Study of Physical Properties of Superficially Porous Silica on Its Superior Chromatographic Performance

Importance of the Topic

The development of superficially porous silica particles addresses key challenges in high performance liquid chromatography by combining high separation efficiency with reduced backpressure. This advancement enables faster analysis of small molecules while maintaining column durability and compatibility with standard HPLC systems.

Study Objectives and Overview

• Compare superficially porous particles with fully porous sub-2 µm particles in terms of efficiency, pressure, and van Deemter behavior.
• Investigate the influence of shell thickness and particle size distribution on chromatographic performance.
• Prepare a series of 2.7 µm core–shell particles (Poroshell 120) with varied shell thickness and size distribution for systematic evaluation.

Methodology

• Particles: 2.7 µm superficially porous silica with a 1.7 µm solid core and 0.5 µm porous shell (120 Å pores); alternative batches with shell thickness 1.57 and 1.87 µm and varied D90/D10 ratios.
• Comparisons made against 1.8 µm totally porous particles.
• Performance metrics: reduced plate height, van Deemter plots (terms A, B, C), and backpressure measurements across flow rates.

Used Instrumentation

• Column dimensions: 4.6 × 50 mm.
• Mobile phase: 40 / 60 water / acetonitrile.
• Column temperature: 25 °C.
• Detector: UV at 254 nm.
• Sample: naphthalene standard.

Main Results and Discussion

• Poroshell 120 particles achieved a minimum reduced plate height of 1.49, significantly lower than 1.97 for 1.8 µm totally porous particles.
• Backpressure for superficially porous particles was 40 – 50 % of that observed with sub-2 µm totally porous particles.
• Term A (eddy dispersion) decreased with narrower particle size distribution; particles with D90/D10 of 1.10 – 1.17 outperformed those with wider distributions.
• Term B (axial diffusion) increased with shell thickness; thinner shells yielded lower B values and flatter van Deemter curves at higher flow rates.
• Term C (mass transfer) showed minimal variation across shell thickness and was similar to that of 1.8 µm totally porous particles for small molecules.

Benefits and Practical Applications

• Enables high speed separations with sub-2 µm level efficiency on conventional HPLC equipment.
• Significant reduction in system backpressure extends column lifetime and reduces pump wear.
• Improved peak capacity and resolution for pharmaceutical, environmental, and biochemical analyses.

Future Trends and Opportunities

• Extension of core–shell technology to larger biomolecules and more complex matrices.
• Integration with ultra-high performance systems to further exploit low diffusion paths and narrow size distributions.
• Development of tailored shell chemistries to enhance selectivity and robustness.

Conclusion

The Poroshell 120 superficially porous silica demonstrates superior chromatographic performance by combining sub-2 µm particle efficiency with significantly reduced backpressure. Optimization of shell thickness and particle size distribution enables fine-tuning of van Deemter terms, making these materials highly attractive for high-throughput and high-resolution HPLC applications.

Reference

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