3. History
Chromatography dates to 1903 in the work of the
Russian scientist, Mikhail Semenovich Tswett who
separated plant pigments via liquid column
chromatography.
1930’s – schuftan and Eucken use vapor as the mobile
phase gas solid chromtography
4. Continued…
The suggestion that separation of components of a
mixture in the gaseous state could be achieved using a
gaseous mobile phase was first Martin and Synge in
1941.
Archer John Porter Martin , who was awarded the Nobel
prize for his work in developing liquid-liquid (1941 )
and paper (1944) chromatography, laid the foundation
for the development of gas chromatography and he later
produced liquid-gas chromatography (1950).
The first description of instrumentation and application
was made by James and Martin in 1952.
5. Definition
Gas Chromatography
It is a technique where by the components of a mixture in
the gaseous state are separated as the sample passes over a
stationary liquid or solid phase and a gaseous mobile
phase.
6. What is gas chromatography?
• Gas chromatography differs from other forms of
chromatography in that the mobile phase is a gas and
the components are separated as vapors.
• It is thus used to separate and detect small molecular
weight compounds in the gas phase.
• It is widely used for the determination of organic
compounds. The separation of benzene and cyclohexane
(bp 80.1 and 80.8◦C) is extremely simple by gas
chromatography.
7. Continued…
• The sample is either a gas or a liquid that is vaporized in the
injection port. The mobile phase for gas chromatography is a
carrier gas, typically helium because of its low molecular
weight and being chemically inert.
• The pressure is applied and the mobile phase moves the analyte
through the column. The separation is accomplished using a
column coated with a stationary phase.
8. Two major types of gas
chromatography
1. Gas Solid Chromatography(GSC)
2. Gas Liquid Chromatography(GLC)
9. • Gas Solid Chromatography(GSC) :
The stationary phase, in this case, is a solid. It is the affinity
of solutes towards adsorption onto the stationary phase which
determines, in part, the retention time. The mobile phase is, of
course, a suitable carrier gas. This gas chromatographic
technique is most useful for the separation and analysis of
gases like CH4, CO2, CO, ... etc.
• Gas Liquid Chromatography(GLC)
The stationary phase is a liquid with very low volatility
while the mobile phase is a suitable carrier gas. GLC is the
most widely used technique for separation of volatile species..
10.
11. Principle of GC
• Gas chromatography is based on the principle of
partition(differential distribution) of an volatile
compound(gas) in two phases - a liquid phase covering
the adsorbent surface and a gaseous phase of the eluting
gas. With a fixed set of parameters (length and diameter
of column, temp., nature and flow rate of the eluting gas
etc.)
12. Continued…
• Compounds A and B interact with the stationary phase through
intermolecular forces.
A interacts more strongly with the stationary liquid phase and is
retained relative to B, which interacts weakly with the stationary
phase. Thus B spends more time in the gas phase and advances
more rapidly through the column and has a shorter retention time
than A.
• Typically, components with similar polarity elute in order of
volatility. Thus alkanes elute in order of increasing boiling points;
lower boiling alkanes will have shorter retention times than higher
boiling alkanes.
13. Continued…
• Sample is injected into the injection port. Sample vaporizes and is
forced into the column by the carrier gas ( = mobile phase which in
GC is usually helium)
• Components of the sample mixture interact with the stationary phase
so that different substances take different amounts of time to elute
from the column.
• The separated components pass through a detector. Electronic
signals, collected over time, are sent to the GC software, and a
chromatogram is generated
15. Chromatographic Separation
Deals with both the stationary phase and and the mobile phase .
• Mobile phase – inert gas used as carrier.
• Stationary phase – liquid coated on a solid or a solid within a
column.
• In the mobile phase, components of the sample are uniquely
drawn to the stationary phase and thus, enter this phase at
different times.
The parts of the sample are separated within the column.
16. Continued…
Compounds used at the stationary phase reach the detector at
unique times and produce a series of peaks along a time sequence.
The peaks can then be read and analyzed by a forensic scientist to
determine the exact components of the mixture.
Retention time is determined by each component reaching the
detector at a characteristic time.
18. The two types of columns used in GC on the based of nature
are:
1. Packed columns
2. Capillary columns.
Packed columns came first and were used for man years.
Capillary columns are more commonly used today, but
packed columns are still used for applications that do not
require high resolution or when increased capacity is
needed.
Packed columns can be used with large sample sizes and
are convenient to use.
20. Column classification on the bases of
its use:
1. Analytical column
(1-1.5 meter length and 3-6 mm diameter)
2. Preparative column
(3-6 meter length and 6-9mm diameter)
21. Column Oven
The thermo stated oven serves to control the temperature
of the column within the few tenth of degree of a degree
to conduct precise work .
The oven operate in two manners:
Isothermal programming
In this the temperature of column is hold constant
through the entire separation.
Temperature programming
In this the optimum column temperature is about to
middle point of the boiling range of the sample.
22. Packed column
• Shapes
Columns can be in any shape that will fill the heating oven.
1. Coiled tubes
2. U-shaped tubes
3. W-shaped tubes, but coils are most commonly used.
23. Packed Column
• Size
1 to 10 m long and 0.2 to 0.6 cm in diameter. Well-packed columns
may have 1000 plates/m, and so a representative 3-m column would
have 3000 plates.
These are further classified as:
1. Short column
Can be made of glass or glass/silica-lined stainless steel.
2. Long column
May be made of stainless steel or nickel so they can be straightened
for filling and packing. For inertness, glass is still preferred for
longer columns. Long columns require high pressure and longer
analysis times and are used only when necessary (e.g., analytes that
are poorly retained require more stationary phase to achieve
adequate retention).
Columns are also made of Teflon.
24. Separation on the base of
column strength
• Separations are generally attempted by selecting columns in
lengths of multiples of 3, such as 1 or 3 m.
• If a separation isn’t complete in the shorter column, then the
next longer one is tried.
25. Stationary phase for pack column
• The column is packed with small particles that may
themselves serve as the stationary phase (adsorption
chromatography) .
• It commonly are coated with a nonvolatile liquid phase
of varying polarity (partition chromatography).
26. • Gas–solid chromatography (GSC) is useful for the separation of
small gaseous species such as H2, N2, CO2, CO, O2, NH3, and CH4
and volatile hydrocarbons, using high surface area inorganic packing
such as alumina (Al2O3) or porous polymers (e.g., Porapak Q—a
polyaromatic cross-linked resin with a rigid structure and a distinct
pore size).
• The gases are separated by their size due to retention by adsorption
on the particles. Gas–solid chromatography is preferred for aqueous
samples.
27. Characteristic of stationary phase
use in pack column
1. It is highly specific ,and have specific surface area,
chemical inert but wettable by the liquid phase.
2. Its thermal stable and available in uniform size.
3. It is mostly common support prepare from
diatomaceous earth, a spongy siliceous material.
28. Types of support material
available in market
• Chromosorb P is a pink-colored diatomaceous earth
prepared from crushed firebrick.
• Chromosorb W is diatomaceous earth that has been heated
with an alkaline flux to decrease its acidity; it is lighter in
color.
• Chromosorb 750 is a very inert and efficient support that
is acid washed and DMCS treated.
• Chromosorb T is useful for separating permanent gases
and small molecules, it is largely based on fluorocarbon
(Teflon) particles.
Chromosorb P is much more acidic than Chromosorb W, and it
tends to react with polar solutes, especially those with basic
functional groups.
29. • Chromosorb G was the first support expressly developed for
GC, combining the good efficiency and handling
characteristics of Chromosorb G while having the low
adsorptive properties of Chromosorb W.
• Generally, all of the above are available in non-acid washed,
acid washed, and silanized with dimethylchlorosilane (DMCS,
this greatly reduces polarity) and in high-performance versions
(HP, controlled uniform fine particles).
30. Coating of support material
• Column-packing support material is coated by mixing
with the correct amount of liquid phase dissolved in a
low-boiling solvent such as acetone or pentane.
• About a 5 to 10% coating (wt/wt) will give a thin layer.
After coating, the solvent is evaporated by heating and
stirring; the last traces may be removed in a vacuum.
• A newly prepared column should be conditioned at
elevated temperature by passing carrier gas through it for
several hours, preferably before connecting detectors or
other downstream components.
31. Selection of liquid phase for
pack column
• Particles should be uniform in size for good packing
• They have diameters in the range of 60 to 80 mesh (0.25
to 0.18 mm), 80 to 100 mesh (0.18 to 0.15 mm), or 100 to
120 mesh (0.15 to 0.12 mm).
• Smaller particles are impractical due to high pressure
drops generated.
32. Capillary column /open tubular
column
• Marcel J. E. Golay, inventor of capillary GC who first established the
theory of such columns. He is shown with early stainless steel
columns.
• His equation predicted increased number of plates in a narrow open-
tubular column with the stationary phase supported on the inner wall.
• Band broadening due to multiple paths (eddy diffusion) would be
eliminated. And in narrow columns, the rate of mass transfer is
increased since molecules have small distances to diffuse.
• Higher flow rates can be used due to decreased pressure drop, which
decreases molecular diffusion.
• Golay’s work led to the development of various open-tubular columns
that today provide extremely high resolution and have become the
mainstay for gas-chromatographic analyses.
33. Preparation of capillary
column
• These columns are made of thin fused silica (SiO2) coated on the
outside with a polyimide polymer for support and protection of the
fragile silica capillary, allowing them to be coiled.
• The polyimide layer is what imparts a brownish color to the columns,
and it often darkens on use. The inner surface of the capillary is
chemically treated to minimize interaction of the sample with the
silanol groups (Si–OH) on the tubing surface, by reacting the Si–OH
group with a silane-type reagent (e.g., DMCS).
• Capillaries can also be made of stainless steel or nickel. Stainless
steel interacts with many compounds and so is deactivated by
treatment with DMCS, producing a thin siloxane layer to which
stationary phases can be bonded.
• Stainless steel columns, though less common, are more robust than
fused silica columns and are used for applications requiring very high
temperatures.
34. Size of column
• The capillaries are 0.10 to 0.53 mm internal diameter, with lengths of
15 to 100 m and can have several hundred thousand plates, even a
million.
• They are sold as coils of about 0.2 m diameter.
• Capillary columns offer advantages of high resolution with narrow
peaks, short analysis time, and high sensitivity (with detectors
designed for capillary GC) but are more easily overloaded by too
much sample. Split injectors by and large alleviate the overloading
problem.
• Improvements in separation power in going from a packed column
(6.4 × 1.8 m) to a very long but fairly wide-bore stainless steel
capillary column (0.76 mm × 150 m), to a narrow but shorter glass
capillary column (0.25 mm × 50 m).
• Note that the resolution increases as the column becomes narrower,
even when the capillary column is shortened.
• Note Increasing the film thickness increases capacity but increases
plate height and retention time.
35. Types of capillary column
Wall-coated open-tubular(WCOT) columns
• They have a thin liquid film coated on and supported by the
walls of the capillary. The walls are coated by slowly passing a
dilute solution of the liquid phase through the columns. The
solvent is evaporated by passing carrier gas through the
columns.
• Following coating, the liquid phase is cross-linked to the wall.
The resultant stationary liquid phase is 0.1 to 0.5 μm thick.
• Wall-coated open-tubular columns typically have 5000
plates/m. So a 50-m column will have 250,000 plates.
36. Support coated open-tubular
(SCOT) columns
• solid micro particles coated with the stationary phase (much like in
packed columns) are attached to the walls of the capillary.
• They have higher surface area and have greater capacity than WCOT
columns. The tubing diameter of these columns is 0.5 to 1.5 mm,
larger than WCOT columns.
• The advantages of low pressure drop and long columns is maintained,
but capacity of the columns approaches that of packed columns.
• Flow rates are faster and dead volume connections at the inlet and
detector are less critical. Sample splitting is not required in many
cases, so long as the sample volume is 0.5 μL or less.
• If a separation requires more than 10,000 plates, then a SCOT
column should be considered instead of a packed column.
37. Porous layer open-tubular
(PLOT) columns
• They have solid-phase particles attached to the column wall for
adsorption chromatography.
• Particles of alumina or porous polymers (molecular sieves) are
typically used. These columns like packed GSC columns, are useful
for separating permanent gases, as well as volatile hydrocarbons.
• The order of resolution for open-tubular columns is WCOT >
SCOT > PLOT.
• Note : SCOT columns have capacities approaching those of packed
column.
39. Limitation of capillary column
detection
• Columns can tolerate a limited amount of analyte.
• Before becoming overloaded causing peak distortion and
broadening and shifts in retention time.
• Sample capacity ranges are from approximately 100 ng
for a 0.25-mm-i.d. column with 0.25-μm-thick film, up to
5 μg for a 0.53-mm-i.d. column with a 5-μm-thick
stationary phase.
41. Carrier gas
The cylinder/ gas tank is fitted with a pressure controller to
control the pressure of gas, a pressure gauge that indicates the
pressure, a molecular sieve to transfer filtered dry gas and a flow
regulator to ensure a constant rate of flow of mobile phase to the
column.
It should meet the following criteria:
Should be chemically inert
Should be cheap and readily available
Should be of high quality and not cause any fire accidents
Should give best possible results
Should be suitable for the sample to be analyzed and for the
detector
42. • Hydrogen, helium, nitrogen and carbon dioxide are commonly
used.
• Hydrogen has low density and better thermal conductivity.
However, it reacts with unsaturated compounds and is
inflammable and explosive in nature.
• Nitrogen is inexpensive but it gives reduced sensitivity.
• He is the most preferred gas.
• Inlet pressure ranges from: 10-50 psi -Flow rate : 25-150
mL/min for packed columns -Flow rate: 2-25 mL/min for open
tubular column
43. Sampling unit
Sampling unit or injection port is attached to the column head.
Since the sample should be in vaporized state, the injection port is
provided with an oven that helps to maintain its temperature at about
20-500 C above the boiling point of the sample.
Gaseous samples may be introduced by use of a gas tight
hypodermic needle of 0.5-10 ml capacity.
For Liquid samples , micro syringes of 0.1-100µL capacity may be
used. Micro syringe.
44. Injections of samples into capillary columns:-
a) Split injections- it splits the volume of sample stream into
two unequal flows by means of a needle valve , and allow
the smaller flow to pass on to the columns and the bigger
part is allowed to be vented to the atmosphere. This
technique is not suitable when highest sensitivity is
required.
b) Split less injectors- They allow all of the sample to pass
through the column for loading. Sample should be very
dilute to avoid overloading of the column and a high
capacity column such as SCOT or heavily coated WCOT
columns should be used.
45.
46. c. On column injectors: A syringe with a very fine quartz needle is
used. Air cooled to -200c below the b.p. of the sample. After then
the warmer air is circulated to vaporize the sample.
d. Automatic injectors: For improving the reproducibility and if
a large number of samples are to be analyzed or operation is
required without an attendant, automatic injectors are used.
• The solid samples are introduced as a solution or in a sealed
glass ampoule, crushed in the gas stream with the help of a
gas tight plunger, and the sample gets vaporized and flows
into column under the influence of carrier gas.
47. Liquid phase:-
It should have the following requirements:
It should be non-volatile
Should have high decomposition temperature
Should be chemically inert
Should posses low vapour pressure at column temperature
Should be chemically and structurally similar to that of the solute
i.e., polar for polar solute.
48. Examples of different liquid phases:
CATEGORY EXAMPLES
Non-polar hydrocarbon phases Paraffin oil (nujol), silicon oil,
silicon rubber gum (used for
high temp of about 4000
Polar compounds (having
polar groups like -CN, -CO
and –OH)
Polyglycols (carbowaxes)
Liquids having hydrogen
bonding
Glycol, glycerol, hydroxy
acids
49. Detectors:-
• The eluted solute particles along with the carrier gas exit from
the column and enter the detector.
• The detector then produces electrical signals proportional to
the concentration of the components of solute.
• The signals are amplified and recorded as peaks at intervals on
the chromatograph.
50. Properties of an ideal detector:
• Sensitive
• Operate at high T (0-400 °C)
• Stable and reproducible
• Linear response
• Wide dynamic range
• Fast response
• Simple (reliable)
• Nondestructive
• Uniform response to all analytes.
51. Thermal conductivity detector:-
• “TCD is based upon the fact that the heat lost from a filament
depends upon the thermal conductivity of the stream of
surrounding gas as well as its specific heat.”
• When only carrier gas flows heat loss to metal block is
constant, filament T remains constant.
• When an analyte species flows past the filament generally
thermal conductivity changes, thus resistance changes which is
sensed by Wheatstone bridge arrangement.
• The imbalance between control and sample filament
temperature is measured and a signal is recorded.
52.
53. Advantages :-
• Simple and inexpensive
• Durable and posses long life
• Accurate results
• Non-selective, hence known as universal detectors •
Disadvantages:-
• Low sensitivity
• Affected by fluctuations in temperature and flow rate.
54. Electron capture detector:-
• Molecules of compounds, which posses affinity for electrons, differ
in their electron absorbing capacities. This difference is utilized in
this detector for identification of the compounds.
• Working- A foil made up of a radioactive metal like Ni63 (β-
emitter) is placed inside a Teflon coated cell which also contains a
cathode and an anode.
• In the absence of organic species, the produced electrons migrate
towards positive electrode and produce a certain constant standing
current.
• When a sample/eluent is present it captures the electrons, elutes from
column, there is a drop in this constant current.
• The potential across two electrodes is adjusted to collect all the ions
and a steady saturation current, is therefore, recorded.
55.
56. Advantages:-
• Highly selective
• Highly sensitive for the detection of compounds like halogens,
quinones, peroxides, nitrites, etc.
• It is non-destructive
• More sensitive than TCD and FID.
Disadvantages:-
• Least sensitive to compounds whose molecules have negligible
affinity for electrons.
• Carrier gas used should be of pure form like pure nitrogen.
57. Flame ionization detector:-
• This employs hydrogen flame that is maintained in a small
cylindrical jet made up of platinum or quartz.
• Effluent from the column with helium or nitrogen as carrier
gas are fed into the hydrogen flame, gets ignited and undergoes
pyrolysis to produce ions.
• For detection of these ions, two electrodes are used that
provide a potential difference.
• The ions produced are repelled by the positive electrode which
hit the collector plate. The current produced in doing so is
amplified and fed to an appropriate recorder.
58.
59. Flame photometric detector:-
• It is a selective detector that is responsive to compounds
containing sulphur or phosphorous
• The detection principle is the formation of excited sulphur
(S2*) and excited hydrogen phosphorous oxide species
(HPO*) in a reducing flame.
• A photomultiplier tube measures the characteristic
chemiluminescent emission from these species. The optical
filter can be changed to allow the photomultiplier to view light
of 394 nm for sulphur measurement or 526 nm for phosphorus.
61. Flame photometric detector
Applications:-
• For detection of heavy metals like chromium, selenium, tin,
etc, in organometallic compounds.
• Also for analysis of pesticides, coal, hydrogenated products as
well as air and water pollutants.
64. Head space analysis:
• Headspace analysis is a technique for sampling and
examining the volatiles associated with a solid or liquid
sample. The actual headspace itself is the volume of vapor or
gas above the sample.
• For most headspace analysis purposes the sample and its
associated headspace are held within an enclosed Container.
65.
66. • G = the gas phase (headspace)
• The gas phase is commonly referred to as the headspace and
lies above the condensed sample phase.
• S = the sample phase
• The sample phase contains the compound(s) of interest. It is
usually in the form of a liquid or solid in combination with a
dilution solvent or a matrix modifier.
• Once the sample phase is introduced into the vial and the vial
is sealed, volatile components diffuse into the gas phase until
the headspace has reached a state of equilibrium as depicted by
the arrows. The sample is then taken from the headspace.
67. Applications of head space analysis
Headspace analysis is the determination of residual solvents in
pharmaceutical products.
Also the analysis of alcohol in blood can be done with
headspace down to ppm levels.
In principle the (dirty) matrix of the sample is not injected, so
both the injector and the column will remain clean even after
numerous injections. Also the chromatogram does contain only
a small solvent peak, which results in clean chromatograms.
68. Thermal desorption:
• Introduction/principles:
• Thermal desorption is a physical separation process,in this
contaminated soils are heated to volatilise water and organic
contaminants.
• A carrier gas or vacuum system transports volatilised water
and organics to the gas treatment system.
69.
70. Working:
• By applying heat the wastes with low boiling points are forced
to turn into a vapor which can be collected and treated in an off
gas treatment unit. In the thermal desorption mode, a tube
containing material from which compounds are to be desorbed
is placed in the carrier gas flow line.The tube is electrically
heated to a suitable temperature to volatilize the volatiles and
the gas flow carries them to a cold trap where they are
condensed .The cold trap consists of a length of fused silica
capillary tubing which may be coated with either a chemically
bonded phase, or a layer of adsorbent such as aluminium
oxide, and it is cooled in a suitable refrigerant.
71. Continued…
• When the volatiles have been completely removed from the
sample matrix they are quickly released from the cold trap by
rapidly heating it via an electrical heating jacket. They
consequently pass on to the column which then Starts its
working. Thus the total volatiles are sampled by the column as
a sharply focused zone.
72. Methods of thermal desorption:
There are generally three methods of thermal desorption:
• Indirect heated: An externally fired rotary dryer volatilises
the water and organics from the contaminated media into an
inert carrier gas stream, steam can also be used as an indirect
heating method.
• Indirect fired: A direct-fired rotary dryer heats an air stream
which is in contact with the contaminated soil.
• Direct fired: Fire is applied directly upon the surface of
contaminated media.
73. Thermal desorption processes can be separated into two
groups:
• Low temperature thermal desorption (LTTD)
In LTTD, soils are heated to between 90°C and 320°C, this
system is used for VOC.
• High temperature thermal desorption (HTTD)
HTTD soils are heated to 320°C to 960°C, this system is used
for higher chain hydrocarbons and petroleum removal, pesticides
etc. HTTD systems are often combined with incineration,
solidification treatments.
74. Applicability
• Thermal desorption systems remove:
• Volatile organic (VOCs)
• Semi-volatile organic compounds (SVOCs
• Fuels
• Pesticides
• some metals from soil. High temperature units are more effective for
removing volatile metals and SVOCs.
75. Limitations:
• Not suitable for water logged
• Very high fuel costs
• Gas treatment system required
• Larger particle size can cause incomplete desorption
• Clay, silts and high humic content in soils increase required
residence times in desorption unit, increasing costs
•
76. Applications of Gas
chromatography :
1. Food analysis:
This technique is essential to ensuring the quality of food
products, ensuring that the flavour and taste and smell remain
consistent.
• Mycellaneous analysis of food like:
• carbohydrates
• Lipids
• Proteins
• Vitamins
• Dairy products analysis
77. 2. Quality control:
• The pharmaceutical industry uses gas chromatography to help
produce pure products in large quantities. The method is used
to ensure the purity of the produced material.
78. 3. Forensics:
• Gas chromatography has been used in forensic science. Mostly,
it is used to determine the circumstances of a person’s death,
such as whether they ingested poison, or consumed drugs or
alcohol in the hours prior.
79. 5. Measuring air pollutants :
• Gas chromatography is being used for monitoring the levels of
harmful pollutants in the air so that scientists can visualize
where air pollution is more concentrated, and how this Brings
change in climates and develop effective preventative methods.
80. 6. Petrochemical analysis:
• Petroleum products are analysed by GC. The impurities
present in jet fuel are hydrocarbons in nature can be detected
by this technique.
7. Determination of pesticides residue:
• Determination of pesticides residue present in aquaculture
products detection and quantitative analysis is done by gas
chromatography.Pesticides analysis is very important due to
the need to ensure that foodstuff stuff is not contaminated with
pesticide residues, which can be harmful to human health.
81.
82. 8. Volatile organic compounds analysis:
• Some volatile organic compounds such as:
• Toulene,ethylbenzene and o-xylene in air analysed and
quantified by using Gas-chromatography with flame ionisation
detection.The presence of these VOCs cause sick building
syndrome in humans.
83. 9. Isolation and identification of plant extracts:
• Isolation and identification of mixture of plant
extracts,carbohydrates,volatile oil, amino
acids,lipids,proteins,preservatives,vitmanins,colorants,flavour
etc is done by Gas chromatography.Identification and
determination of fate of drugs in the body fluids like
plasma,serum,urine etc by this technique .
84. 10. Gas chromatography also helps in analysis of
• Fertilizers
• Rubber
• Cosmetics
• Perfumes
11. Inorganic analysis:
• Volatile metals can be extracted by Gas-chromatography technique.
85. Advantages of Gas Chromatography
• Requires only very small samples with little preparation
• Good at separating complex mixtures into components
• Results are rapidly obtained (1 to 100 minutes)
• Very high precision
• Only instrument with the sensitivity to detect volatile organic
mixtures of low concentrations
• Equipment is not very complex (sophisticated oven)
86. Disadvantages of Gas
Chromatography
• Limited to volatile samples
T limited to ~ 380 °C
Need Pvap ~ 60 Torr at that temperature
• Not suitable for thermally labile samples
• Some samples may require extensive preparation
• Requires spectroscopy (usually MS) to confirm peak identify
