Lecture11-12 Flashcards
Comparing problems with GC and HPLC:
1.both difficult separation (possible) 2. both speed 3. both automation (possible) 4. adaptation of system to separation problem (by change in stationary phase) (by change in stationary and mobile phase) 5. application restricted (lack of volatility, thermal decomposition) (insolubility)
HPLC restricted to analytes that are soluble to elute analyte: ____ ____ and suitable ____ ____ must be chosen.
stationary phase
mobile phase
Gas chromatography:
Mobile phase: ____
stationary phase: _____________
analyte: _________
gas
usually a nonvolatile liquid, but sometimes a solid
gas or volatile liquid
Three important differences between GC and HPLC:
- Diffusion coefficient of the sample in mobile phase much smaller in HPLC than in GC (reduces speed of analysis by HPLC). 2. viscosity of mobile phase higher in HPLC than GC (high flow resistance in HPLC vs GC). 3. compressibility of mobile phase under pressure negligibly small in HPLC (not in GC) -> not dangerous.
Gas Chromatography: can only cope with analytes that are _____/ can be _____ intact at higher temperature. only ______ of known organic compounds can use this method.
volatile
evaporated
~20%
Separation process in GC: ____ ____ transported through column by ____ ____ phase = ____ ____ (high purity,
gaseous analyte gaseous mobile carrier gas stationary nonvolatile liquid fine solid
Carrier gas could be: ___, ___, ___. Sample injected to injector oven through a ___ ___ ___. Column -> ____ enough to provide sufficient ____ ____ for elution of analytes.
He, N2 or H2
Silicone rubber septum
hot
vapor pressure
Open tubular columns (____): most frequently used ____ ____ in GC (___ ___) compared to packed columns they offer: ___, ___, ___ and ___.
A-term: ____; ____
capillary columns
stationary phase fused-silica
higher resolution, shorter analysis time, greater sensitivity, lower sample capacity.
flow-rate; amount of sample injected.
Outer wall of column: ____ ____ (____um thick); inner column: ____ ____ (____ um thick), up to ____oC
WCOT
SCOT
PLOT
stationary phase 0.1-5 polyimide coating 0.1-5 350oC Wall-coated open tubular column Support-coated open tubular column Porous-Layer open tubular column
Particles’ diameter ____ mm cannot use MS as detector (need ____).
____ column -> ____ resolution
____ pressure -> _____ sample capacity
Resolution = root(N) /4 * (r -1)
As column length _____, so does # of theoretical plates N.
>0.32 vacuum narrower higher higher less N = plate number r = unadjusted relative retention increases
As GC column ages -> ____ ____ can be lost, ____ group (____) exposed and tailing can increase “____”.
stationary phase
silanol
Si-OH
bleeding
Retention determined by ____.
Strong retention on ____ ____ ____(H-bonding)
volatility
polar stationary phase
To reduce tendency of stationary phase to “bleed” from column at high temperature, ____ bond (____ attach) it to ____ surface good idea: ____ ____ ____ (k of standard or N).
chemically covalently silica monitor column performance
High operating temperatures -> ____ phase will ____ -> ____ bleed -> ____ background in detector -> ____ signal-to-noise and detector ____.
____ liquids ____ volatility at elevated temperature; potential: offer ____ ____. Solid for ____ ___ columns: ____, ____(____) and ____ ____.
stationary decompose slow
elevated reduced contamination
Ionic low novel selectivities
porous OT polymers alumina(Al2O3) molecular sieves
Packed columns: contains ____ ____ ____ coated with ____ stationary phase or solid itself = ____ ____. ____ sample capacity, but give ____ peaks, ____tr and ____ resolution.
fine solid particles non-volatile stationary phase
Better broader longer less
Despite inferior resolution used for ____ ____. (ie. to isolate mg amounts)
Solid support: often ____ that has been ____ to reduce ____ ____ to ____ ____.
preparative separations
silica silanized hydrogen bonding polar solutes
Temperature and pressure programming: in GC temperature often ____ ____ separation, ____ analyte vapour pressure.
____ temperature at different rates, ____ retention time and ____ peaks.
increased during increases
Increase decreases sharpens
Most GC columns come with 2 temperature labels:
- ____ temperature limit: ____ kept at this for a long time without damaging it.
- ____ temperature limit: ____ ____
Isothermal column
Programmed few minutes
Carrier gas: ____ compatible with most detectors -> frequently used.
____ often not used as > 4% explosive. Sample injection through ____ ____ -> sample not immediately ____ + ___ washed needle and ____ plug expels solvent from needle (many ____)
He H2
rubber septum evaporated
solvent air autosamplers
Split injection: if analytes of interest __0.1% of sample -> complete injection contains ____ ____ material -> split injection (____ on column).
Proportion of sample that ____ ____ reach column: split ratio (_______). Quantitative analysis can be ____ because ____ ____ may not be ____ from run to run.
> too much 0.2-2%
does not (50:1 - 600:1)
inaccurate split ratio reproducible
Splitless injection: analytes of interest ____ of sample -> ____ ____. most appropriate (___ on column).
Initial cold temperature 40C ___ BP of solvent -> solvent ____ -> ____ peaks.
< trapping sharp
On-column injection: preferred for quantitative purposes and for samples that ____ above their ___. Detectors: qualitative analysis: use ____ ____ (MS) and compare results to spectral library. Co-chromatography (___): ____ compound added to unknown sample if added compound identical with component -> ____ peak area ____
decompose BP
mass spectrometry spiking
authentic relative increases
____ = tentative with 1 column, but firmer when carried out on several columns/ different ____ ____. Quantitative analysis based on ____ of ____ ____. It’s ____ response concentration range: ____ which peak area ~ to ____ of component.
Identification stationary phases
area chromatographic peak
linear over quantity
Thermal conductivity detector: since ____ sensitive than other detectors used for ___ columns -> useful for packed columns and operated with ___.
Electrical resistance ____ and voltage across filament changes -> ____.
Measures ability of a substance to conduct heat analyte -> ___. He high____.
less OT He
increases signal
hotter
thermal conductivity
