instrumental exam 1

chromatography

separation of a mixture by distribution of sample components between two immiscible phases

mobile phase

gas, liquid, supercritical fluid

stationary phase

liquid, solid

planar chromatography

\-SP supported on a flat surface

\-MP moves through SP by capillary action or gravity

\-uses a plate

column chromatography

\-SP is packed in a narrow column

\-MP is forced through SP (gravity or pressure)

gas chromatography

MP is gas

liquid chromatography

MP is liquid

supercritical fluid chromatography

MP is SCF

mobile phase

solvent

solute

dissolved sample

elute

what exits the column

eluent

what is put in the column

small MP

strong SP

large MP

weak SP

time spent in MP

average rate of solute movement depends on_____

Kc

distribution coefficient

MP

k depends on?

tR

retention time

tM

dead time

t’R

adjusted retention time

retention time

the time the solute spends in a column (MP and SP)

dead time

the time it takes to go from insertion to out of the column

adjusted retention time

tR-tM (time in SP)

v

average linear rate of solute migration

u

average linear velocity of MP molecules

L

length of column packing (cm)

kA

independent of column geometry and MP flow rate

k is the same for

each combination of solute, MP, and SP

k

solute elutes too fast

k>20

solute elutes too slow

1

ideal solute elution

selectivity factor

describes the separation of two compounds in chromatography

broad peak

a sample being in the column for too long leads to a

selectivity and separation efficiency

overall goal of chromatography

fronting

occurs from too much sample

gaussian curve

ideal chromatography peak

tailing

happens from degradation of the SP, analyte sticks to the SP in a bad way

N

\# of plates

H

height of plate (cm)

L

length of column

transfer of mobile phase from plate to plate

total movement of the solute down the column is due to_______

W 1/2

width of peak at half height

better separation

more plates + smaller plate height=

resolution

the spacing of two peaks relative to the lengths of the peaks

A

multiple paths coefficient (Eddy Diffusion Term)

B

longitudinal diffusion coefficient

Cs

mass-transfer coefficient for SP

Cm

mass-transfer coefficient for MP

factors influencing A term

\-particle size (dp)

\-particle shape

\-particle pore structure

\-quality of column packing

\-wall effects

diffusion

migration of molecules from more concentrated region to more dilute region

factors influencing B term

\-linear velocity of MP

\-diffusion coefficient of analyte in MP (Dm)

\-temp

\-molecular mass of analyte

\-quality of packing

B decreases

mobile phase rate is increased

factors influencing Cs term

\-thickness of SP film

\-diffusion coefficient in SP (Ds)

\-retention factor (k)

\-particle size

\-MP velocity (u)

small c term

fast mobile phase and thin film=

factors influencing Cm term

\-particle size (dp)

\-diffusion coefficient in MP (Dm)

\-retention factor (k)

\-MP velocity (u)

\-temp

\-viscosity of MP

\-porosity of packing particles

Cm wants a ______ MP

slow

H(CSA)

resistance to mass transfer due to adsorption on the SP

H(CSP)

resistance to mass transfer due to partitioning (gas, liquid;liquid, liquid)

H(CM)(OTC)

resistance to mass transfer in open tubular column

H(CM)(packed)

resistance to mass transfer in MP in packed column

H(CM)(ST)

resistance to mass transfer in “stagnant” MP surrounding SP particles

constant

Van Deemter Plot A:

inversely proportional

Van Deemter Plot B:

directly proportional

Van Deemter Plot Cu:

HPLC

high pressure/high performance liquid chromatography

smaller

the ______ the SP particle size the better the separation

variables that influence column efficiency

\-linear MP rate (u)

\-Dm and Ds

\-retention factor

\-diameter of particles (dp)

\-thickness of SP film (df)

particle diameter

Cm term in Van Deemter equation is dependent on

improves

as dp decreased, column efficiency_____

GC

in ______ band broadening affects are offset by diffusion

LC

in ______ extracolumn broadening is significant

gases

_____ diffuse more than liquids

r

radius of tubing

fix elution problems in GC and LC

\-vary N (plate #)

\-vary retention factor (k)

\-vary selectivity factor

gas-liquid chromatography

\-inert gaseous MP (He, Ar, N2, H2)

\-immobilized liquid SP

gas-solid chromatography

\-inert gaseous MP (He, Ar, N2, H2)

\-solid SP

ideal injection

sample introduced as sharp plug of vapor

poor resolution

caused by slow injection or too much sample

sample injection methods

micro syringe or solid phase microexctraction

50C

heated injection port is _____ above the least volatile component

on column injection

don’t heat injector port until sample is added

splitless injection

analyte sample vaporized in the injector and goes onto the column

headspace

gas above the sample

solid phase microextraction (SPME)

\-fiber adsorbs onto accelerant

\-fiber put into injector and analyte is vaporized

peak height is dependent on

\-column temp

\-MP flow rate

\-sample injection rate

peak area is dependent from

\-column temp

\-MP flow rate

\-sample injection

external standard

known concentrations of analyte is separate from unknown

standard addition

known amounts of analyte are added to the unknown

internal standard

similar substance to analyte is added to the blank

packed column

\-length:1-5 m

\-ID: 2-3 mm

\-stainless steel

OTC column

\-length: few-100 m

\-ID: 0.25-1 mm

\-fused silica, glass, teflon

packed column

solid support packing particles coated with thin film of liquid SP

ideal particles

\-small, uniform particles

\-strong

\-inert

\-thermally stable

\-large surface area

ideal GC SP

\-low volatility

\-thermally stable

\-inert

\-polar

\-bonded to walls

SP

separation depends on interaction with___

matches

polarity of SP______ polarity of analyte

polar SP

cyano, carbonyl, alcohol, polyester

non-polar SP

hydrocarbons, dialkyl siloxanes

polysiloxane

\-most common SP

\-non-polar

\-used for hydrocarbons, drugs, and steroids

polyethylene glycole

\-lower temp range

\-less stable

\-acids, alcohols, ethers