Exploitation of a microporous organic polymer as a stationary phase for capillary gas chromatography

Microporous organic polymers (MOPs) have emerged as a new class of functional porous materials with unique characteristics and potential uses in diverse areas. However, the field of MOPs for gas chromatographic (GC) separations has not been well explored. Herein, a MOP namely KAPs-1 was dynamic coated onto a capillary column for the first time. The fabricated column exhibited a nonpolar nature and the column efficiency for n-dodecane was up to 7769 plates m⁻¹. The KAPs-1 coated column showed high GC separation performance for a series of volatile organic compounds (VOCs) including the challenging ethylbenzene and xylene isomers, which could not be resolved at baseline on the commercial 5% phenyl polysiloxane stationary phase. Moreover, the relative standard deviations for five replicate determinations of the studied analytes were 0.0–0.6%, 0.9–3.2%, 1.1–5.9%, 0.8–3.7% for retention time, peak area, peak height and peak width, respectively. To investigate the interaction between some analytes and the stationary phase, thermodynamic and kinetic parameters were also evaluated. The results of this study show it is very promising to utilize MOPs as stationary phases for capillary GC.     

Fabrication of microporous organic network@silica composite for high-performance liquid chromatographic separation of drugs and proteins

Microporous organic networks (MONs) that exhibit good stability and hydrophobicity are promising candidates for performing HPLC separation of small organic compounds. However, their applications in separating large analytes as well as biomolecules are still limited by the microporous nature of MONs. Herein, we demonstrated the fabrication of a MON-functionalized silica (MON@SiO₂), exhibiting micro and mesopores for the HPLC separations of small drugs as well as large analytes, such as flavones, nonsteroidal anti-inflammatory drugs (NSAIDs), endocrine disrupting chemicals (EDCs), and proteins. MON was successfully modified on SiO₂ microspheres to yield the uniform and mono-dispersed MON@SiO₂. The separation mechanisms and performance of the MON@SiO₂ packed column were evaluated for a wide range of analytes, including neutral, acidic, basic compounds, drugs, and proteins. Compared with commercial C18 and SiO₂–NH₂ packed columns, the proposed MON@SiO₂ column afforded superior performance in the separations of flavones, NSAIDs, EDCs, and proteins. Moreover, the MON@SiO₂ column also offered good repeatability with intraday RSDs (n = 7) of <0.1%, <2.0%, <2.3%, and <0.7% for the retention time, peak height, peak area, and half peak width, respectively, for separating EDCs. This work proved the potential of using MONs in the HPLC separations of drugs and proteins.     

Gas chromatography of hydrocarbons using packed liquid chromatographic capillary columns

Capillary columns of 0.3-0.5 mm i.d. packed with 3- to 30-μm silica-based stationary phases for liquid chromatography were used for gas chromatographic separation of hydrocarbons. Column efficiencies were evaluated for various commercially available packing material. The best column efficiency was achieved with 5-μm octadecyl group bonded silica gel, the surface of which was coated with a poly (dimethylsiloxane) film. The 30-cm column produced 11,000 theoretical plates.     

Single fiber-in-capillary annular column for gas chromatographic separation

A method for preparation of a stationary phase-adjustable column with in-column stationary phase-coated fused-silica fiber annular column was successfully developed. The surface of a 0.12 mm o.d. bare optical fiber was first coated with a stationary phase and then inserted into a fused-silica capillary (non-coated or coated) as an annular column for gas chromatographic study. The optical fiber and capillary were coated with polydimethylsiloxane (SE-30) and polyethylene glycol 20M (PEG-20M) as nonpolar and polar stationary phases, respectively. Among the investigated annular and open tubular columns, the PEG-20M-coated fiber-in-PEG-20M-coated capillary annular column showed the highest column efficiency with a minimum plate height of 0.35 mm and an optimum gas velocity of 25 cm/s. When a SE-30/PEG-20M-coated fiber-in-uncoated capillary annular column was applied to separate a 9-component complex mixture, the total analysis time was 5.3 min and the column length was 12 m. By contrast, when a SE-30-coated fiber-in-PEG-20M-coated capillary annular column was used to separate the same 9-component mixture, the analysis time was reduced to 3.5 min and the column length was shortened by half to 6 m. Our results show that the stationary phase-coated fiber-in-stationary phase-coated capillary annular column is a better choice for gas chromatographic separation as it is more efficient and flexible. In addition, the proposed annular column design provides flexibility in using two or even more types of stationary phases to achieve optimal analytical separation.     

Equilibrium chromatographic characteristics of capillary column coated with polytrimethylpropyne for separating polar and non-polar organic compounds by gas capillary chromatography

The temperature dependence (50—180 °C) of the retention factor for 35 hydrocarbons and their oxygen-containing derivatives was studied using a capillary column coated with a new film-forming polymeric adsorbent polytrimethylsilylpropyne (PTMSP). The heats of adsorption for 24 organic polar and non-polar compounds on PTMSP were determined. They turned out to be lower than the heats of adsorption of the same compounds on Porapak Q widely used in gas chromatography. The new adsorbent PTMSP is characterized by high selectivity suitable for practical application.     

Gas chromatographic resolution of enantiomeric and diastereoisomeric amino acid esters on Chirasil-Val capillary column

Summary D,L-amino acids were derivatized with (+), (±)-2-butanol or N-trifluoroacetyl-L-prolyl chloride (L-TPC) and then chromatographed. Four optical isomers were separated on a Chirasil-Val capillary column. By this method, the concentration of optical impurities arising from the commercial optically active reagents can be determined. The observed abnormal elution orders of enantiomeric amino acid esters may be caused by a selective intermolecular force.     

Gas chromatographic separation of expoxystyrenes on carbowax 20 M capillary column

Summary The separation of some epoxystyrenes on fused silica capillary columns coated with poly(ethylene glycol) was investigated, Retention indices were determined at two temperatures to interpret chromatographic behaviour, The standard deviation was 0.3 index units.     

Prediction of the separation number of capillary columns in programmed temperature gas chromatographic analysis

The efficiency of capillary columns in programmed temperature analysis can be evaluated by calculation of the separation number (“Trennzahl”). A procedure for the prediction of this parameter at various initial temperatures, carrier gas pressures and heating rates, by using as the starting data the retention times and the peak widths obtained in some isobaric and isothermal runs is described. An equation is proposed that permits to obtain the values of the peak width at half height in any isothermal and linearly programmed temperature gas chromatographic run and therefore to calculate the separation number value. The effect on this parameter of the column polarity was investigated by using polar and non-polar compounds (n-alkanes and 1-alcohols).     

Design and evaluation of a mixed-phase capillary column for the gas chromatographic separation of the volatile components of cheese

Summary A mixed-phase capillary GC column has been designed for the separation of the compounds commonly present in the volatile fraction of cheeses. The design includes the calculation of the optimum phase concentration and the operating conditions. The evaluation of the resulting column indicates that its performance in the qualitative and quantitative analysis of cheese volatile compounds is better than those of other columns coated with a single stationary phase.     

Preparation of core-shell microporous organic polymer-coated silica microspheres for chromatographic separation and N-glycopeptides enrichment

Through a “one-pot” strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2 μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.     

A fast derivatization procedure for gas chromatographic analysis of perfluorinated organic acids

A rapid and simple derivatization procedure has been developed for gas chromatographic determination of perfluorinated organic acids (PFCAs, C₆–C₁₂), using isobutyl chloroformate (IBCF) to convert the acids into the more volatile isobutyl esters, under catalysis by pyridine. The procedure was optimized in an acetonitrile medium and applied to GC techniques with electron-capture detection (GC-ECD) and mass spectrometry with electron-impact ionization (GC-EI-MS); for the sake of comparison, HPLC with electrospray-ionization MS (HPLC-ESI(−)-MS) was also tested. The LOD and LOQ values obtained for these three techniques were compared, and the lowest LODs were obtained with GC-ECD (0.06–1.80 μg mL⁻¹). The procedure was further optimized in an aqueous medium, obtaining the best results in a phosphate buffer (pH 2.5, 50 mmol L⁻¹), in which the LOD and LOQ values were measured for GC-ECD a GC-EI-MS. The lowest LODs were found for GC-EI-MS (0.030–0.314 μg mL⁻¹). The practical applicability was tested on Vltava river water samples.     

Headspace gas chromatographic separation of toxic organic impurities from air

Summary To determine toxic organic compounds (methanol, ethanol, n-propanol, acetone, methyl ethyl ketone, methyl isobutyl ketone) in air a method was developed for their headspace gas chromatographic analysis with preconcentration in n-butanol (alcohols) and in n-pentanol (ketones). The distribution coefficients of analytes in the air-absorbent system have been measured: 1051 (MeOH), 5630 (EtOH), 6773 (n-PrOH), 307 (Me₂CO), 580 (MeCOEt), 1035 (MeCOBu-i). The minimum detectable level (mg m⁻³) was determined as low as 0.9 (MeOH), 4.0 (EtOH), 0.9 (n-PrOH), 0.2 (Me₂CO), 0.1 (MeCOEt), 0.4 (MeCOBu-i). The method was effectively used for gas effluent air control in the workplace and in the atmosphere. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Optimization of performance of monolithic capillary column in gas chromatographic separations

Dependence of monolithic column efficiency on column pressure was analyzed using modified Van Deemter relationship with incorporated inlet and outlet column pressures as independent variables. It was demonstrated that the highest column efficiency is observed at high pressures. Inlet and outlet pressure increase has to be controlled in such a way that the relative pressure approaches 1 and the pressure drop across the column is close to zero. Experimental results obtained for open and monolithic capillary columns confirm up to 50% higher column efficiency as compared to column efficiency under standard conditions found using conventional Van Deemter plot. Pressure increase also results in a decrease in the optimal carrier gas velocity and corresponding increase in the analysis time. This drawback can be compensated via an increase in the column temperature.     

New approach to the GC separation of hydrocarbons by using LC-like microcolumns

Summary Micropacked columns for liquid chromatography were evaluated for the gas chromatographic separation of hydrocarbons. A glass-lined stainless-steel tube of 30 cm×0.3 mm i.d., packed with 5-m alkyl-modified silica, was employed as the separation column. The micropacked columns were successfully applied to the separation of components of a light oil and a kerosine.     

A gas-solid chromatographic study of the adsorption of hydrocarbons and alcohols on graphite

Summary The Henry's law region of the adsorption isotherms for several hydrocarbons and alcohols on a graphite was studied by gas-solid chromatography. The thermodynamic functions at zero surface coverage were determined. The low heats of adsorption indicate a highly homogeneous surface. A constant increment of the standard free energy with the number of carbon atoms in the lineal adsorbates was found. Attemps were made to estimate the London contribution to the surface free energy of the adsorbents. A non-specific interaction between the graphite and the adsorbates was shown.     

Chemometric studies of retention in capillary gas chromatographic separation of hydrocarbons in coupled columns

This paper describes how different multivariate analysis and classification methods can be used, to characterize the gas chromatographic separation of complex hydrocarbon mixtures in three columns coupled in series. Principal component analysis (PCA), correspondence factor analysis (CFA), and hierarchical ascending classification (HAC) were used as potential tools for evaluating the experiments on single columns and on column series. It has been demonstrated that: (1) multivariate analysis with PCA and CFA offers a powerful strategy to search for the main factors influencing the separation of hydrocarbons without a priori knowledge of the key factors of the separation. (2) With CFA the contribution of retention due to vapour pressure can be minimized. The use of retention indices, which use the n-alkanes as reference compounds, also helps to decrease the dominant focus on vapour pressure in favor of the more selectivity-based interaction forces. (3) CFA helps to analyze the degree of relevance of the chosen experimental design to the most important factors, controlling chromatographic selectivity.