Options for rapid analysis of peptides and proteins, using wide-pore, superficially porous, high-performance liquid chromatography particles with unique bonded-phase ligands

The large size and complexity of many proteins constrains the reversed-phase high-performance liquid chromatography packings that are useful for their separation. Wide-pore, superficially porous, silica-based packings with solid 4.5-microm cores and a 0.25-microm porous outer layer (Poroshell) demonstrate a variety of characteristics that are beneficial for the separation of proteins. A shorter diffusion distance allows separations of large molecules at high linear velocities. This benefit over totally porous particles is clearly shown using separations of a peptide-protein standard. The structure and reduced surface area (4.5 m2/g) of these superficially porous particles simplifies interactions with its surface, resulting in improved peak shapes and resolution. Specialized bonding chemistries for low- and high-pH operation may be used to change band-spacing and achieve atypical separations. These rapid analysis options are demonstrated using protein standards and very high molecular weight glycosylated proteins including intact monoclonal antibodies, IgM, alpha2-macroglobulin, and glycophorin. In liquid chromatography-mass spectrometry analysis of a myoglobin peptide digest, bidentate-C18-bonded superficially porous packings achieve complete runs in 4 min and demonstrate an elution pattern that is unique from that of material bonded with sterically protected C18 ligands.     

Atypical silica-based column packings for high-performance liquid chromatography

Column packings widely used for high-performance liquid chromatography (HPLC) mostly are based on porous silica microspheres with certain pore sizes and pore size distributions. Such materials have the most desirable compromise of properties that provide for effective and reproducible separations over a wide range of operating conditions. To provide desired separation characteristics, several manufacturers specially synthesize the silica particles for these packings. While such column packing materials have general utility for a wide range of needs, special silica-based particles have been synthesized with different physical conformations for special separation goals. This presentation describes some atypical types of silica-based particles with unique separation properties that enlarge the capabilities of HPLC methods.     

Practical comparison of LC columns packed with different superficially porous particles for the separation of small molecules and medium size natural products

Commercial C(18) columns packed with superficially porous particles of different sizes and shell thicknesses (Ascentis Express, Kinetex, and Poroshell 120) or sub-2-μm totally porous particles (Acquity BEH) were systematically compared using a small molecule mixture and a complex natural product mixture as text probes. Significant efficiency loss was observed on 2.1-mm id columns even with a low dispersion ultra-high pressure liquid chromatography system. The Kinetex 4.6-mm id column packed with 2.6-μm particles exhibited the best overall efficiency for small molecule separations and the Poroshell 120 column showed better performance for mid-size natural product analytes. The Kinetex 2.1-mm id column packed with 1.7-μm particles did not deliver the expected performance and the possible reasons besides extra column effect have been proved to be frictional heating effect and poor column packing quality. Different column retentivities and selectivities have been observed on the four C(18) columns of different brands for the natural product separation. Column batch-to-batch variability that has been previously observed on the Ascentis Express column was also observed on the Kinetex and Poroshell 120 column.     

Characteristics of superficially-porous silica particles for fast HPLC: some performance comparisons with sub-2-microm particles

Columns of 2.7-microm fused-core (superficially porous) Type B silica particles allow very fast separations of small molecules at pressures available in most high-performance liquid chromatography instruments. These highly-purified particles with 1.7-microm solid silica cores and 0.5-microm-thick shells of 9 nm pores exhibit efficiencies that rival those of totally porous sub-2-microm particles but at one-half to one-third of the column back pressure. This presentation describes other operating features of fused-core particle columns, including sample loading characteristics and packed bed stability. The superior mass transfer (kinetic) properties of the fused-core particles result in much-improved separation efficiency at higher mobile phase velocities, especially for > 600 molecular weight solutes.     

Comparative study of new shell-type,sub-2 μm fully porous and monolith stationary phases,focusing on mass-transfer resistance

Today sub-2 μm packed columns are very popular to conduct fast chromatographic separations. The mass-transfer resistance depends on the particle size but some practical limits exist not to reach the theoretically expected plate height and mass-transfer resistance. Another approach applies particles with shortened diffusion path to enhance the efficiency of separations. In this study a systematical evaluation of the possibilities of the separations obtained with 5 cm long narrow bore columns packed with new 2.6 μm shell particles (1.9 μm nonporous core surrounded by a 0.35 μm porous shell, Kinetex™, Core-Shell), packed with other shell-type particles (Ascentis Express™, Fused-Core), totally porous sub-2 μm particles and a 5 cm long narrow bore monolith column is presented. The different commercially available columns were compared by using van Deemter, Knox and kinetic plots. Theoretical Poppe plots were constructed for each column to compare their kinetic performance. Data are presented on polar neutral real-life analytes. Comparison of a low molecular weight compounds (MW = 270–430) and a high molecular weight one (MW ∼ 900) was conducted. This study proves that the Kinetex column packed with 2.6 μm shell particles is worthy of rivaling to sub-2 μm columns and other commercially available shell-type packings (Ascentis Express or Halo), both for small and large molecule separation. The Kinetex column offers a very flat C term. Utilizing this feature, high flow rates can be applied to accomplish very fast separations without significant loss in efficiency.     

Polybutadiene-coated zirconia packing materials in solvating gas chromatography using carbon dioxide as mobile phase

Summary In this paper, practical considerations of column efficiency, separation speed, thermal stability, and column polarity of capillary columns packed with polybutadiene-coated zirconia were investigated under solvating gas chromatography (SGC) conditions using carbon dioxide as mobile phase. When compared with results obtained from conventional porous octadecyl obtained from conventional porous octadecyl bonded silica (ODS) particles, PBD-zirconia particles produced greater change in mobile phase linear velocity with pressure than conventional ODS particles under the same conditions. The maximum plate number per second (N_t) obtained with a 30 cm PBD-zirconia column was approximately 1.5 times higher than that obtained with an ODS column at 100 °C. Therefore, the PBD-zirconia phase is more suitable for fast separations than conventional ODS particles in SGC. Maximum plate numbers per meter of 76,900 and 63,300 were obtained using a 57 cm×250 μm i.d. fused silica capillary column packed with 3 μm PBD-zirconia at 50 °C and 100 °C, respectively. The PBD-zirconia phase was stable at temperatures up to 320 °C under SGC conditions using carbon dioxide as mobile phase. Polarizable aromatic compounds and low molecular weight ketones and aldehydes were eluted with symmetrical peaks from a 10 cm column packed with 3 μm PBD-zirconia. Zirconia phases with greater inertness are required for the analysis of more polar compounds by SGC.     

Kinetic optimisation of open-tubular liquid-chromatography capillaries coated with thick porous layers for increased loadability

The kinetic optimisation of open-tubular liquid chromatography (OTLC) columns has been revisited by taking the thick-film effects for porous coatings on retention, column resistance, band broadening and mass loadability into account. Considering the most advantageous case (i.e. where the retentive layer allows for the same high internal diffusion coefficient as conventional porous particles), calculations show the need for the development of coating procedures leading to porous films filling up approximately 50-70% of the total column diameter. Furthermore, to achieve optimum kinetic performance for separations of small molecules with total analysis times of less than 8h (k'=9), total column diameters should be less than 6 μm with lengths typically greater than 0.8m for N values of 125,000-500,000 at a pressure of 400 bar. The use of elevated temperature LC (90°C) is also shown to increase the allowable total column diameter to up to 9 μm for a larger range of N values (100,000-880,000).     

Fast supercritical fluid chromatography of polymers using packed capillary columns

Summary Fast separations of perfluorinated polyethers and polymethylsiloxanes that are composed of 50–80 oligomers were demonstrated in packed capillary column supercritical fluid chromatography (SFC) using a carbon dioxide mobile phase. Separations were accomplished within 10 min using a 13 cm×250 μm i.d. column packed with 2 μm porous octadecyl bonded silica (ODS) particles. Effects of particle diameter of the packing material and pressure programming on separation were investigated, and packed column SFC was compared with open tubular column SFC. Results show that as the particle diameter was decreased from 5 to 3 to 2 μm and the column length was reduced from 85 to 43 to 13 cm, the separation time could be reduced from 70 to 20 to 10 min while still maintaining similar separation (resolution). Short columns packed with small porous particles are very suitable for fast SFC separations of polymers.     

A study of the effects of column porosity on gradient separations of proteins

The type of the stationary phase for reversed-phase liquid chromatography significantly affects the sample elution. Hydrodynamic properties, efficiency and gradient elution of proteins were investigated on five commercial C18 columns with wide-pore totally porous particles, with superficially porous layer particles, non-porous particles and a silica-based monolithic bed. The efficiency in the terms of reduced plate height is higher for low-molecular ethylbenzene than for proteins, but depends on the character of the pores in the individual columns tested. The superficially porous Poroshell and the non-porous Micra columns provide the best efficiency for proteins at high mobile phase flow rates, probably because of similar pore architecture in the stationary phase. The Zorbax column with similar pore architecture as the Poroshell active layer, i.e. narrow pore distribution of wider pores shows better efficiency than the packed column with narrow pores and broad pore distribution. The monolithic column shows lower efficiency for proteins at high flow rates, but it performs better than the broad-pore distribution totally porous particulate columns. Different pore architecture affects also the retention and selectivity for proteins on the individual columns. The retention times on all columns can be predicted using the model for reversed-phase gradient elution developed originally for low-molecular compounds. Consideration of the limited pore volume accessible to the biopolymers has negligible effect on the prediction of retention on the columns packed with non-porous or superficially porous particles, but improves the accuracy of the predicted data for the totally porous columns with broad pore distribution.     

Monolithic silica rod columns for high-efficiency reversed-phase liquid chromatography

Chromatographic properties of a new type of monolithic silica rod columns were examined. Silica rod columns employed for the study were prepared from tetramethoxysilane, modified with octadecylsilyl moieties, and encased in a stainless-steel protective column with two polymer layers between the silica and the stainless-steel tubing. A 25 cm column provided up to 45,000 theoretical plates for aromatic hydrocarbons, or a minimum plate height of about 5.5 μm, at optimum linear velocity of ca. 2.3 mm/s and back pressure of 7.5 MPa in an acetonitrile-water (80/20, v/v) mobile phase at 40°C. The permeability of the column was similar to that of a column packed with 5 μm particles, with K(F) about 2.4×10(-14) m(2) (based on the superficial linear velocity of the mobile phase), while the plate height value equivalent to that of a column packed with 2.5 μm particles. Generation of 80,000-120,000 theoretical plates was feasible with back pressure below 30 MPa by employing two or three 25 cm columns connected in series. The use of the long columns enabled facile generation of large numbers of theoretical plates in comparison with conventional monolithic silica columns or particulate columns. Kinetic plot analysis indicates that the monolithic columns operated at 30 MPa can provide faster separations than a column packed with totally porous 3-μm particles operated at 40 MPa in a range where the number of theoretical plates (N) is greater than 50,000.     

Evaluation of the properties of a superficially porous silica stationary phase in hydrophilic interaction chromatography

The sample capacity, column efficiency (and its variation with flow) of a superficially porous unbonded silica phase (Halo) was investigated using hydrophilic interaction chromatography (HILIC), particularly for separation of basic compounds. Sample capacity compared with totally porous silica phases was somewhat reduced, broadly in line with the decreased surface area, but still favourable compared with reversed-phase separations of these solutes. Efficiencies in excess of 100,000 plates were obtained at room temperature in reasonable analysis times by using a 45 cm coupled column, while generating back pressures compatible with conventional HPLC. Shorter columns offered the possibility of fast analysis of bases, and the unfavourable mass transfer properties reported by others at high flow rate for similar reversed-phase columns, were not apparent. While excellent peak shapes were obtained for many bases on silica HILIC phases, problems may still occur for some solutes.     

含酯基包覆聚合物液相色谱柱填料

以丙烯酸甲酯或辛酯和二乙烯苯为原料，在溶液中用游离基聚合法制备了一系列含酯基包覆聚合物反相液相色谱柱填料．用傅立叶红外光谱、电子显微镜和元素分析鉴定了聚合物层，并评价了诸如硅羟基、柱压降、柱效和峰对称性等特性．该类填料适合于含氨基和羟基化合物的分离，作为应用实例，对洛伐他汀（Lovastatin）的分析展示其优良的色谱性能。     

Comparison of performance of high-performance liquid chromatography columns packed with superficially and fully porous 2.5 μm particles using kinetic plots

A recently introduced 2.5?μm fully porous support (Kromasil Eternity) is compared with three different brands of superficially porous material (Kinetex, Halo and Poroshell 120) by means of the kinetic plot method using pharmaceutical compounds from GlaxoSmithKline as probe molecules. The kinetic plot method immediately shows the range of plate numbers wherein a support performs better than another. Results from experiments carried out at pH 4.5 and 8.0 are presented in order to assess the pH stability of the tested phases. Moreover, since all supports are able to withstand pressures higher than 400?bar, they have been evaluated both on HPLC and UHPLC instrumentation. True average particle sizes were determined by SEM images taken from loose stationary phases. Kinetex outperforms the other columns in HPLC conditions for practically relevant efficiencies, but shows poor packing quality in the 100×2.1-mm format. Kromasil is advantageous for simple and fast separations on short columns both in HPLC and in UHPLC conditions. Halo achieves the highest efficiencies of all columns at the lowest pressure cost and shows a noticeable lower axial diffusion. Poroshell 120 has the best packing quality reproducibility across the tested formats. All columns preserve their performance at high pH.     

硅胶基质高效液相色谱填料研究进展

高效液相色谱(HPLC)不仅是一种有效的分析分离手段,也是一种重要的高效制备分离技术。色谱柱是HPLC系统的核心,不同性能的填料是HPLC广泛应用的基础。硅胶是开发最早、研究最为深入、应用最为广泛的HPLC固定相基质,其制备方法主要有喷雾干燥法、溶胶-凝胶法、聚合诱导胶体凝聚法及模板法等。近年来,亚2μm小粒径硅胶、核-壳型硅胶、双孔径硅胶、介孔性硅胶、有机杂化硅胶等新型硅胶应用于HPLC并取得了色谱分离技术的飞速发展,例如基于亚2μm填料的超高压液相色谱技术、基于核-壳型填料的快速分离技术、基于杂化硅胶填料的高温液相色谱技术等。硅胶经表面化学键合、聚合物包覆等有机改性可制得先进的大分子限进填料、温敏性填料、手性填料等,大大扩展了HPLC的应用范围。本文对液相色谱用硅胶的制备方法、改性与修饰方法以及硅胶基质固定相的评价方法加以系统综述,概述了新型硅胶在HPLC中的应用进展,并对硅胶基质填料的发展方向与应用前景进行了展望。     

The impact of extra-column band broadening on the chromatographic efficiency of 5 cm long narrow-bore very efficient columns

Small columns packed with core-shell and sub-2 μm totally porous particles and monolith columns are very popular to conduct fast and efficient chromatographic separations. In order to carry out fast separations, short (2-5 cm) and narrow-bore (2-2.1 mm) columns are used to decrease the analyte retention volume. Beside the column efficiency, another significant issue is the extra-column band-spreading. The extra-column dispersion of a given LC system can dramatically decrease the performance of a small very efficient column. The aim of this study was to compare the extra-column peak variance contribution of several commercially available LC systems. The efficiency loss of three different type 5 cm long narrow bore, very efficient columns (monolith, sub-2 μm fully porous and sub-2 μm core-shell packing) as a function of extra-column peak variance, and as a function of flow rate and also kinetic plots (analysis time versus apparent column efficiency) are presented.     

Fast supercritical fluid chromatography using capillaries packed with nonporous particles

Summary Packed columns containing microparticles provide high column efficiency per unit time and strong retention characteristics compared with open tubular columns, and they are favored for fast separations. Nonporous particles eliminate the contribution of solute mass transfer resistance in the intraparticle void volume characteristic of porous particles, and they should be more suitable for fast separations. In this paper, the evaluation of nonporous silica particles of sizes ranging from 5 to 25 μm in packed capillary columns for fast supercritical fluid chromatography (SFC) using neat CO₂ is reported. These particles were first deactivated using polymethyl-hydrosiloxanes and then encapsulated with a methylphenylpolysiloxane stationary phase. The retention factors, column efficiencies, column efficiencies per unit time, separation resolution, and separation resolution per unit time for fast SFC were determined for various length capillaries packed with various sizes of polymerencapsulated nonporous particles. It was found that 15 μm nonporous particles provided the highest column efficiency per unit time and resolution per unit time for fast packed capillary SFC. Under certain conditions, separations were completed in less than 1 min. Several thermally labile silylation reagent samples were separated in times less than 5 min. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

A New Monolithic‐Type HPLC Column For Fast Separations

The application of a new silica‐based, monolithic‐type HPLC‐column for fast separations is presented. The column is prepared according to a new sol‐gel process, which is based on the hydrolysis and polycondensation of alkoxysilanes in the presence of water soluble polymers. The method leads to “rods” made of a single piece of porous silica with a defined pore structure, i. e. macro‐ and mesopores. The main feature of silica rod columns is a higher total porosity, about 15% higher than of conventional particulate HPLC columns. The resulting column pressure drop is therefore much lower, allowing operation at higher flow rates including flow gradients. Consequently, HPLC analysis can be performed much faster, as it is demonstrated by various applications.     

Fundamental and practical aspects of ultrahigh pressure liquid chromatography for fast separations

The ongoing development of HPLC has been focused on increasing the speed and efficiency of separations over the past decade. The advances in separation speed have been primarily related to the development of column technology and instrumentation. Relatively short columns packed with sub-2 microm particles provide high-speed separations while maintaining or increasing resolution. Ultrahigh pressure pump systems have been developed to overcome the high-pressure drop generated by such sub-2 microm packings. In this review, fundamental and practical aspects of ultrahigh pressure or ultrahigh performance liquid chromatography (U-HPLC) are discussed. Applications of fast U-HPLC separations are also presented.     

A practical approach to maximizing peak capacity by using long columns packed with pellicular stationary phases for proteomic research

Maximization of peak capacity is a very important step in developing one-dimensional separations of complex samples. In recent work, it was shown that the use of small particles in combination with the new technique of ultrahigh pressure liquid chromatography (UHPLC) was able to generate very high peak capacities. Here we show the ability of conventional HPLC instrumentation to give comparable peak capacities to those obtained in UHPLC for the important case of complex mixtures of peptides but at much lower pressures by using a 60 cm long set of columns packed with 5 microm pellicular (superficially porous) particles. We first show, in complete agreement with the well known results of the theory of isocratic separations that, when time is not limiting, the best peak capacities in gradient elution chromatography are obtained by using large particles and the longest column that can be operated at the pump's pressure limit. Two different types of 5 microm particles (superficially porous and totally porous) were compared for their efficiency in gradient chromatography of peptides. We find that the pellicular material gave about 50% higher peak capacity compared to the analogous porous material. A 60 cm column set packed with pellicular particles was made by connecting short columns in series; a peak capacity of about 460 was obtained in 4 h at room temperature. Increasing the column temperature to 70 degrees C reduced the analysis time to 2 h and further increased the peak capacity to more than 500. The number of peaks observed in the separation of bovine serum albumin tryptic peptides was greatly increased and the separation quality was significantly improved.     

Characterization of internal surface reversed-phase silica supports for liquid chromatography

Internal surface reversed-phase (ISRP) supports synthesized from commercially available porous silica particles with a variety of nominal pore diameters and specific surface areas are characterized with regard to physical and chromatographic properties. Bonded phase coverage, pore size, capacity and efficiency measurements are made upon the various ISRP supports in order to evaluate the effect that the physical properties of silica have upon the chromatographic performance of ISRP packings. In addition, various models that describe the pore structure of silica supports are discussed.