Question 11 (6 marks) (a) Both capacity factor, , and resolution, Rs, are used t

Question

Question 11 (6 marks) (a) Both capacity factor, , and resolution, Rs, are used to gauge the efficiency of separation between two components in a chromatographic experiment. Which of the two is a more reliable parameter to use? Explain your answer. (b) Consider HPLC chromatograms 1 and 2 given below obtained under the same conditions using two different columns of identical length. Compare the expected number of theoretical plates (N) between the two columns. Column 1 I Column 2 0 2 8 10 12 Time-

Explanation / Answer

Chromatographic separation

(a) Both capacity factor and resolution are used to determine the efficiency of separation. Of the two resolution is more reliable parameter as it takes care of both the peak retention time so it becomes as average of two and also employ width of each peak. So the separation becomes more accurate between two peaks on the column.

(b) Number of theoretical plates (N),

using formula,

N = 16(retention time of peak/width of peak)^2

For column 1,

N(A) = 16(8/1)^2 = 1024

N(B) = 16(10/1.2)^2 = 1111

For column 2,

N(A) = 16(8/2.2)^2 = 212

N(B) = 16(10/2.1)^2 = 363

Thus as can be clearly seen, the number of theoretical pates in column 1 is greater than that in column 2, therefore, the resolution of peaks A and B is also more efficient in column 1. Column 1 is preferable choice for the separation of the two compounds.

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