新型侧链聚硅氧烷高分子液晶作毛细管柱气相色谱固定液的研究

 以合成的新型胆甾酯类侧链聚硅氧烷高分子液晶作固定液 ,涂渍在弹性石英毛细管柱上 ,获得了具有较高的柱效和选择性、良好的热稳定性、适于分离多种异构体混合物的毛细管柱。     

Comprehensive two‐dimensional monolithic liquid chromatography of polar compounds

Two‐dimensional liquid chromatography largely increases the number of separated compounds in a single run, theoretically up to the product of the peaks separated in each dimension on the columns with different selectivities. On‐line coupling of a reversed‐phase column with an aqueous normal‐phase (hydrophilic interaction liquid chromatography) column yields orthogonal systems with high peak capacities. Fast on‐line two‐dimensional liquid chromatography needs a capillary or micro‐bore column providing low‐volume effluent fractions transferred to a short efficient second‐dimension column for separation at a high mobile phase flow rate. We prepared polymethacrylate zwitterionic monolithic micro‐columns in fused silica capillaries with structurally different dimethacrylate cross‐linkers. The columns provide dual retention mechanism (hydrophilic interaction and reversed‐phase). Setting the mobile phase composition allows adjusting the separation selectivity for various polar substance classes. Coupling on‐line an organic polymer monolithic capillary column in the first dimension with a short silica‐based monolithic column in the second dimension provides two‐dimensional liquid chromatography systems with high peak capacities. The silica monolithic C₁₈ columns provide higher separation efficiency than the particle‐packed columns at the flow rates as high as 5 mL/min used in the second dimension. Decreasing the diameter of the silica monolithic columns allows using a higher flow rate at the maximum operation pressure and lower fraction volumes transferred from the first, hydrophilic interaction dimension, into the second, reversed‐phase mode, avoiding the mobile phase compatibility issues, improving the resolution, increasing the peak capacity, and the peak production rate.     

Two-dimensional and serial column reversed-phase separation of phenolic antioxidants on octadecyl-, polyethyleneglycol-, and pentafluorophenylpropyl-silica columns

The separation selectivity of octadecyl-silica (C18) and of bonded pentafluorophenylpropyl-silica (F5) and PEG-silica columns was compared for natural phenolic antioxidants. The separation selectivities for phenolic antioxidants on C18 and F5 columns are strongly correlated, but low selectivity correlation indicating strong differences in the retention mechanism was observed between the C18 and PEG columns. Hence, the combination of a C18 and a PEG column is useful for separation of phenolic antioxidants that are not fully separated on single columns. Two-dimensional comprehensive liquid chromatography using a short PEG-silica column in the first dimension and a conventional C18-silica in the second dimension has the advantage of on-column focusing of the fractions transferred onto the C18 column in the second dimension, as a weaker mobile phase is used in the first dimension than in the second dimension. However, a stop-flow set-up in the first dimension system is necessary after the transfer of each fraction to the second dimension. Peak capacity is considerably larger but the separation time is much longer than with serially coupled PEG and C18 columns, which were employed for separation of beer and hop extract samples in connection with coulometric detection.     

Selectivity of stationary phases in reversed-phase liquid chromatography based on the dispersion interactions

Selectivity of 15 stationary phases was examined, either commercially available or synthesized in-house. The highest selectivity factors were observed for solute molecules having different polarizability on the 3-(pentabromobenzyloxy)propyl phase (PBB), followed by the 2-(1-pyrenyl)ethyl phase (PYE). Selectivity of fluoroalkane 4,4-di(trifluoromethyl)-5,5,6,6,7,7,7-heptafluoroheptyl (F13C9) phase is lowest among all phases for all compounds except for fluorinated ones. Aliphatic octyl (C8) and octadecyl (C18) phases demonstrated considerable selectivity, especially for alkyl compounds. While PBB showed much greater preference for compounds with high polarizability containing heavy atoms than C18 phase, F13C9 phase showed the exactly opposite tendency. These three stationary phases can offer widely different selectivity that can be utilized when one stationary phase fails to provide separation for certain mixtures. The retention and selectivity of solutes in reversed-phase liquid chromatography is related to the mobile phase and the stationary phase effects. The mobile phase effect, related to the hydrophobic cavity formation around non-polar solutes, is assumed to have a dominant effect on retention upon aliphatic stationary phases such as C8, C18. In a common mobile phase significant stationary phase effect can be attributed to dispersion interaction. Highly dispersive stationary phases such as PBB and PYE retain solutes to a significant extent by (attractive) dispersion interaction with the stationary phase ligands, especially for highly dispersive solutes containing aromatic functionality and/or heavy atoms. The contribution of dispersion interaction is shown to be much less on C18 or C8 phases and was even disadvantageous on F13C9 phase. Structural properties of stationary phases are analyzed and confirmed by means of quantitative structure-chromatographic retention (QSRR) study.     

Enhanced Resolution of Conjugated Linoleic Acid Isomers by Tandem-Column Silver-Ion High Performance Liquid Chromatography

A commercial mixture of conjugated linoleic acid (CLA) isomers, reportedly consisting of six components, was recently resolved into 12 peaks attributed to CLA isomers using silver-ion high performance liquid chromatography (Ag⁺-HPLC). In this study, the coupling of two analytical silver-ion high performance liquid chromatography columns (tandem-column Ag⁺-HPLC) in series led to the enhanced resolution of CLA isomers. Many CLA isomers were baseline resolved and the pair 18 : 2 8,10 c/t and 18 : 2 7,9 c/t found in cheese products, was resolved for the first time. In this work, a similar commercial CLA mixture was separated into 16 peaks, while CLA isomers from cheese also gave rise to 16 peaks. As expected, the CLA isomers were separated into three geometric groups in the order trans,trans, cis/trans, and cis,cis. Semi-preparative Ag⁺-HPLC, followed by gas chromatography–mass spectroscopy of the dimethyloxazoline derivatives, was used to confirm the identity of the newly resolved positional CLA isomers. The double bond configuration of CLA isomers was established by gas chromatography–Fourier transform infrared spectroscopy. Two minor t,t CLA isomers found in cheese, presumably 18 : 2 t6t8 and 18 : 2 t13t15, were also separated. The CLA isomeric composition of 16 commercial cheese products was determined.     

高效液相色谱-电喷雾离子阱飞行时间质谱法鉴定乙酰甲喹及其代谢物

利用高效液相色谱分离、电喷雾-线性离子阱质谱法(LC-ESI/LTQ)、电喷雾-离子阱/飞行时间串联质谱法(LC-ESI/IT-TOF)鉴定鸡血浆中乙酰甲喹及其代谢物的结构。分别采用Hypersil Gold和Symmetry ShieldTM色谱柱,以含有0.01%甲酸水溶液(A)和甲醇(B)为流动相,梯度洗脱,电喷雾离子源(ESI)正离子模式进行检测。鸡口服给药乙酰甲喹(20mg/kg)后,翅下静脉采血,待分析血浆用乙腈-乙酸乙酯(3:2,V/V)混合液提取,吹干。残渣用30%甲醇水溶液复溶,上机检测。用Shimadzu′s Composition分子预测软件推测分子离子及其子离子质量,Xcalibur2.0.7软件分析线性离子阱质谱仪测得质谱图。鉴定出5种主要代谢物,分别为3-甲基-2-(1-羟基)乙基-喹啉-N1,N4-二氧化物(M1)、3-甲基-2-(1-羟基)乙基-喹啉-N4-一氧化物(M2)、3-甲基-2-乙酰基-喹啉-N4-一氧化物(M3)、3-甲基-2-乙酰基-喹啉(M4)和3-羟甲基-2-(1-羟基)乙基-喹啉-N1,N4-二氧化物(M5)。同时根据推测结果对代谢物M1～M4进行...     

Gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains

Summary Comparative gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains (10 and 16 carbons called Poly 10 and Poly 16 respectively) are studied.Their thermal properties were established with differential scanning calorimetry (DSC) and gas chromatography. They present a cholesteric liquid crystal in a large temperature range.The chromatographic separation abilities of the two polymers in the liquid crystal state were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds and cis and trans isomers. Some differences were noticed in their behaviours; 2 and 3-methyloctane and xylene isomers are separated only on Poly 10 while limonene and eucalyptol are separated only on Poly 16.     

High-performance liquid chromatography and capillary supercritical-fluid chromatography separation of vegetable carotenoids and carotenoid isomers

Carotenoids from carrots and tomatoes were separated with high-performance liquid chromatography (HPLC) and capillary supercritical fluid chromatography (SFC). All trans alpha- and beta-carotene were separated from their respective cis-isomers with capillary SFC. Carotenoids extracted from tomatoes included xanthophyll, lycopene and beta-carotene, while alpha- and beta-carotene were extracted from carrots. The HPLC separations were accomplished isocratically with a 25-cm column containing 5-microns ODS and methanol-acetonitrile-chloroform (47:47:6) or acetonitrile-dichloromethane (80:20). beta-Carotene cis-isomers were separated with SFC with a SB-cyanopropyl-25-polymethylsiloxane column, while alpha-carotene isomers were separated with two SB-cyanopropyl-50-polymethylsiloxane columns. Carotenoids from carrots and tomatoes were separated with a SB-phenyl-50-polymethylsiloxane column. Carbon dioxide with 1% ethanol was the SFC mobile phase. The eluent was monitored at 461 nm for HPLC and either 453 or 461 nm for SFC.     

Separation of carotenol fatty acid esters by high-performance liquid chromatography

Employing isocratic and gradient-elution high-performance liquid chromatography (HPLC) a number of straight-chain fatty acid esters (decanoate, laurate, myristate, palmitate) of violaxanthin, auroxanthin, lutein, zeaxanthin, isozeaxanthin, and beta-cryptoxanthin, prepared by partial synthesis, have been separated on a C18 reversed-phase column. Several chromatographic conditions were developed that separated a mixture of di-fatty acid esters (dimyristate, myristate palmitate mixed ester, dipalmitate) of violaxanthin, auroxanthin, lutein, and zeaxanthin in a single chromatographic run. Hydroxycarotenoids such as lutein, zeaxanthin, and isozeaxanthin that are not easily separated by HPLC on C18 reversed-phase columns, can be readily separated after derivatization with fatty acids and chromatography of their esters. Chromatographic conditions for optimum separation of carotenoids from various classes are discussed.     

Chromatographic behavior of small organic compounds in low‐temperature high‐performance liquid chromatography using liquid carbon dioxide as the mobile phase

Low‐temperature high‐performance liquid chromatography, in which a loop injector, column, and detection cell were refrigerated at –35ºC, using liquid carbon dioxide as the mobile phase was developed. Small organic compounds (polyaromatic hydrocarbons, alkylbenzenes, and quinones) were separated by low‐temperature high‐performance liquid chromatography at temperatures from –35 to –5ºC. The combination of liquid carbon dioxide mobile phase with an octadecyl‐silica (C₁₈) column provided reversed phase mode separation, and a bare silica‐gel column resulted in normal phase mode separation. In both the cases, nonlinear behavior at approximately –15ºC was found in the relationship between the temperature and the retention factors of the analytes (van't Hoff plots). In contrast to general trends in high‐performance liquid chromatography, the decrease in temperature enhanced the separation efficiency of both the columns.     

Preparation and structural characterization of the Ih and the D5h isomers of the endohedral fullerenes Tm3N@C80: icosahedral C80 cage encapsulation of a trimetallic nitride magnetic cluster with three uncoupled Tm3+ ions

We report an efficient method for the preparation and purification of the Ih and the D5h isomers of Tm3N@C80. Following preparation in a Kratschmer-Huffman electric-arc generator, the Tm3N@C80 isomers were obtained by a chemical separation process followed by a one-stage isomer selective chromatographic high-performance liquid chromatography (HPLC) separation (pyrenyl, 5PYE column). The HPLC chromatographic retention behavior on a pentabromobenzyl (5PBB) column suggests a charge transfer of approximately 6 electrons; [M3N] 6+@C80(6-) and the chromatographic retention mechanisms of the Ih and the D5h isomers of Tm3N@C80 on both 5PBB and 5PYE columns are discussed. Single-crystal X-ray diffraction data demonstrate that the Tm3N cluster has a planar structure but represents a tight fit for trapping the Tm3N cluster inside the I h - and the D 5h -C 80 cages. Specifically, the Tm atoms punch out the cage carbon atoms adjacent to them. The "punched out" effect can be demonstrated by cage radii and pyramidal angles at cage carbon atoms near the Tm atoms. The magnetic susceptibility (chiT) for Tm3N@ Ih -C80 was found to exhibit Curie-Weiss behavior with C = 23.4 emu.K/mol, which is consistent with the calculated value for three uncoupled Tm3+ ions by considering the spin and orbital contributions with no quenching of the orbital angular momentum ( L = 5, S = 1, and J = 6; Ccalcd = 23.3 emu.K/mol). The electrochemical measurements demonstrate that both the Ih and the D5h isomers of Tm3N@C80 have a large electrochemical gap.     

猪肉中63种有机磷农药的气相色谱筛选与气质联用确证方法

建立了固相萃取-气相色谱筛选和气相色谱-质谱联用确证猪肉中63种有机磷农药的分析方法。样品用正己烷配合乙腈-水溶液均质提取,加入氯化钠继续均质,离心分层后取部分乙腈层经C18柱和PSA柱净化后供GC和GC-MS分析。气相色谱筛选采用火焰光度检测器（FPD）,气相色谱-质谱联用确证采用选择离子扫描方式（SIM）,外标法定量。该方法简便、快速,优化条件下测定方法的定量下限（S/N=10）为0.001～0.043 mg/kg,在加标水平为0.16 mg/kg时,回收率为70%～121%,相对标准偏差为4.1%～13.9%。     

Characterization of immobilized artificial membrane (IAM) and XTerra columns by means of chromatographic models

Immobilized artificial membranes (IAMs) prepared from phosphatidylcholine analogs are used as stationary phases in liquid chromatography systems to model drug partitioning between an aqueous phase (mobile phase) and a cell membrane (IAM column). Two different chromatographic models, which describe retention as a function of solute and column-mobile phase properties, have been applied to characterization of an IAM and two reversed phase C18 columns (Waters XTerra MSC18 and XTerra RP18) with acetonitrile-water mobile phases. The comparison of the results shows that the phosphatidylcholine group makes IAM column more polar than both XTerra columns, specially in terms of hydrogen-bond acceptor ability. XTerra RP18 is slightly more polar than XTerra MSC18 because of the presence of the embedded carbamate polar group.     

Hydrophilic interaction liquid chromatography in the separation of a moderately lipophilic drug from its highly polar metabolites--the cardioprotectant dexrazoxane as a model case

This paper presents a systematic study of the retention behavior of a model bisdioxopiperazine drug, dexrazoxane (DEX) and its three polar metabolites (two single open-ring intermediates-B and C and an EDTA-like active compound ADR-925) on different stationary phases intended for hydrophilic interaction liquid chromatography (HILIC). The main aim was to estimate advantages and limitations of HILIC in the simultaneous analysis of a moderately lipophilic parent drug and its highly polar metabolites, including positional isomers, under MS compatible conditions. The study involved two bare silica columns (Ascentic Express HILIC, Atlantis HILIC) and two stationary phases with distinct zwitterionic properties (Obelisc N and ZIC HILIC). The chromatographic conditions (mobile phase strength and pH, column temperature) were systematically modified to assess their impact on retention and separation of the studied compounds. It was found that the bare silica phases were unable to separate the positional isomers (intermediates B and C), whereas both columns with zwitterionic properties (Obelisc N and ZIC HILIC) were able to separate these structurally very similar compounds. However, only ZIC HILIC phase allowed appropriate separation of DEX and all its metabolites to a base line within a single run. A mobile phase composed of a mixture of ammonium formate (0.5 mM) and acetonitrile (25:75, v/v) was suggested as optimal for the simultaneous analysis of DEX and its metabolites on ZIC HILIC. Thereafter, HILIC-LC-MS analysis of DEX and all its metabolites was performed for the first time to obtain basic data about the applicability of the suggested chromatographic conditions. Hence, this study demonstrates that HILIC could be a viable solution for the challenging analysis of moderately polar parent drug along with its highly polar metabolites including the ability to separate structurally very similar compounds, such as positional isomers.     

Ultra high-performance liquid chromatography of porphyrins in clinical materials: column and mobile phase selection and optimisation

Ultra high-performance liquid chromatographic (UHPLC) systems on columns packed with materials ranging from 1.9 to 2.7 μm average particle size were assessed for the fast and sensitive analysis of porphyrins in clinical materials. The fastest separation was achieved on an Agilent Poroshell C(18) column (2.7 μm particle size, 50 × 4.6 mm i.d.), followed by a Thermo Hypersil Gold C(18) column (1.9 μm particle size, 50 × 2.1 mm i.d.) and the Thermo Hypersil BDS C(18) column (2.4 μm particle size, 100 × 2.1 mm i.d.). All columns required a mobile phase containing 1 m ammonium acetate buffer, pH 5.16, with a mixture of acetonitrile and methanol as the organic modifiers for optimum resolution of the type I and III isomers, particularly for uroporphyrin I and III isomers. All UHPLC columns were suitable and superior to conventional HPLC columns packed with 5 μm average particle size materials for clinical sample analysis.     

Comparison of two gas–liquid chromatograph columns for the analysis of fatty acids in ruminant meat

Two gas–liquid chromatograph capillary columns for the analysis of fatty acids (FA) in ruminant fat are compared. Those columns are the CP-Sil 88 of 100 m long with a highly polar stationary phase and the Omegawax 250 of 30 m long with a stationary phase of intermediate polarity. Fatty acid methyl ester (FAME) patterns of branched-chain, cis and trans octadecenoate isomers, as well as conjugated and non-conjugated 18:2 and 18:3 isomers are fairly different between columns, even though most of the FAME could be separated on either column. However, the CP-Sil 88 showed better resolution of 18:1 isomers than Omegawax 250. The analysis of 96 samples of ruminant meat fat in both chromatographic systems showed that averages obtained for total FA content and for most of the individual FA did not differ between columns. Moreover, regression analysis of Omegawax and CP-Sil 88 data is highly correlated. Quantitative differences between chromatographic systems were detected for samples containing more than 66 mg fatty acids per gram of muscle dry matter.     

Chiral Resolution of Cypermethrin on Cellulose-tris(3,5-dimethylphenyl-carbamate) Chiral Stationary Phase

Cellulose-tris(3,5-dimethylphenylcarbamate)was synthesized and coated on aminopropylsilica to prepare a chiral stationary phase. Cypermethrin, alpha-, theta-and beta-cypermethrin were well resolved by high-performance liquid chromatography on this material using n-hexane as mobile phase and isopropyl alcohol as modifier. Two columns of different length were used, and the influence of the volume percentage of isopropyl alcohol in the mobile phase was studied. The impact of temperature on the separation of alpha- and theta-cypermethrin was also investigated. The two enantiomers of alpha- and theta-cypermethrin were both complete resolved. The four isomers of beta-cypermethrin and the seven of eight isomers of cypermethrin were separated.     

Analysis of fentanyl derivatives by ultra high performance liquid chromatography with diode array ultraviolet and single quadrupole mass spectrometric detection

Fentanyl has become pervasive as a drug of abuse and as adulterant in seized drugs. Positional isomers analyzed by gas chromatography with mass spectrometry can follow the same fragmentation pathway and therefore may not be differentiated. Additionally, electron ionization leads to lack of discernible molecular ion for most fentanyl related compounds. Liquid chromatography may be used as an orthogonal identification technique with diode array ultraviolet and mass spectrometric detection. Here we provide a chromatographic method for the separation of 20 different fentanyl analogues, homologues and positional isomers using ultra high performance liquid chromatography with photodiode array ultraviolet and mass spectrometry detection. Five different columns were investigated utilizing reverse phase chromatography and hydrophilic interaction chromatography. Chromatographic systems were evaluated to determine which could separate the most compounds overall, as well as the most positional isomers. We found that isocratic elution, with a methanol modifier (35%) and formic acid (0.1%) as an additive, on a C18 column at a temperature of 25°C could resolve 10/20 compounds overall and 16/20 positional isomers. Using electrospray ionization, compounds with different masses could easily be distinguished based on their pseudo molecular ions. Ultraviolet detection facilitated differentiation of positional isomers that could not be distinguished by either electron ionization or electrospray ionization mass spectrometry alone.     

直观推导式演进特征投影法分辨枸杞类胡萝卜素的异构体

采用高效液相色谱-二极管阵列检测方法,初步分离了枸杞子中的类胡萝卜素。以乙腈-二氯甲烷(体积比为60∶40)为流动相,流速为1.0 mL/min,用C18柱从枸杞类胡萝卜素中分离出7个峰。但由于类胡萝卜素的结构多样性,尤其是顺反异构体的出现使得分离并不完全。利用所得三维数据提供的信息和化学计量学方法直观推导式演进特征投影法(HELP),对其中某些在二维色谱中被定性为单组分的峰进行解析,结果发现原来在二维色谱中被定性为单组分的峰大多是一些多组分峰。以其中第4个峰为例对其进行解析,得到了该类胡萝卜素的同分异构体色谱流出曲线及紫外光谱信息。该方法表明,化学计量学方法与现代分析手段有机结合,大大降低了此类复杂体系对色谱分离的要求,对同分异构体的分析具有一定的借鉴和指导意义。