W9 Chromatography Flashcards
what is chromatography
technique in which components of a mixture are separated based on differential partitioning between mobile and stationary phase
how does column chromatography work
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
difference between adsorption and partition chromatography
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
definition of retention time, void time and adjusted retention time
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)
definition of linear flow rate and volume flow rate
linear: how many cm the solvent travelled in one minute
volume: how many ml of solvent per minute that travelled through the column
what does it mean to scale up chromatography
increasing size of chromatography to handle larger volume samples > produce more purified products
what are the rules of scaling chromatography
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
definition of retention factor
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
definition of selective factor
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
relationship between retention factor and partition coefficient
the greater the ratio of partition coefficients between mobile and stationary phases, the greater the separation between the two components of a mixture
