In: Chemistry
How is plate height affected (increased, decreased, unchanged) by each of the following, briefly justifying your answer in each case:
A. very high linear flow velocity
B. longer column length
Ans A: According to Van deemtrental equation
HETP= A+ ( B/) +(Cs + Cm)
HETP- Height equivalent to theoretical plate
A- Eddy- diffusion
B- longitudinal Diffusion of eluting particles
C- Resistance to mass transfer coefficient between Mobile phase and stationary phase
- linear
velocity
If linear velocity() is increased the
longitudinal diffusion (B) decreases and plate height will also
decrease.
If linear velocity() is
decreased the longitudinal diffusion (B) increases and plate height
will also increase.
If linear velocity () is unchanged the
longitudinal diffusion (B) will not change and plate height will
also remain unchanged.
Ans B)
H= L/ N
H- Plate height
L- Column length
N- Number of theoretical plates
The plate height will increase if column length is increased.
The plate height will decrease if column length is decreased.
The plate height will remain unchanged if the column length is not changed.