Superficially Porous Particles Research Articles

Teicoplanin bonded sub-2 μm superficially porous particles for enantioseparation of native amino acids

Superficially porous particles (SPPs) demonstrate superior efficiency than totally porous particles in chiral separations. In order to obtain high efficiency and fast separation, sub-2μm SPPs with high surface area are synthesized, and with teicoplanin bonded, such materials are successfully applied into the rapid enantioseparation of native amino acids. In brief, 1.27±0.06μm nonporous silica particles are prepared by a modified seeded growth method, followed by mesoporous shell fabrication via one-pot templated dissolution and redeposition strategy, and pore size expansion via acid-refluxing. The diameter of the formed SPPs is 1.49±0.04μm, with the shell thickness as 206nm. Nitrogen physisorption experiments show that the Brunauer–Emmett–Teller (BET) specific surface area is 213.6m2/g and pore size is 9nm. After teicoplanin derivatization with bonding capacity as 83.3μmol/g, the prepared chiral stationary phase is packed into a stainless steel tube with the geometry of 50mm×2.1mm i.d.. In less than 6.4min, six native amino acids (norleucine, alanine, valine, methionine, leucine, norvaline) are enantioseparated with resolution factors ranging from 1.9 to 5.0. Besides, the resolution for chiral separation is improved with ethanol-water instead of methanol-water as the mobile phase. Moreover, the low temperature gives higher resolution, but longer retention time and higher backpressure. Finally, the effect of flow rate on enantiomeric separation is studied and fast chiral separation within 1min is obtained with flow rate of 0.4mL/min. All these results show that the synthesized teicoplanin bonded sub-2μm SPPs have great potential to achieve the enantioseparation of native amino acids with high resolution and rapid speed.

Gone in seconds: praxis, performance, and peculiarities of ultrafast chiral liquid chromatography with superficially porous particles.

A variety of brush-type chiral stationary phases (CSPs) were developed using superficially porous particles (SPPs). Given their high efficiencies and relatively low back pressures, columns containing these particles were particularly advantageous for ultrafast "chiral" separations in the 4-40 s range. Further, they were used in all mobile phase modes and with high flow rates and pressures to separate over 60 pairs of enantiomers. When operating under these conditions, both instrumentation and column packing must be modified or optimized so as not to limit separation performance and quality. Further, frictional heating results in axial thermal gradients of up to 16 °C and radial temperature gradients up to 8 °C, which can produce interesting secondary effects in enantiomeric separations. It is shown that the kinetic behavior of various CSPs can differ from one another as much as they differ from the well-studied C18 reversed phase media. Three additional interesting aspects of this work are (a) the first kinetic evidence of two different chiral recognition mechanisms, (b) a demonstration of increased efficiencies at higher flow rates for specific separations, and

Are sub-2 μm particles best for separating small molecules? An alternative

Superficially porous particles (SPP) in the 2.5–2.7μm range provide almost the same efficiency and resolution of sub-2μm totally porous particles (TPP), but at one-half to one-third of the operating pressure. The advantage of SPP has led to the introduction of sub-2μm SPP as a natural extension of this technology. While short columns of both SPP and TPP sub-2μm particles allow very fast separations, the efficiency advantages of these very small particles often are not realized nor sufficient to overcome some of the practical limitations and disadvantages of such small particles. Advantages and disadvantages of columns packed with sub-2μm particles are described for comparison with the characteristics of larger particles. The authors conclude that while sub-2μm particles have utility in research studies, columns of larger particles are often better suited for most applications. A suggested 2.0μm superficially porous particle diameter retains many of the advantages of sub-2μm particles, but minimizes some of the disadvantages. The characteristics of these new 2.0μm SPP are described in studies comparing some present sub-2μm SPP commercial columns for efficiency, column bed homogeneity and stability.

Comparison of superficially porous and fully porous silica supports used for a cyclofructan 6 hydrophilic interaction liquid chromatographic stationary phase

A new HILIC stationary phase comprised of native cyclofructan-6 (CF6) bonded to superficially porous silica particles (2.7μm) was developed. Its performance was evaluated and compared to fully porous silica particles with 5μm (commercially available as FRULIC-N) and 3μm diameters. Faster and more efficient chromatography was achieved with the superficially porous particles (SPPs). The columns were also evaluated in the normal phase mode. The peak efficiency, analysis time, resolution, and overall separation capabilities in both HILIC and normal phase modes were compared. The analysis times using the superficially porous based column in HILIC mode were shorter and the theoretical plates/min were higher over the entire range of flow rates studied. The column containing the superficially porous particles demonstrated higher optimum flow rates than the fully porous particle packed columns. At higher flow rates, the advantages of the superficially porous particles was more pronounced in normal phase separations than in HILIC, clearly demonstrating the influence that the mode of chromatography has on band broadening. However, the minimum reduced plate heights (hmin) were typically lower in HILIC than in the normal phase mode. Overall, the superficially porous particle based CF6 column showed clear advantages over the fully porous particle columns, in terms of high throughput and efficient separations of polar compounds in the HILIC mode.

Superficially porous particles vs. fully porous particles for bonded high performance liquid chromatographic chiral stationary phases: Isopropyl cyclofructan 6

This work reports a comparison of HPLC separations of enantiomers with chiral stationary phases (CSPs) prepared by chemically bonding cyclofructan-6, functionalized with isopropyl carbamate groups on fully and superficially porous particles (SPPs). The chromatographic performance of the superficially porous CSP based column was compared with columns packed with 5μm and 3μm fully porous particles (FPPs). At a flow rate of 3.0mL/min the number of plates on column afforded by the SPP column was ∼7× greater than the number of plates on column (same length) obtained when using the 5μm FPP based column. The flow rate providing the highest efficiency separation was ∼1.0mL/min for the SPP column while it was ∼0.5mL/min for both FPP columns. It was found that the selectivity and resolution of the separations were comparable between fully porous and superficially porous based columns (under constant mobile phase conditions), even though the SPP column contained lower absolute amounts of chiral selector. When tested under constant retention conditions, the SPP based CSP greatly improved resolution compared to the FPP based columns. At high flow rates the efficiency gained by using superficially porous CSP was accentuated. The advantages of columns based on SPPs become more obvious from the viewpoint of plate numbers and resolution per analysis time.

Evaluation of stationary phases packed with superficially porous particles for the analysis of pharmaceutical compounds using supercritical fluid chromatography

Superficially porous particles (SPP), or core shell particles, which consist of a non-porous silica core surrounded by a thin shell of porous silica, have gained popularity as a solid support for chromatography over the last decade. In the present study, five unbonded silica, one diol, and two ethylpyridine (2-ethyl and 4-ethyl) SPP columns were evaluated under SFC conditions using two mixtures, one with 17 drug-like compounds and the other one with 7 drug-like basic compounds. Three of the SPP phases, SunShell™ 2-ethylpyridine (2-EP), Poroshell™ HILIC, and Ascentis® Express HILIC, exhibited superior performances relative to the others (reduced theoretical plate height (hmin) values of 1.9–2.5 for neutral compounds). When accounting for both achievable plate count and permeability of the support using kinetic plot evaluation, the Cortecs™ HILIC 1.6μm and Ascentis® Express HILIC 2.7μm phases were found to be the best choices among tested SPPs to reach efficiencies up to 30,000 plates in the minimum amount of time. For desired efficiencies ranging from 30,000 to 60,000 plates, the SunShell™ 2-EP 2.6μm column clearly outperformed all other SPPs. With the addition of a mobile phase additive such as 10mM ammonium formate, which was required to elute the basic components with sharp peaks, the Poroshell™ HILIC, SunShell™ Diol and SunShell™ 2-EP phases represent the most orthogonal SPP columns with the highest peak capacities. This study demonstrates the obvious benefits of using columns packed with SPP on current SFC instrumentation.

Ultra high efficiency/low pressure supercritical fluid chromatography with superficially porous particles for triglyceride separation

This paper reports the development of the separation of vegetable oil triglycerides (TG) in supercritical chromatography (SFC), using superficially porous particles (SPPs). The SPP, having a small diameter (2–3μm), provide a higher theoretical plate number (N), which allows to improve separation of critical pairs of compounds. However, compared to fully porous particles of larger diameter (5μm), the pressure drop is also increased. Fortunately, supercritical fluids have a low viscosity, which allows coupling several columns to achieve high N values, while maintaining flow rate above 1ml/min, ensuring a ultra high efficiency (UHE) at low pressure (LP) (below 40MPa), with regards to the one reached with liquid and sub-two micron particles (around 100MPa). The use of two detector systems (UV and ELSD) connected in series to the UHE–LP-SFC system provides complementary responses, due to their specific detection principles. Working in a first part with three coupled Kinetex C18 columns (45cm total length), the effect of modifier nature and percentage were studied with two reference oils, argan and rapeseed, chosen for their different and well-known TG composition. The analytical method was developed from previous studies performed with fully porous particles (FPP). Optimized conditions with three Kinetex were as follows: 17°C, 12% of ACN/MeOH (90/10; v/v). With these conditions, and by using an increased length of Kinetex C18 column (60cm), another additional column was selected from ten different commercial SPP C18 bonded phases, by applying a Derringer function on varied parameters: theoretical plate number (TPN), separation index (SI) for critical pairs of peaks (the peaks of compounds difficult to separate due to subtle structural differences), the analysis duration, and the total peak number. This function normalizes the values of any parameters, between 0 and 1, from the worst value to the better, allowing to take account of various parameters in the final choice. Finally, by using four Kinetex C18 plus one Accucore C18 (75cm total column length), a high-performance separation of triglycerides was achieved, with reasonable analysis duration and isocratic conditions. These conditions can be applied to varied vegetable oils. Identification of the numerous separated peaks of rapeseed oil was achieved by using published data and chromatographic retention behaviour.

Fused-core particle technology in high-performance liquid chromatography: An overview

The advent of superficially porous particles (SPPs) for packed HPLC columns has changed the way that many practitioners have approached the problem of developing needed separations. The very high efficiency of such columns, combined with convenient operating conditions, modest back pressures and the ability to use conventional HPLC instruments has resulted in intense basic studies of SPP technology, and widespread applications in many sciences. This report contains an overview of the SPP technology first developed in 2006 by Advanced Materials Technology, Inc., for sub-3-μm particles, then expanded into a family of SPP products with different particle sizes, pore sizes and other physical parameters. This approach was designed so that each particle of the family could be optimized for separating a particular group of compounds, usually based on solute size.

Superficially porous silica particles with wide pores for biomacromolecular separations

Since 2006, columns of superficially porous particles (SPPs), often called Fused-core®, porous–shell or core–shell particles, have had serious impact on HPLC separations. These particles have pore diameters of about 100Å designed for separating small molecules. More recently, SPPs with 160–200Å pore diameter have been made available for separating peptides and small proteins. This report describes the effects of fused-core particle size, pore size, shell thickness and ligand type for the rapid, efficient separation of larger molecules such as intact proteins and other biomacromolecules up to at least 400kDa. Optimization of these parameters resulted in particles that show no restricted diffusion that would compromise separating efficiency for large biomolecules. The thin porous shell provides excellent mass transfer (kinetics) for these large molecules, resulting in superior separations compared to conventional totally porous particles. Sample loading capacity can be adjusted to allow good detection sensitivity for minor components in a complex mixture. Strong particle strength ensures the loading of stable, high-efficiency columns. Stationary phases with different alkyl ligands were tested to provide data on retention, column efficiency and peak shapes for proteins. The development of these new wide-pore fused-core particles now allows the HPLC separation of a wide range of molecules of different sizes with advantages of the SPP configuration.

Applications of superficially porous particles: High speed, high efficiency or both?

The new generation of superficially porous particles (SPPs) offers impressive chromatographic efficiency compared to totally porous particles. Specifically, modern sub-3-μm SPPs generate much improved reduced plate height but at lower backpressure compared to sub-2-μm totally porous particles. This feature makes them attractive for various types of applications and SPPs are quickly being adopted in many analytical laboratories. In this review, we use optimization theory to compare the performance limit of modern SPPs and totally porous particles under optimized conditions, in order to answer the question: what are the optimal applications for modern SPPs? Are they most suitable for fast separations, or for high efficiency separations, or for both? Successful examples of using modern SPPs in different application areas are reviewed, over a wide range of sample complexity and analysis time. Practical aspects of the use of such particles and future development possibilities are also discussed.