Analysis of tert-butyldimethylsilyl derivatives in heavy gas oil from Brazilian naphthenic acids by gas chromatography coupled to mass spectrometry with electron impact ionization

Naphthenic acids, C(n)H(2n+Z)O(2), are a complex mixture of alkyl-substituted acyclic and cycle-aliphatic carboxylic acids. The content of naphthenic acids and their derivatives in crude oils is very small, which hinders their extraction from matrixes of wide and varied composition. In this work, liquid-liquid extraction, followed by solid phase extraction with an ion exchange resin (Amberlyst A-27) and ultrasound desorption were used to isolate the acid fraction from heavy gas oil of Marlim petroleum (Campos, Rio de Janeiro, Brazil). The analysis was accomplished through gas chromatography coupled to mass spectrometry with electron impact ionization, after derivatization with N-methyl-N-(tert-butyldimethylsilyl)trifluoracetamide (MTBDMSTFA). The results indicate the presence of carboxylic acids belonging to families of alicyclic and naphthenic compounds which contain up to four rings in the molecule.     

万古霉素键合固定相的分离性能

万古霉素作为一种大环抗生素,具有复杂的分子结构。在充分考虑万古霉素分子结构特征的情况下,采用戊二醛间隔臂法制备了万古霉素键合固定相,在反相、亲水、离子交换等分离模式下研究了其色谱分离性能。结果表明,当流动相中有机调节剂含量较低时,该色谱柱表现出典型的反相色谱分离模式特征;随着有机调节剂含量的增加,逐渐转变成亲水模式,分离特性发生明显改变。由于万古霉素分子结构中含有可以解离的氨基,因此该固定相也能够用于阴离子交换模式下的分析方法的发展。分别在反相、亲水和阴离子交换模式下,将其应用于扑尔敏等多种非对映体药物和新型甜味剂甜菊糖的高效液相色谱分离;仅通过改变分离条件,即可在3种不同分离模式下完成分离。这些结果可以为新型色谱固定相的设计,以及发展采用特殊结构改性基团的色谱固定相在相应分离模式下的分析方法提供指导。     

Hypercrosslinked strong anion‐exchange resin for extraction of acidic pharmaceuticals from environmental water

Two novel high‐specific surface area polymeric sorbents (HXLPP‐SAXa and HXLPP‐SAXb) were synthesised and evaluated as solid‐phase extraction sorbents. The novel sorbents under study are based on hypercrosslinked polymer microspheres and designed specifically to offer ion‐exchange properties; the specific polymers of interest in the current work have been chemically modified in such a way as to impart a tuneable level of strong anion‐exchange character onto the sorbents. The novel sorbents were applied as strong anion‐exchange sorbents in solid‐phase extraction studies, with the goal being to selectively extract a group of acidic compounds from complex environmental samples in an efficient manner. Out of two HXLPP‐SAX resins evaluated in this study, it was found that the sorbent with the lower ion‐exchange capacity (HXLPP‐SAXa) gave rise to the best overall performance characteristics and, indeed, was found to compare favourably to the solid‐phase extraction performance of commercial strong anion‐exchange sorbents. When the HXLPP‐SAXa sorbent was applied to the solid‐phase extraction of environmental water samples, the result showed quantitative and selective extraction of low levels of acidic pharmaceuticals from 500 mL of river water and 100 mL of effluent wastewater.     

Dicationic ionic liquid stationary phase for GC-MS analysis of volatile compounds in herbal plants

The seeming “dual nature” of ionic liquids (ILs) for separating both apolar and polar compounds suggests that ILs may have a great potential for complex samples like essential oils from herbal plants that contain a great variety of compounds. In the present work, a geminal dicationic IL, 1,9-di(3-vinylimidazolium)nonane bis[(trifluoromethyl)sulfonyl]imidate, was investigated for this purpose. To find the best way to achieve satisfactory separations simultaneously for the compounds in essential oils, the dicationic IL was used as the stationary phase for capillary gas chromatography (GC) in two ways, either in its pure state or as a mixed stationary phase with monocationic ILs and a polysiloxane diluent. Interestingly, it was found that the mixed stationary phase exhibited a much better selectivity for polar and nonpolar compounds than either the dicationic IL or the polysiloxane, suggesting that a kind of synergistic effect occurred when these stationary phases were combined in the way described. A comparison with two commercial stationary phases (polar and nonpolar) indicated that this novel mixed stationary phase behaved in a way closer to a polar stationary phase in terms of selectivity and elution order. The present work demonstrates that the mixed stationary phase is efficient and selective and can be an alternative choice for the GC analysis of samples of complex composition. Figure Divinyldiimidazolium-based ionic liquid stationary phase     

Preparation of l‐phenylalanine‐imprinted solid‐phase extraction sorbent by Pickering emulsion polymerization and the selective enrichment of l‐phenylalanine from human urine

A novel l‐ phenylalanine molecularly imprinted solid‐phase extraction sorbent was synthesized by the combination of Pickering emulsion polymerization and ion‐pair dummy template imprinting. Compared to other polymerization methods, the molecularly imprinted polymers thus prepared exhibit a high specific surface, large pore diameter, and appropriate particle size. The key parameters for solid‐phase extraction were optimized, and the result indicated that the molecularly imprinted polymer thus prepared exhibits a good recovery of 98.9% for l‐ phenylalanine. Under the optimized conditions of the procedure, an analytical method for l‐ phenylalanine was well established. By comparing the performance of the molecularly imprinted polymer and a commercial reverse‐phase silica gel, the obtained molecularly imprinted polymer as an solid‐phase extraction sorbent is more suitable, exhibiting high precision (relative standard deviation 3.2%, n = 4) and a low limit of detection (60.0 ± 1.9 nmol·L^?1) for the isolation of l‐ phenylalanine. Based on these results, the combination of the Pickering emulsion polymerization and ion‐pair dummy template imprinting is effective for preparing selective solid‐phase extraction sorbents for the separation of amino acids and organic acids from complex biological samples.     

Silica gel-immobilized-dithioacetal derivatives as potential solid phase extractors for mercury(II)

Dithioacetal derivatives with different para-substituents, XH, CH(3), OCH(3), Cl and NO(2) were synthesized and chemically immobilized on the surface of silica gel for the formation of five newly synthesized silica gel phases (I-V). Characterization of the silica gel surface modification by the organic compounds was accomplished by both the surface coverage determination as well as the infrared spectroscopic analysis. The metal sorption properties of the silica gel phases were studied to evaluate their performance toward metal-uptake, extraction and selective extraction processes of different metal ions from aqueous solutions based on examination of the various controlling factors. The studied and evaluated factors are the pH effect of metal ion solution on the metal capacity values (mmol g(-1)), equilibration shaking time on the percent extraction as well as the structure and substituent (X) effects on the determined mmol g(-1) values. The results of these studies revealed a general rule of excellent affinity of these silica gel phases-immobilized-dithioacetal derivatives for selective extraction of mercury(II) in presence of other interfering metal ions giving rise to a range of 94-100% extraction of the spiked mercury(II) in the metal ions mixture. The potential application of the newly synthesized silica gel phases (I-V) for selective extraction of mercury(II) from two different natural water samples, namely sea and drinking tap water, spiked with 1.0 and 10.0 ng ml(-1) mercury(II) were also studied by column technique followed by cold vapour atomic absorption analysis of the unretained mercury(II). The results indicated a good percent extraction and removal (90-100+/-3%) of the spiked mercury(II) by all the five silica gel phases. In addition, insignificant contribution by the matrix effect on the processes of selective solid phase extraction of mercury(II) from natural water samples was also evident.     

聚合离子液体毛细管气相色谱固定相的性能评价

离子液体作为毛细管气相色谱固定相的选择性和热稳定性是近年人们关注的课题。本文合成了1-烯基-3-苄基咪唑-二(三氟甲基磺酰)亚胺盐(VBIm-NTf2)离子液体并经毛细管柱内聚合制得了聚合离子液体PVBIm-NTf2色谱柱。与VBIm-NTf2色谱柱相比,PVBIm-NTf2色谱柱具有良好的色谱选择性和热稳定性。PVBIm-NTf2色谱柱对Grob试剂、醇混合物、酯混合物和苯系物等都表现了很好的分离能力,并且色谱峰峰形窄且对称。该聚合色谱柱在250 ℃下老化6 h后仍具有良好的分离能力和选择性。本文还测定了PVBIm-NTf2的Abraham溶剂化参数,解析了该固定相与溶质间的相互作用,相关研究国内尚未见报道。研究表明,对常规离子液体进行柱内聚合是改善常规离子液体气相色谱固定相的热稳定性和选择性的有效途径。     

PEG-linked geminal dicationic ionic liquids as selective, high-stability gas chromatographic stationary phases

It is known that room-temperature ionic liquids (RTILs) have wide applicability in many scientific and technological fields. In this work, a series of three new dicationic room-temperature ionic liquids functionalized with poly(ethylene glycol) (PEG) linkages were synthesized and characterized via a linear solvation model. The application of these ILs as new GC stationary phases was studied. The efficient separation of several mixtures containing compounds of different polarities and 24 components of a flavor and fragrance mixture indicated comparable or higher resolving power for the new IL stationary phases compared to the commercial polysiloxane and poly(ethylene glycol)-based stationary phases. In addition, the selectivities of the IL stationary phases could be quite unique. The separation of a homologous alkane and alcohol mixture displayed the “dual nature” of these ionic liquids as GC stationary phases. The thermal stability study showed the column robustness up to 350 °C. The high separation power, unique selectivity, high efficiency and high thermal stability of the new dicationic ionic liquids indicate that they may be applicable as a new type of robust GC stationary phase.     

Bonded stationary phases for reversed phase liquid chromatography with a water mobile phase: application to subcritical water extraction

Reversed phase high-performance liquid chromatography (RP-HPLC) is demonstrated for hydrophobic analytes such as aromatic hydrocarbons on a chemically bonded stationary phase and a mobile phase consisting of only water. Reversed phase liquid chromatography separations using a water-only mobile phase has been termed WRP-LC for water-only reversed phase LC. Reasonable capacity factors are achieved through the use of a non-porous silica substrate resulting in a chromatographic phase volume ratio much lower than usually found in RP-HPLC. Two types of bonded WRP-LC columns have been developed and applied. A brush phase was synthesized from an organochlorosilane. The other phase, synthesized from an organodichlorosilane, is termed a branch phase and results in a polymeric structure of greater thickness than the brush phase. A baseline separation of a mixture containing benzaldehyde, benzene, toluene, and ethyl benzene in less than 5 min is demonstrated using a water mobile phase with 12 000 plates generated for the unretained benzaldehyde peak. The theoretically predicted minimum reduced plate height is also shown to be approached for the unretained analyte using the brush phase. As an application, subcritical water extraction (SWE) at 200°C is combined with WRP-LC. This combination allows for the extraction of organic compounds from solid matrices immediately followed by liquid chromatographic separation of those extracted compounds all using a solvent of 100% water. We demonstrate SWE/WRP-LC by spiking benzene, ethyl benzene, and naphthalene onto sand then extracting the analytes with SWE followed by chromatographic separation on a WRP column. A sand sample contaminated with gasoline was also analyzed using SWE/WRP-LC. This extraction process also provides kinetic information about the rate of analyte extraction from the sand matrix. Under the conditions employed, analytes were extracted at different rates, providing additional selectivity in addition to the WRP-LC separation.     

羧基甜菜碱型亲水作用色谱柱的制备及性能研究

以甲基丙烯酰氧乙基二甲基乙酸铵(CBMA)为功能单体,利用表面引发原子转移自由基聚合(Surface-initiated atom transfer radical polymerization, SI-ATRP)技术,将CBMA接枝到硅胶表面,得到接枝聚合物CBMA的亲水作用色谱固定相(Silica-CBMA).通过改变SI-ATRP反应体系中单体的浓度,制备了3种不同接枝量的亲水作用色谱固定相.考察了Silica-CBMA固定相对有机酸类化合物的分离性能以及流动相中pH值、盐浓度、水含量等因素对溶质保留行为的影响.结果表明,在亲水作用色谱模式下,Silica-CBMA固定相对有机酸类化合物的分离是离子交换作用与亲水作用的混合色谱模式.流动相中盐浓度增大,溶质保留减弱,符合离子交换作用特征;固定相和溶质的离子化程度受流动相pH值影响较大,pH值增大,溶质保留增强;而溶质的保留时间随流动相水含量增加而降低则是典型的亲水作用色谱特征.使用自制Silica-CBMA柱,建立了芦丁片中维生素C、芦丁含量的亲水作用色谱测定方法,操作方法简单,为强极性样品的分离测定提供了新方法.     

固相微萃取新型涂层的制备和特性(英文)

 以聚甲基苯基乙烯基硅氧烷为主要成分 ,采用溶胶 凝胶技术和自由基引发交联反应的方法首次制备了一种固相微萃取新涂层 ,并与气相联用 ,分析了芳香族化合物 ,考察了它的萃取性能。结果表明 :该涂层提供了大的比表面积 ,可获得高的萃取效率。与相应的商用固相微萃取涂层相比 ,该涂层具有更好的灵敏度和选择性 ,且热稳定性好 ,使用寿命长。     

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high‐performance liquid chromatography stationary phases with reversed‐phase eluents

Unbonded silicon oxynitride and silica high‐performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pK_a, and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion‐exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed‐phase mobile phase. An ion‐exclusion‐type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.     

Improving selectivity in gas chromatography by using chemically modified multi-walled carbon nanotubes as stationary phase

Amino-terminated alkyl MWCNTs (MWCNTs-R-NH₂), synthesized by chemical modification of the nanotube skeleton by nucleophilic substitution with 2,2′-(ethylenedioxy)diethylamine, were successfully used as stationary phases for gas chromatographic separation of esters and chloroaromatics. The presence of alkyl chains with polar embedded groups made the functionalized MWCNTs (f-MWCNTs) a mixed-mode GC separation material able to interact in different ways with the analytes. Compared with non-functionalized MWCNTs (nf-MWCNTs), MWCNTs-R-NH₂ had higher selectivity, enhanced resolution, and optimum retention behaviour, and they were proved to perform better than the commercial stationary phase Porapak QS (PQS), claimed to be suitable for similar applications. The so-prepared stationary phase was used for analysis of a synthetic mixture containing different classes of analytes, viz. esters, ketones, alcohols, alkanes, and aromatic hydrocarbons, and finally used for investigation of similar real matrices. In particular, the constituents of a commercial paint thinner were determined by direct injection of the sample, with good reproducibility (inter-day precision RSDs from 5 to 19%). Two unknown samples of commercial white spirit were also analysed for determination of the aromatic hydrocarbon content, and their composition was profiled on the basis of the different compounds identified.     

Analysis of basic compounds at high pH values by reversed-phase liquid chromatography

Reversed phase high performance liquid chromatography (RPLC) is currently the method of choice for the analysis of basic compounds. However, with traditional silica materials, secondary interactions between the analyte and residual silanols produce peak tailing which can negatively affect resolution, sensitivity, and reproducibility. In order to reduce these secondary interactions, which comprise ion exchange, hydrogen bonding, and London forces interactions, chromatographic analyses can be carried out at low or high pH values where silanol groups and basic compounds are mostly uncharged. The chromatographic behaviour of a particular bidentate stationary phase, Zorbax Extend C18, was studied with a set of basic and neutral compounds. Thanks to a higher chemical stability than traditional silica based supports, analyses were carried out with a high pH mobile phase, which represents a good alternative to the acidic mobile phases generally used to reduce ion exchange interactions. The performance of this bidentate stationary phase was also compared with that of other supports and it was proved that it is advantageous to work with high pH mobile phases when analyzing basic compounds.     

Preparation, characterization, and application of a new stationary phase containing different kinds of amine groups

A new stationary phase containing primary amine and tertiary amine groups was synthesized and its structure was confirmed by infrared spectra, elemental analysis, and zeta potential. This new material was packed into a stainless steel column and the effect of acetonitrile (ACN) content in mobile phase on retention was evaluated using probes of nucleosides, sulfanilamides, and quinolone compounds. This showed hydrophilic interaction, ion interaction, or a mixed-mode retention mechanism for different kinds of solutes, respectively. The effects of the pH and ion strength of the mobile phase were investigated to further understand the retention mechanism of the new stationary phase. The interaction forces caused by the new phase included adsorption, electrostatic function, and ion exchange. The new material could be used as a stationary phase in different high-performance liquid chromatography modes.     

Phenylboronic acid modified solid‐phase extraction column: Preparation,characterization, and application to the analysis of amino acids in sepia capsule by removing the maltose

Maltose, a common auxiliary material of pharmaceutical preparation, may disturb the analysis of total amino acids in sepia capsule by aldolization. Therefore, it is necessary to remove the maltose through a convenient method. In this work, a phenylboronic acid modified solid‐phase extraction column has been synthesized and used to remove the maltose. The materials were synthesized by one step “thiol‐ene” reaction and the parameters of the column such as absorption capacity, recovery, and absorption specificity have been investigated. The results showed the column (0.5 cm of length × 0.5 cm of inner diameter) can absorb 4.6 mg maltose with a linear absorption and absorption specificity. Then this technique was applied in the quantification of amino acids in sepia capsule. After the optimization of the method, four kinds of amino acids, which were the most abundant, were quantified by high‐performance liquid chromatography with diode array detection. The amounts of the four kinds of amino acids are 1.5～2 times more than that without the treatment of solid‐phase extraction column, which almost overcomes the influence of the maltose. All the results indicate that the phenylboronic acid modified solid‐phase extraction column can successfully help to accurately quantify the total amino acids in sepia capsule.     

表面接枝型离子色谱固定相的制备

以苯乙烯-二乙烯基苯微球为基质,建立了一种新型离子色谱固定相的制备方法。在基质微球表面合成一层聚缩水甘油甲基丙烯酸酯聚合物层(GMA),随后与甲胺及1,4-丁二醇二环氧甘油醚(BDDE)交替反应,与其表面接枝上带正电荷的季铵基团,可用于阴离子的分离。通过改变接枝反应的次数,控制交换树脂的交换容量。自制色谱固定相能够用于7种常规阴离子分离分析,并用于自来水中常规阴离子的检测。分离检测结果可与商用离子色谱柱相比,同时水负峰能与氟离子完全分离,不影响氟离子的定量检测。     

High temperature fast chromatography of proteins using a silica-based stationary phase with greatly enhanced low pH stability

Reversed-phase liquid chromatography (RPLC) is very widely used for the separation and characterization of proteins and peptides. A novel type of highly stable silica-based stationary phase has been developed for protein separations. A dense monolayer of dimethyl-(chloromethyl)phenylethyl)-chlorosilane (DM-CMPES) on the surface of silica is "hyper-crosslinked" with a polyfunctional aromatic crosslinker through Friedel-Crafts chemistry resulting in stationary phases with extraordinary stability in acidic media. Elemental analysis data confirm the high degree of cross-linking among the surface groups. The hyper-crosslinked phases are extremely stable under highly acidic mobile phase conditions even at a temperature as high as 150 degrees C. A wide-pore (300 A) material made in this way is used here to separate proteins by a reversed-phase mechanism and compared to a commercially available "sterically protected" C18 phase. For small molecules, including neutral and basic compounds, these crosslinked phases give comparable peak shape and efficiency to the commercial phase. Our results show that no pore blockage takes place as commonly afflicts polymer coated phases. In consequence, protein separations on the new phases are acceptable. Using strong ion-pairing reagents, such as HPF6, improves the separation efficiency. Compared to the commercial phases, these new phases can be used at lower pHs and much higher temperatures thereby enabling much faster separations which is the primary focus of this work. Better efficiency for proteins was obtained at high temperature. However, at conventional linear velocities the instability of proteins at high temperature becomes a problem which establishes an upper temperature limit. Uses of a narrowbore column and high flow rates both solves this problem by reducing the time that proteins spend on the hot column and, of course, speeds up the separation of the protein mixture. Finally, an ultrafast gradient (<1 min) protein separation was obtained by utilizing the high temperature and thus high linear velocities afforded by the extreme stability of these new phases. The phases are stable even after 50h of exposure to 0.1% TFA at 120 degrees C. This paper is dedicated to the memory of Csaba Horvath whose work in high temperature HPLC inspired the development of the stationary phases described here.     

Automated solid‐phase extraction of phenolic acids using layered double hydroxide–alumina–polymer disks

The application of layered double hydroxide–Al₂O₃–polymer mixed‐matrix disks for solid‐phase extraction is reported for the first time. Al₂O₃ is embedded in a polymer matrix followed by an in situ metal‐exchange process to obtain a layered double hydroxide–Al₂O₃–polymer mixed‐matrix disk with excellent flow‐through properties. The extraction performance of the prepared disks is evaluated as a proof of concept for the automated extraction using sequential injection analysis of organic acids (p‐hydroxybenzoic acid, 3,4‐dihydroxybenzoic acid, gallic acid) following an anion‐exchange mechanism. After the solid‐phase extraction, phenolic acids were quantified by reversed‐phase high‐performance liquid chromatography with diode‐array detection using a core–shell silica–C18 stationary phase and isocratic elution (acetonitrile/0.5% acetic acid in pure water, 5:95, v/v). High sensitivity and reproducibility were obtained with limits of detection in the range of 0.12–0.25 μg/L (sample volume, 4 mL), and relative standard deviations between 2.9 and 3.4% (10 μg/L, n = 6). Enrichment factors of 34–39 were obtained. Layered double hydroxide–Al₂O₃–polymer mixed‐matrix disks had an average lifetime of 50 extractions. Analyte recoveries ranged from 93 to 96% for grape juice and nonalcoholic beer samples.     

Histidine‐modified organic‐silica hybrid monolithic column for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography

A novel organic‐silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro‐osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water‐rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed‐mode mechanism of hydrophobic and ion‐exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine‐modified organic‐silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.