A) How many moles of an analyte are present in a 10.0 micro-M solution that occu
ID: 826306 • Letter: A
Question
A) How many moles of an analyte are present in a 10.0 micro-M solution that occupies 1% of the length of a 25 micrometer internal diameter by 60.0 cm long capillary?
B) Assume that this particular analyte travels the entire length of the column at a rate of 3.22 mm/s with absolutely no natural diffusion. What would be the number of theoretical plates that one could obtain for this column (recall N = tr^2/W^2) where tr and W are the analyte retention time and peak width respectively? Note that both peak width and retention can be in time units.
Explanation / Answer
1.
First find volume.
For cylinder
V = (pi)r^2 x h
= (pi)(25 x 10^-6 m) x (0.6 m)
= 4.7 x 10^-5 m^3
1 m^3 = 1000 L
V = 4.7 x 10^-2 L
Analye takes up 1 % of this, so volume of analyte is 4.7 x 10^-2 x 0.01 L = 4.7 x 10^-4 L
Moles = concentration x volume
= 10x10^-6 mol/L x 4.7 x 10^-4 L
= 4.7 x 10^-9 mole
2.
Retention time is how long the analyte is in the column.
Peak width is how long it takes for the analyte to pass a certain point.
Analyte takes up 1 % of 60.0 cm = 600 mm column, thus it is 6 mm thick.
this moves at 3.22 mm/s
Retention time = 600mm / (3.22 mm/s) = 186 s
Peak width = 6 mm / (3.22 mm/s) = 1.86 s
N = rt^2/W^2
= 186^2/1.86^2
= 10000 plates