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what are criteria for an adequate isocratic chromatographic separation?

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Criteria for an adequate isocratic chromatographic separation

If k is too small. The first peak must be distorted by the solvent front. If k is too great, the separation takes too long.

Step by step solution

01

definition of criteria adequate isocratic chromatographic separation

The criteria for an adequate isocratic chromatographic separation is K for all peaks must be in the range.0.5-20 If k is too small.

K for all peaks must be in the range 0.5-20.

If k is too small.

The first peak must be distorted by the solvent front.

If k is too great, the separation takes too long.

The minimum resolution of 1.5between the two closest peaks is desired.

ruggedness, a resolution of2 is desirable.

02

The separation

The pressure must be below15MPa150barso that it prolongs the life of the pump, valves, seals, and autosampler all peaks should be symmetric, with an asymmetry factor B/A in the range0.9-1.5.

Hence,

If k is too small. The first peak must be distorted by the solvent front. If k is too great, the separation takes too long.

The minimum resolution of 1.5between the two closest peaks is desired.ruggedness, a resolution of 2is desirable.

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Most popular questions from this chapter

(a) List ways in which the resolution between two closely spaced peaks might be changed.

(b) After optimization of an isocratic elution with several solvents, the resolution of two peaks is 1.2How might you improve the resolution without changing solvents or the kind of stationary phase?

what is the difference between extra-column volume and dwell volume? How do each of these volumes affect a chromatogram?

(a) Make a graph showing retention times of peaks 6, 7, and 8 in Figure 25-12 as a function of %acetonitrile (%B). Predict the retention time of peak 8 at 45% B.

(b) Linear-solvent-strength model: In Figure 25-12, tm = 2.7 min. Compute k for peaks 6, 7, and 8 as a function of %B. Make a graph of log k versus Φ, where Φ= %B/100. Find the equation of a straight line through a suitable linear range for peak 8. The slope is -S and the intercept is log kw. From the line, predict tr for peak 8 at 45% B and compare your answer with (a).

(c) Gradient elution: A linear eluent gradient from 40 to 80% acetonitrile over 30 min is performed on the column in Figure 25-12. Assuming a dwell volume of 0 mL, use your data from (b) to plot the retention factor of peaks 6 and 8 during the gradient. What are the general characteristics of the plot?

(d) Why are the peaks in a gradient separation sharp?

a. Why is high pressure needed in HPLC?

b. For a given column length , why do smaller particles give a higher plate number?

c. What is bonded phase in liquid chromatography?

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

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