quiz#6 Terms Flashcards
types of liquid chromatography:
1) partition
2) ion exchange
3) adsorption
4) size-exclusion
partition LC
analytes with varying palarity interact with a nonpolar stationary phase and aqueous mobile phase
ion exchange LC
analytes with different charges/charge densities are resolved by a charged stationary pahse
adsorption LC
analytes preferentially adsorb to a solid support
size-exclusion LC
sort by the size of the molecule (good for macromolecules)
t0
time of totally unretained solute; velocity = u0:
H2O
t1
time of somewhat retained solute; velocity u1:
MeOH
t2
time of somewhat more retained solute; velocity u2:
PrOH
retention
a way to describe the length of time an analyte spends on its column relative to its length
how is retention reported?
capacity (retention) factor:
k1= (tr-t0)/(t0)
selectivity factor
a= KB/KA
column performance :
-efficiency= # of theoretical plates AKA # of partitioning opportunities
-HETP=height equivalence to a theoretical plate – H=L/N OR N=L/H
SMALLER HEIGHT = BETTER!
Gaussian peaks
N= (tr/s)^2
asymmetric peaks
if tailing : assymetric factor/ratio =T=B/A
N=((4.17tr^2)/(1/10w^2))/t+1.25)
real samples
implies that some degree of sample preparation will be required
neat samples
run as is
procedure for sample prep
LOT/Gross–> representive bulk sample–>homogenous lab sample–>aliquots–>analysis
BIG 5 Qs?
1- how much sample 2- where to pull withing the sample pool 3- how much of each sample 4-how to minimize error in sampling 5-what kinds of samples to get
types of sampling:
1-random
2-biased(judgemental)
3-systematic
ways to sample:
- grab
- composite
- in-situ
grab
taditional taking a lot
composite
multiple grabs from multiple times and then sampled
in situ
many tiny pulls from a sampling stream (flow injection analysis)