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Analytical chem315 > 11-12(4) > Flashcards

11-12(4) Flashcards

1
Q

What is the stationary phase of GC?

A

usually a nonvolatile liquid but sometimes a solid

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2
Q

What is the limit of GC?

A

It can only analyze the sample that are volatile or can be evaporated intact at higher temperature with out breaking down.

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3
Q

_____ of known organic compounds can be analyzed with this technique therefore it is some what limited

A

20%

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4
Q

The _____ needs to be in high purity (______ppb O2).

A

carrier gas; < 1 ppb O2

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5
Q

In gas-liquid partition chromatography: stationary phase is ______ liquid bonded to inside of column or to a fine solid support.

A

nonvolatile

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6
Q

What type of carrier gas usually used depend on the ______

A

detector

example Ne2, H2, N2

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7
Q

silicon rubber septumpoked through with needle and analyte immediately ______ in the injector oven.

A

volatilize

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8
Q

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).

A

vapor pressure

condensation

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9
Q

In gas-solid adsorption chromatography:

Analyte _____ ______ on solid particles of stationary phase.

A

adsorbed directly

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10
Q

______ _____ columns (capilary columns) are most frequently used stationary phase in GC(fused silica)

A

Open tubular

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11
Q

Open tubular columns in comparison to the packed columns would offer: (4 things)

A 
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)
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12
Q

The length of the GC column is about _____ long and ____ for polyimide coating (up to 350 degree).

A

15-100m

stationary phase = 0.1-5um(0.1-0.53mm for diameter of the inner column)

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13
Q

There are three kinds of open tubular columns: ____ (WCOT) _____ (SCOT) _____ (PLOT)

A

wall-coated (stationary liquid phase)
support-coated (solid support coated with stationary liquid phase)
Porous layer (stationary solid phase particles)

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14
Q

____ _____ (2um) on inside wall of OT column.

A

Porous carbon

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15
Q

Narrower column will create a ____ resolution, which can also be increased with _____. Increased resolution means more _______.

High ______ is required for less sample capacity.

A

higher (improved separation)
square root of column length(retention time increased)
theoretical plate (N) ->gives baseline separation

pressure

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16
Q

If the diameter is ______ mm cannot use MS as detector because it needs ______ and if too much gas, it goes down.

A

> 0.32

vacuum

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17
Q

increases retention time and resolution of k< 5 peaks

A

if k=capacity factor is less than 5,
leads to thicker inner later
and higher resolution

P568

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18
Q

Choice of liquid stationary phase is like dissolve like.

Therefore chose the one that is good for ______ of molecule.

A

separation

P569

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19
Q

As GC column ages, ______ can be lost due to exposure to _____.
________ (Si-OH) exposed and _______ can increase. which is referred to as “bleeding”

A

stationary phase
high temperature

silanol group
tailing

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20
Q

“Bleeding” is the signal difference from GC system that is not from the _____.

A

analyte

tailing are asymmetrical signals peaks
- which is due to stationary phase degradation

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21
Q

Most retened compounds are the ones with ____ boiling point.

Thus retention is determined by ______.

A

highest

volatility

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22
Q

___ 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.

A

more

selectivity

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23
Q

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)

A

silica
column performance
k=capacity factor
N=theoretical plate N

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24
Q

high operation temperature will cause stationary phase to ________ and leads to slow bleed which cause elevated ______ in detector.
And lastly, reduced ______ and _______.

A

decompose
background
signal to noise
detector contamination

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25
Q

A new type of GC stationary phase uses ____ _____.

It has low ____ at elevated temperature, and is potential to offer novel _____.

A

ionic liquids
volatility
selectivites

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26
Q

Solids for porous OT columns: polymers, ______ and molecular sieves.

A

alumina (Al2O3)

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27
Q

Packed columns contain solid particles coated with _______ stationary phase or _____for stationary phase.

A

non-volatile

solid itself

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28
Q

Packed sample has better sample ______. but give _____ peaks, _____ tr (retention time), and ____ resolution.

A

capacity (more)
broader
longer
less

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29
Q

Less resolution is generally not good but is good for ______

A

preferrtively isolate compound

30
Q

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

A protective surface (CH3)3 SiO

31
Q

uniform particle size decreases ________ (multiple path term) which decreases _____(H)
If particle size are not uniform, there will be different _____.

A

A-term
plate height
retention time

32
Q

In GC temperature often increased _______ separation which increases analyte ______.
(difference between HPLC)

A

during

vapor pressure

33
Q

Increase temperature from 30 to 150 degree at different rates can reduce ______ required for separation, with baseline resolution still present.

A

time

Decreases retention time and sharpens peaks

34
Q

linear alkanes on a 3.0m (Dimethylpolysioxane) long poly in the column etched in a silicone chip.

A

a chip with square maze in it

35
Q

Most GC columns come with 2 temperature labels.

should always stay under these limits

A

1) isothermal temperature limit: column kept at this for a long time with out damaging it
2) programmed temperature limit: few minutes

36
Q

carrier gas has to be compatible with the _____.

____ gas is compatible with most.

A

detector

He(frequently used)

37
Q

Change of carrier gas result in different _______.

A

linear velocity
(how fast the gas move through the column)
(The faster linear velocity with smaller plate height the better)

38
Q

H is very good to use as carrier gas, but it is not often used due to more than ____ in the air is explosive

A

4%

39
Q

needle inserted through rubber septum and sample is not immediately ______ and _____ washes needle and ____ expels solvent from needle

A

evaporated
solvent
air plug

40
Q

_________ gets dirty during usage and need to get replaced

A

Silane glass liner

41
Q

_______ injection is more appropriate if analyte of interest is >0.1% of sample. ____% of sample will be on column
Complete injection contains _________.

A

split injection
(>0.1% is important)
0.2 - 2%
too much material

42
Q

Split ration A : B, and which goes to the wast?

A

A

do not reaches to the column

43
Q

Quantitative analysis can be inaccurate because split ration may not be _______ from run to run.

A

reproducible

44
Q

________ injection is good when analyte of interest is <0.01 % of sample and ____% will be on column.

A

splitless injection
80%
(almost everything injected goes to the column)

45
Q

There are three types of injection: ____, _____, ____.

A

split (99% goes to waste)
splitless
on column (direct to the column)

*in decreasing temperature

46
Q

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.

A

40 degree less
solvent trapping

condense
analyte
(analyte is concentrated initially with solvent)

47
Q

On-column injection is preferred for __________ and for samples that decompose _____ their BP.

A

quantitative purposes

above

48
Q

co-chromatography (______): authentic compound added to unknown sample if added compound identical with a component there will be a relative______increase

A

spiking

peak area

49
Q

identification by tentative with 1 column, but firmer when carried out on several columns or different stationary phases

A

for spiking

50
Q

Detectors that tells you if compound is present or not.

A

Thermal conductivity
Flame ionization
Electron capture

51
Q

Quantitative analysis is based on _____ of chromatographic peak.
_____ ______ _____ ____of detectors are over which peak area is approximent to the quantity of component.

A

area

Linear response concentration range

52
Q

____ _____ ____ (TCD) is less ______ than other detectors used for OT columns but is useful for ______ and operated with ____ gas.

A

Thermal conductive detector
sensitive
packed
He gas

53
Q

When analyte reaches, _____ _____increases (because not enough He to get rid of the heat)
And _____ across filament changes that produce a signal.

A

electrical resistance
Voltage

He has high thermal conductivity

54
Q

TCD measures ability of a substance to _____ _____analyte therefore hotter.

A

conduct heat

*TCD has a linear response range of 10^5

55
Q

Low volume TCD is for _____ column

A

open tubular

56
Q

_____ ____ ____(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-

A

Flame ionization detector
eluate
carbon atoms

57
Q

FID is _____ sensitive than TCD, with a response range ___

A

more
100 fold lower DL

10^7
(has a collector of positive electrode)

58
Q

No analyte: 10^-14 A between flame tip and collector analyte: 10^-12 A

A

FID

59
Q

_____ _____ _____(ECD) is particular sensitive to ____ ____ molecules, conjugated carbonlys, nitriles, nitro compounds and organometallic compounds, but relatively insensitive to hydrocarbons, alcohols and ketones.

A

electron capture detector

Halogen-containing (good for certain molecules)

60
Q

For ECD, carrier gas must be ___ or ______ in Ar.

A

N2

5% CH4 (small current due to methane in the gas)

61
Q

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.

A

high-energy electrons
small current
high electron affinity
decrease conductivity

62
Q

Other detectors such as ____ _____ ____measures optical emission from phosphorus, sulfur, lead, tin or other selected elements.

A

flame photometric detector

63
Q

Organosulfur compounds are too _____ to be detected by FID.

A

dilute

64
Q

Selected ion monitoring or selected reaction monitoring measures one component in a _____ chromatogram of _____ separated compounds.

A

complex
poorly

They lowers DL by factor of 10^2-10^3 compared to m/z scanning
Isolation of one peak!

65
Q

Element-specific plasma detector

A

one element at a time

66
Q

Solid phase microextraction (SPME) extract compounds with out using a ______.
It is done with thick file of _____ _____ as used in GC.

A 
solvent
stationary phase (as the needle)
67
Q

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

A

fraction

fixed time

68
Q

Components of HPLC

A

mobile phase, pump, column with theoretical plates, detector and recorder

69
Q

HPLC is restricted to analyte that are _____.
Both phases must be chosen!
In which GC only needed change in _____ phase.

A

soluble

stationary

70
Q

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)

A

D (diffusion coefficient)
viscosity
compressibility (water is not compressible)

71
Q

To increase efficiency in chromatography is to increase the rate at which solute molecules ________ between stationary and mobile phase.

A

equilibrate

Analytical chem315 (5 decks)

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