Question

(a). Sketch a graph of the van Deemnter equation (plate height versus linear flow rate).what would the curve look like if the multiple path term were 0? If the longtitundinal diffusinal diffusion term were 0?

(b). Explain why the van Deemter curve for $\mathbf{1}\mathbf{.}\mathbf{8}\mathbf{\mu m}$particles in figure $\mathbf{25}\mathbf{-}\mathbf{3}$is nearly flat at high flow rate.what can you say about each of the terms in the van Deemeter equation for $\mathbf{1}\mathbf{.}\mathbf{8}\mathbf{\mu m}$particles.

(c). Explain why the $\mathbf{2}\mathbf{.}\mathbf{7}\mathbf{\mu m}$superficially porous particle enables separations similar to those achieved by $\mathbf{1}\mathbf{.}\mathbf{8}\mathbf{\mu m}$totally porous particles,but the superficially porous particle requires lower pressure.

Short answer

a) Sketch a graph of the van Deemnter.

b) Comparing the van Deemter curve of the particles in Figure to the graph

c) Superficially porous particles have a diameter non porous silica core.

Step-by-step solution

Sketch a graph of the van Deemnter 

The van Deemter equation was graphed to help visualise each term in the equation. Figure 24-3 was then examined using the van Deemter equation and its implications.

The figure below shows the graph of the van Deemter equation when the multiple paths term ( A) is , when the longitudinal diffusion term ( B) is , when the equilibration time term (C ) is constant, and when all terms are .

Comparing the van Deemter

b) why the van Deemter curve

Comparing the van Deemter curve of the $1.8\mathrm{\mu m}$particles in Figure $24-3$to the graph in (a), we can see that the graph that it most resembles is the graph of c=0. Although not obvious from the graphs, the equation of the curve of $1.8\mathrm{\mu m}$particles has a small multiple paths term (A ) relative to that of the other larger particles in the graph.

Based on the graph, the curve of the particles plateaus at the smallest plate height ( H) compared to the other graphs. The reduction in plate heights can be related to the decrease in the band spreading due to multiple flow paths.

Given this relationship, the decrease in the H plateau value of the particles means that there is a decrease in A as the particle size decreases.

c) superficially porous particle

Superficially porous particles have a $5\mathrm{\mu m}$diameter non porous silica core. Compared to other fully porous particles with a larger radii, superficially porous particles can perform at the same level or better.

This is due to the structure of superficially porous particles, having a 0.25 thick porous silica layer on the outside of its $5\mathrm{\mu m}$diameter non porous silica core