Lecture11-12

Question 0

Comparing problems with GC and HPLC:

Answer 0

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)

Question 1

HPLC restricted to analytes that are soluble to elute analyte: ____ ____ and suitable ____ ____ must be chosen.

Answer 1

stationary phase

mobile phase

Question 2

Gas chromatography:
Mobile phase: ____
stationary phase: _____________
analyte: _________

Answer 2

gas
usually a nonvolatile liquid, but sometimes a solid
gas or volatile liquid

Question 3

Three important differences between GC and HPLC:

Answer 3

1. 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.

Question 4

Gas Chromatography: can only cope with analytes that are _____/ can be _____ intact at higher temperature. only ______ of known organic compounds can use this method.

Answer 4

volatile
evaporated
~20%

Question 5

Separation process in GC: ____ ____ transported through column by ____ ____ phase = ____ ____ (high purity,

Answer 5

gaseous analyte 
gaseous mobile     carrier gas
stationary
nonvolatile liquid
fine solid

Question 6

Carrier gas could be: ___, ___, ___. Sample injected to injector oven through a ___ ___ ___. Column -> ____ enough to provide sufficient ____ ____ for elution of analytes.

Answer 6

He, N2 or H2
Silicone rubber septum
hot
vapor pressure

Question 7

Open tubular columns (____): most frequently used ____ ____ in GC (___ ___) compared to packed columns they offer: ___, ___, ___ and ___.
A-term: ____; ____

Answer 7

capillary columns
stationary phase fused-silica
higher resolution, shorter analysis time, greater sensitivity, lower sample capacity.
flow-rate; amount of sample injected.

Question 8

Outer wall of column: ____ ____ (____um thick); inner column: ____ ____ (____ um thick), up to ____oC
WCOT
SCOT
PLOT

Answer 8

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

Question 9

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.

Answer 9

>0.32    vacuum
narrower   higher    higher   less
N = plate number
r = unadjusted relative retention
increases

Question 10

As GC column ages -> ____ ____ can be lost, ____ group (____) exposed and tailing can increase “____”.

Answer 10

stationary phase
silanol
Si-OH
bleeding

Question 11

Retention determined by ____.

Strong retention on ____ ____ ____(H-bonding)

Answer 11

volatility

polar stationary phase

Question 12

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).

Answer 12

chemically covalently silica monitor column performance

Question 13

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 ____ ____.

Answer 13

stationary decompose slow
elevated reduced contamination
Ionic low novel selectivities
porous OT polymers alumina(Al2O3) molecular sieves

Question 14

Packed columns: contains ____ ____ ____ coated with ____ stationary phase or solid itself = ____ ____. ____ sample capacity, but give ____ peaks, ____tr and ____ resolution.

Answer 14

fine solid particles non-volatile stationary phase

Better broader longer less

Question 15

Despite inferior resolution used for ____ ____. (ie. to isolate mg amounts)
Solid support: often ____ that has been ____ to reduce ____ ____ to ____ ____.

Answer 15

preparative separations

silica silanized hydrogen bonding polar solutes

Question 16

Temperature and pressure programming: in GC temperature often ____ ____ separation, ____ analyte vapour pressure.
____ temperature at different rates, ____ retention time and ____ peaks.

Answer 16

increased during increases

Increase decreases sharpens

Question 17

Most GC columns come with 2 temperature labels:

• ____ temperature limit: ____ kept at this for a long time without damaging it.
• ____ temperature limit: ____ ____

Answer 17

Isothermal column

Programmed few minutes

Question 18

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 ____)

Answer 18

He H2
rubber septum evaporated
solvent air autosamplers

Question 19

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.

Answer 19

> too much 0.2-2%
does not (50:1 - 600:1)
inaccurate split ratio reproducible

Question 20

Splitless injection: analytes of interest ____ of sample -> ____ ____. most appropriate (___ on column).
Initial cold temperature 40C ___ BP of solvent -> solvent ____ -> ____ peaks.

Answer 20

< trapping sharp

Question 21

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 ____

Answer 21

decompose BP
mass spectrometry spiking
authentic relative increases

Question 22

____ = 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.

Answer 22

Identification stationary phases
area chromatographic peak
linear over quantity

Question 23

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____.

Answer 23

less OT He
increases signal
hotter
thermal conductivity

Question 24

Flame ionization detector: column eluate burned in a mixture of ___ and ___: ___ atoms -> ___ radicals. DL 100-fold lower than ____ ____ ____, linear response range: ___. Electron capture detector: particularly sensitive to ___ containing molecules, conjugated carbonyls, nitriles, nitro compounds and organometallic compounds, but relatively insensitive to ____, ____ and ____

Answer 24

H2 and air carbon CH
thermal conductivity detector 10^7
carbons, alcohols and ketones.

Question 25

Carrier gas must either be ___ or ____. Gas ionized by ____ electrons (___). formed electrons attracted to ___ -> produce a small ____ when analyte with high ____ ____ enter -> they capture some ____ and decrease ____.
____ -> extremely sensitive (comparable to MS)

Answer 25

N2 or 5% CH4 in Ar.
high-energy    beta-rays
anode    current     electron affinity
electrons     conductivity
ECD

Question 26

Other detectors: ____ ____ detector measures ____ ____ from phosphorus, sulfur, lead, tin or other selected elements.

Answer 26

flame photometric

optical emission

Question 27

GC-MS: MS is a sensitive detector that provides both ____ and ____ information (identification of spills). Selected ion monitoring or selected reaction monitoring -> measure one component in a complex ____ of poorly ____ compounds. Lower detected limit by factor ____ compared to m/z scanning.

Answer 27

qualitative quantitative
chromatogram
separated 100-1000

Question 28

m/z 293 (____ ion) selected by mass filter Q1, passed on to ____ cell Q2, ____ ____ ion m/z 264 Q3. Sample preparation: process of ____ sample into a form suitable for analysis. ____ ____ ____ extracts compounds from liquids, air or even sludge ___ using a solvent. Key component: ____ thich film of stationary phase as used in GC. Procedure of analysis expose ____ to sample -> analyte is ____.

Answer 28

precursor      collision
fragmentation prominent
transforming
Solid phase micro-extraction
without     10-100um     fiber     extracted

Question 29

The Chromatographic process: to increase ____ in chromatography: increase the rate at which ____ ____ ____ between stationary and mobile phase. In GC with ___ ___ (OT) column -> ____ established rapidly by ____ diameter of column -> ____ can diffuse quickly between ____ and ____ phase.

Answer 29

efficiency solute molecules equilibrate
open tubular equilibration reducing
molecules channel stationary

Question 30

Continue for the Chromatographic process: since ____ in a liquid is several-fold ____ than in gases -> ____ of solvent channel too great for analyte molecules to traversed in short time -> not ____ to use __ columns in ____. HPLC conducted with ____ columns -> ____ ____ don’t have to diffuse far to encounter ____ phase.

Answer 30

diffusion slower diameter
feasible OT HPLC
packed solute molecules stationary

Question 31

Small particles -> ____ efficiency, but require high ____. It needed to force solvent through ____ ____ (contains fine ____/____). Particle size: ____. The ____ the particles, the ____ the pressure.

Answer 31

high pressure packed column particles/silica

1.7-10um smaller higher

Question 32

Smaller particle size leads to: ____ plate number, ____ pressure, ____ optimum run time and ____ detection limit. 2004, equipment became available to employ ____ um particles with pressures up to ____ MPa (____ bar, ____ psi) -> substantially ____ resolution and ____ run time -> less ____ phase consumption.

Answer 32

higher higher shorter lower
1.5-2 100 1000 15000
increased decreased mobile

Question 33

Another penalty for small particle diameter is increased ____ ____: _____ of a column up to ___ oC warmer than ____ wall -> to avoid band ____ column diameter ____ mm for ___ um particles. The column: ____ columns (____cm): stainless steel can be easily clogged if small dust particles enter column(____), if you filter ____ phase through ___ um filter and use a ____ column (same ____ phase as main column).

Answer 33

frictional heating     
centre     2     outer     broadening
<=2.1mm      1.7um
HPLC     3-30cm     (sample/solvent)
mobile     0.5um      guard      stationary

Question 34

The stationary phase: most common support: ____ ____ particles. Bare silica -> ____ chromatography. ____ groups form weak bonds (____, ____, ____ and ____) which is referred to as ____ with any molecule in ____.

Answer 34

microporous silica
adsorption
Silanol (dipole-dipole, interactions, H-bonding and pi-complex bonding)
adsorption vicinity

Question 35

Absorption strengths: saturated hydrocarbons < ____ < aromatics < ____ < nitro compounds < ____~ aldehydes ~ ____ < alcohols < ____ < amides < ____.

Answer 35

olefins ethers esters ketones sulfoxides carboxylic acids

Question 36

If molecule has several functional groups -> most ____ one determines ____ properties. ____ gel surrounded on all sides by ____ phase -> sample molecule can only be ____ if it ____ more strongly than solvent. All sample molecules arranged on ____ surface so their ____/ ____ close to ____ group. Strength of ____ also depends on ____ factors -> ideal to separate ____.

Answer 36

polar retention Silica
mobile absorbed interacts
silica functional group / double bond silanol
interaction steric isomers