final exam 2 stuff

Question 1

whats the difference between capillary and packed column GC’s

Answer 1

capillary columns are long and thin and have a stationary “waxy” coating on the inside

packed columns have “balls” of stationary phase

Question 1

what’s the differen

Question 2

how do we adjust the retention in a GC?

Answer 2

we can adjust the temperature, the flow rate, and the chemical nature of the stationary phase

Question 3

what does adjusting the temperature do to a GC?

Answer 3

if we heat the colum, it will cause less retention since more of the molecules will be in the gaseous phase

Question 4

how do we adjust the chemical nature of the stationary phase

Answer 4

we can make it more polar or nonpolar

Question 5

how do we generally adjust the retention of analytes in LC and GC

Answer 5

it’s easier to adjust the mobile phase rather than the stationary phase

Question 6

what affects the retention in gas chromatography

Answer 6

a combination of the boiling point and the polarity

Question 7

how does the boiling point play into gas chromatography

Answer 7

analytes with low boiling points are more volatile and will go into the mobile phase easier

Question 8

in GC, the separation is based on the difference in partitioning between:

Answer 8

the stationary and gas (mobile phase)

Question 9

When we increase the column temperature, what happens to the gas phase concentration? To what solutes?

Answer 9

The gas phase concentration of ALL solutes increases with increased temperatures

Question 10

why is it a problem when we increase the temperature?

Answer 10

all the analytes are affected and may not be completely resolved

Question 11

why is it a problem when we decrease the temperature

Answer 11

it is inefficient we get better resolution and separation but the peaks become broader and it takes more time

Question 12

what is temperature programmed chromatography?

Answer 12

it is where we increase the temperature of the column during a run

Question 13

when we don’t use temperature programmed chromatography what happens when we get resolution with early eluters

Answer 13

the late eluters get too broad or do not elute

Question 14

when we don’t use temperature programmed chromatography what happens when we get resolution/narrow peaks with late eluters?

Answer 14

the early eluters do not get resolved

Question 15

what is a gradient in liquid chromatography

Answer 15

it is when we alter the composition of the mobile phase during the run in order to achieve better separation in less amounts of time

Question 16

what is the difference in mobile phases for HPLC and GC

Answer 16

in GC we have a gas mobile phase

in HPLC we have a liquid mobile phase

Question 17

is HPLC isothermal?

Answer 17

yes, it is difficult to change the temperature

Question 18

is GC isothermal

Answer 18

no, we often change the temperature to change the mobile phase

Question 19

in a GC, how do the analytes interact with the mobile and stationary phases

Answer 19

the analyte interacts with the stationary phase only, the mobile phase serves as a carrier

Question 20

in a HPLC, how do the analytes interact with the mobile and stationary phases?

Answer 20

the analytes interact with both the mobile and stationary phases

Question 21

if we make the mobile phase and stationary phases in a HPLC more similar what happens to the retention times?

Answer 21

the times decrease

Question 22

if we make the mobile phase and stationary phase in a HPLC less similar, what happens to the retention times?

Answer 22

the times increase

Question 23

what are the best analytes for LC

Answer 23

analytes that are non-volatile

Question 24

what are the best analytes for GC

Answer 24

analytes that are volatile

Question 25

why do we not use normal phase HPLC very often?

Answer 25

normal phase HPLC has a nonpolar mobile phase,

usually nonpolar analytes are more volatile and can be used more easily in a GC separation