Instrumental Analysis Chemistry

Chromatography Article:

1. Using the information provided below derive an expression using Equation 1 given in the

article to describe the change in the diffusion coefficient of an analyte as a function of

temperature. The information below shows the change in viscosity as a function of temperature

at pressures similar to those used in this paper. You will need to fit these data to a polynomial

function in Excel and then use that function in Equation 1. Show all work.

Viscosity Temperature (°C)

(Pascal seconds (Pas))

9 x 10-4 25

3 x 10-4 100

2 x 10-4 150

1.7 x 10-4 175

1.5 x 10-4 200

1.35 x 10-4 225

1.25 x 10-4 250

1.2 x 10-4 275

b) Graph the resulting expression from room temperature to 180 C (highest temperature used in

this paper).

c) Use the expression derived in part a) to find the change in H (equation 2 in the paper) as a

function of temperature. You will need to use the equations given in your book for A, B, and C.

Assume changes to diffusion in the stationary phase are not as important as changes in the

diffusion in the mobile phase. You will have to make some assumptions for the retention factor

k. State all assumptions

d) Graph the change in each of the components of Equation 2 (A, B, C) and H as a function of

temperature (do these on separate graphs).

e) Does the data in Figures 1 and 2 of the paper correlate to what you would expect based upon

the behavior of equation 2 plotted in part d of this question? Specifically address the differences

seen in internal column diameter and particle size. If the behavior does not match the expected

results propose some explanations of why it does not match the expected results.

2. For the 2.1 mm I.D. column no minimum plat height can be calculated at 180 °C. From a

thermodynamic point of view why is this the case?

3. Figure 3 shows that the efficiency of smaller particles in the separation decreases for longer

dead volume times. Why is this the case and is that result predicted from the equations given in

the paper?