitamins on p-tert-butyl-calix[8]arene-bonded silica gel stationary phase by HPLC

In this paper, the chromatographic behavior of some water-soluble vitamins was studied on a new p-tert-butyl-calix[8]arene-bonded silica gel stationary phase (CABS, 5mum particle size, the bonded amount 0.071mmolg(-1)) by using vitamin standards as probes for HPLC. The comparative study of the separation of these compounds was done by using CABS and ODS as stationary phases under the same chromatographic conditions. The better separation of six vitamins including: B(1), B(2), B(6), B(12), C, and nicotinic acid (B(5)), on CABS can be achieved by using isocratic mode with methanol-phosphate buffer (25:75, (v/v)) as mobile phase within 20min. The results show that the calix[8]arene-bonded phase exhibits high selectivity for water-soluble vitamins. We found that the elution order of B(2) (12.08min) and B(12) (16.42min) on CABS was very different from that of B(12) (7.76min) and B(2) (18.47min) on ODS, which indicate that different retention mechanisms exist in the chromatographic processes of the two stationary phases. According to the chromatographic data, it can be concluded that various chromatographic retention mechanisms are responsible for the separation of above compounds on CABS, such as hydrophobic interaction, hydrogen bonding interaction, and pi-pi interaction. The new packing has two advantages over ODS. On one hand, the polar and ionized analytes, such as C and B(5), exhibited stronger affinities to CABS because of hydrogen bonding interaction. On the other hand, the retention of B(2) and B(12) became shorter on CABS with weaker hydrophobicity in comparison with ODS. The new material exhibits the promising application in the separation of water-soluble vitamins.

Preparation and evaluation ofp-tert-butyl-calix[4]arene-bonded silica stationary phases for high performance liquid chromatography

SummaryA new method is proposed for preparation of ap-tert-butyl-calix[4]arene-bonded silica stationary phase. The chemically modifiedp-tert-butyl-calix[4]arene is attached to silica gel via the silane coupling reagent γ-(ethylenediamino)-propyl-triethoxyl-silane. The bonded phase has been characterized by29Si and13C cross polarization/magic angle spinning solid-state nuclear magnetic spectrometry. The retention behavior of polycyclic aromatic hydrocarbons (PAHs), nucleosides and bases has been investigated on the bonded phase in the reversed-phase mode.

HPLC separation of positional isomers on a dodecylamine-N, N-dimethylenephosphonic acid modified zirconia stationary phase

The chromatographic performance of a new zirconia stationary phase (DPZ) modified with dodecylamine-N,N-dimethylenephosphonic acid (DDPA) is studied by using positional isomers as probes. The DDPA modified zirconia via one phosphonic group has a polar inner-layer and a non-polar outer-layer on its surface. The alkyl chain of outer-layer provides the hydrophobic interaction, while the polar inner-layer that consists of an amine group and a free phosphonic group provided dipolar and ion-exchange/columbic repellent interaction sites. The effects of methanol content, ionic strength and pH of mobile phase on capacity factors of the solutes are studied in detail, and baseline separations of toluidine, nitroaniline, aminophenol, dihydroxybenzene, and nitrophenol isomers were achieved on the new zirconia stationary phase. In addition, retention mechanism of the isomers on the DDPA-modified zirconia stationary phase is also proposed.