W9 Chromatography

Question 1

what is chromatography

Answer 1

technique in which components of a mixture are separated based on differential partitioning between mobile and stationary phase

Question 2

how does column chromatography work

Answer 2

solution containing solutes A and B placed on top of column packed with solid particles and filled with solvent

solutes A and B flow down into column

if solute B more strongly adsorbed than A on solid particles > B spends longer time in column > moves down more slowly than A and emerges at bottom later than A

Question 3

difference between adsorption and partition chromatography

Answer 3

adsorption: based on adsorption of solute molecules onto surface of solid stationary phase

partition: distribution of solute molecules between two immiscible phases: stationary liquid and mobile phase

Question 4

definition of retention time, void time and adjusted retention time

Answer 4

retention time: the time needed after the injection on the column to reach the detector for each component

void time: the time taken for an unretained species to pass through a column (all components spend this amount of time in the mobile phase)

adjusted retention time: the time a solute spends in stationary phase (difference between retention time and column’s void time)

Question 5

definition of linear flow rate and volume flow rate

Answer 5

linear: how many cm the solvent travelled in one minute

volume: how many ml of solvent per minute that travelled through the column

Question 6

what does it mean to scale up chromatography

Answer 6

increasing size of chromatography to handle larger volume samples > produce more purified products

Question 7

what are the rules of scaling chromatography

Answer 7

column length must be kept constant

cross sectional area of column is proportional to mass of analyte

must maintain constant linear velocity

sample volume applied to column is proportional to mass of analyte

if column length changes, mass of sample can be increased in proportion to total length

Question 8

definition of retention factor

Answer 8

measurement of how long a compound is retained in the column compared to the mobile phase

longer the compound is retained > higher retention factor

retention factor is constant for given column, analyte and conditions

Question 9

definition of selective factor

Answer 9

for any two components A and B, the selectivity factor is the ratio of their adjusted retention time

greater selectivity factor > greater the separation between the components

Question 10

relationship between retention factor and partition coefficient

Answer 10

the greater the ratio of partition coefficients between mobile and stationary phases, the greater the separation between the two components of a mixture