Question

I was analyzing the sample in Agilent HPLC

and I got 3 peaks at 3.654min, 4.540min and 7.839min with 0.1175, 0.1366 and 0.1571 width values

anyone knows how to calculate N value (#of plates), retention factor, selectivity factor and resolution value for this chromatograms?

Answer 1

N, the number of theoretical plates, is one index used to determine the performance and effectiveness of columns, and is calculated using equation (1).

???1) where tr: retention time, and W: peak width

This peak width, W, is based on the baseline intercepts of tangent lines to a Gaussian peak, which is equivalent to the peak width at 13.4 % of the peak height.
However, to simplify the calculation and accommodate non-Gaussian peaks, the following calculation methods are used in actual practice.

So the N value will be 15468

B)

retention factor,

in column chromatography

A measure of the time the sample component resides in the stationary phase relative to the time it resides in the mobile phase; it expresses how much longer a sample component is retarded by the stationary phase than it would take to travel through the column with the velocity of the mobile phase. Mathematically, it is the ratio of the adjusted retention volume (time) and the hold-up volume (time):

If the distribution constant is independent of sample component concentration, then the retention factor is also equal to the ratio of the amounts of a sample component in the stationary and mobile phases respectively, at equilibrium:

If the fraction of the sample component in the mobile phase is , then the fraction in the stationary phase is ; thus

So the retention factor is 0.8

C)

We define a quantity called the selectivity factor, a , which describes the separation of two species (A and B) on the column;

a = k 'B / k 'A

Hence selectivity factor =0.222

D)

Although the selectivity factor, a, describes the separation of band centres, it does not take into account peak widths. Another measure of how well species have been separated is provided by measurement of the resolution. The resolution of two species, A and B, is defined as

Baseline resolution is achieved when R = 1.5

It is useful to relate the resolution to the number of plates in the column, the selectivity factor and the retention factors of the two solutes;

So resolution is 0.5632