Column Efficiency Research Articles

Performance and selectivity of amphiphilic pillar[5]arene as stationary phase for capillary gas chromatography

Pillar[n]arenes possess highly symmetrical and rigid pillar-shaped architecture with π-electron rich cavity that afford their reliable host-guest recognition interactions towards matched guests. In this work, a novel amphiphilic pillar[5]arene (P5A-C10-2NH2) was designed, synthesized and employed as the stationary phase for capillary gas chromatography. To date, they have not been reported in the field of chromatography. The P5A-C10-2NH2 capillary column (10 m × 0.25 mm i.d.) was prepared by static coating method. Its capillary column exhibited moderate polarity and column efficiency of 2265 plates/m determined by naphthalene at 120 °C. As evidenced, the P5A-C10-2NH2 column achieved advantageous separation performance for a mixture of 24 analytes of diverse types and exhibited different chromatographic selectivity from two pillar[5]arene derivatives columns and commercial HP-35 column with 35%-phenyl-methylpolysiloxane. Moreover, the P5A-C10-2NH2 column baseline resolved more than a dozen positional and cis-trans isomers. Furthermore, the separation mechanism of P5A-C10-2NH2 column was discussed by quantum chemical calculations. In addition, the P5A-C10-2NH2 column had high thermal stability and excellent separation repeatability 0.01–0.04% for run-to-run, 0.03–0.17% for day-to-day and 3.2–3.9% for column-to-column. The special amphiphilic structure and high resolution for various analytes reveal the good potential of pillararenes as a new class of stationary phases for chromatographic analyses. Moreover, the TPG column achieved improved thermal stability over the GIL column and excellent repeatability.

Experimental Study of Enzyme-Induced Carbonate Precipitation for High Temperature Applications by Controlling Enzyme Activity

Biomineralization is a popular reinforcement technology, but which is rarely studied at high temperatures. Some potential application targets are high-temperature environments. So it's essential to study the feasibility of biomineralization at high temperatures. In this article, plant urease was selected as a cost-effective enzyme for enzyme-induced carbonate precipitation (EICP) at high temperatures. Urease activity and urease enzyme-induced carbonate precipitation were studied as a function of temperature, urease concentration, and N-(n-butyl)-thiophosphoric triamide (NBPT) addition. The effects of reaction time, number of perfusions, urease concentration, temperature, and NBPT addition on the curing efficiency of sand columns were studied by unconfined compressive strength tests and by determining the resulting concentration of CaCO3. The results demonstrated that the urease could maintain a stable activity at temperatures below 65 °C. At temperatures higher than 65 °C, urease was gradually inactivated with increasing temperature, which would influence the yield of precipitation. However, increasing the urease concentration and the number of infusions could ensure the sand solidified with adequate CaCO3. In addition, NBPT was proposed as a new way to control urease activity, which resulted in a high UCS of the sand columns formed at high temperatures. This paper bears out that sand solidification can be achieved at high temperatures using EICP and lays the foundation for future application of EICP at high temperatures.

Separation performance of pentiptycene-functionalized triblock copolymers towards the isomers of xylenes, phenols and anilines and the complex components in essential oil

This work presents the investigation of two new pentiptycene (PP)-functionalized triblock copolymers (PEPE1, PEPE2) for gas chromatographic (GC) analyses with an aim to address the separation problems toward analytes of high resemblance in properties and a wide variety of components in complex samples. Up to date, these two materials are not reported in any fields. The PEPE1 and PEPE2 columns showed close column efficiency (above 4000 plates/m) but differed in polarity, morphology and separation performance. As testified by the challenging Grob test mixture, the PEPE1 column exhibited comprehensively higher separation capability than the PEPE2 column and the commercial reference columns. Also, the PEPE1 column achieved high-resolution performance for both apolar and polar isomers of high resemblance, such as xylenes, phenols and anilines. Moreover, it displayed high inertness towards carboxylic acids and excellent separation repeatability and reproducibility tested by the aniline isomers with the RSD values in the range of 0.01–0.04% for run-to-run, 0.09–0.13% for day-to-day and 1.2–2.0% for column-to-column, respectively. Its application to GC–MS analysis of the essential oil from tea flowers demonstrated its advantageous separation performance towards a wide range of components and proved its feasibility for practical analyses of complex samples.

But Why Doesn’t It Get Better? Kinetic Plots for Liquid Chromatography, Part III: Pulling It All Together

Choosing a liquid chromatography (LC) column for a particular application can be a surprisingly challenging task. On one hand, column manufacturers give us many options to choose from, including particle types, pore sizes, particle sizes, and different lengths and diameters. On the other hand, we usually don’t have time to experimentally evaluate many combinations of these parameters, and sometimes we end up picking something similar to the columns that are already in the drawer. The “kinetic plot” is a powerful graphical tool that can help leverage the best available theory to help us understand how different combinations of parameters (that is, particle size and length) will perform in terms of the time needed to get to a particular column efficiency (and thus resolution), and therefore make well-informed decisions when choosing columns.

Photo-assisted generation of versatile zwitterionic carboxybetaine-based hypercrosslinked polymers for separation science

Zwitterionic super-hydrophilic polymeric monoliths showed fascinating attributes because of their excellent biocompatibility, hydrophilicity, and antifouling properties. However, their commercial developments are limited by their tedious preparation process and unsatisfactory performance. 1-Carboxy-N-methyl-N-di(2-methacryloyloxyethyl)methanaminium inner salt (CBMAX), an important zwitterionic functional monomer, which exhibits excellent hydrophilicity and extremely low protein adsorption from undiluted serum. However, no carboxybetaine based monolith has been reported to date. In this study, a rapid photo-assisted generation strategy based on a sole-monomer system (CBMAX being simultaneously used as monomer and crosslinker) was proposed for preparing versatile hyper-crosslinked zwitterionic carboxybetaine polymers in capillaries within only 5 min. It is significantly faster than the conventional sole-monomer (1 h) and multi-monomer system (over 12 h) via thermally-initiated polymerization approach. Moreover, a high column efficiency of 82,000 plates/m, abundant electrostatic and hydrophilic interactions were achieved on the novel monolith due to the unique advantages of carboxybetaine. These excellent features were beneficial for the high-performance separation of various bioactive compounds (including nucleotide bases, phenols, benzoic acid and its derivatives, urea and allantoin) on this monolith. It is worth noting that this zwitterionic monolith exhibited good anti-protein adsorption ability as well as excellent enrichment capacity for N-glycopeptides from hIgG tryptic digest. In summary, the proposed photo-assisted generation strategy based on sole-monomer CBMAX is very successful and opens up a promising solution for the commercial development of zwitterionic super-hydrophilic polymeric monoliths.

Are two liquid chromatography columns in tandem better than one?: Answers from the hydrophobic subtraction model

An approach is described for determining if there is an intrinsic advantage, from a selectivity and resolution perspective, of using two different UHPLC/HPLC reversed-phase columns in tandem for a separation of a given sample compared to a single U/HPLC reversed-phase column that provides the same plate number. Retention data for 16 compounds extracted directly from the hydrophobic subtraction model (HSM) database at HPLCColumns.org are used to simulate and then compare the critical resolution of those compounds obtained using HSM conditions (isocratic elution at 35°C using 50% acetonitrile, 50% aqueous phosphate buffer at pH 2.8 or 7) for each of 662 U/HPLC single columns or 218,791 combinations of tandem columns and assuming a modest plate number of 8000. The critical resolution obtained for 16 additional “n-1” samples created by the systematic removal of one of the original 16 compounds was also compared using single- and tandem-column LC, as was the critical resolution obtained for thousands of synthetic samples generated by randomly varying HSM solute descriptors for each synthetic compound. When all possible single-column or tandem-column results were compared, a significant advantage was observed with tandem-column liquid chromatography (TC-LC), with an average increase in critical resolution of 0.63 (pH 2.8) or 0.75 (pH 7) units observed for the synthetic samples with the smallest number of components (m = 5). As the number of components in a sample increased, the average improvement in critical resolution (∆Rs,crit) using TC-LC gradually decreased from about 0.70 for m = 5 to 0.18 for m = 32 components. The average improvement in critical resolution achieved by switching from SC-LC to TC-LC was also lower when a smaller number of columns and column combinations were available to explore, as would be the case for a finite column inventory in a real laboratory. Nevertheless, on average there does appear to be an intrinsic advantage of tandem-column liquid chromatography, however small, which can be amplified by using high efficiency columns.

Preparation and evaluation of ultra-long open-tubular capillary columns modified with zeolitic imidazolate framework-8 incorporated polymeric porous layer for liquid chromatography

An ultra-long (5 m) open tubular capillary liquid chromatographic column was prepared by incorporating Metal Organic Framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), directly into polymer coating, which was synthesized by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene, on the capillary inner surface. The prepared ZIF-8 incorporate polymeric open tubular capillary column (denoted as ZIF-8-p(VBC/DVB) OTCC) was evaluated with thiourea, alkylbenzenes and polycyclic aromatic hydrocarbons as probe molecules. The results showed that the ultra-long column achieved absolute column efficiency of 130,000 plates for thiourea, and the incorporation of ZIF-8 effectively improved the chromatography performance of the OTCC. Baseline separation of aromatic compounds and position isomers was achieved based on multiple interactions provided by the zeolitic imidazolate framework and polymer, including hydrophobic interaction, π-π stacking interaction and the coordination effect. The RSD values (run-to-run, day-to-day, column-to-column, n = 3) of retention time of phenylenediamine isomers and propylbenzene isomers were less than 0.7%, 1.2% and 4.0% respectively, suggesting excellent repeatability. Finally, the prepared ZIF-8-p(VBC/DVB) OTCC was applied to the separation of hydroxyacetophenone isomers with satisfied results.

Thermodynamic and economic comparison of extractive distillation sequences for separating methanol/dimethyl carbonate/water azeotropic mixtures

The separation of dimethyl carbonate (DMC)/methanol/water azeotropic mixtures has been a hot topic in the study of DMC synthesis process. In this work, the efficient organic solvent methyl salicylate, ionic liquids (ILs) 1‐butyl‐3‐methylimidazolium chloride ([BMIM][Cl]), or 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) was employed to break azeotropic mixtures. Interaction mechanisms between DMC/methanol/water and entrainers were revealed by sigma-profile. Energy and economic comparison of two alternative separation sequences including pre-separation integration with extractive-heterogeneous distillation and direct extractive distillation processes were investigated. The average relative deviations (ARD) were used to check the reliability of the NRTL model. The effect of high viscosity fluid on the mass transfer was analyzed from the perspective of the overall efficiency of column. For [BMIM][Cl], the separation mechanism is the formation of H-bond between [BMIM][Cl] and methanol/water. Direct extractive distillation process is superior to pre-separation integration with extractive-heterogeneous distillation process in terms of steam consumption, capital cost, mass transfer efficiency and total annual cost (TAC), and [BMIM][Cl]-based direct extractive distillation process is the best. This work provides a green and efficient separation route for replacing organic solvent-based process.

But Why Doesn’t It Get Better? Kinetic Plots for Liquid Chromatography, Part II: Making and Interpreting the Plots

Choosing a liquid chromatography (LC) column for a particular application can be a surprisingly challenging task. On the one hand, column manufacturers provide us many options to choose from, including particle types, pore sizes, particle sizes, and different lengths and diameters. On the other hand, we usually do not have time to experimentally evaluate many combinations of these parameters, and sometimes we end up picking something similar to the columns that are already available. The “kinetic plot” is a powerful graphical tool that can help leverage the best available theory to help us understand how different combinations of parameters (that is, particle size, length, among others) will perform in regard to the time needed to get to a particular column efficiency (and thus resolution), and therefore make well-informed decisions when choosing columns.

Influence of chromatographic column selection on the determination of 23 preservatives

以化妆品中23种防腐剂检测方法为例,探讨色谱柱选择对液相色谱方法测定结果的影响。参照《化妆品安全技术规范》甲基异噻唑啉酮等23个组分的检验方法,在2台不同的高效液相色谱仪上用15款不同品牌、型号的C18色谱柱检测23种防腐剂,计算色谱峰的理论塔板数和分离度,对23种组分的分离效果进行分析,并应用USP (United States Pharmacopeia)数据库和PQRI (Product Quality Research Institute)数据库等2种等效色谱柱选择方法,对不同色谱柱的分离效果及等效性进行评价和预测。实验结果表明,15款色谱柱对23种防腐剂的分离效果差异显著,仅有2款色谱柱可以实现23种组分的完全分离。USP和PQRI数据库中2种等效色谱柱选择方法均无法预测出合适的等效色谱柱,对23种防腐剂的液相色谱分析参考价值均较小。色谱柱是影响23种防腐剂液相色谱法测定结果准确性的关键因素,有关实验室在应用该方法时,应考虑色谱柱选择性差异。化妆品基质复杂,如何在现有研究成果的基础上,开发色谱柱的筛选和预测评价体系,进而指导实际样品的分离是下一步研究的重点、难点。建议有关部门在制修订检测方法时,注重色谱柱的耐用性考察,完善系统适应性指标,细化色谱柱分类和增加描述信息,指导色谱柱的合理选择,从而规避由于色谱柱使用过程中选择依据缺失而导致测定结果不准确的风险。

Column study of Cd(II) removal and longevity by nitrate-mediated zero-valent iron with mixed anaerobic microorganisms

In this study, hydrogen-autotrophic microorganisms and zero-valent iron (Fe0) were filled into columns to investigate hydrogenotrophic denitrification effect on cadmium (Cd(II)) removal and column life-span with sand, microorganisms, Fe0 and bio-Fe0 columns as controls. In terms of the experiment results, the nitrate-mediated bio-Fe0 column showed a slow Cd(II) migration rate of 0.04 cm/PV, while the values in the bio-Fe0 and Fe0 columns were 0.06 cm/PV and 0.14 cm/PV respectively, indicating much higher Cd(II) removal efficiency and longer service life of the nitrate-mediated bio-Fe0 column. The XRD and SEM-EDX results implied that this improvement was attributed to hydrogenotrophic denitrification that caused more serious iron corrosion and larger amount of secondary mineral generation (e.g., green rust, lepidocrocite and goethite). These active minerals provided more reaction sites for Cd(II) adsorption and further immobilization. In addition, the decrease of Cd(II) migration front and the increase of removal capacity along the bio-Fe0 column mediated by nitrate presented an uneven distribution in reactive zone. The latter half part was identified to be a more active region for Cd(II) immobilization. The above results indicate that the introduction of nitrate and microorganisms will improve the performance of iron-based permeable reactive barriers for the remediation of Cd(II)-containing groundwater.

EXPERIMENTAL STUDY ON THE PERFORMANCE OF ASSEMBLED STEEL-STRUCTURE BOX-SHAPED COLUMN FLANGE CONNECTION ACHIEVED BY PLUG WELDING- CORE SLEEVE

In order to solve the problems of a complicated construction procedure, low construction efficiency and high labor costs of the box-shaped columns with full penetration welded connection in assembled steel-structure, an assembled box-shaped column flange connection achieved by plug welding-core sleeve and its design method were proposed. It is designed to conduct the pseudo-static tests for three different forms of flange connections achieved by plug welding-core sleeve (PWCS), a connection with flange (FC), and a box-shaped column without connection (BCWC). The tests results indicated that: the initial rigidity of PWCS was increased by 16.6% and the maximum bearing capacity was increased by 9.97% compared to FC. The mechanical properties of the connection can be significantly improved by the setting of the core sleeve. Compared with 10.9s high strength bolts, the employment of bolts with larger pretension of 12.9s high strength can increase the extrusion force between flange plates, restrict the opening between flange plates, and improve the overall rigidity of the connection. The stiffeners can effectively prevent weld from cracking between the flange and column and, slightly improve the mechanical properties. It can be concluded that PWCS possesses similar mechanical properties compared with that of BCWC, and it can be designed as a rigid connection when applied in actual engineering. Besides, PWCS can be assembled efficiently on site, and the engineering costs can be controlled appropriately.

An integrated plastic microchip for enhancing electrophoretic separation using tunable pressure-driven backflows.

Microfluidic CE (MCE) is an effective solution for rapid and sensitive determination of multiple analytes. Herein, a dynamic coated cyclic olefin copolymer microchip was developed having an on-chip micropump for fluid velocity adjusting in electrophoretic separations. This micropump was fabricated by constructing a polyacrylamide gel membrane at one channel terminal. Once applying electric field across the membrane, a pressure-driven flow generated automatically to balance the electroosmotic flow (EOF) mismatch at the channel-membrane interface. The influence of gel precursor concentration and operating voltages on the fluid velocity was carefully evaluated. Moreover, the highly integration of injection, separation, and pumping units of the MCE system minimized the dead volume and provides satisfied column efficiency. Experiments showed that by adjusting of pumping voltage reduced the fluid velocity by a factor of 6, resulting six- and threefold resolving power enhancements of rhodamine dye mixture and amino acid mixture, respectively. Furthermore, the developed MCE method was applied for rhodamines and amino acids quantitation in food and cosmetics, with standard addition recoveries of 87.3-106.9% and 89.9-117.4%, respectively. These results were also confirmed by standard HPLC method, revealing the application potential in fast and onsite analysis of complex samples.

Analysis and experimental demonstration of temperature step gradients in preparative liquid chromatography

The amount of substance adsorbed on solid surface depends on temperature. Therefore, the migration velocities of the solutes in a chromatographic column can be altered by introducing temperature gradients. Such gradients designed to change retention behaviours can be exploited to improve the separation performances in preparative chromatography. To describe key process features, we used analytical solutions of the equilibrium model with instant stepwise shift of temperature. To achieve a more realistic description, the equilibrium dispersion model was additionally applied to treat finite column efficiencies. The effect of temperature gradients was illustrated experimentally using two identical columns sequentially connected. Temperature of the second column was modulated by thermostats. Wide pulse injections of a single component led to instructive elution profiles in a preliminary investigation. The observations were found to be in qualitative agreement with predictions of the equilibrium dispersion model. Subsequently, the separation of a ternary model mixture was investigated considering a simple two-step temperature gradient. To support the quantitative analysis and to identify suitable switching and cycle times, the temperature dependencies of the Henry constants were determined by short pulse injections. A meaningful variation of the parameters of the temperature gradient is required for adjusting the cycle times, which is the time difference between two consecutive injections that needs to shorten. Decreasing this time is connected with a desirable increase in process productivity. The results achieved revealed that relatively simple to implement stepwise temperature gradients offer an option to improve and fine-tune the performance of repetitive batch chromatography.

Rapid and efficient column separation of Re(VII) as a surrogate for Tc(VII) with benzimidazole-based cross-linked poly(ionic liquid)s

Rapid and efficient column separation of Re(VII) as a surrogate for Tc(VII) with benzimidazole-based cross-linked poly(ionic liquid)s

A covalent organic framework for chiral capillary electrochromatography using a cyclodextrin mobile phase additive.

Covalent organic frameworks (COFs) have been recognized as promising solid phases in capillary electrochromatography (CEC). Imine-based COF-coated open-tubular CEC column (COF TpBD-coated OT column) was prepared and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectra, thermogravimetric analysis (TGA), nitrogen adsorption/desorption (Brunauer-Emmett-Teller [BET]), and scanning electron microscopy (SEM). The results showed that the column efficiency was up to 26,776 plate/m, and the thickness of stationary phase was about 6.00 μm for the column prepared under the optimal conditions. Enantioseparation of 15 kinds of the single chiral compounds (histidine, arginine, lysine, leucine, threonine, methionine, valine, aspartic acid and glutamic acid, fipronil, diclofop, imazamox, quizalofop-p, imazethapyr, and acephate) and 3 kinds of mixed amino acids racemaces (valine, methionine, and glutamic acid) were performed with three methods: capillary electrochromatography with COF TpBD-coated OT column (Method 1), CEC with COF TpBD-coated OT column as the separation channels, and capillary electrophoresis (CE) with HP-β-CD as the chiral mobile phase additive (Method 2) and CE with HP-β-CD as the chiral mobile phase additive (Method 3). Separation efficiency and chiral selectivity of Method 2 was best among the three methods. Under the optimal separation conditions of Method 2, all the enantiomers reached the baseline separation regardless of the single chiral compounds or the mixed amino acids. Relative standard deviation (RSDs) of the mean column efficiency for reproducibility and stability was in the range of 0.46-1.49%. This combination of CEC and CE has great potential for use in chiral separation.

Open-tubular capillary electrochromatography with hydroxypropyl-β-cyclodextrin imprinted polymers: hybrid polyhedral oligomeric silsesquioxane as a coating for enantioseparation.

A hydroxypropyl-β-cyclodextrin (HP-β-CD) imprinted coating based on polyhedral oligomeric silsesquioxane (POSS) for open tubular electrochromatography was prepared. The mixture of methacryl-POSS (MA0735), HP-β-CD (template), methacrylic acid (MAA, monomer), N,N′-methylenebisacrylamide (MBA, crosslinker) and toluene-dimethyl sulfoxide (porogen) was used to synthesize the chiral selective coating. The influence of synthesis parameters on the imprinting effect and separation performance, including the amount of HP-β-CD, POSS, and MAA, was investigated systemically. The optimum polymerization was prepared by mixing HP-β-CD, MA0735, MAA, and MBA with the molar ratio of 1 : 1.87 : 1.60 : 1.60. Five racemates were separated by the modified capillary columns using aqueous buffer. Column efficiency on the POSS-based MIPs coating column was greater than 22 000 plates/m. MIPs-POSS hybrid coating capillaries had improved resolution (3.36 times) and the greatest resolution was up to 6.15 within 10 min.

But Why Doesn’t It Get Better? Kinetic Plots for Liquid Chromatography, Part I: Basic Concepts

Choosing a liquid chromatography (LC) column for a particular application can be a surprisingly challenging task. On the one hand, column manufacturers give us many options to choose from, including particle types, pore sizes, particle sizes, and different lengths and diameters. On the other hand, we usually do not have time to experimentally evaluate many combinations of these parameters, and sometimes we end up picking something similar to the columns that are already in the drawer. The “kinetic plot” is a powerful graphical tool that can help leverage the best available theory to help us understand how different combinations of parameters (such as particle size and length) will perform in relation to the time needed to get to a particular column efficiency (and thus resolution), and therefore make well-informed decisions when choosing columns.

Isomeric separation of permethylated glycans by extra-long reversed-phase liquid chromatography (RPLC)-MS/MS.

Glycosylation is known as a critical biological process that can largely affect the properties and the functions of proteins. Glycan isomers have been shown to be involved in a variety of disease progressions. However, the separation and identification of glycan isomers has been a challenge for years due to the microheterogeneity of glycan isomeric structures. Therefore, effective and stable techniques have been investigated over the last few decades to improve isomeric separations of glycans. RPLC has been widely used in biomolecule analysis because of its extraordinary reproducibility and reliability in retention time and separation resolution. However, so far, no studies have achieved high resolution of glycan isomers using this technique. In this study, we focused on further boosting the isomeric separation of permethylated glycans using a 500 mm reversed-phase LC column. To achieve better resolutions on permethylated glycans, different LC conditions were optimized using glycan standards, including core- and branch-fucosylated N-glycan isomers and sialic acid linked isomers, which were both successfully separated. Then, the optimal separation strategy was applied to achieve separations of N- and O-glycan isomers derived from model glycoproteins, including bovine fetuin, ribonuclease B and κ-casein. Baseline separations were observed on multiple sialylated linkage isomers. However, the separation performance of high-mannose isomers needs further improvement. The reproducibility and stability of this long C18 column was also tested by doing run-to-run, day-to-day and month-to-month comparisons of retention times on multiple glycans and the %RSD was found less than 0.92%. Finally, we applied this approach to separate glycan isomers derived from complex biological samples, including blood serum and cell lines, where baseline separations were attained on several isomeric structures. Compared to the separation efficiency of PGC and MGC columns, the RPLC C18 column provides lower resolution but more robust reproducibility, which makes it a good complementary alternative for isomeric separations of glycans.

О возможности оценки характеристик фракционного состава тяжелых нефтей по спектрам оптического поглощения

The possibility of estimating the fractional composition by the parameters of optical absorption spectra is shown for heavy oils and gas oils of catalytic cracking. The characteristics of the normal distribution of the composition by boiling points were obtained by processing experimental data on the ITK curves using the Newton - Raphson optimization method. The dependences linkingthe average boiling point μ and the dispersion of the normal distribution law for the composition are established.The obtained dependences can be used for primary estimates of the fractional composition for raw materials and the efficiency of the fractionating columns on the refinery.