11-12(4) Flashcards
What is the stationary phase of GC?
usually a nonvolatile liquid but sometimes a solid
What is the limit of GC?
It can only analyze the sample that are volatile or can be evaporated intact at higher temperature with out breaking down.
_____ of known organic compounds can be analyzed with this technique therefore it is some what limited
20%
The _____ needs to be in high purity (______ppb O2).
carrier gas; < 1 ppb O2
In gas-liquid partition chromatography: stationary phase is ______ liquid bonded to inside of column or to a fine solid support.
nonvolatile
What type of carrier gas usually used depend on the ______
detector
example Ne2, H2, N2
silicon rubber septumpoked through with needle and analyte immediately ______ in the injector oven.
volatilize
Column needs to be hot enough to provide sufficient ____ ____ for elution of analyte.
Because there are probability of molecule _______ and do not get to the detector(analyte lost).
vapor pressure
condensation
In gas-solid adsorption chromatography:
Analyte _____ ______ on solid particles of stationary phase.
adsorbed directly
______ _____ columns (capilary columns) are most frequently used stationary phase in GC(fused silica)
Open tubular
Open tubular columns in comparison to the packed columns would offer: (4 things)
higher resolution (make A term nonexistence) shorter analysis time (higher flow rate) greater sensitivity (Also associate with A term) lower sample capacity (smaller amount of sample injection-limited)
The length of the GC column is about _____ long and ____ for polyimide coating (up to 350 degree).
15-100m
stationary phase = 0.1-5um(0.1-0.53mm for diameter of the inner column)
There are three kinds of open tubular columns: ____ (WCOT) _____ (SCOT) _____ (PLOT)
wall-coated (stationary liquid phase)
support-coated (solid support coated with stationary liquid phase)
Porous layer (stationary solid phase particles)
____ _____ (2um) on inside wall of OT column.
Porous carbon
Narrower column will create a ____ resolution, which can also be increased with _____. Increased resolution means more _______.
High ______ is required for less sample capacity.
higher (improved separation)
square root of column length(retention time increased)
theoretical plate (N) ->gives baseline separation
pressure
If the diameter is ______ mm cannot use MS as detector because it needs ______ and if too much gas, it goes down.
> 0.32
vacuum
increases retention time and resolution of k< 5 peaks
if k=capacity factor is less than 5,
leads to thicker inner later
and higher resolution
P568
Choice of liquid stationary phase is like dissolve like.
Therefore chose the one that is good for ______ of molecule.
separation
P569
As GC column ages, ______ can be lost due to exposure to _____.
________ (Si-OH) exposed and _______ can increase. which is referred to as “bleeding”
stationary phase
high temperature
silanol group
tailing
“Bleeding” is the signal difference from GC system that is not from the _____.
analyte
tailing are asymmetrical signals peaks
- which is due to stationary phase degradation
Most retened compounds are the ones with ____ boiling point.
Thus retention is determined by ______.
highest
volatility
___ polar stationary phase should be used to help the separation of the polar compounds.
______ is important for stationary phase for the choice between polar and non-polar.
more
selectivity
To reduce the bleed from high temperature, chemically bond it to ______ surface is required.
It is also a good idea to monitor _______ (k of standard or N)
silica
column performance
k=capacity factor
N=theoretical plate N
high operation temperature will cause stationary phase to ________ and leads to slow bleed which cause elevated ______ in detector.
And lastly, reduced ______ and _______.
decompose
background
signal to noise
detector contamination
A new type of GC stationary phase uses ____ _____.
It has low ____ at elevated temperature, and is potential to offer novel _____.
ionic liquids
volatility
selectivites
Solids for porous OT columns: polymers, ______ and molecular sieves.
alumina (Al2O3)
Packed columns contain solid particles coated with _______ stationary phase or _____for stationary phase.
non-volatile
solid itself
Packed sample has better sample ______. but give _____ peaks, _____ tr (retention time), and ____ resolution.
capacity (more)
broader
longer
less
Less resolution is generally not good but is good for ______
preferrtively isolate compound
despite inferior resolution used for preparative separation (ie to separate mg amounts)
Solid support often silica that has been silanized to reduce H-bond to polar solute.
A protective surface (CH3)3 SiO
uniform particle size decreases ________ (multiple path term) which decreases _____(H)
If particle size are not uniform, there will be different _____.
A-term
plate height
retention time
In GC temperature often increased _______ separation which increases analyte ______.
(difference between HPLC)
during
vapor pressure
Increase temperature from 30 to 150 degree at different rates can reduce ______ required for separation, with baseline resolution still present.
time
Decreases retention time and sharpens peaks
linear alkanes on a 3.0m (Dimethylpolysioxane) long poly in the column etched in a silicone chip.
a chip with square maze in it
Most GC columns come with 2 temperature labels.
should always stay under these limits
1) isothermal temperature limit: column kept at this for a long time with out damaging it
2) programmed temperature limit: few minutes
carrier gas has to be compatible with the _____.
____ gas is compatible with most.
detector
He(frequently used)
Change of carrier gas result in different _______.
linear velocity
(how fast the gas move through the column)
(The faster linear velocity with smaller plate height the better)
H is very good to use as carrier gas, but it is not often used due to more than ____ in the air is explosive
4%
needle inserted through rubber septum and sample is not immediately ______ and _____ washes needle and ____ expels solvent from needle
evaporated
solvent
air plug
_________ gets dirty during usage and need to get replaced
Silane glass liner
_______ injection is more appropriate if analyte of interest is >0.1% of sample. ____% of sample will be on column
Complete injection contains _________.
split injection
(>0.1% is important)
0.2 - 2%
too much material
Split ration A : B, and which goes to the wast?
A
do not reaches to the column
Quantitative analysis can be inaccurate because split ration may not be _______ from run to run.
reproducible
________ injection is good when analyte of interest is <0.01 % of sample and ____% will be on column.
splitless injection
80%
(almost everything injected goes to the column)
There are three types of injection: ____, _____, ____.
split (99% goes to waste)
splitless
on column (direct to the column)
*in decreasing temperature
Initial column temperature is ______ than BP of solvent and is a method called _____ which provides sharp peaks.
It helps the solvent _____ initally in the GC column so it can retain the _____ that is coming in to the system.
40 degree less
solvent trapping
condense
analyte
(analyte is concentrated initially with solvent)
On-column injection is preferred for __________ and for samples that decompose _____ their BP.
quantitative purposes
above
co-chromatography (______): authentic compound added to unknown sample if added compound identical with a component there will be a relative______increase
spiking
peak area
identification by tentative with 1 column, but firmer when carried out on several columns or different stationary phases
for spiking
Detectors that tells you if compound is present or not.
Thermal conductivity
Flame ionization
Electron capture
Quantitative analysis is based on _____ of chromatographic peak.
_____ ______ _____ ____of detectors are over which peak area is approximent to the quantity of component.
area
Linear response concentration range
____ _____ ____ (TCD) is less ______ than other detectors used for OT columns but is useful for ______ and operated with ____ gas.
Thermal conductive detector
sensitive
packed
He gas
When analyte reaches, _____ _____increases (because not enough He to get rid of the heat)
And _____ across filament changes that produce a signal.
electrical resistance
Voltage
He has high thermal conductivity
TCD measures ability of a substance to _____ _____analyte therefore hotter.
conduct heat
*TCD has a linear response range of 10^5
Low volume TCD is for _____ column
open tubular
_____ ____ ____(FID) is the most widely used. Column ____ burned in a mixture of H2 and air : where ____ ____ are used to form CH radicals and only 1 in 10^5 carbon atoms become ion +1 e-
Flame ionization detector
eluate
carbon atoms
FID is _____ sensitive than TCD, with a response range ___
more
100 fold lower DL
10^7
(has a collector of positive electrode)
No analyte: 10^-14 A between flame tip and collector analyte: 10^-12 A
FID
_____ _____ _____(ECD) is particular sensitive to ____ ____ molecules, conjugated carbonlys, nitriles, nitro compounds and organometallic compounds, but relatively insensitive to hydrocarbons, alcohols and ketones.
electron capture detector
Halogen-containing (good for certain molecules)
For ECD, carrier gas must be ___ or ______ in Ar.
N2
5% CH4 (small current due to methane in the gas)
ECD
Gas is ionized by ____ (beta rays). formed electrons attracted to anode and produce a _____ ____.
When analyte with _____ ____ ___ enter, they capture some electrons and _____ _____.
It is extremely sensitive compare to MS.
high-energy electrons
small current
high electron affinity
decrease conductivity
Other detectors such as ____ _____ ____measures optical emission from phosphorus, sulfur, lead, tin or other selected elements.
flame photometric detector
Organosulfur compounds are too _____ to be detected by FID.
dilute
Selected ion monitoring or selected reaction monitoring measures one component in a _____ chromatogram of _____ separated compounds.
complex
poorly
They lowers DL by factor of 10^2-10^3 compared to m/z scanning
Isolation of one peak!
Element-specific plasma detector
one element at a time
Solid phase microextraction (SPME) extract compounds with out using a ______.
It is done with thick file of _____ _____ as used in GC.
solvent stationary phase (as the needle)
SPME only _____ is extracted and when injected in to the column, it is expose to carrier gas for ____ and needs to optimized for = to the concentration of analyte in solution
fraction
fixed time
Components of HPLC
mobile phase, pump, column with theoretical plates, detector and recorder
HPLC is restricted to analyte that are _____.
Both phases must be chosen!
In which GC only needed change in _____ phase.
soluble
stationary
There are three important difference between GC and HPLC:
1) _______ of the sample in mobile phase is much smaller in HPLC (reduces speed of analysis by HPLC)
2) ______ of mobile phase is higher in HPLC (higher flow resistance in HPLC)
3) _______ of mobile phase under pressure is negligibly small in HPLC (not dangerous)
D (diffusion coefficient)
viscosity
compressibility (water is not compressible)
To increase efficiency in chromatography is to increase the rate at which solute molecules ________ between stationary and mobile phase.
equilibrate
