12 February / March 2017
with smooth surface tends to slip quickly and results in a rapid change in bed strain, causing a more heterogeneous packing consisting of large variation in the local value of external porosity and resulting in a large A term.
The B term contribution to band broadening on the Manufacturer A-C18 column was the largest (7.89) amongst the three columns. In the linear velocity region where the B-term is significant, the solute will spend more time inside the column and diffuse axially resulting to distortion of the solute band. The Solas™ Monodense™ has the smallest B term coefficient (4.85) compared to the other two columns.
The C term coefficient for Solas™ Monodense™ was the lowest at 0.005. This effect can be ascribed to the homogeneous nature of the pore structure leading to shorter solute diffusional path in and out of the particle substructure. An analysis of the backpressure plots for Solas™ Monodense™ and the other 2 commercial columns is shown in Figure 7B it is evident that the backpressure for monodense particles is higher than that of traditional particles as seen in Figure 7B, possibly due to the slightly smaller particle size of the Solas Monodense particle.
Figure 7. Van Demeter and back pressure profile for Manufacture A (A) Manufacturer B (B) and SOLAS Monodense 1.8 µm
Other benefits of monodense particles
Due to the monodense nature of the particles, it has been shown that the packing of these particles is somewhat easier than with traditional silica’s, resulting in a reduction in the number of columns that fail to pack. This is most likely due to the homogeneous distribution of particles within the packing solvent with little or no flocculation or settling of particles during the packing process. Early results have shown a reduction of almost 10% of scraped or failed columns. From the production of large amounts of columns this could represent a significant cost saving.
Voids in Superficially porous (Core Shell) particles
Figure 8. FIB images of several core shell particles
The issue of voids is not a problem confined to fully porous particles (FPPs), it is also observed in core shell or superficially porous particles (SPPs), as can been seen in Figure 8. Whist the process for the manufacture of core shell particles is different to that that utilised in the manufacture of FPPs, several steps are transferable between the two. For example condensation and hydrolysis
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