Core-shell column shows high column efficiency, low back pressure, high sensitivity, but majority of people may not know the reasons. In order to understand the characteristics of the core and shell column, Van Deemter equation is recommended to know first.

When we study chromatographic theory, rate theory is required to explain the broadening of peak. Figure 1 is the classical Van Deemter equation:

Fig 1

 H theoretical tower height

 A eddy current diffusion term

 B/μ vertical proliferation

 Cμ mass transfer resistance item

 Or a more detailed equation as Fig 2

Fig 2
  1. λ as filling non-uniform factor in the eddy current diffusion term while dp as the average particle size of the stationary phase;
  2. In the molecular diffusion term, G as the bending factor among packing materials in the column (≈0.6), while the Dm as the diffusion coefficient of solute in the mobile phase of liquid, Dm≈10⁻⁵cm²/s and μ is the average linear flow rate in the packed column cm/s;
  3. In mass transfer resistance term, df as the diffusion coefficient of solute in the stationary solution, cm²/s;  W as the packing factor of the column, and the W value as small for the short column with thick inner diameter.

Compared with the full porous column, the high column efficiency and high analytical efficiency that core-shell column shows can be explained by the Van Deemter equation, as shown in figure 2.

Packing materials of core-shell column (Fused-Core), generally composed by the internal solid sphere (its material and formation depends on the manufacturer and techniques), porous silica gel or hybrid granular silica gel.

Firstly, the core of the packing material is a solid sphere, which leads to a weaker axial diffusion effect, reflecting in the Van Deemter equation, which mainly affects the second parameter Dm and reduces the axial expansion of the peak.

Secondly, due to the existence of solid spheres, the radial temperature transfer is accelerated, which makes the temperature distribution more uniform and accelerates the mass transfer speed. In addition, the mass transfer path of core-shell packing particles is much shorter than that of all porous packing, which makes the mass transfer rate faster than that of all porous packing materials.

Last but not least, due to the differences in the preparation process (the first thing to make core-shell column packing materials is to prepare solid spheres, and then “coated” full porous silica gel on its surface) The particle size distribution of core-shell column is more uniform and continuous than that of full porous column. The main impact is on the first parameter dp manifests in Van Deemter equation, as eddy current diffusion term.

If the particle size distribution is more uniform and the eddy current diffusion term is smaller, the contribution to the theoretical plates height will be smaller and theoretical plates of the column will be more. The eddy current diffusion term is the main factor affecting the diffusion in the peak column as shown in figure 3 below. Figure 3 B has a more uniform and continuous particle size distribution than figure 3 A, so it has the smaller eddy current diffusion effect and higher column efficiency.

Fig 3

The theoretical plates height is greatly reduced because of the above three reasons, so the core-shell column has higher column efficiency and wider optimum flow rate range than the full-porous column. Thus, it has higher analytical speed and lower system back pressure.

Boltimate core-shell column

○ Ultra-high resolution, high speed and high efficiency while the column back pressure is less than 50% of  fully porous sub-2μm;

○ Compared with the traditional 3 and 5 micron analytical columns, the column efficiency, flow rate,  resolution and sensitivity are greatly improved, the diffusion path is reduced, and the column efficiency is improved.

○ Narrower particle size distribution and use of 2 micron frits mitigates high column back pressure, and results in reliable high performance and durabllity for samples having a complex matrix;

○ Compatible with existing HPLC or UHPLC  and HPLC/UHPLC systems.

○ Operates at pressures up to 600 bar (8,700 psi)

Bonded PhasesFeaturesParticle Size(μm)Solid Core Diameter(μm)Porous Shell Depth(μm)Pore Size(Å)Surface Area(m2/g)C%End/cappedpH RangeUSP List
C18Excellent peak shape and resolution for acids, bases, and neutrals. Exceptional resolution and lifetime.
Phenyl-HexylAlternative selectivity for phenyl groups2.71.70.5901207Double2-8.5L11
EXT-C18The exist of hybrid organic/inorganic layer extend pH range of silica. pH range: 1.5-
EXT-PFPAn alternative selectivity for halogenatedcompounds and polar analytes. Wide pH range2.71.70.5901205Double1.5-12L43
HILICWith its unbonded silica, Boltimate HILIC retains and separates polar analytes.
LP-C18Excellent peak shape and resolution at low pH.

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