Co-reporter:Hui Xu, Zongqing Ding, Lili Lv, Dandan Song, Yu-Qi Feng
Analytica Chimica Acta 2009 Volume 636(Issue 1) pp:28-33
Publication Date(Web):16 March 2009
DOI:10.1016/j.aca.2009.01.028
A new dispersive liquid–liquid microextraction based on solidification of floating organic droplet method (DLLME-SFO) was developed for the determination of five kinds of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. In this method, no specific holder, such as the needle tip of microsyringe and the hollow fiber, is required for supporting the organic microdrop due to the using of organic solvent with low density and proper melting point. Furthermore, the extractant droplet can be collected easily by solidifying it in the lower temperature. 1-Dodecanol was chosen as extraction solvent in this work. A series of parameters that influence extraction were investigated systematically. Under optimal conditions, enrichment factors (EFs) for PAHs were in the range of 88–118. The limit of detections (LODs) for naphthalene, diphenyl, acenaphthene, anthracene and fluoranthene were 0.045, 0.86, 0.071, 1.1 and 0.66 ng mL−1, respectively. Good reproducibility and recovery of the method were also obtained. Compared with the traditional liquid-phase microextraction (LPME) and dispersive liquid–liquid microextraction (DLLME) methods, the proposed method obtained about 2 times higher enrichment factor than those in LPME. Moreover, the solidification of floating organic solvent facilitated the phase transfer. And most importantly, it avoided using high-density and toxic solvent in the traditional DLLME method. The proposed method was successfully applied to determinate PAHs in the environmental water samples. The simple and low-cost method provides an alternative method for the analysis of non-polar compounds in complex environmental water.
Co-reporter:Jun Yin, Bin Hu, Man He, Mingming Zheng and Yu-Qi Feng
Journal of Analytical Atomic Spectrometry 2009 vol. 24(Issue 1) pp:76-82
Publication Date(Web):24 Oct 2008
DOI:10.1039/B810442E
A novel method of polymer monolith microextraction (PMME) using a poly(acrylamide-vinylpyridine-N,N′-methylene bisacrylamide) (AA-VP-Bis) monolithic column combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of trace Cd, Tl, and Pb with Pd as chemical modifier has been proposed. Several factors that influence the microextraction efficiency including pH value, sample flow rate, extraction time, sample volume, eluent volume, and coexisting ions, were investigated and the optimal microextraction conditions were established. The chemical modification of Pd in ETV-ICP-MS has been studied and the results indicated that the pyrolysis temperature for the target analytes could be increased up to 600 °C and the signal intensities were increased by 4.1, 2.1, and 13.8 times for Cd, Tl, and Pb, respectively. Under the optimized conditions, with a consumption of 0.4 mL sample, the limits of detection (LODs) were 1.1, 0.5, and 0.2 ng L−1 for Cd, Tl, and Pb, and the relative standard deviations (RSDs) were 10.3, 9.7, and 9.2% (C = 0.05 µg L−1, n = 5) for Cd, Tl, and Pb, respectively. The proposed method was successfully applied to the determination of trace Cd, Tl, and Pb in human serum and urine samples, and the recovery for the spiked samples were in the range of 90–110%. In order to validate the proposed method, certified reference material of GBW09103 human urine was analyzed, and the determined values were in good agreement with the certified values. The poly(AA-VP-Bis) monolith can be used more than 40 times without decrease in the extraction efficiency.
Co-reporter:Lan-Ying Xu, Zhi-Guo Shi, Yu-Qi Feng
Microporous and Mesoporous Materials 2008 Volume 115(Issue 3) pp:618-623
Publication Date(Web):1 November 2008
DOI:10.1016/j.micromeso.2008.03.004
We have initiated a method for the synthesis of a carbon monolith with trimodal porous structure of macro/macro/mesopores by nano-casting and phase separation. In this method, a silica monolith was employed as the hard template. A mixture of styrene and divinylbenzene, in the presence of initiator and porogenic reagent (dodecanol), was filled into the void of the silica monolith template. After the subsequent polymerization, carbonization and removal of the silica template, a carbon monolith with bimodal perfusion pores was successfully prepared. The primary perfusion pores were resulted from the dissolution of the silica template and the secondary perfusion pores were originated from the phase separation in the polymerization. In addition to macropores, mesopores also existed in the skeletons of the carbon monolith. Such structure of the carbon monolith has been characterized by scanning electron microscopy, mercury porosimetry and nitrogen sorption.
Co-reporter:Fang Wei, Yu-Qi Feng
Talanta 2008 Volume 74(Issue 4) pp:619-624
Publication Date(Web):15 January 2008
DOI:10.1016/j.talanta.2007.06.030
Aristolochic acids (AAs) are commonly found in medicinal plants such as Radix aristolochiae and have been reported to cause acute hepatitis and end-stage renal failure. Hence, quantitative analysis and quality control for the plants containing AAs is of great importance. In this study, a novel macrocylcic molecule, cucurbit[7]uril (CB[7]) was employed as a modifier in capillary zone electrophoresis (CZE) for rapid determination of aristolochic acid I and II in medicinal plants. In similarity to other macrocyclic molecules, such as cyclodextrins (CDs), CB[7] can be used to manipulate selectivity in CE because it can form inclusion complexes with a variety of guest molecules. During the running process, CB[7] bears a positive charge in the pH range of 2.5–7.5 and can be adsorbed onto the inner wall of a fused-capillary, leading to a reversal of the electroosmotic flow (EOF). By applying a negative polarity, a rapid separation of AA-I and AA-II was achieved within 7 min using 100 mM phosphate buffer (pH 7.5) containing 3 mM CB[7] and 10% acetonitrile (v/v) as modifiers, due to the same directions of the EOF and the electrophoretic mobilities of the analytes. By applying electrokinetic injection with field-enhanced sample stacking, two kinds of aristolochic acids in four medicinal plants were successfully determined with high sensitivity, high separation efficiency, repeatability and recovery. The proposed method was also used to determine AA-I and AA-II in two slimming pills with complex matrix.
Co-reporter:Ming-Ming Zheng, Bo Lin, Yu-Qi Feng
Journal of Chromatography A 2007 Volume 1164(1–2) pp:48-55
Publication Date(Web):14 September 2007
DOI:10.1016/j.chroma.2007.07.020
An octyl-functionalized hybrid silica monolithic column was developed for in-tube solid-phase microextraction (SPME) to perform on-line preconcentration coupled to capillary high-performance liquid chromatography (μHPLC) analysis. A hybrid silica monolithic column functionalized with octyl groups was conveniently synthesized by a two-step acid/base-catalyzed hydrolysis/co-condensation of tetraethoxysilane (TEOS) and n-octyltriethoxysilane (C8-TEOS). The size of through-pores as well as the carbon content can be adjusted by changing the ratio of TEOS to C8-TEOS in the polymerization mixture. The extraction characteristics of the monolithic column prepared under optimized fabrication conditions were studied by using polycyclic aromatic hydrocarbons (PAHs) as the analytes. The sample volume that could be injected into the system was increased up to 1 mL with simultaneous increase of column efficiency, when hybrid silica monolithic column was used as a precolumn. Good linear calibration curves (R > 0.999) were obtained, and the limits of detection (signal-to-noise ratio, S/N = 3) for the analytes were found to be between 2.4 and 8.1 ng/mL with a UV absorbance detector, which are 299–456 times lower than those obtained without preconcentration. The column-to-column RSD values were 1.3–8.0% for recoveries of PAHs investigated.
Co-reporter:Ying Wang;Yi Wen
Journal of Separation Science 2007 Volume 30(Issue 17) pp:2874-2880
Publication Date(Web):10 OCT 2007
DOI:10.1002/jssc.200700321
A hydroxylated poly(glycidyl methacrylate-co-ethylene dimethacrylate) (GMA-co-EDMA) monolithic capillary was prepared for polymer monolith microextraction (PMME). Coupled to HPLC with UV detection, this extraction medium was successfully applied to establish a simple and fast method for the analysis of clenbuterol (CLB) in urine. To obtain optimum extraction performance, the effects of pH value and ionic strength of the sample matrix on extraction efficiency were investigated. The linearity of the method was evaluated over a concentration range of 10–2000 ng/mL and the correlation coefficient (R2 value) was 0.9985. The detection limit and quantification limit were 2.3 and 7.7 ng/mL, respectively. Good reproducibility of the method was obtained, yielding the intra- and interday RSDs less than 5.1 and 9.1%, respectively. Moreover, the hydroxylated poly(GMA-co-EDMA) monolithic capillary exhibited good preparation reproducibility and long-term extraction life. When applied to the determination of CLB in urine samples, an effective removal of interfering compounds was achieved and recoveries were in the range of 87.6–106%. The determination of CLB from one real sample including pretreatment, extraction, and analysis could be finished within 30 min.
Co-reporter:Qiong-Wei Yu;Ting Li;Bo Lin
Journal of Separation Science 2007 Volume 30(Issue 6) pp:804-812
Publication Date(Web):20 MAR 2007
DOI:10.1002/jssc.200600336
A novel bovine serum albumin (BSA)-modified magnesia-zirconia stationary phase was prepared using the sodium salt of cis-(3-methyloxiranyl)phosphonic acid (fosfomycin) as spacer and glutaraldehyde as coupler. Baseline separation of six derivatized amino acids (DNB-Leu, Dansyl-Val, etc.) was achieved on this column using ammonium acetate buffer-isopropanol mobile phase at a flow rate of 1.0 mL/min. The effects of mobile phase composition, eluent pH value, column temperature, and flow rate on the retention and separation of chiral compounds were also investigated. The BSA chiral stationary phase (BSA-CSP) was relatively stable under experimental conditions. The coupling reaction in this method was mild, reliable, and reproducible; thus it was also suitable for the immobilization of various biopolymers with amino groups in the preparation of chromatography stationary phases.
Co-reporter:Lan-Ying Xu, Zhi-Guo Shi, Yu-Qi Feng
Microporous and Mesoporous Materials 2007 Volume 98(1–3) pp:303-308
Publication Date(Web):5 January 2007
DOI:10.1016/j.micromeso.2006.09.020
In this paper, bi-continuous silica monolith with highly ordered mesopores and tunable through pores (macropores or macro channels) has been successfully synthesized through nanocasting method. The starting urea formaldehyde (UF) resin, which is hydrophilic and contains adjustable through pores in micrometer scale, was for the first time used as a hard template in nanocasting. The silica replica has the same macroscopic morphology and macropore structure as the starting UF resin template, indicating that the macropores in silica monolith could also be adjusted. More interestingly, long-range ordered domains with highly ordered mesopores of hexagonal arrays existed in the frameworks of the silica monolith.
Co-reporter:Qiong-Wei Yu, Jun Yang, Bo Lin, Yu-Qi Feng
Analytica Chimica Acta 2006 Volume 559(Issue 1) pp:79-88
Publication Date(Web):10 February 2006
DOI:10.1016/j.aca.2005.11.076
A novel method was proposed for the preparation of pyrenebutyric acid-modified magnesia–zirconia stationary phases. Pyrenebutyric acid was grafted to magnesia–zirconia composites with different pore sizes via the sodium salt of cis-(3-methyloxiranyl)phosphonic acid (fosfomycin) as spacers. Aminated fosfomycin was first absorbed onto the surface of magnesia–zirconia composites during the preliminary step to provide amino and hydroxy reactive sites. And then the pyrenebutyric acid was covalently attached to the amine or hydroxyl groups via amide or ester bonds. The resulting stationary phases were characterized by elemental analysis, diffused reflectance FT-IR, nitrogen adsorption analysis and 13C solid state NMR spectra. The HPLC separation of fullerenes on the new stationary phases with different pore sizes was also investigated. The chromatographic performance showed a dependence on the pore size of the magnesia–zirconia matrix. Little retention of fullerenes was observed on the stationary phase with pore sizes about 4.5 nm. However, on the modified magnesia–zirconia with pore sizes about 10 nm, selectivity factors (α) for C70/C60 separation were determined to be 1.76, 2.29, 2.41, 3.10, with carbon disulfide, chlorobenzene, xylene and toluene as mobile phases, respectively. And the high solubility of fullerenes in these solvents dramatically increased the overall potential with regard to preparative fullerene purification. Among the reported stationary phases with pyrene ligands, the pyrenebutyric acid-modified magnesia–zirconia (PYB-F-(ZrO2–MgO)) with larger pore sizes exhibited the best selectivity for fullerenes. The thermodynamic and kinetic behavior of fullerenes was also examined.
Co-reporter:Yi Wen, Bing-Sheng Zhou, Ying Xu, Shi-Wei Jin, Yu-Qi Feng
Journal of Chromatography A 2006 Volume 1133(1–2) pp:21-28
Publication Date(Web):10 November 2006
DOI:10.1016/j.chroma.2006.08.049
A simple, rapid and sensitive on-line method for simultaneous determination of four endocrine disruptors (17β-estradiol, estriol, bisphenol A and 17α-ethinylestradiol) in environmental waters was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with fluorescence detection (FLD). A poly(acrylamide-vinylpyridine-N,N′-methylene bisacrylamide) monolith, synthesized inside a polyether ether ketone (PEEK) tube, was selected as the extraction medium. To achieve optimum extraction performance, several parameters were investigated, including extraction flow-rate, extraction time, and pH value, inorganic salt and organic solvent content of the sample matrix. By simply filtered with nylon membrane filter and adjusting the pH of samples to 6.0 with phosphoric acid, the sample solution then could be directly injected into the device for extraction. Low detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method were achieved in the range of 0.006–0.10 ng/mL and 0.02–0.35 ng/mL from spiked lake waters, respectively. The calibration curves of four endocrine disruptors showed good linearity ranging from quantification limits to 50 ng/mL with a linear coefficient R2 value above 0.9913. Good method reproducibility was also found by intra- and inter-day precisions, yielding the RSDs less than 12 and 9.8%, respectively. Finally, the proposed method was successfully applied to the determination of these compounds in several environmental waters.
Co-reporter:Zhi-Guo Shi, Li Xu, Shi-Lu Da, Yu-Qi Feng
Microporous and Mesoporous Materials 2006 Volume 94(1–3) pp:34-39
Publication Date(Web):8 September 2006
DOI:10.1016/j.micromeso.2006.03.017
Zirconia composite with varying amounts of magnesia was prepared by sol–gel technique. A series of carefully designed experiments were conducted to obtain data needed to assist the comparison of the resultant composites in terms of surface area, pore diameter, pore volume, crystalline phase and their stability to temperature. The results show that the presence of magnesia can be helpful for stabilization of zirconia composite, and different amounts of magnesia doping result in ultimate composite materials with different properties. We can tailor the structural and surface characteristics through changing the reactant ratio of magnesium chloride to zirconyl chloride to cater for its various applications, such as catalysts, chromatographic packings and so on.
Co-reporter:Qiong-Wei Yu;Zhi-Guo Shi;Bo Lin;Yan Wu
Journal of Separation Science 2006 Volume 29(Issue 6) pp:837-843
Publication Date(Web):13 MAR 2006
DOI:10.1002/jssc.200500445
Two charge-transfer stationary phases were prepared by immobilizing p-nitrobenzoic acid and naphthyl acetic acid onto silica. The nitrophenyl moiety and the naphthyl moiety were grafted to silica gel through the spacer of aminoalkyl silanes. The HPLC separation of C60, C70, and higher fullerenes on the new stationary phases was also studied. The influence of mobile phase and column temperature on the separation of C60 and C70 was examined, respectively. The retentions of C60 and C70 on the two stationary phases increased with decreasing toluene content in the mobile phase or with increasing column temperature. Higher fullerenes can be separated well using toluene as the mobile phase on the stationary phase of p-nitrobenzoic acid-bonded silica.
Co-reporter:Jing Nie;Qun Zhao;Jingfang Huang;Bingren Xiang
Journal of Separation Science 2006 Volume 29(Issue 5) pp:650-655
Publication Date(Web):14 MAR 2006
DOI:10.1002/jssc.200500370
A poly(methacrylic acid-ethylene glycol dimethacrylate, MAA-EGDMA) monolithic capillary was used for the direct and on-line extraction of telmisartan from Sprague-Dawley rat tissue (heart, kidney, and liver) homogenates. Under optimized conditions, the tissue homogenates were simply diluted with a mixture of phosphate buffer (pH 2)/ACN (90 : 8 v/v), and then injected for extraction only after centrifugation and filtration. Coupled to HPLC with fluorescence detection, the method was linear over the range of 1.25–1500 ng/g for telmisartan in heart and kidney, 12.5–15 000 ng/g in liver with correlation coefficients over 0.9992. The detection limits were found to be in the range from 0.24 to 1.8 ng/g. RSDs for intra- and inter-day ranged from 1.2 to 8.1%. The determination of telmisartan in treated rat tissues was achieved by using the proposed method.
Co-reporter:Zhi-Guo Shi, Yu-Qi Feng, Li Xu, Shi-Lu Da, Yun Liu
Materials Chemistry and Physics 2006 Volume 97(2–3) pp:472-475
Publication Date(Web):10 June 2006
DOI:10.1016/j.matchemphys.2005.08.049
A carbon monolith was prepared via a templating method by using an appropriate silica monolith as the hard template. The resultant carbon monolith exhibits hierarchical structure, full interconnect porosity, high mechanical strength and bimodal mesopores with narrow pore size distributions.
Co-reporter:Yi Fan, Yu-Qi Feng, Zhi-Guo Shi, Jian-Bo Wang
Analytica Chimica Acta 2005 Volume 543(1–2) pp:1-8
Publication Date(Web):6 July 2005
DOI:10.1016/j.aca.2005.04.024
Ordered mesoporous silica coating modified with octadecyl groups was introduced into the capillary for in-tube solid phase microextraction coupled to high performance liquid chromatography (in-tube SPME–HPLC). Improved extraction efficiency was demonstrated for the capillary when comparing with those of non-mesoporous structural coatings. The coatings produced by using different structure directing agents were compared and the highest sample capacity was achieved with the most ordered mesostructural coating.The capillary with the octadecyl modified ordered mesoporous silica coating was used to perform in-tube SPME–HPLC analysis of bisphenol A in water samples. Tap water and Donghu lake (Wuhan, China) water samples spiked with bisphenol A were tested under optimized conditions with the linearity ranged from 0.01 to 1 μg/mL and the detection limits were found to be 2.8 and 2.9 ng/mL, respectively. The precision of the method was satisfactory with the R.S.D. values smaller than 2.7%.
Co-reporter:Hai-Bo He, Yu-Qi Feng, Qu-Li, Shi-Lu Da, Zhi-Xiong Hu
Analytica Chimica Acta 2005 Volume 542(Issue 2) pp:268-279
Publication Date(Web):29 June 2005
DOI:10.1016/j.aca.2005.04.010
Three n-octadecylphosphonic acid-modified magnesia–zirconia reversed stationary phases (C18PZM) are prepared via the strong Lewis base interactions between organophosphonate and magnesia–zirconia composite. And two of them are end-capped by using trimethylchlorosilane as end-capping agent in different procedures. Stability studies at extreme high pH conditions (pH 9–12) show that both the non-endcapped and endcapped columns are quite stable at pH 12 mobile phase. The reversed-phase liquid chromatographic behavior of three C18PZM stationary phases are comparatively investigated in detail using a variety of basic compounds as probes. The retention of basic compounds on the three phases is studied over a wide range of pHs. And the possible retention mechanisms of basic compounds on the three stationary phases are discussed. The results show that the basic solutes retain by a hydrophobic and cation-exchange interaction mixed mechanism on three stationary phases when they are operated in eluents at pH values near to the pKa of the Brönsted conjugate acid form of the analyte, suggesting that inherent zirconol groups on ZM are not expected to interact with bases via cation-exchange interaction at lower pH. Nonetheless, the non-endcapped phase differs markedly from the edncapped ones in retention and selectivity of basic solutes using eluents at pH 4.1, implying a complex retention mechanism at this pH. The cation-exchange sites under such conditions are more likely due to the adsorbed Lewis base anionic buffer constituents (acetate) on accessible ZM surface sites than the chemisorbed phosphonate. Although the three phases exhibit very similar chromatographic behavior with eluents at pH 10.1, and show in general satisfactory separation of basic compounds and alkaloids studied, the performance for a specific analyte, however, differs largely from column to column.
Co-reporter:Qiong-Wei Yu, Yu-Qi Feng, Zhi-Guo Shi, Jun Yang
Analytica Chimica Acta 2005 Volume 536(1–2) pp:39-48
Publication Date(Web):22 April 2005
DOI:10.1016/j.aca.2004.12.055
Spherical particles (6–8 μm) of magnesia–zirconia composite were prepared by means of sol–gel process. The composites were modified with 2,4,6-trinitrophenol and pyrenebutyric acid, respectively, and then used as charge-transfer stationary phases. The resulting stationary phases were characterized by elemental analysis, diffused reflectance FT-IR, nitrogen adsorption analysis and solid state NMR. The separation of C60, C70 and higher fullerenes was investigated on the two stationary phases. The influence of the mobile phase (toluene–cyclohexane) with different composition and the column temperature on the separation of C60 and C70 was examined, respectively. The retention time of C60 and C70 on the two stationary phases increases with decreasing toluene content in the mobile phase or with increasing the column temperature. Higher fullerenes can be separated well at 90 °C using toluene as the mobile phase on the 2,4,6-trinitrophenol modified magnesia–zirconia. Based on the results of column loading capacity test, the magnesia–zirconia modified with 2,4,6-trinitrophenol and pyrenebutyric acid are probably considered as potential materials for the separation of fullerenes in large amounts.
Co-reporter:Hai-Bo He, Yu-Qi Feng, Shi-Lu Da, Zhong-Hua Wang
Analytica Chimica Acta 2005 Volume 551(1–2) pp:213-221
Publication Date(Web):17 October 2005
DOI:10.1016/j.aca.2005.07.022
The cation-exchange and Lewis-base interactions of a n-octadecylphosphonic acid-modified magnesia–zirconia (C18PZM) stationary phase have been studied in greater detail than previous studies, which are characterized by the chromatography of some basic drugs of high pKa and some hard Lewis base analytes, respectively. The effect of mobile phase constituents such as pH, type of buffer and buffer concentration on the surface chemistry properties on C18PZM are elucidated. The results show that at an intermediate pH, the cation-exchange sites are due to both the chemisorbed phosphonate and the adsorbed buffer anion, i.e. acetate, at the hard Lewis acid sites on the C18PZM phase; at high pH, the cation-exchange interactions mainly result from the chemisorbed phosphonate rather than the inherent zirconol groups. The chromatography of the hard Lewis base analytes indicates that a strong Lewis acid–base interaction still exists on C18PZM even in the presence of Lewis base buffer (such as acetate or phosphate) in the mobile phase or a high-pH eluents is used. Moreover, the chemisorbed n-octadecylphosphonic acid (C18P) is found to slowly bleed out of the C18PZM column when exposed to a phosphate buffer. As expected, the resulting mobile-phase phosphate modified C18PZM column (p-C18PZM) exhibits significantly stronger cation-exchange interactions towards the test basic solutes than the “original” C18PZM column. And the p-C18PZM column demonstrates a tremendous improvement on the chromatography of the Lewis base analytes over the “original” C18PZM column. An approach designed to overcome the Lewis acid sites problem by attaching methylphosphonic acid (MPA) onto the C18PZM column, however, is not successful in improving the chromatography of the troublesome Lewis base solutes.
Co-reporter:Yi Fan, Min Zhang, Shi-Lu Da and Yu-Qi Feng
Analyst 2005 vol. 130(Issue 7) pp:1065-1069
Publication Date(Web):29 Apr 2005
DOI:10.1039/B502311D
A method for the determination of endocrine disruptors, bisphenol A and 17α-ethinylestradiol, in environmental water samples was developed using in-tube solid-phase microextraction followed by liquid chromatography and fluorescence detection. A poly(acrylamide-vinylpyridine) monolithic capillary column was applied as the extraction media in view of its greater phase ratio than open-tubular capillaries and thus higher extraction efficiency. After optimizing the extraction conditions, bisphenol A and 17α-ethinylestradiol were extracted directly from water samples in a wide dynamic linear range of 0.5–1000 ng mL−1, with the detection limits obtained as 0.064 and 0.12 ng mL−1, respectively. The precision of the method was satisfactory with the intraday and interday RSD values smaller than 7.2%. Environmental water samples of different sources were successfully analyzed with the presented method and the monolithic capillary was proved to be robust and reusable in analyzing real water samples.
Co-reporter:Hai-Bo He;Shi-Lu Da;Zhi-Xiong Hu;Li Qu
Journal of Separation Science 2005 Volume 28(Issue 13) pp:1577-1586
Publication Date(Web):15 AUG 2005
DOI:10.1002/jssc.200500042
The high-performance liquid chromatographic behavior of some basic drugs was studied on a n-octadecylphosphonic acid modified magnesia-zirconia (C18PZM) stationary phase. The effect of mobile phase variables such as methanol content, ionic strength, and pH on their chromatographic behavior was investigated. The retention mechanism of basic drugs on the stationary phase was elucidated. The results indicate that both hydrophobic and cation-exchange interactions contribute to solute retention under most chromatographic conditions. The inherent Brönsted-acid sites and also the adsorbed Lewis base anionic buffer constituents on accessible ZM surface Lewis acid sites play a role in the retention of ionized solutes by cation-exchange interaction. However, especially at high mobile phase pH, the retention of basic drugs depends mainly on hydrophobic interactions between solutes and support. Separations of the basic drugs on the C18PZM phase by a predominantly reversed-phase retention mode were very promising. The mixed-mode retention feature on this phase, as a result of the adsorbed Lewis base anionic buffer constituents acting as sites for cation-exchange, could also be very useful, e.g. for enhancing the chromatographic selectivity of such analytes. The C18PZM seems to be an excellent alternative to silica-based reversed-phase stationary phase for the separation of strongly basic solutes.
Co-reporter:Jing Nie, Min Zhang, Yi Fan, Yi Wen, Bingren Xiang, Yu-Qi Feng
Journal of Chromatography B 2005 Volume 828(1–2) pp:62-69
Publication Date(Web):15 December 2005
DOI:10.1016/j.jchromb.2005.09.015
A poly (methacrylic acid-ethylene glycol dimethacrylate, MAA-EGDMA) monolithic capillary was used for the in-tube solid-phase microextraction (in-tube SPME) of several angiotensin II receptor antagonists (ARA-IIs) from human plasma and urine. Under the optimized extraction condition, the protein component of the biological sample was flushed through the monolithic capillary, while the analytes were successfully trapped. Coupled to HPLC with fluorescence detection, this on-line in-tube SPME method was successfully applied for the determination of candesartan, losartan, irbesartan, valsartan, telmisartan, and their detection limits were found to be 0.1–15.3 ng/mL and 0.1–15.2 ng/mL in human plasma and urine, respectively. The method was linear over the range of 0.5–200 ng/mL for telmisartan, 5–2000 ng/mL for candesartan and irbesartan, 10–2000 ng/mL for valsartan, and 50–5000 ng/mL for losartan with correlation coefficients being above 0.9985 in plasma sample and above 0.9994 in urine sample. The method reproducibility was evaluated at three concentration levels, resulting in the R.S.D. <7%. The poly (MAA-EGDMA) monolithic capillary was demonstrated to be robust and biocompatible by using direct injections of biological samples.
Co-reporter:Yi Fan, Yu-Qi Feng, Shi-Lu Da, Zhong-Hua Wang
Talanta 2005 Volume 65(Issue 1) pp:111-117
Publication Date(Web):15 January 2005
DOI:10.1016/j.talanta.2004.05.040
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 β-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 28 ng/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.
Co-reporter:Wei-Nong Zhang, Zhi-Xiong Hu, Yan Liu, Yu-Qi Feng, Shi-Lu Da
Talanta 2005 Volume 67(Issue 5) pp:1023-1028
Publication Date(Web):31 October 2005
DOI:10.1016/j.talanta.2005.04.039
The interactions between drug molecules and membrane were studied using the new chromatography stationary phase of liposome coated zirconia–magnesia. log Ks(ZrO2–MgO) on this new chromatography for some drugs, compared with that on liposome coated silica chromatography and other reported data, fair correlations were observed between them when excluding effect of special adsorption. log Ks(ZrO2–MgO) values for barbitalum, diazepam, benzene, benzocaine and toluene correlated well with corresponding values on liposome coated silica chromatography (R = 0.99778, P < 0.001; R = 0.98229, P < 0.003; R = 0.9985, P < 0.0001; R = 0.99925, P < 0.0001, pH value of mobile phase at pH 7.4, 7.0, 6.4 and 5.4, respectively). They also correlated well with the literature data on immobilized artificial membrane chromatography (R = 0.99999, P < 0.004 at pH 7.4) and liposome chromatography (R = 0.99994, P < 0.008) for procaine, lidocaine and bupivacaine. Liposome coated zirconia–magnesia chromatography can thus be used for studying drug–membrane interaction and prediction of drug absorption as another liposome chromatography method.
Co-reporter:Hai-Bo He, Wei-Nong Zhang, Shi-Lu Da, Yu-Qi Feng
Analytica Chimica Acta 2004 Volume 513(Issue 2) pp:481-492
Publication Date(Web):25 June 2004
DOI:10.1016/j.aca.2004.03.034
A new stationary phase of magnesia–zirconia composite matrix for high-performance liquid chromatography was first prepared by modification of β-cyclodextrin (β-CD) via fosfomycin as a spacer. Various modification procedures were attempted for achievement of successful modification. The modified composite was characterized by using coloration, elemental analysis, diffused reflectance FT-IR, surface area and pore size distribution. The separation of alkylbenzenes, polycyclic aromatic hydrocarbons, positional isomers of some acidic, basic and amphoteric disubstituted benzenes was studied on the new stationary phase. The effect of pH and methanol content in the mobile phase on retention and separation selectivity for the positional isomers were investigated. The chromatographic performance of CD modified magnesia–zirconia was compared with fosfomycin modified magnesia–zirconia as intermediate material and bare magnesia–zirconia as raw material. The results show that various retention mechanisms such as hydrophobicity, inclusion complexation and hydrogen bond interaction exist in the chromatography process of the packing modified with CD. The β-CD played the major role in the chromatographic property of this new stationary phase. The modified magnesia–zirconia exhibits superiority of separation for basic aromatics and high stability above pH 11.
Co-reporter:Li Xu, Yu-Qi Feng, Zhi-Guo Shi, Shi-Lu Da, Yao-Yao Ren
Journal of Chromatography A 2004 Volume 1028(Issue 1) pp:165-170
Publication Date(Web):27 February 2004
DOI:10.1016/j.chroma.2003.11.085
In this work, an ordered mesoporous titania film was introduced to coat a capillary by means of the sol–gel technique. Its electroosmotic flow (EOF) property was investigated in a variety of nonaqueous media (methanol, formamide and N,N′-dimethylformamide and mixtures of methanol and acetonitrile). The titania-coated capillary exhibited a distinctive EOF behavior, the direction and magnitude of which were strongly dependent on various parameters such as the solvent composition, apparent pH (pH*) and the electrolytes. The nonaqueous capillary electrophoresis separation of several alkaloids was investigated in the positively charged titania-coated capillary. Comparison of separation between coated and uncoated capillaries under optimal nonaqueous conditions was also carried out.
Co-reporter:Zhi-Guo Shi, Yu-Qi Feng, Li Xu, Shi-Lu Da, Yao-Yao Ren
Microporous and Mesoporous Materials 2004 Volume 68(1–3) pp:55-59
Publication Date(Web):8 March 2004
DOI:10.1016/j.micromeso.2003.12.009
Silica monolith with textural pores and ordered mesopores was fabricated through a sol–gel process by using triblock polymer of F127 as pore directing reagent. In the reaction, F127 demonstrated its dual functions––phase separation inducing function and template function. The former resulted in co-continuous structure of silica skeletons and textural pores, while the latter led to the formation of ordered mesopores.
Co-reporter:Si-Min Liu, Li Xu, Cheng-Tai Wu, Yu-Qi Feng
Talanta 2004 Volume 64(Issue 4) pp:929-934
Publication Date(Web):15 November 2004
DOI:10.1016/j.talanta.2004.04.012
In this paper, perhydroxyl-cucurbit[6]uril ((HO)12CB[6]) was, for the first time, grafted to silica gel as a hydrophilic-interaction chromatographic stationary phase. Several alkaloids were used as probes to investigate the retention mechanism on the new stationary phase. The effect of mobile phase variables such as acetonitrile content, ionic strength and pH on their chromatographic behavior was investigated. The results indicate that the stationary phase behaves as a hydrophilic-interaction chromatographic packing. Finally, several alkaloids were separated on the stationary phase.
Co-reporter:Z.-G Shi, Y.-Q Feng, L Xu, M Zhang, S.-L Da
Talanta 2004 Volume 63(Issue 3) pp:593-598
Publication Date(Web):17 June 2004
DOI:10.1016/j.talanta.2003.11.030
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 80,000 m−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.
Co-reporter:Li-Feng Yao, Hai-Bo He, Yu-Qi Feng, Shi-Lu Da
Talanta 2004 Volume 64(Issue 1) pp:244-251
Publication Date(Web):8 September 2004
DOI:10.1016/j.talanta.2004.02.019
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.
Co-reporter:Weinong Zhang, Haibo He, Yuqi Feng, Shilu Da
Journal of Chromatography B 2003 Volume 798(Issue 2) pp:323-331
Publication Date(Web):25 December 2003
DOI:10.1016/j.jchromb.2003.10.005
Natural phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were separated and purified from soybean degummed oil residues in this work. Crude PC and PE were first separated from degummed oil residues by extraction with 95% ethanol, and then the crude PC and PE were used as raw materials to prepare high purity PC and PE by using column chromatography of silica gel (100–200 mesh) with different eluents and elution modes. The high purity PC (content >90%) was obtained from the crude PC by using isocratic elution with methanol as eluent. Compared with the methods reported by using isocratic elution with mixed solvents as eluent or gradient elution, the procedure proposed exhibits low cost and industry potentialities because of some advantages, such as operation simplicity, cheap equipment and solvent to be recovered easily. The purity of the PE product prepared from the crude PE was more than 75%. The gradient elution was preferable to isocratic elution for reducing the elution time and eluent consumption when to prepare PE from the crude PE. The effects of loading amount and the flow-rate on separation efficiency were also investigated. For obtaining high separation efficiency, the loading amount should be less than 2.0 g crude PC or PE/100 g silica gel, and the flow-rate should be controlled under 4 ml/min for crude PC and 3 ml/min for crude PE, respectively.
Co-reporter:Yu-Xiu Xiao, Xiang-Zhu Xiao, Yu-Qi Feng, Zhong-Hua Wang, Shi-Lu Da
Talanta 2002 Volume 56(Issue 6) pp:1141-1151
Publication Date(Web):8 April 2002
DOI:10.1016/S0039-9140(01)00667-1
The high-performance liquid chromatographic behavior of some sulfonamides and quinolones was studied on a p-tert-butyl-calix[6]arene-bonded silica gel stationary phase. The effect of mobile phase variables such as methanol content, ionic strength and pH on their chromatographic behavior was investigated. The retention behavior of sulfonamides on the stationary phase was compared with that on both Zorbax C18-bonded silica gel and γ-(ethylenediamino)propyltriethoxylsilane-bonded silica gel (diamino-bonded phase). The retention mechanism of sulfonamides and quinolones on the stationary phase was also discussed. The results indicate that the stationary phase behaves as a reversed-phase packing and its separation selectivity is much better than that of not only Zorbax C18 phase but also diamino-bonded phase. Some sulfonamides and quinolones were separated on the stationary phase, but the separation of sulfonamides is far more successful.
Co-reporter:Min-Jie Xie, Yu-Qi Feng, Shi-Lu Da, Di-Ya Meng, Li-Wei Ren
Analytica Chimica Acta 2001 Volume 428(Issue 2) pp:255-263
Publication Date(Web):9 February 2001
DOI:10.1016/S0003-2670(00)01228-9
A novel magnesia–zirconia coating was fabricated inside fused-silica capillaries. The capillaries coated with magnesia–zirconia exhibited switchable electro-osmotic flow (EOF) whose magnitude and direction can be manipulated by changing the pH of running electrolyte. In Tris electrolyte at high pH (>5.2), the direction was from anode toward cathode, whereas at low pH (<5.2), the direction of EOF was reversed. The magnesia–zirconia coated capillary can be modified by SO42− and alkylphosphonate easily based on strong Lewis acid–base interaction. The separations of six basic compounds were compared on magnesia–zirconia coated capillary and SO42− modified magnesia–zirconia coated capillary under different conditions. It was found that the SO42− modified magnesia–zirconia coated capillary with reversed EOF in Tris–methanol (80/20, v/v) at pH 2.5 was suitable for the separation of the six basic compounds. For the alkylphosphonate modified magnesia–zirconia coated capillary, the alkyl moiety on the inner wall enabled it to separate polycyclic aromatic hydrocarbon (PAH). Six PAHs were separated on the alkylphosphonate modified magnesia–zirconia coated capillary with CH3CN+20 mmol/l Tris (25/75, v/v) as the mobile phase within 13 min. The magnesia–zirconia coated capillary was stable over a wide pH range.
Co-reporter:Min-Jie Xie;Shi-Lu Da
Journal of Separation Science 2001 Volume 24(Issue 1) pp:62-66
Publication Date(Web):31 JAN 2001
DOI:10.1002/1615-9314(20010101)24:1<62::AID-JSSC62>3.0.CO;2-1
Co-reporter:Y.-L. Hu, Y.-Q. Feng, J.-D. Wan, S.-L. Da, L. Hu
Talanta 2001 Volume 54(Issue 1) pp:79-88
Publication Date(Web):30 March 2001
DOI:10.1016/S0039-9140(00)00636-6
Porous ceria–zirconia composite with narrow particle size distribution and large specific surface area was synthesized by a sol–gel process. Chromatographic properties of the native supports was investigated in normal phase mode for the separation of test mixtures of basic, neutral and acidic compounds. The new packing material exhibited polar and basic properties, which are suitable for the separation of basic compounds. Lypophilic packing has been obtained by the modification of the ceria–zirconia with stearic acid, which exhibited strong hydrophobicity relative to the native packing. Therefore, the modified ceria–zirconia behaves as a reversed-phase packing material. Different selectivity towards basic compounds was observed on the new packing compared to the native ceria–zirconia and conventional ODS stationary phase.
Co-reporter:Yu-Ling Hu, Yu-Qi Feng, Qing-He Zhang, Shi-Lu Da
Talanta 1999 Volume 49(Issue 1) pp:47-52
Publication Date(Web):June 1999
DOI:10.1016/S0039-9140(98)00361-0
2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a sensitive photometric reagent for determination of zirconium, when fosfomycin is added, it can quantitatively replace 5-Br-PADAP by complexing with zirconium, thus, an indirect spectrophotometric method based on ligand exchange has been established. The detection wavelength is at 605 nm, and the apparent molar absorption coefficient was found to be 4.59×104 l mol−1 cm−1. Beer’s law is obeyed in the range of 0–28×10−6 M. The composition and stability constant of zirconium with 5-Br-PADAP and with fosfomycin has also been estimated. The proposed method is simple and reproducible, it was applicable to the analysis of fosfomycin from pharmaceutical manufacture.
Co-reporter:Jun Yin, Bin Hu, Man He, Mingming Zheng and Yu-Qi Feng
Journal of Analytical Atomic Spectrometry 2009 - vol. 24(Issue 1) pp:NaN82-82
Publication Date(Web):2008/10/24
DOI:10.1039/B810442E
A novel method of polymer monolith microextraction (PMME) using a poly(acrylamide-vinylpyridine-N,N′-methylene bisacrylamide) (AA-VP-Bis) monolithic column combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of trace Cd, Tl, and Pb with Pd as chemical modifier has been proposed. Several factors that influence the microextraction efficiency including pH value, sample flow rate, extraction time, sample volume, eluent volume, and coexisting ions, were investigated and the optimal microextraction conditions were established. The chemical modification of Pd in ETV-ICP-MS has been studied and the results indicated that the pyrolysis temperature for the target analytes could be increased up to 600 °C and the signal intensities were increased by 4.1, 2.1, and 13.8 times for Cd, Tl, and Pb, respectively. Under the optimized conditions, with a consumption of 0.4 mL sample, the limits of detection (LODs) were 1.1, 0.5, and 0.2 ng L−1 for Cd, Tl, and Pb, and the relative standard deviations (RSDs) were 10.3, 9.7, and 9.2% (C = 0.05 µg L−1, n = 5) for Cd, Tl, and Pb, respectively. The proposed method was successfully applied to the determination of trace Cd, Tl, and Pb in human serum and urine samples, and the recovery for the spiked samples were in the range of 90–110%. In order to validate the proposed method, certified reference material of GBW09103 human urine was analyzed, and the determined values were in good agreement with the certified values. The poly(AA-VP-Bis) monolith can be used more than 40 times without decrease in the extraction efficiency.
![L-Leucine, N-[[(1R,2R)-3-oxo-2-(2Z)-2-pentenylcyclopentyl]acetyl]-](http://img.cochemist.com/ccimg/120400/120330-91-8.png)
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![(5Z,8Z)-10-{(2R,3S)-3-[(2Z)-oct-2-en-1-yl]oxiran-2-yl}deca-5,8-dienoic acid](http://img.cochemist.com/ccimg/87200/87173-81-7.png)
![(5Z,8Z)-10-{(2R,3S)-3-[(2Z)-oct-2-en-1-yl]oxiran-2-yl}deca-5,8-dienoic acid](http://img.cochemist.com/ccimg/87200/87173-81-7_b.png)
![8-{(1S,5S)-4-Oxo-5-[(2Z)-2-penten-1-yl]-2-cyclopenten-1-yl}octano ic acid](http://img.cochemist.com/ccimg/85600/85551-10-6.png)
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![(5Z)-7-{(2R,3S)-3-[(2Z,5E)-undeca-2,5-dien-1-yl]oxiran-2-yl}hept-5-enoic acid](http://img.cochemist.com/ccimg/82900/82864-43-5.png)
![(5Z)-7-{(2R,3S)-3-[(2Z,5E)-undeca-2,5-dien-1-yl]oxiran-2-yl}hept-5-enoic acid](http://img.cochemist.com/ccimg/82900/82864-43-5_b.png)
![[2-(Triethoxysilyl)ethylthio]acetic acid](http://img.cochemist.com/ccimg/82800/82778-99-2.png)
![[2-(Triethoxysilyl)ethylthio]acetic acid](http://img.cochemist.com/ccimg/82800/82778-99-2_b.png)
![Glycine, N-(carboxymethyl)-N-[2-(2,6-dioxo-4-morpholinyl)ethyl]-](http://img.cochemist.com/ccimg/81400/81329-81-9.png)
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![5-Heptenoic acid,7-[3-(2,5-undecadien-1-yl)-2-oxiranyl]-](http://img.cochemist.com/ccimg/81300/81246-85-7.png)
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![6H-Benz[c]indeno[5,4-e]oxepin-6-one,1-[(1S,2S,3S,4R)-2,3-dihydroxy-1,4,5-trimethylhexyl]hexadecahydro-8,9-dihydroxy-10a,12a-dimethyl-,(1R,3aS,3bS,6aS,8S,9R,10aR,10bS,12aS)-](http://img.cochemist.com/ccimg/78900/78821-42-8.png)
![6H-Benz[c]indeno[5,4-e]oxepin-6-one,1-[(1S,2S,3S,4R)-2,3-dihydroxy-1,4,5-trimethylhexyl]hexadecahydro-8,9-dihydroxy-10a,12a-dimethyl-,(1R,3aS,3bS,6aS,8S,9R,10aR,10bS,12aS)-](http://img.cochemist.com/ccimg/78900/78821-42-8_b.png)
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![2-Pentenal,5-(methylthio)-2-[(methylthio)methyl]-](http://img.cochemist.com/ccimg/60000/59902-01-1_b.png)
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![Carbamic acid,N-[6-(phenylsulfonyl)-1H-benzimidazol-2-yl]-, methyl ester](http://img.cochemist.com/ccimg/54100/54029-20-8_b.png)
![Adenosine, N-[(2Z)-4-hydroxy-3-methyl-2-butenyl]-2-(methylthio)-](http://img.cochemist.com/ccimg/52100/52049-48-6.png)
![Adenosine, N-[(2Z)-4-hydroxy-3-methyl-2-butenyl]-2-(methylthio)-](http://img.cochemist.com/ccimg/52100/52049-48-6_b.png)
![2-Buten-1-ol, 2-methyl-4-[[2-(methylthio)-1H-purin-6-yl]amino]-, (Z)-](http://img.cochemist.com/ccimg/52100/52020-11-8.png)
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![7-beta-D-glucopyranosyl-N-[(2E)-4-hydroxy-3-methylbut-2-en-1-yl]-7H-purin-6-amine](http://img.cochemist.com/ccimg/38200/38165-56-9.png)
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![Benzenemethanol, 4-amino-3,5-dichloro-α-[[(1,1-dimethylethyl)amino]methyl]-](/data/chemimg/568900/37148-27-9_b.png)
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![L-Threonine, N-[[(9-b-D-ribofuranosyl-9H-purin-6-yl)amino]carbonyl]-](http://img.cochemist.com/ccimg/24800/24719-82-2.png)
![L-Threonine, N-[[(9-b-D-ribofuranosyl-9H-purin-6-yl)amino]carbonyl]-](http://img.cochemist.com/ccimg/24800/24719-82-2_b.png)
![2-[(2-sulfanylacetyl)amino]acetic Acid](http://img.cochemist.com/ccimg/21200/21115-85-5.png)
![2-[(2-sulfanylacetyl)amino]acetic Acid](http://img.cochemist.com/ccimg/21200/21115-85-5_b.png)
![N-{4-[(E)-2-(4-BROMOPHENYL)VINYL]PHENYL}ACETAMIDE](/data/chemimg/415000/20134-29-6.png)
![N-{4-[(E)-2-(4-BROMOPHENYL)VINYL]PHENYL}ACETAMIDE](/data/chemimg/415000/20134-29-6_b.png)
![1-[(2R,3R,4S,5R)-3,4-DIHYDROXY-5-(HYDROXYMETHYL)OXOLAN-2-YL]-4-(DIMETHYLAMINO)PYRIMIDIN-2-ONE](http://img.cochemist.com/ccimg/13100/13007-43-7.png)
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![Imidazo[4,5-d][1,3]diazepin-8-ol,3,4,7,8-tetrahydro-3-b-D-ribofuranosyl-, (8R)-](http://img.cochemist.com/ccimg/11100/11033-22-0.png)
![Imidazo[4,5-d][1,3]diazepin-8-ol,3,4,7,8-tetrahydro-3-b-D-ribofuranosyl-, (8R)-](http://img.cochemist.com/ccimg/11100/11033-22-0_b.png)
![2,9,10-trimethoxy-5,6-dihydroisoquinolino[2,1-b]isoquinolin-7-ium-3-ol](http://img.cochemist.com/ccimg/3700/3621-38-3.png)
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![1,2,2-TRIMETHYL-3-[(2-OXOTETRAHYDRO-3-THIOPHENYL)CARBAMOYL]CYCLOP<WBR />ENTANECARBOXYLIC ACID](http://img.cochemist.com/ccimg/3000/2922-24-9.png)
![1,2,2-TRIMETHYL-3-[(2-OXOTETRAHYDRO-3-THIOPHENYL)CARBAMOYL]CYCLOP<WBR />ENTANECARBOXYLIC ACID](http://img.cochemist.com/ccimg/3000/2922-24-9_b.png)
![(1S,2R,3S,4aR,4bR,7R,9aR,10S,10aR)-2,3-dihydroxy-1-methyl-8-methylidene-13-oxododecahydro-4a,1-(epoxymethano)-7,9a-methanobenzo[a]azulene-10-carboxylic acid](http://img.cochemist.com/ccimg/32700/32630-92-5.png)
![(1S,2R,3S,4aR,4bR,7R,9aR,10S,10aR)-2,3-dihydroxy-1-methyl-8-methylidene-13-oxododecahydro-4a,1-(epoxymethano)-7,9a-methanobenzo[a]azulene-10-carboxylic acid](http://img.cochemist.com/ccimg/32700/32630-92-5_b.png)
![Adenosine, N-[(2Z)-4-hydroxy-3-methyl-2-butenyl]-](http://img.cochemist.com/ccimg/15900/15896-46-5.png)
![Adenosine, N-[(2Z)-4-hydroxy-3-methyl-2-butenyl]-](http://img.cochemist.com/ccimg/15900/15896-46-5_b.png)
![(1S,3S,4S)-3-(4-CHLOROPHENYL)-5'-(4-MORPHOLINYL)-3',4'-DIHYDROSPI<WBR />RO[BICYCLO[2.2.1]HEPTANE-2,2'-PYRROLE]](http://img.cochemist.com/ccimg/7100/7044-72-6.png)
![(1S,3S,4S)-3-(4-CHLOROPHENYL)-5'-(4-MORPHOLINYL)-3',4'-DIHYDROSPI<WBR />RO[BICYCLO[2.2.1]HEPTANE-2,2'-PYRROLE]](http://img.cochemist.com/ccimg/7100/7044-72-6_b.png)
