Fast gel permeation chromatography–mass spectrometry method for polymer and additive analysis

This study presents gel permeation chromatography (GPC) coupled with mass spectrometry (MS) as a suitable method to evaluate molecular weight distribution, oligomeric structure, and additives of commercial polystyrene resins in just 4?min. The chromatogram recorded by ultraviolet (UV) detection gives information on the high molecular mass fractions, while the mass detector provides knowledge on the chemical structure and concentration of oligomers and additives. A good agreement for the average molecular weights of the broad polystyrene reference SRM 706 and an excellent correlation with the expected isotope distributions for oligomers and additives were obtained using this fast GPC–UV–MS method.     

Gas chromatography — evolution and revolution

The development of gas chromatography since its inception is briefly traced, current demands of users are outlined and the present situation and future prospects are considered using the latest instrumentation as an example.     

Supercritical-fluid chromatography — prospects and problems

Recently, there has been a renewed interest in supercritical-fluid chromatography (SFC) as an alternative technique for the rapid and efficient separation of non-voltatile or thermally labile compounds. In this contribution the potential of SFC is investigated, the current status of instrumentation is reviewed and areas for further research are identified.     

Ultrasonication extraction and gel permeation chromatography clean-up for the determination of polycyclic aromatic hydrocarbons in edible oil by an isotope dilution gas chromatography–mass spectrometry

An analytical method for the determination of US EPA priority pollutant 16 polycyclic aromatic hydrocarbons (PAHs) in edible oil was developed by an isotope dilution gas chromatography–mass spectrometry (GC–MS). Extraction was performed with ultrasonication mode using acetonitrile as solvent, and subsequent clean-up was applied using narrow gel permeation chromatographic column. Three deuterated PAHs surrogate standards were used as internal standards for quantification and analytical quality control. The limits of quantification (LOQs) were globally below 0.5 ng/g, the recoveries were in the range of 81–96%, and the relative standard deviations (RSDs) were lower than 20%. Further trueness assessment of the method was also verified through participation in international cocoa butter proficiency test (T0638) organised by the FAPAS with excellent results in 2008. The results obtained with the described method were satisfying (z ≤ 2). The method has been applied to determine PAH in real edible oil samples.     

Rapid and sensitive analysis of disaccharide composition in heparin and heparan sulfate by reversed-phase ion-pair chromatography on a 2 μm porous silica gel column

A rapid and sensitive method was developed for the analysis of disaccharide composition in heparin (HP) and heparan sulfate (HS) by reversed-phase ion-pair chromatography on a 2 μm porous silica gel column. HP and HS were digested with heparin lyase I, II and III in combination, and the produced unsaturated disaccharides were separated within 15 min. Calibration graphs were linear in the range 1 ng–1 μg with the fluorometoric post-column detection using 2-cyanoacetamide.     

Are axial and radial flow chromatography different?

Radial flow chromatography can be a solution for scaling up a packed bed chromatographic process to larger processing volumes. In this study we compared axial and radial flow affinity chromatography both experimentally and theoretically. We used an axial flow column and a miniaturized radial flow column with a ratio of 1.8 between outer and inner surface area, both with a bed height of 5 cm. The columns were packed with affinity resin to adsorb BSA. The average velocity in the columns was set equal. No difference in performance between the two columns could be observed. To gain more insight into the design of a radial flow column, the velocity profile and resin distribution in the radial flow column were calculated. Using mathematical models we found that the breakthrough performance of radial flow chromatography is very similar to axial flow when the ratio between outer and inner radius of the radial flow column is around 2. When this ratio is increased, differences become more apparent, but remain small. However, the ratio does have a significant influence on the velocity profile inside the resin bed, which directly influences the pressure drop and potentially resin compression, especially at higher values for this ratio. The choice between axial and radial flow will be based on cost price, footprint and packing characteristics. For small-scale processes, axial flow chromatography is probably the best choice, for resin volumes of at least several tens of litres, radial flow chromatography may be preferable.     

Assessing the suitability of a green solvent for gel permeation chromatography–mass spectrometry analysis

The study presents the possibility of performing the analysis of oligomeric structures and polymer additives by gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) in dibuthoxymethane (DBM, butylal), a halogen-free and less hazardous solvent than typically used chloroform and tetrahydrofuran. Polystyrene oligomers and Irganox® additives were analyzed in DBM using 2.1?mm internal diameter GPC columns, allowing to decrease the flow rate down to 50?µL/min, compatible with APCI–MS interface. The ionization was controlled by adding 1% chloroform in DBM to obtain (M+Cl)^? adducts, allowing a fast optimization of method parameters.     

Csaba Horváth and preparative liquid chromatography

Few chromatographers have been interested in furthering preparative liquid chromatography. The pioneers, Tswett, Kuhn and Lederer, A.J.P. Martin, Tiselius, isolated fractions but as an intermediate step in the analysis of their samples. The progress in electronics and sensors, and in their miniaturization has lead to the paradoxical situation that the analysts never see the transient pure fractions that their detector quantitates. Yet, over the last 25 years, preparative liquid chromatography has become an important industrial process for the separation, the extraction, and/or the purification of many pharmaceuticals or pharmaceutical intermediates, including pure enantiomers, purified peptides and proteins, compounds that are manufactured at the relatively large industrial scale of a few kilograms to several hundred tons per year. This development that has strongly affected the modem pharmaceutical industry is mainly due to the pioneering work of Csaba Horváth. His work in preparative HPLC was critical at both the practical and the theoretical levels. He was the first scientist in modem times to pay serious attention to the relationships between the curvature of the equilibrium isotherms, the competitive nature of nonlinear isotherms, and the chromatographic band profiles of complex mixtures. The thermodynamics of multi-component phase equilibria and mass transfer kinetics in chromatography attracted his interest and were the focus of ground-breaking contributions. He investigated displacement chromatography, an old method invented by Tiselius that Csaba was first to implement in HPLC. This choice was explained by the essential characteristic of displacement chromatography, in that it delivers fractions that can be far more concentrated than the feed. Remarkably, once the basics of nonlinear chromatography had been mastered in his group, most of the applications that were studied by his coworkers dealt with peptides of various sizes and with proteins. Thus, all the applications of preparative HPLC in the biotechnologies derive directly from Csaba's work. Although displacement did not pan out as a general method, the reasons are related more to practical constraints of the production of pharmaceuticals and to the long period of cheap energy that might be ending now. This report reviews Csaba's work in nonlinear chromatography.     

Synthesis and sol–gel assembly of nanophosphors

Some recent works made in our group on inorganic nanophosphors are briefly reviewed in this paper. We first present the synthesis of highly concentrated semiconductor quantum dot colloids allowing the extension of the well-known oxide sol–gel process to chalcogenide compounds. Secondly, we show the synthesis and the chemical functionalization of lanthanide-doped insulator nanoparticles. In particular, the annealing process of these particles at high temperature leads to highly bright nanocrystals, which can be used as biological luminescent labels or for integration in transparent luminescent coatings. Finally, we consider luminescent transition metal clusters, which combine the inorganic structure of nanoparticles with the monodispersity and the easy functionalization of the organic molecules. Emphasis is put on the original thermochromic luminescence properties of copper iodide clusters trapped in siloxane-based films.     

Elucidation of n-butyl benzyl phthalate biodegradation using high-performance liquid chromatography and gas chromatography–mass spectrometry

n-Butyl benzyl phthalate (BBP) is an endocrine-disrupting chemical. A bacterium species capable of using BBP as the sole source of carbon and energy was isolated from mangrove sediment. Effects of BBP concentration, pH, temperature, and salinity on BBP biodegradation were studied. The optimum pH, temperature, and salinity for the BBP biodegradation were 7.0, 37°C, and 15 g L⁻¹, respectively. BBP was completely degraded within 6 days under optimum conditions, and the biodegradation of BBP could be fitted to a first-order kinetic model. The major metabolites of BBP biodegradation were identified as mono-butyl phthalate, mono-benzyl phthalate, phthalic acid, and benzoic acid by using high-performance liquid chromatography and gas chromatography–mass spectrometry. A preliminary metabolic pathway was proposed for the biodegradation of BBP.      

Synthesis and characterization of sol–gel alumina nanofibers

Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m² g⁻¹ has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. ²⁷Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA. Graphical Abstract      

Sol–gel derived mesoporous and microporous alumina membranes

Stable polymeric and colloidal boehmite sols were prepared by sol–gel process through controlled hydrolysis/condensation reactions. The particle sizes of the colloidal sols were in the 12–25 nm range depending on the process parameters and about 2 nm for polymeric sols. The presence of a significant increase in the microporosity content of the heat treated polymeric membranes relative to the mesoporous colloidal membranes might make the design of thermally stable microporous alumina membranes with controlled pore structures possible. The phase structure evolution in the 600–800 °C range had shown that the crystallization of the gamma alumina in the amorphous matrix starts at about 800 °C. This indicated that the pore structure stability may be enhanced through processing up to this relatively high temperature in polymeric alumina derived unsupported membranes. The permeance values of the two and three layered colloidal alumina membranes were observed to be independent of pressure which implies that the dominant gas transport mechanism is Knudsen diffusion in these structures. This was also supported by the 2.8 nm BJH pore sizes of the colloidal membranes. The Knudsen diffusion equation derived permeances of the polymeric alumina membranes with thicknesses of about 300 nm were determined to be very close to the experimentally determined permeance values.     

Regularities of the sorption of cycloalkenyl-substituted thiophenes and 2,2′-bithiophenes from water-acetonitrile solutions on hexadecyl silica gel under conditions of high-performance liquid chromatography

Regularities of the sorption of newly synthesized cycloalkenyl-substituted thiophenes and 2,2′-bithiophenes from water-acetonitrile solutions of different compositions on hexadecyl silica gel are investigated by high-performance liquid chromatography (HPLC). The retention factors and Henry constants of adsorption of these substances are determined. We discuss the effect of the molecular structure of the investigated heterocycles, and the nature and positions of the substituents, on the sorption. The equilibrium constants for the quasi-chemical reactions of sorption of the investigated compounds at the interface, and their solvation in a multicomponent bulk solution, are calculated using the Lanin-Nikitin equation. Based on the obtained results, we suggest that structural self-organization in the bulk solution and at the interface with the hydrophobic surface of hexadecyl silica gel plays an important part in the sorption of cycloalkenylsubstituted thiophenes and 2,2′-bithiophenes from multicomponent solutions.     

Sol–gel composite coatings from methyltriethoxysilane and polymethylhydrosiloxane

New composite coatings were prepared by mixing pre-hydrolyzed methyltriethoxysilane (MTES) sol by an acidic catalyst dibutyltin dilaurate (DBTDL) and polymethylhydrosiloxane (PMHS) in gasoline at room temperature. The gel process was thoroughly investigated regarding the use of different basic catalyst [3-aminopropyltriethoxysilane (APTES) or triethylamine (TEA)], as well as the ratios of pre-hydrolyzed MTES sol and PMHS with various content of active H. It was revealed that the composite coating from 2:1 ratio (w/w) of pre-hydrolyzed MTES sol with equimolar amounts of water and PMHS_1.55 under the catalysis of APTES demonstrated high pencil hardness, and excellent resistance against contamination and corrosion. This composite coating (MTPM21-A) was further characterized by FTIR, ²⁹Si NMR, DSC and TGA.     

Separation and characterisation of beta2-microglobulin folding conformers by ion-exchange liquid chromatography and ion-exchange liquid chromatography–mass spectrometry

In this work we present for the first time the use of ion-exchange liquid chromatography to separate the native form and a partially structured intermediate of the folding of the amyloidogenic protein beta₂-microglobulin. Using a strong anion-exchange column that accounts for the differences in charge exposure of the two conformers, a LC–UV method is initially optimised in terms of mobile phase pH, composition and temperature. The preferred mobile phase conditions that afford useful information were found to be 35 mM ammonium formate, pH 7.4 at 25 °C. The dynamic equilibrium of the two species is demonstrated upon increasing the concentration of acetonitrile in the protein sample. Then, the chromatographic method is transferred to MS detection and the respective charge state distributions of the separated conformers are identified. The LC–MS results demonstrate that one of the conformers is partially unfolded, compared with the native and more compact species. The correspondence with previous results obtained in free solution by capillary electrophoresis suggest that strong ion exchange LC–MS does not alter beta₂-microglobulin conformation and maintains the dynamic equilibrium already observed between the native protein and its folding intermediate.     

Preparative separation of α- and β-santalenes and (Z)-α- and (Z)-β-santalols using silver nitrate-impregnated silica gel medium pressure liquid chromatography and analysis of sandalwood oil

The major sesquiterpene constituents of East-Indian sandalwood oil (Z)-α- and (Z)-β-santalols have shown to be responsible for most of the biological activities and organoleptic properties of sandalwood oil. The work reported here describes the strategic use of medium pressure liquid chromatography (MPLC) for the separation of both α- and β-santalenes and (Z)-α- and (Z)-β-santalols. Silver nitrate impregnated silica gel was used as the stationary phase in MPLC for quantitative separation of α- and β-santalenes and (Z)-α- and (Z)-β-santalols with mobile phases hexane and dichloromethane, respectively. The purities of α-santalene and (Z)-α-santalol obtained were >96%; however, β-santalene and (Z)-β-santalol were obtained with their respective inseparable epi-isomers. Limits of quantification (LoQ) relative to the FID detector were measured for important sesquiterpene alcohols of heartwood oil of S. album using serial dilutions of the standard stock solutions and demonstrated that the quality of the commercial sandalwood oil can be assessed for the content of individual sesquiterpene alcohols regulated by Australian Standard (AS2112-2003), International Organization for Standardization ISO 3518:2002 (E) and European Union (E. U.).     

Detailed study of polystyrene solubility using pyrolysis–gas chromatography–mass spectrometry and combination with size-exclusion chromatography

Measuring polymer solubility accurately and precisely is challenging. This is especially true at unfavourable solvent compositions, when only very small amounts of polymer dissolve. In this paper, pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS) is demonstrated to be much more informative and sensitive than conventional methods, such as ultraviolet spectroscopy. By using a programmed-temperature-vapourisation injector as the pyrolysis chamber, we demonstrate that Py-GC-MS can cover up to five orders of magnitude in dissolved polymer concentrations. For polystyrene, a detection limit of 1 ng mL^?1 is attained. Dissolution in poor solvents is demonstrated to be discriminating in terms of the analyte molecular weight. Py-GC-MS additionally can yield information on polymer composition (e.g. in case of copolymers). In combination with size-exclusion chromatography, Py-GC-MS allows us to estimate the molecular weight distributions of minute amounts of a dissolved polymer and variations therein as a function of time.

Fate of tris(2-chloroethyl)amine in water and alkaline environment determined by thin-layer chromatography and gas chromatography–mass spectrometry

Tris(2-chloroethyl)amine is a chemical warfare agent which is considered to be a persistent contaminant highly resistant to decontamination. The time dependence of tris(2-chloroethyl)amine degradation on the water pH value is observed to determine decontamination options using the decontamination of hydroxide-based mixtures which are used by a number of armed forces. The kinetics was observed using thin-layer chromatography and gas chromatography. The time development of tris(2-chloroethyl)amine concentration decrease in the environment with the pH ranging from 7.5 to 12.5 was recorded. The reaction rate constants were established at all observed pH values, half-lifes of reactions and the influence of temperature on the reaction rate at a slightly alkaline pH of 8.5. The equation to estimate the rate constant of the first step of tris(2-chloroethyl)amine hydrolysis at various temperatures was formed. The rate of triethanolamine formation in the samples of neutral to alkaline pH was recorded. The results indicate the substantial influence of pH on tris(2-chloroethyl)amine hydrolysis. The rate constant was significantly increased from a neutral environment to the pH of 12.5 reaching 500% of the original value using alkalisation. The hydrolysis in a neutral environment was also influenced by the analyte concentration. The concentrated solutions hydrolysed more slowly as a result of hydrochloric acid release as the acid lowered the pH value of the environment. The results demonstrate that there is an important kinetic difference between sulphur and nitrogen mustard hydrolysis in an alkaline environment.