The H (height equivalent of a theoretical plate) value for an HPLC column at mobile phase flow rates of 1ml/min, 3ml/min and 4ml/min are 4.1mm, 4.7mm and 5.675mm. Calculate:
1. The van Deemter parameters A, B and C
2. The flow rate at which H is a minimum and the value of H at this flow rate
3. The efficiency N if the length of the column is 18cm
You have three unknowns and three simultaneous equations.
H = A + B/u + C(u)
where H is the plate heights, u is the flow rates and A, B, C are unknown.
The equations become:
4.1 = A + B/1 + C(1) or multiply out 1 4.1 = A + B + C
the next equation is:
4.7 = A + B/3 + C(3) multiply sides by 3 14.1 = 3A ...
You have three unknowns and three simultaneous equations H = A + B/u + C(u) where H is the plate heights, u is the flow rates and A, B, C are unknown.