PARTICLE SIZE CONSIDERATIONS OF SUPERFICIALLY POROUS PARTICLES Joseph J. DeStefano, Stephanie A. Schuster, Robert S. Bichlmeir, and William L. Johnson Advanced Materials Technology, Inc., 3521 Silverside Road, Suite 1 K, Wilmington, DE 19810
ABSTRACT Columns of fused-core core, superficially porous particles demonstrate higher efficiency than columns packed with totally porous particles of similar size. This result likely is because of superior eddy and longitudinal diffusion properties (smaller van Deemter A and B terms) observed for core-shell particles resulting from exceptionally narrow particle size distributions ib ti and higherh density contributing to an ability to form homogeneous packed beds. The achievement of efficiencies comparable to those obtained using columns of sub-2-μm totally porous particles without the need for ultra high pressure instrumentation is a distinct advantage of fused-core columns. Fused-core particles with a wide range of uniform particle sizes were synthesized to allow the preparation of stable, efficient packed columns for this study. These columns were used to measure the effects of particle size on chromatographic performance and pressure requirements. This report describes the effect of particle size on several factors of separation importance, including plate heights, reduced plate heights, pressure, and ease of use. Depending on the intended application, certain particle sizes are recommended for use over others. The performance of larger fused-core particles exceeds even the high expectations observed for smaller superficially porous particles, likely because larger particles form more homogeneous packed beds than smaller particles. The utility of larger and smaller superficially porous particles are compared and evaluated for high-speed and high-resolution applications.
HALO Fused-Core Particles particle size shell thickness SEM of HALO Fused-core Graphical representation of HALO Fused-core
CHARACTERISTICS OF PARTICLES USED IN THIS STUDY Total Particle Size Shell Thickness Core Diameter Surface Area 2.0 microns 0.5 micron 1.0 micron 100 m 2 /g 2.7 microns 0.5 micron 1.7 microns 125 m 2 /g 4.1 microns 0.55 micron 3.0 microns 105 m 2 /g 4.6 microns 0.6 micron 3.4 microns 95 m 2 /g
95 TEST CHROMATOGRAM Test Conditions: Columns: 3.0 x 50 mm Mobile Phase: 60/40 ACN/H 2 O Flow Rate: varied Temperature: ambient (ca. 22 o C) Detector: semi-micro UV @ 254nm Peak Identities: 1. Uracil (t 0 marker) 2. Phenol 3. 4-Cl-1-nitrobenzene 4. Naphthalene (k values 3.3 to 3.8) 75 55 1 2 3 4 35 15 5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Time, minutes
Plate Height Vs Velocity Plots 8.0 7.5 4.6 µm 7.0 micrometers Plate Height, 6.5 4.1 µm 6.0 55 5.5 5.0 4.5 2.7 µm 4.0 2.0 µm 3.5 3.0 Linear Mobile Phase Velocity, mm/sec Data fitted to Knox equation 1 2 3 4 5 6 7 The Plate Heights of columns packed with particles of different sizes, as expected, get smaller as the particle size gets smaller.
Reduced Plate Height Vs Velocity Plots 2.6 2.4 2.2 Reduced Plate Height 2.0 1.6 1.4 2.0 µm 1.8 2.7 µm 4.1 µm 4.6 µm 1.2 1.0 1 2 3 4 5 6 7 Linear Mobile Phase Velocity, mm/sec Data fitted to Knox equation Reduced Plate Heights (h = H/d p ) get smaller as the particle size is increased, indicating more homogeneity in packed beds for the larger particles.
Overlay of Size Distributions of Individual Batches of 2.7 µm and 4.1 µm Fused-core Particles Individual batches of Fused-core particles exhibit very narrow particle size distributions.
Actual Size Distributions of a 50/50 Mixture of 2.7 and 4.1-Micron Particles By Number By Volume 0 1 2 3 4 5 6 7 8 Particle Size, microns Mixtures of different sized particles can be measured by Coulter Counter and give different values if assessed by number or volume. Measurement of particle size by volume is more representative ti of the contents of a column than is size by number.
Plate Height Vs Velocity Plots Including Mixed Particles 8.0 7.5 4.1 µm 7.0 Height, microme eters Plate 6.5 6.0 5.5 5.0 4.5 4.0 50%/50% 2.7/4.1 µm 2.7 µm 3.5 Data fitted to Knox equation 1 2 3 4 5 6 7 Linear Mobile Phase Velocity, mm/sec 50/50 mix of 2.7 and 4.1 µm particles produces a column with plate heights intermediate to the components of the mixture.
Comparison of Single-Sized Particles and a Mixture Packing Particles d p 90 a d p 10 b d p 90/d p 10 Plate Number (N)* Plate Height (H)* Pressure (bar)* Plates per bar 41µm 4.1 430 4.30 389 3.89 111 1.11 8590 558 5.58 34 253 2.7 µm 3.02 2.69 1.12 11950 4.19 128 93 50/50 mix 4.1/2.7 µm 4.26 2.63 1.62 10650 4.69 94 113 a d p 90 indicates that 90% of the particles are smaller than the given size b d p 10 indicates that 10% of the particles are smaller than the given size * Values taken at optimum flow High efficiency is still possible for a mixed bed of particles of different sizes, but the pressure increase is not favorable.
Plate Number Per Unit of Pressure (Plate number and pressures taken at optimum flow for each particle size) 5 113 50/50 mix of 2.7 and 4.1 µm 4 269 4.6 µm 3 253 4.1 µm 2 93 2.7 µm 1 69 2.0 µm 0 50 100 150 200 250 300 Plate number per bar of pressure The plate number available per unit of pressure greatly increases as the particle size is increased. The column containing a mixture of large and small particles is not a good compromise of performance features because pressure changes faster than plate number with changes in average particle size.
Comparison of 5μm and 2.7μm particle separation 0.5 ml/min, 40 C, 1 L of ginseng root extract A: 10 mm Amm. Formate/0.1% formic acid, B: ACN 20 50% in 10.0 min. 254 nm, Agilent 1100 Expanded view 65 30 2.1 x 50 mm, HALO-5, C18 Pressure: 66 bar 55 45 25 20 35 25 15 15 10 4 5 5 4.2 4.4 4.6 4.9 5.1 4.8 5 30 0 1 2 3 4 5 6 7 8 2.1 x 50 mm, 2.7 µm HALO, C18 Pressure: 150 bar 65 55 45 9 10 25 20 15 35 10 4.5 25 4.7 5.3 5.5 15 5 5 0 1 2 3 4 5 6 7 8 9 10 Use shorter columns for faster separations For shorter columns, improved resolution is observed when smaller particles are used
Use 5 µm SPP Columns to Achieve High Resolution at Low Pressure Volts 0.020 1.797 2.486 3.505 3.831 4.322 6.380 6.679 7.127 Fused-Core, 2.1 x 150 mm, 5- m SPP 0.5 ml/min, 30 C, 3 L of~50:50 ACN/water DNPH standard mix A: water, B: 80/20 ACN/THF 45% B, hold 5 min, 45 80% in 20 min. 360 nm, bandwidth 8 nm; 40 Hz Worst Case Pressure ~189 bar Volts 0.0 000 0.010 0.000 0.010 0 0.020 0.553 4.088 2.874 4.082 5.648 5.926 6.310 8.384 0 2 4 6 8 10 12 14 16 Time (min) 1.519 3.928 5.807 6.681 7.058 9.546 9.999 10.791 12.221 12.627 Totally Porous, 2.1 x 150 mm, 1.8- m 0.5 ml/min, 30 C, 3 L of ~50:50 ACN/water DNPH standard mix A: water, B: 80/20 ACN/THF 45% B, hold 5 min, 45 80% in 20 min. 360 nm, bandwidth 8 nm; 40 Hz Worst Case Pressure ~855 bar 8.820 8.583 9.286 9.565 10.009 11.393 12.345 12.825 13.738 13.860 14.961 15.393 0 2 4 6 8 10 12 14 16 Time (min) PEAK IDENTITIES (in order): Formaldehyde-2,4-DNPH, Acetaldehyde-2,4-DNPH,Acetone-2,4-DNPH,Acrolein-2,4-DNPH,Propionaldehyde-2,4-DNPH, Crotonaldehyde-2,4-DNPH, 2-Butanone-2,4-DNPH, Methacrolein-2,4-DNPH, Butyraldehyde-2,4-DNPH, Benzaldehyde-2,4-DNPH,Valeraldehyde-2,4-DNPH,m-Tolualdehyde-2,4-DNPH, and Hexaldehyde-2,4-DNPH Note: Small peaks preceding labeled aliphatic aldehyde peaks are minor geometric isomers (syn/anti).
Use 5-µm Fused-Core Particles for Ballistic Gradients 0.450 0.639 60 0.377 0.392 0.493 0.504 5-µm Fused-Core C18, 2.1 x 50 mm 2.0 ml/min, 40 C, 1 L of 8 flavonoids in MeOH A: 10 mm Amm. Formate/0.1% formic acid, B: ACN 5 60% B in 1.0 min. 254 nm, bandwidth 8 nm; 80 Hz; Agilent 1200 SL; Low Delay Volume Configuration ~ 120 µl; ADVR ON mau 40 0.514 Max pressure: 210 bar 0 20 0.0 0.2 0.4 0.6 0.8 1.0 Time (min) Analytes, in elution order: hesperidin, myricetin, quercetin, naringenin & apigenin (coeluted), hesperetin, kaempferol, biochanin Larger particles enable faster flow rates at lower back pressures
Conclusions 1. Fused-core particles can be synthesized with different particle diameters to produce columns with high efficiencies. 2. Columns packed with Fused-core particles of different diameters show improvement in Plate Heights as the particle size is reduced. 3. Reduced Plate Heights (column efficiencies normalized for particle size) show the opposite effect with columns of larger particles having smaller Reduced Plate Heights than smaller particles indicating larger particles may be easier to pack into homogeneous beds. 4. Mixtures of larger and smaller particles can provide good column performance but the resulting pressure makes this a bad compromise. 5. Narrow particle size distributions for Fused-core packings may not be solely responsible for the exceptionally high performance of columns packed with superficially porous particles. 6. Longer columns of 5µm Fused-core particles are recommended for high resolution separations while short columns of 5µm Fused-core particles are recommended for very fast gradients.
Acknowledgements Special thanks to Jason Lawhorn for providing the Coulter analysis data and to Jack Kirkland for discussions and help in organizing and graphing the information used in this poster. Additional thanks to Thomas Waeghe for the applications using HALO-5 columns.