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Chapter 25: Q31P (page 710)

Question: Explain how to use a gradient for the first run to decide whether isocratic or gradient elution would be more appropriate.

Short Answer

Expert verified

Gradient elution would be more appropriate.

The measure difference in retention time∆tbetween peaks. We use gradient elution∆t/tG>025, if it is smaller, we use isocratic elution.

Step by step solution

01

definition of gradient

Change in the value of a quantity as temperature, pressure, or concentration with variation in a given variable, particularly per unit on a linear scale.

The use a gradient for the first run to decide whether isocratic or gradient elution would be more appropriate.

To do that, we must run a wide gradient 5%Bto100%Bin a gradient time tGwhich must be selected to produce k*≈5uusing the equation:

02

Gradient elution

Then,

k*=tG‐F∆Φ‐vm‐S

measure difference in retention time ∆tbetween peaks. We use gradient elution∆t/tG>025, if it is smaller, we use isocratic elution

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Most popular questions from this chapter

Why are silica stationary phase height limited to operating in the pH range 2-8?why does the silica in figure25-8have improved stability at low pH?

To which kinds of analytes do these liquid chromatography detectors respond?

(a) ultraviolet

(b) refractive index

(c) evaporative light scattering

(d) charged aerosol

(e) electrochemical

(f) fluorescence

(g) nitrogen chemiluminescence

(h) conductivity

what are criteria for an adequate isocratic chromatographic separation?

(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 1.8μmparticles in figure 25-3is nearly flat at high flow rate.what can you say about each of the terms in the van Deemeter equation for 1.8μmparticles.

(c). Explain why the 2.7μmsuperficially porous particle enables separations similar to those achieved by 1.8μmtotally porous particles,but the superficially porous particle requires lower pressure.

A known mixture of compounds A and B gave the following HPLC results:

A solution was prepared by mixing 12.49mgof Bplus 10.00mLof unknown containing just and diluting to 25.00mL. Peak areas of 5.97and 6.38were observed for AandB, respectively. Find the concentration of A(mg/mL)in the unknown.
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