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)
How many samples to collect?
nsamples= (t^2s^2)/e^2
direct analysis
get the mass of analyte directly
indirect analysis
measure the mass of a related compound and then calculate the mass
traditional [analysis]
involves the precipitation of your analyte
what is the key to gravimetric analysis?
conservation of mass!
what is so great about gravimetric analysis?
it is a definitive technique! aka its not derived, but rather, it uses base SI units
steps in GA
1-prepare your sample solution 2-precipitation of the analyte 3-digestion 4-filtration 5-washing 6-drying/ignition 7-weighing 8-calculation
% analyte (w/w)
(mass of analyte(x)/mass of sample)x100
colloids
particle of size 10-100nm
electrical double layer
++++++
gooy chapman layer
layer of non-randomness ---------- \++++++ ----+---- \++-++-+
zeta potential
the charge that desists* on a colloidal particle
types of impurities:
1) inclusions
2) occlusions
3) surface adsorption
inclusions
impurities scattered within the crystal lattice
occlusions
impurities within the crystal lattice that a large/ clustered
surface adsorption
impurities of the surface
co-precipitation
this is the generic term for any incorporation of impurities in ion crystal lattice –> inclusions/occlusions/surface adsorption
How do you solve surface adsorption?
1- wash your crystals
2-digestion!- allow precipitate to settle in mother liquor for a long time with slow temperature change
Types of Filtration:
1) fast
2) medium
3) slow
4) ashless
fast filtration
pore size~20microm
medium filtration
pore size~15microm
slow filtration
pore size~2microm
ashless filtration
leaves you with 0.1mg or less
drying
oven@110*C
ignition
fire!
slurry
mixture of solids and liquids
filtrate
what you ore filtering
decant
to carefully pour surface liquid
creeping
loss of product when it exceeds filter paper
hygroscopic
if something is hygroscopic it absorbs water from the atmosphere
dessicant
salts that absorb moisture
—-> CaSO4
Inorganic analysis:
- selective reagents
2. specific reagents
selective reagents
targets a small group of ions.
ie. AgNO3
specific reagents
target one ion
chelating structure using dimethylgloxine for Ni(+2)
TGA
thermal gravimetric analysis
