Current-day employment of the micro-bore open-tubular capillary column in the gas chromatography field

Chromatographic speed classification for liquid chromatography using average theoretical peak time (ATPT)

BACKGROUND

The development of analytical techniques in the field of liquid chromatography has brought new frontiers in performance and analytical speed for the technique. The proper evaluation of the analytical boundaries achieved with those developments was not addressed in the literature, since different liquid chromatography (LC) techniques have not yet received any classification regarding their chromatographic speed. Defining chromatographic analysis speed based simply on analysis time is an outdated concept since it is sample and analyte-dependent. In this context, the application of the Average Theoretical Peak Time concept (ATPT) is proposed as a unified metric for chromatographic speed classification.

RESULTS

This metric was evaluated using PCA analysis in a group of more than 50 publications, which generated the classification of LC methods in normal, high, hyper, and ultra-high-speed separations using ATPT. Normal speed (ATPT values greater than 18000 ms/peak) was found in HPLC, nano-LC, SFC, and CEC methods. Therefore, high-speed methods (ATPT values between 4000 and 18000 ms/peak) were found in UHPLC techniques, while LC × LC methods presented higher ATPT values between 1000 and 4000 ms/peak being classified as hyper-speed separations. ATPT can also be used as an optimization parameter, since older methods show higher ATPT values, while recent published papers show lower values of this metric. This behavior is justified due to the improvement of the LC methods over the years.

SIGNIFICANCE

This work fulfills the gap in chromatographic definitions and metrics, regarding analytical speed in one-dimensional and multidimensional liquid chromatographic techniques and shows that ATPT metrics is a robust parameter that can be used to classify the separation speed as well as a metric to evaluate the LC Method optimization. It also corrects the historical application of separation time as a metric for chromatographic speed.

In-situ growth of a spherical vinyl-functionalized covalent organic framework as stationary phase for capillary electrochromatography-mass spectrometry analysis

Column technology is an important part in capillary electrochromatographic science. Developing novel stationary phase with high separation efficiency and high loading capacity is an essential work. In this work, a novel spherical vinyl-functionalized covalent-organic framework (COF-V) was synthesized at room temperature and firstly employed as stationary phase for CEC-MS analysis. The COF-V based CEC column was characterized by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The results proved the successful modification of COF-V. The COF-V based column possesses the advantages like strong electroosmotic flow, high separation efficiency and high loading capacity. The CEC column showed powerful separation selectivity to several kinds of compounds, and the highest column efficiency (theoretical plates, N) was over 1.4 × 10⁵ plates·m^-1 for methylbenzene. Besides, the COF-V modified column exhibited excellent repeatability and stability. The relative standard deviations (RSDs) of retention times for intra-day (n = 5), inter-day (n = 3) runs and column-to-column (n = 3) were all less than 2.1%. Hence, the COF-V modified column was successfully applied in CEC-MS for determination of antiepileptic drug, triazine herbicides and active ingredients in traditional Chinese medicine.

Rational Strategy for Space-Confined Seeded Growth of ZnO Nanowires in Meter-Long Microtubes

Seeded crystal growths of nanostructures within confined spaces offer an interesting approach to design chemical reaction spaces with tailored inner surface properties. However, such crystal growth within confined spaces tends to be inherently difficult as the length increases as a result of confinement effects. Here, we demonstrate a space-confined seeded growth of ZnO nanowires within meter-long microtubes of 100 μm inner diameter with the aspect ratio of up to 10 000, which had been unattainable to previous methods of seeded crystal growths. ZnO nanowires could be grown via seeded hydrothermal crystal growth for relatively short microtubes below the length of 40 mm, while any ZnO nanostructures were not observable at all for longer microtubes above 60 mm with the aspect ratio of 600. Microstructural and mass spectrometric analysis revealed that a conventional seed layer formation using zinc acetate is unfeasible within the confined space of long microtubes as a result of the formation of detrimental residual Zn complex compounds. To overcome this space-confined issue, a flow-assisted seed layer formation is proposed. This flow-assisted method enables growth of spatially uniform ZnO nanowires via removing residual compounds even for 1 m long microtubes with the aspect ratio of up to 10 000. Finally, the applicably of ZnO-nanowire-decorated long microtubes for liquid-phase separations was demonstrated.

Preparation and Thermal Evaluation of Novel Polyimide Protective Coatings for Quartz Capillary Chromatographic Columns Operated over 320 °C for High-Temperature Gas Chromatography Analysis

Protection of intrinsically brittle quartz chromatographic columns (CCs) from breakage or property deterioration in gas chromatography (GC) analysis has become an important research topic regarding high-temperature GC techniques. Polyimide (PI) has proved to be the most suitable protective coating for quartz CCs. In the current research, a series of novel high-temperature-resistant PI coatings for quartz CCs operated over 320 °C have been successfully prepared. For this purpose, the aromatic diamine with a rigid skeleton structure 2-(4-aminophenyl)-5-aminobenzimidazole (APBI) was copolymerized with two aromatic dianhydrides—3,3’,4,4’-benzophenotetracarboxylic acid dianhydride (BTDA) and 4,4’-oxydiphthalic anhydride (ODPA)—and an aromatic diamine with flexible ether linkages—4,4’-oxydianiline (ODA)—by a two-step polymerization procedure via soluble poly(amic acid) (PAA) precursors, followed by thermal imidization at elevated temperatures. The developed PI coatings exhibited good comprehensive properties, including glass transition temperatures (T_g) as high as 346.9 °C, measured by dynamic mechanical analysis (DMA), and coefficients of linear thermal expansion (CTEs) as low as 24.6 × 10⁻⁶/K in the range of 50–300 °C. In addition, the PI coatings exhibited good adhesion to the fused quartz capillary columns. No cracking, delamination, warpage, or other failures occurred during the 100-cycle thermal shock test in the range of 25–320 °C.

Determination of n-alkanes contamination in soil samples by micro gas chromatography functionalized by multi-walled carbon nanotubes

A new method for separation of 11 n-alkanes: octane, o-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentdecne, n-hexadecath, heptadecane, n-octadecane in soil samples was developed. Kuderna-Danish (K.D.) concentrator enrichment prior to ultrasonic extraction and the silicone chromatography column purification and with gas chromatography flame ionization detection (GC-FID) could be used for n-alkanes determination. The micro channels of open tubular column were fabricated onto a silicon wafer to replace the quartz capillary chromatographic column. The column structure and analysis parameters that affected the column separation were investigated and optimized. Under optimal conditions, the extract reagent was centrifuged and collected. A silicone chromatography column and a K.D. concentrator were used for further clean-up and enrichment. Using this method, the limits of detection (LOD) and limits of quantification (LOQ) were obtained in the range of 0.03-0.15 and 0.1-0.5 mg kg(-1) in soil samples, respectively. The relative standard deviation (RSD) was under 12%. The optimized procedure that presented good analytical performance (with recoveries ranging from 56.5% to 89.2%), was successfully applied to determine n-alkane content in farmland soil samples adjacent to a highway. The results showed that the MWCNTs-functionalized column is capable of separating the alkane contaminations with high resolution in about 3 min, which is much shorter than that of GC-MS and other conventional analytical methods, demonstrating its great potential for rapid analysis.

Research on the separation properties of empty-column gas chromatography (EC-GC) and conditions for simulated distillation (SIMDIS)

Previous studies have revealed it is possible to separate a high-boiling mixture by gas chromatography in empty fused-silica capillary tubing rather than in columns coated with stationary phase. Chromatographic separation occurs solely on the basis of the different boiling points of the substances separated. The high similarity of such separations to those in classic distillation seems advantageous when gas chromatography is used for simulated distillation. This paper presents results from further research on the separation properties of empty fused silica tubing. The efficiency of this chromatographic system has been examined. The usefulness of such conditions has been studied for simulated distillation, i.e. to determine the boiling-point distribution of complex mixtures, mainly petroleum fractions and products, on the basis of their retention relative to reference substances. The results obtained by use of empty-column gas chromatography (EC-GC) and by use of classical simulated distillation columns have been compared for solutes of different polarity. Studies revealed boiling points determined by EC-GC were more accurate than those obtained by the standard method of simulated distillation.