Porous microparticles with solid cores

Abstract

The present invention relates to microparticles, particularly spherical silica microparticles, which may be useful in liquid chromatography. Specifically, the microparticles include a solid core and an outer porous shell surrounding and irreversibly joined to the core. The shell is composed of a plurality of colloidal nanoparticles, which are applied using an electrostatic multi-multilayering method. The resulting microparticles have a small particle diameter, such as about 1 μm to 3.5 μm, a high particle density, such as about 1.2 g/cc to 1.9 g/cc, and a high surface area, such as about 50 m2/g to 165 m2/g. These microparticles can be used to form packed beds and liquid chromatographic columns, which are more efficient and rugged than conventional liquid chromatographic columns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a partially cut-away cross-section of a spherical microparticle in accordance with the present invention.

FIG. 2 is an electron micrograph image of a cross-section of a spherical microparticle in accordance with the present invention.

FIG. 3 is a schematic diagram of a process for preparing a microparticle in accordance with the present invention.

FIG. 4 shows the extremely narrow particle size distribution of the microparticles in accordance with the present invention. The diagram shows the particle size distribution of 2,324 microparticles at 2.65 μm average particle diameter.

FIG. 5 shows column back pressure versus mobile phase velocity data obtained with liquid chromatographic columns packed with microparticles in accordance with the present invention having a 2.7-μm particle diameter as compared to totally porous particles having a 1.7-μm particle diameter and totally porous particles having a 3.5-μm particle diameter.

FIG. 6 shows plate height (also referred to as HETP, or height equivalent to a theoretical plate) versus mobile phase velocity data obtained with liquid chromatographic columns packed with microparticles in accordance with the present invention having a 2.7-μm particle diameter as compared to totally porous particles having 5-μm, 3.5-μm and 1.8-μm particle diameters. The plots demonstrate the superior efficiency of the microparticles of the present invention for liquid chromatographic separations.

FIG. 7 is a chromatogram of a liquid chromatographic separation of uracil, phenol, 4-chloro-1-nitrobenzene and naphthalene, which demonstrates the ruggedness and stability of a liquid chromatographic column packed with microparticles in accordance with the present invention.

Claims

1. A microparticle comprising: a solid core; andan outer porous shell surrounding said core, said shell comprising a plurality of colloidal inorganic nanoparticles,wherein said microparticle has a diameter of about 1 μm to about 3.5 μm, a density of about 1.2 g/cc to about 1.9 g/cc and a surface area of about 50 m2/g to about 165 m2/g.

2. The microparticle of claim 1, wherein said microparticle is spherical.

3. The microparticle of claim 1, wherein said core is impervious.

4. The microparticle of claim 1, wherein said outer porous shell is irreversibly joined to said core.

5. A spherical silica microparticle comprising: a solid silica core; andan outer porous shell surrounding said core, said shell comprising a plurality of colloidal silica nanoparticles,wherein said microparticle has a diameter of about 1 μm to about 3.5 μm, a density of about 1.2 g/cc to about 1.9 g/cc and a surface area of about 50 m2/g to about 165 m2/g.

6. The microparticle of claim 5, wherein said core is impervious.

7. The microparticle of claim 5, wherein said core has a diameter of about 1 μm to about 3 μm.

8. The microparticle of claim 5, wherein said shell is irreversibly joined to said core.

9. The microparticle of claim 5, wherein said shell has a thickness of about 0.1 μm to about 0.75 μm.

10. The microparticle of claim 5, wherein said shell comprises about 25% to about 90% by volume of said microparticle.

11. The microparticle of claim 5, wherein said colloidal silica nanoparticles comprise alike silica nanoparticles.

12. The microparticle of claim 5, wherein said colloidal silica nanoparticles are in a random open-packed structure.

13. The microparticle of claim 5, wherein said colloidal silica nanoparticles are solid.

14. The microparticle of claim 5, wherein said outer porous shell has a pore size of about 4 nm to about 175 nm.

15. The microparticle of claim 5, wherein said outer porous shell has a pore size distribution of about 40% to about 50% (one sigma) of the average pore size.

16. The microparticle of claim 15, wherein said microparticle has a porosity of about 55% to about 65% by volume of the outer porous shell.

17. A packed bed for liquid chromatography comprising: a plurality of microparticles comprising a solid core and an outer porous shell surrounding said core, said shell comprising a plurality of colloidal inorganic nanoparticles,wherein said microparticles have an average diameter of about 1 μm to about 3.5 μm, an average density of about 1.2 g/cc to about 1.9 g/cc and an average surface area of about 50 m2/g to about 165 m2/g, andwherein said packed bed has a reduced plate height of less than about 2 at the plate height minimum under optimum operating conditions.

18. The packed bed of claim 17, wherein said packed bed has a reduced plate height of about 1.3 to about 2 at the plate height minimum under optimum operating conditions.

19. The packed bed of claim 17, wherein said microparticles have a particle size distribution of about ±10% (one sigma) or less of the volume average diameter.

20. The packed bed of claim 17, wherein said microparticles have a particle size distribution of about ±5% (one sigma) of the volume average diameter.

21. The packed bed of claim 17, wherein said solid core comprises a solid silica core.

22. The packed bed of claim 17, wherein said colloidal inorganic nanoparticles comprise solid silica nanoparticles.

23. An apparatus for liquid chromatographic separations comprising: a region through which materials to be separated are passed; anda packed bed comprising a plurality of microparticles contained in said region, said microparticles comprising a solid core and an outer porous shell surrounding said core, said shell comprising a plurality of colloidal inorganic nanoparticles,wherein said microparticles have an average diameter of about 1 μm to about 3.5 μm, an average density of about 1.2 g/cc to about 1.9 g/cc and an average surface area of about 50 m2/g to about 165 m2/g, andwherein said packed bed has a reduced plate height of less than about 2 at the plate height minimum under optimum operating conditions.

24. The apparatus of claim 23, wherein said apparatus comprises a high performance liquid chromatography column.