(M1030-01-03) Monodisperse Fully Porous Particles (MFPP) for Use in Increasing Resolution in Liquid Chromatography

Purpose: There are many developments in the silica particles used in liquid chromatography that have been well documented over the years. The move from irregular silica to spherical silica, the decrease in particle size from >5um in HPLC to sub 2um particles in UHPLC, the improved silica purity of type B silica over that of type A silica, and more recently the adoption of superficially porous particles versus traditional fully porous particles. One area of development that has been discussed less and is still open to debate is the particle size distribution (psd) of these chromatographic materials. In this article we discuss the move towards improved monodispersity of silica particles for the use in high performance liquid chromatography (HPLC) and how the use of more monodisperse stationary phases can impact the resulting chromatographic parameters such as column efficiency.

Methods: The silica particle size and distribution were measured using a Coulter Multisizer 3 along with samples from two different commercial 3um silicas. As can be seen in figure 2 both commercial silicas have a much broader size distribution than the new monodisperse material, with one having a slightly smaller mean particle size and the other a slightly larger mean particle size. When assigning a measurement to characterise a particle size distribution the ratio of D90/10 is often quoted, and as such can be used to gauge the degree of size uniformity of the particles. The parameter D90 signifies the point in the size distribution, up to and including which, 90% of the total volume of material in the sample is ‘contained’. For example; if the D90 is 6µm, this means that 90% of the sample has size of 6µm or smaller. The definition for D50, is then the size point below which 50% of the material is contained. Similarly, the D10 is the size below which 10% of the material is contained. This description has long been used in size distribution measurements. As the particle size distribution for chromatographic silica moves towards monodisperse then the D90 and D10 values become closer together and the D90/10 value tends towards a value of 1. Once it was determined that the new particle manufacturing process was successful in creating a truly monodisperse packing material.  The silica based monodisperse packing was packed into a column for efficiency measurements (N). The efficiency of columns packed with the new monodisperse particles were then compared against a number of existing commercial (non-monodisperse) columns and the results can be seen in figures 4 and 5.

Results: Whilst measuring the efficiency (N) the new fully porous monodisperse silica generates ~45-60% compared to traditional standard fully porous commercially available silica materials.  This was measured via UV absorbance at 254 NM wavelength using well behaved neutral probes in reversed-phase mode.

Conclusion: The monodisperse particle platform is used to increase efficiency which increases resolution by the square root.  While the novel bonded chemistries improve selectivity which is directly proportional to resolution, as such, this significant improvement in chromatographic resolution compared to commercially available fully porous particles is gained by the chromatographer.


Figure 1


Figure 4


Figure 5