Evaluation of thermionic detector for packed capillary supercritical fluid chromatography of nitrogen-containing compounds

Summary A TID was evaluated for packed capillary column supercritical fluid chromatography. Different test mixtures of nitrogen-containing compounds were separated and detected. Detection limits are determined to be 100 pg of 2-nitrodiphenylamine via packed capillary column SFC/TID. Detector linearity is about three orders of magnitude. The most critical detector parameters were the hydrogen flow rate and bead heating current.     

Coupling miniaturized liquid chromatography to capillary gas chromatography (micro-LC-CGC): Possibilities of reversed phase LC

Retention gaps with different polarity treatments were evaluated for reversed phase solvents. Aminopropyl- and cyanopropyl-deactivated retention gaps showed the best results for methanol-water mixtures. A reversed phase packed fused silica capillary LC column is connected on-line with a capillary gas chromatography column. The combination was used for the analysis of diazepam in urine. Volume overloading on packed fused silica columns without loss of too much efficiency was demonstrated for propranolol.     

CEC separation of peptides using a poly(hexyl acrylate-co-1,4-butanediol diacrylate-co-[2-(acryloyloxy)ethyl]trimethyl ammonium chloride) monolithic column

A polyacrylate-based monolithic column bearing cationic functionalities and designed for capillary electrochromatography (CEC) has been prepared via photopolymerization of a mixture of hexyl acrylate, butanediol diacrylate, 2-(acryloyloxy) ethyltrimethyl ammonium chloride (monomers), azobisisobutyronitrile (photoinitiator), acetonitrile, phosphate buffer, and ethanol (porogens). The polymerization process was initiated with UV light at 360 nm. The column performance was evaluated via the separations of alkylbenzenes, substituted anilines, basic drugs, peptides, and a protein digest. The separation of complex peptide mixtures was then studied since such separations constitute a promising application of capillary electrochromatography. In particular, the effects of mobile phase composition, including ionic strength of the buffer solution and the percentage of acetonitrile on the retention factor, the column efficiency, and the resolution were determined. The separations were affected by both interaction of the peptides with the stationary phase and their own electrophoretic mobility. Excellent separations with column efficiencies of up to 160 000 plates/m were achieved for both a mixture of ten well-defined peptides and a tryptic digest of cytochrome c. The fractions of eluent containing peptides of the digest separated in the monolithic column were collected and characterized using matrix-assisted laser desorption ionization mass spectrometry.     

Enantioselective supercritical fluid chromatography using ristocetin A chiral stationary phases

Racemic mixtures of five acidic drugs have been successfully separated by supercritical fluid chromatography (SFC) using macrocyclic antibiotic chiral stationary phases (CSPs). A ristocetin A CSP has been prepared 'in-house' and effectively applied in packed capillary SFC to separate the enantiomers of dichlorprop (R(s) = 1.4), ketoprofen (R(s) = 0.9) and warfarin (R(s) = 0.9). The commercial ristocetin A CSP (Chirobiotic R) was subsequently studied in packed column SFC with similar results where the enantiomers of warfarin (R(s) = 2.2), coumachlor (R(s) = 2.5) and thalidomide (R(s) = 0.6) were separated. Interestingly, differences were observed between the two differently immobilised CSPs where the enantiomers of dichlorprop and ketoprofen, which were separated on the 'in-house' CSP, could not be separated on the commercial phase.     

The application of capillary SFC,packed column SFC,and capillary SFC-MS in the analysis of controlled drugs

Multi–component mixtures of controlled drugs, drug impurities, and adulterants have been analyzed by capillary SFC-FID, packed column SFC-UV, and capillary SFC-MS. Isocratic packed column SFC has been performed with binary and ternary mobile phases using a single syringe pump. The combination of capillary SFC and double focusing MS is described with reference to MS source pressures and the spectra obtained. The use of negative temperature programming in SFC is described.     

Fabrication and characterization of open-tubular CEC modified with tentacle-type metal-chelating polymer chains

A novel stationary phase with tentacle-type metal-chelating polymer chains was fabricated for open-tubular CEC. The preparation procedure of the stationary phase included the synthesis of monomer, silanization of capillary inner wall, in situ polymerization, and metal complexation. The effects of initiator concentration and reaction time on the column capacity were investigated. To compare with the tentacle-type metal-chelating capillary column, a monolayer ligand-modified capillary was also prepared. Immobilized copper(II) capacity of the tentacle-type polymer stationary phase was nearly 900 times higher than that of the monolayer one. The electroosmotic mobility was examined for its dependence on pH as well as phosphate and ACN concentrations. The tentacle-type metal-chelating capillary with high ligand capacity has proven to afford better retention and resolution for the separation of phenylalanine, tryptophan, and tyrosine mixtures and three purine derivatives. The separation was considered to be effected by a combination of ligand exchange and electrophoretic mobility.     

Comparison of ultra high performance supercritical fluid chromatography,ultra high performance liquid chromatography,and gas chromatography for the separation of synthetic cathinones

A comparison of ultra high performance supercritical fluid chromatography, ultra high performance liquid chromatography, and gas chromatography for the separation of synthetic cathinones has been conducted. Nine different mixtures of bath salts were analyzed in this study. The three different chromatographic techniques were examined using a general set of controlled synthetic cathinones as well as a variety of other synthetic cathinones that exist as positional isomers. Overall 35 different synthetic cathinones were analyzed. A variety of column types and chromatographic modes were examined for developing each separation. For the ultra high performance supercritical fluid chromatography separations, analyses were performed using a series of Torus and Trefoil columns with either ammonium formate or ammonium hydroxide as additives, and methanol, ethanol or isopropanol organic solvents as modifiers. Ultra high performance liquid chromatographic separations were performed in both reversed phase and hydrophilic interaction chromatographic modes using SPP C18 and SPP HILIC columns. Gas chromatography separations were performed using an Elite‐5MS capillary column. The orthogonality of ultra high performance supercritical fluid chromatography, ultra high performance liquid chromatography, and gas chromatography was examined using principal component analysis. For the best overall separation of synthetic cathinones, the use of ultra high performance supercritical fluid chromatography in combination with gas chromatography is recommended.     

Novel open tubular CEC with tentacle-type polymer stationary phase functionalized by phenylalanine

A novel stationary phase with tentacle-type polymer chains with epoxy groups was fabricated for open tubular CEC. The fabrication procedure of the stationary phase included pretreatment of capillary inner wall, silanization, and glycidyl methacrylate (GMA)-grafted polymerization. The influence of initiator concentration and polymerization time on the resulting polymer stationary phase was studied by measuring EOF mobility and hydrophobicity of the prepared capillary column. SEM showed that the capillary inner wall was evenly coated with a polymer film showing a wrinkly surface. The prepared GMA-grafted stationary phase could be easily modified with different chromatographic ligands by the ring-opening reaction of the epoxy groups. In this study, phenylalanine (Phe) was selected as the ligand. Benzene derivatives and three amino acids were then separated, respectively, using the Phe modified tentacle-type capillary column. As a control, separations were also performed on a monolayer Phe-modified capillary. The tentacle-type polymer stationary phase was found affording stronger retention and better resolution in the separation of benzene derivatives and tryptophan, tyrosine, and Phe mixtures compared with the monolayer stationary phase.     

Capillary supercritical fluid chromatography with simultaneous flame ionization and mass spectrometric detection

A simple interface between a capillary supercritical fluid chromatograph and an Extranuclear Simulscan mass spectrometer is described. The SFC column is directly inserted into the ion source through the existing GC-interface. The system is equipped with a splitting device which allows simultaneous EI/MS and flame ionization detection when CO₂ is used as the supercritical phase. The effect of source temperature and pressure on CO₂ clustering was studied for optimization of source conditions. The performance of the system was evaluated with a series of model compounds and standard mixtures.     

超临界流体色谱密度线性程升时保留规律的研究室

推导了密度线性程升时超临界流体色谱中保留值的运动方程和相应的理论板高方程式, 并在超临界色谱条件下用毛细管柱和微填充柱上的数据对保留值方程作了验证, 理论计算值和实验测量值之间的偏差最大不超过5.00%。在推导理论方程时,设一定密度范围内1nk和密度p之间为线性函数, 这个假设也得到了实验验证。     

混合模式毛细管聚合物整体柱的制备及应用

混合模式毛细管整体色谱柱由于保留机理多样,具有很好的应用前景。本文以[2-（甲基丙烯酰基氧基）乙基]二甲基-（3-磺酸丙基）氢氧化铵（SPE）为单体,乙二醇二甲基丙烯酸酯（EDMA）为交联剂,偶氮二异丁腈（AIBN）为引发剂,正丙醇/1,4-丁二醇/水三元体系为致孔剂,制备了聚合物基质SPE-co-EDMA毛细管液相色谱整体柱。通过系统优化致孔剂和反应物种类和配比、引发剂的用量、反应时间和反应温度等因素,提高了整体柱的柱效、机械强度、渗透性和重复性。结果表明该毛细管整体柱在10 MPa内具有良好的机械强度,渗透性为2.17×10^-14 m²,而且批次内和批次间峰面积的重现性（RSD）分别为1.0%和4.6%。以极性和非极性的多种化合物评价了该毛细管整体柱的色谱性能,结果表明该柱在高有机相中具有亲水相互作用机理,在低有机相中具有反相作用机理,显示出混合模式分离特性。     

Open-tubular capillary electrochromatography using a capillary coated with octadecylamine-capped gold nanoparticles

Octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and characterized by using UV-Vis adsorption spectrum, transmission electron chromatography (TEM), SEM, and FT-IR. A simple but robust hydrophobic coating was easily developed by flushing a capillary with a solution of ODA-Au-NPs, because the positive charges were carried by the nanoparticles which strongly adsorb to the negatively charged inner surface of a fused-silica capillary via electrostatic and hydrophobic interactions. The chromatographic characteristics of the coated capillary was investigated by varying the experimental parameters such as buffer pH, buffer concentration, and percentage of organic modifier in the mobile phase. The results show that (i) resolution between thiourea and naphthalene is almost the same when comparing the electrochromatograms obtained using pH 7 buffer as mobile phase after and before the capillary column was operated using pH 11 and 3 mobile phase; (ii) no significant changes in retention time and deterioration in peak efficiency were found after 60 runs of test aromatic mixtures; and (iii) column efficiency up to 189 000 theoretical plates/meter for testosterone was obtained. All of the results indicated that the coating could act as a stable stationary phase for open tubular CEC as well as for bioanalysis.     

A study of polyethoxylated alkylphenols by packed column supercritical fluid chromatography

Alkylphenol polyethoxylates (APEs) are a widely used group of nonionic surfactants in commercial production. Characterization of the composition of APE mixtures can be exploited for the determination of their most effective uses. In this study sample mixtures contain nonylphenol polyethoxylates and octylphenol polyethoxylates. The separation of individual alkylphenols by ethoxylate units is performed by supercritical fluid chromatography (SFC)-UV as well as normal-phase high-performance liquid chromatographic (HPLC)-UV employing packed columns. The stationary phase and column length are varied in the SFC setup to produce the most favorable separation conditions. Additionally, combinations of packed columns of different stationary phases are tested. The combination of a diol and a cyano column is found to produce optimal results. An advantage of using packed columns instead of capillary columns is the ability to inject large amounts of sample and thus collect eluted fractions. In this regard, fractions from SFC runs are collected and analyzed by flow injection analysis-electrospray ionization-mass spectroscopy in order to positively identify the composition of the fractions. In comparing the separation of APE mixtures by SFC and HPLC, it is found that SFC provides shorter retention times with similar resolution. In addition, less solvent waste is produced using SFC.     

Characterization of OV-1/FFAP-mixture coated glass capillary columns used for the separation of free fatty acids

As an alternative to acid pretreated UCON and FFAP capillaries for the analysis of wide-boiling free fatty acid mixtures, OV-1 : FFAP phase mixtures were used on high-temperature silylated inert glass capillary columns. The HETP-carrier gas velocity curves, peak asymmetry factors, coating efficiency, gas phase and stationary phase contributions to the mass transfer resistance were determined for various OV-1 : FFAP ratios. Mixed-phase capillaries showed optimum performance at a 2 : 1 OV-1 : FFAP ratio. The thermal and long-term stability of OV-1-stabilized FFAP columns surpassed those of the UCON and pure FFAP reference column used.     

热解吸调制,顶空—毛细管气相色谱法测定二元液系的活度系数

本文采用热解吸调制器作毛细管气相色谱直接顶空进样测定二元液体混合物苯－甲苯和丙酮－氯仿的活度系数。热解吸调制器是在毛细管柱前端的一段短的加热段。调制器段外部镀以一薄层导电膜。所体样品连续不断地流经调制器和毛细管柱。     

A Study of the Human Urinary Steroid Metabolic Profile Using A DB-1 Fused Silica Capillary Column

This paper reports the performance of a DB-1 fused-silica capillary column for analysis of mixtures of methoxime-trimethylsilyl ether (MO-TMS) derivatives of human urinary steroid extracts. DB-1 is a non-extractable bonded phase, equivalent in polarity to SE-30 and OV-1. In addition, a small reversed-phase Sep-Pak C₁₈ cartridge is used for extraction of steroid conjugates from urine, and for the extraction of freed steroids liberated by hydrolysis. Examples of urinary steroid analysis in normal adult males and in patients with multiple myeloma using the DB-1 bonded phase fused silica capillary column are described.     

Synthesis and characterization of β-cyclodextrin modified hyperbranched carbosilane as stationary phase for GC

A new β-cyclodextrin modified hyperbranched carbosilane stationary phase for gas chromatography was synthesized by substituting the -OH groups ofβ-cyclodextrin with hyperbranched carbosilane and was coated on the inner wall of fused silica capillary column for gas chromatography.The chromatographic behaviors of the stationary phase were studied.The initial testing results showed mat it possessed good separation abilities for several kinds of mixtures,such as benzenes,acrylates,ketones and alkylchlorides.     

Coating properties of a novel water stationary phase in capillary supercritical fluid chromatography

The coating properties of a novel water stationary phase used in capillary supercritical fluid chromatography were investigated. The findings confirm that increasing the length or internal diameter of the type 316 stainless‐steel column used provides a linear increase in the volume of stationary phase present. Under normal operating conditions, results indicate that about 4.9 ± 0.5 μL/m of water phase is deposited uniformly inside of a typical 250 μm internal diameter 316 stainless‐steel column, which translates to an area coverage of about 6.3 ± 0.5 nL/mm² regardless of dimension. Efforts to increase the stationary phase volume present showed that etching the stainless‐steel capillary wall using hydrofluoric acid was very effective for this. For instance, after five etching cycles, this volume doubled inside of both the type 304 and the type 316 stainless‐steel columns examined. This in turn doubled analyte retention, while maintaining good peak shape and column efficiency. Overall, 316 stainless‐steel columns were more resistant to etching than 304 stainless‐steel columns. Results indicate that this approach could be useful to employ as a means of controlling the volume of water stationary phase that can be established inside of the stainless‐steel columns used with this supercritical fluid chromatography technique.     

Screening of inhibitors of uridine diphosphate glucuronosyltransferase with a miniaturized on-line drug-metabolism system

Inhibition of uridine diphosphate glucuronosyltransferase (UGT), a major drug-metabolyzing enzyme, has been studied using an on-line drug-metabolism system integrated into capillary electrophoresis. Microsomes isolated from rat liver were encapsulated in tetramethoxysilane (TMOS)-based silica matrices within a capillary in a single step under mild conditions. This microsome-immobilized capillary column allows both the metabolism of drugs and determination of the metabolites in a single capillary simultaneously, just by injecting the substrate-coenzyme mixture onto the column. Glucuronidation of acetaminophen, a widely used pharmaceutical analgesic and antipyretic agent, was investigated using this system. The glucuronidation was inhibited by 4-nitrophenol (4NP) or probenecid that was injected onto a column along with the substrate-coenzyme mixture. On the other hand, valproate did not inhibit the metabolizing reaction. The extents of inhibition using encapsulated UGT were almost the same as those obtained using free UGT. On the other hand, this electrophoretic enzyme-inhibitor assay in microfabricated devices consumes 10(4) less sample and 10(3) less microsome per experiment compared to the conventional reaction schemes. These results demonstrate that this on-line system can circumvent laborious procedures for the isolation and determination of drug metabolites from the reaction mixtures required in the conventional schemes and can provide an attractive alternative technique for the analysis of drug interactions in the metabolic pathways.