Water treatment

2. Temperature Control Devices and Detectors
used in Gas Chromatography
Fatima Afzal
Msf1900026
MS CHEMISTRY
UE Township Campus

3. Contents:
• Definition of Gas Chromatography
• History
• Principle
• Stationary & Mobile phase
• Instrumentation and working of GC
• Temperature Control Devices
• Detectors used in GC
• Application of GC

4. Definition:
• Gas chromatography is a separation
technique based on partitioning analytes
between two immiscible phase: gaseous
mobile phase(carrier gas) and a stationary
solid or immobilized liquid phase.
• GC is also sometimes known as Vapor
Phase Chromatography or Gas-Liquid
Partition Chromatography.
• It is a process of separating components
from the given crude drug by using a
gaseous mobile phase.

5. History:
• German physical Chemist Erika Cremer in 1947
together with Austrian student in Fritz Prior
developed the theoretical foundations of GC
and built the first liquid –gas chromatography,
but her work was deemed irrelevant and was
ignored for a long times.
• Archer John Porter Martin was awarded the
Nobel prize for his work in developing liquid-
liquid chromatography and credited for the
foundation of gas chromatography.

6. Principle of GC:
• The principle of separation in GC is Partition.
• The mixture of components to be separated is converted to vapor and mixed with gaseous
mobile phase.
• The component which is more soluble in stationary phase travel slower and eluted later. The
component which is less soluble in stationary phase travels faster and eluted out first.
• No two components have same partition coefficient conditions. So the component are
separated according to their partition coefficient.

7. Partition
Coefficient:
• It is the ratio of concentration of analytes in
stationary phase to the concentration of analyte in
the mobile phase.
• Separation occurs between mixtures of analytes,
when each analyte has a different ratio of the
solubility in stationary and mobile phase.
• The partition coefficient (K) is the ratio of
concentration of analytes at equilibrium.
• This coefficient is constant for a compound.
• This coefficient describes the way in which a
compound distributes itself between two
immiscible phases.

8. Stationary
& Mobile
Phase:
• The separation of compounds is based on the
different strengths of interaction of the
compounds with the two phases:
• Mobile Phase which is composed of an inert
gas like helium , argon or nitrogen.
• Stationary Phase consist of a packed column in
which the packaging or solid support itself act
as stationary phase. It is a substance which
stay fixed inside a column.

9. Properties of
Stationary &
Mobile Phase:
• Stationary phase is that part of chromatographic
system where the mobile phase will flow and
distribute the solute between phases.
• Stationary phase plays a vital role in determining
the selectivity and retention of solutes in the
mixture.
• Mobile phase carries the components of the
mixtures through the medium being used.
• Mobile phase is the liquid or gas that flows
through chromatographic system moving the
material to be separated at different rates over the
stationary phase.

10. Instrumentation of GC:
• Gas Chromatography has following components:
1. Carrier Gas.
2. Gas flow regulator.
3. Sample injector.
4. Column.
5.Preheated Oven.
6. Detector.

11. Schematic diagram of GC:

12. Working of Gas
Chromatography:
• Fill the syringe with the sample.
• Record the setting that is column temperature,
injector port temperature and detector
temperature.
• Introduce sample into the injection port by
completely inserting the needle into the ribbon
septum. Note down the injection time.
• The sample gets vaporized due to higher
temperature of injection port and is swept into
column by carrier gas.

13. Working of
GC:
• The sample components now get distributed
between the gas and stationary liquid phase
depending upon their solubilizing tendencies.
• The component with minimal solubility moves
faster and those with maximum solubility
travels slowly.
• The components leaving the column activates
the detector and recorded to give a plot.

14. Temperature
Control Devices
used in GC
HEATERS AND THERMOSTATICALLY
STABLE OVEN

15. Temperature
Control
Devices used
in GC:
• In gas chromatography separations,
temperature is a primary variable used to
control the separation, and it acts in a similar
capacity as mobile-phase strength in LC. Most
workers are aware that the column
temperature can affect the retention time of
sample components in an LC separation.

16. Temperature
affect
resolution:
• The resolution is poor because either the
temperature and/or the flow rate is too high;
they should be lowered. ... Factors such oven
temperature, carrier gas flow rate, column
length and diameter, and the type of mobile
phase all influence retention times.

17. Thermostatically stable oven:
The oven is a fundamental component of the GC system. The oven temperature
must be controlled very accurately over a wide range of temperatures to assure
accurate isothermal temperature settings and temperature programming.
The most important role of the oven temperature is its effect on the partition
coefficient of the analytes between stationary and mobile phase. An increase in
temperature will result in decreased retention of analytes and vice versa.
Separation usually occurs at a higher temperature than the ambient temperature
of about 25°C. The temperature during an analysis should be high enough to
evaporate the sample components.

18. Thermostatically
stable oven:

19. Requirement
for GC oven:
• Requirements for a GC oven:
• Temperature range: 5 - 450oC
• Temperature stability: about 0.1 degrees
• Programming rate: 0.1 - 50oC/minute
• Reproducability: < 1%
• Cooldown time: 350 to 50oC in less than 10 minutes.
• Since temperature is such an important parameter,
there is a high demand on the stability and
reproducibility of temperature settings.

20. Isothermal
Analysis and
Temperature
Programming
• If a sample contains components with closely
similar boiling points, adequate separation with
a short analysis time is obtained at one specific
oven temperature. This is called an isothermal
analysis.
• When the sample components have a wide range of
boiling points, efficient separation within a short
analysis time is not to be expected. Temperature-
programmed analysis is preferred for such samples.
Temperature programming ensures complete and
efficient (sharp peaks) separation of early as well as
late-eluting analytes within resonable analysis
times.

21. Isothermal vs Temperature Gradient

22. Explanation:
In the bottom experiment the
temperature is programmed to
increase in time and the
compounds with higher boiling
temperature show elute faster
and show higher peaks.
The optimum column
temperature is dependent
upon the boiling point of the
sample components.

23. Gas Chromatography Heaters:
Gas Chromatography heaters are designed to provide highly uniform temperature across the
length of the column. This precision allows the operator to capture sample data with
resolutions that are useable and repeatable from run to run.
Small changes in column temperature and unstable temperature gradients can have a
significant effect on elution times resulting in poor and unusable data.
Gas Chromatography heating elements are designed to ramp and hold the temperature of a
column within a very small margin of error.

24. Gas
Chromatography
Heaters:

25. Temperature effect Retention time:
Retention time is the amount of time a compound exists in the column.
A lack of column temperature uniformity will affect retention time.
After separation each compound is going to spend a different amount of time in the column,
hence the different peaks on a gas chromatogram.
No matter what heating method is used (ie. isothermal or programmed), any fluctuations along
the column during sample analysis are going to have a significant effect on retention times.

26. Heater-Column Assembly:
Another method uses a heater
that spans the length of the
column in very close proximity
to the column. The entire
heater/sensor/column assembly
is encased inside another tube
This can be very accurate but
also increases column
replacement cost as the column
and heater become inseparable.
Another version of this involves
the column being etched
into flat material. Heaters are
then attached. Still another
version combines the traditional
oven with the heater-column
assembly.

27. DETECTORS USED IN
GC

28. Detectors:
The detector is the device located at the end of the column which provides a quantitative measurement of
the components of the mixture as they elute in combination with the carrier gas.
Any property of the gaseous mixture that is different from the carrier gas can be used as a detection
method.
These detection properties fall into two categories: bulk properties and specific properties. Bulk
properties, which are also known as general properties, are properties that both the carrier gas and
analyte possess but to different degrees. Specific properties, such as detectors that measure nitrogen-
phosphorous content, have limited applications but compensate for this by their increased sensitivity.

29. Parts of Detector:
Each detector has two main parts that when used together they serve as transducers to convert the
detected property changes into an electrical signal that is recorded as a chromatogram.
Sensor: The first part of the detector is the sensor which is placed as close the column exit as
possible in order to optimize detection.
Electronic Equipment: The second is the electronic equipment used to digitize the analog signal so
that a computer may analyze the acquired chromatogram. The sooner the analog signal is converted
into a digital signal, the greater the signal-to-noise ratio becomes, as analog signal are easily
susceptible to many types of interferences.

30. An ideal detector:
An ideal GC detector is distinguished by several
characteristics which are as follow:
• Adequate sensitivity to provide a high resolution signal for all
components in the mixture.
• The sensitivities of the detectors are in the range of 10-8 to 10-15 g of
solute per second.
• The quantity of sample must be reproducible.
• An ideal column will also be chemically inert.
• The detector should be reliable, predictable and easy to operate.

31. Mass Spectrometry Detectors
Mass spectrometer(MS) detectors are most powerful of all gas chromatography detectors.
In a GC/MS system, the mass spectrometer scans the masses continuously throughout the separation. When
the sample exits the chromatography column, it is passed through a transfer line into the inlet of the mass
spectrometer . The sample is then ionized and fragmented, typically by an electron-impact ion source.
During this process, the sample is bombarded by energetic electrons which ionize the molecule by causing
them to lose an electron due to electrostatic repulsion. Further bombardment causes the ions to fragment.
The ions are then passed into a mass analyzer where the ions are sorted according to their m/z value, or mass-
to-charge ratio. Most ions are only singly charged.

32. Instrumentation
:
• One of the most common types of mass analyzer in GC/MS is
the quadrupole ion-trap analyzer, which allows gaseous anions
or cations to be held for long periods of time by electric and
magnetic fields.
• A simple quadrupole ion-trap consists of a hollow ring electrode
with two grounded end-cap electrodes Ions are allowed into the
cavity through a grid in the upper end cap.
• A variable radio-frequency is applied to the ring electrode and
ions with an appropriate m/z value orbit around the cavity. As
the radio-frequency is increased linearly, ions of a stable m/z
value are ejected by mass-selective ejection in order of mass.
• Ions that are too heavy or too light are destabilized and their
charge is neutralized upon collision with the ring electrode wall.
Emitted ions then strike an electron multiplier which converts
the detected ions into an electrical signal.
• This electrical signal is then picked up by the computer through
various programs. As an end result, a chromatogram is
produced representing the m/z ratio versus the abundance of
the sample.

33. Diagram of MS detector:

34. Mass spectroscopy detectors:
Advantages
• GC/MS units are advantageous
because they allow for the
immediate determination of the
mass of the analyte and can be
used to identify the components
of incomplete separations.
Disadvantages
• The disadvantages of mass
spectrometry detectors are the
tendency for samples to
thermally degrade before
detection and the end result of
obliterating all the sample by
fragmentation.

35. Flame
Ionization
Detectors:
• Flame ionization detectors (FID) are the
most generally applicable and most widely
used detectors.
• In a FID, the sample is directed at an air-
hydrogen flame after exiting the column.
• At the high temperature of the air-
hydrogen flame, the sample undergoes
pyrolysis, or chemical decomposition
through intense heating.
• Pyrolized hydrocarbons release ions and
electrons that carry current. A high-
impedance picoammeter measures this
current to monitor the sample's elution.

36. Instrumentation:
• To detect these ions, two electrode are used to provide a potential difference.
The positive electrode doubles as the nozzle head where the flame is
produced. The other, negative electrode is positioned above the flame.
• When first designed, the negative electrode was either tear-drop shaped or
angular piece of platinum. Today, the design has been modified into a tubular
electrode, commonly referred to as a collector plate.
• The ions thus are attracted to the collector plate and upon hitting the plate,
induce a current. This current is measured with a high-impedance
picoammeter and fed into an integrator.
• The manner in which the final data is displayed is based on the computer and
software. In general, a graph is displayed that has time on the x-axis and total
ion on the y-axis.
• The current measured corresponds roughly to the proportion of reduced
carbon atoms in the flame. Specifically how the ions are produced is not
necessarily understood, but the response of the detector is determined by the
number of carbon atoms (ions) hitting the detector per unit time.
• This makes the detector sensitive to the mass rather than the concentration,
which is useful because the response of the detector is not greatly affected by
changes in the carrier gas flow rate.

37. Schematic Diagram of FID:

38. Flame ionization detectors:
Advantages
• It is advantageous to use FID
because the detector is
unaffected by flow rate,
noncombustible gases and
water. These properties allow
FID high sensitivity and low
noise.
Disadvantages
• This technique does require
flammable gas and also destroys
the sample.

39. Thermal
Conductivity
Detectors:
• Thermal conductivity detectors (TCD) were one the earliest
detectors developed for use with gas chromatography
• The TCD works by measuring the change in carrier gas
thermal conductivity caused by the presence of the sample,
which has a different thermal conductivity from that of the
carrier gas
• Their design is relatively simple, and consists of an
electrically heated source that is maintained at constant
power
• The temperature of the source depends upon the thermal
conductivities of the surrounding gases. The source is
usually a thin wire made of platinum, r . The resistance
within the wire depends upon temperature, which is
dependent upon the thermal conductivity of the gas.

40. Instrumentation:
• The TCD consists of an electrically heated
filament in a temperature-controlled cell. Under
normal conditions there is a stable heat flow
from the filament to the detector body.
• When an analyte elutes and the thermal
conductivity of the column effluent is reduced,
the filament heats up and changes resistance.
• This resistance change is often sensed by a
Wheatstone bridge circuit which produces a
measurable voltage change.
• The column effluent flows over one of the
resistors while the reference flow is over a
second resistor in the four-resistor circuit.

41. Schematic
diagram of
TCD:

42. Description:
• A schematic of a classic thermal conductivity
detector design utilizing a Wheatstone bridge
circuit .
• The reference flow across resistor 4 of the
circuit compensates for drift due to flow or
temperature fluctuations.
• Changes in the thermal conductivity of the
column effluent flow across resistor 3 will result
in a temperature change of the resistor and
therefore a resistance change which can be
measured as a signal.

43. Thermal conductivity detector:
Advantages
• The advantages of TCDs are the
ease and simplicity of use, the
devices' broad application to
inorganic and organic
compounds, and the ability of
the analyte to be collected after
separation and detection.
Disadvantages
• The greatest drawback of the
TCD is the low sensitivity of the
instrument in relation to other
detection methods, in addition
to flow rate and concentration
dependency.

44. Electron-capture Detectors:
Electron-capture detectors
(ECD) are highly selective
detectors commonly used
for detecting environmental
samples as the device
selectively detects organic
compounds with moieties
such as halogens,
peroxides, quinones and
nitro groups and gives little
to no response for all other
compounds.
Therefore, this method is
best suited in applications
where traces quantities of
chemicals such as pesticides
are to be detected and
other chromatographic
methods are unfeasible.
The simplest form of ECD
involves gaseous electrons
from a radioactive ? emitter
in an electric field. In the
absence of organic
compounds, a constant
standing current is
maintained between two
electrodes. With the
addition of organic
compounds with
electronegative functional
groups, the current
decreases significantly as
the functional groups
capture the electrons.

45. Instrumentation:
• This detector operates similar to proportional
counter used for X-ray measurement.
• this detector, the effluent from the column is
passed over a ß emitter (Ni-63). An electron from ß
emitter causes ionization of carrier gas and
production of a burst of electrons.
• In the absence of organic compounds, a constant
standing current between a pair of electrodes
results from this ionization process. However in
presence of organic compounds the current
decreases significantly.
• The response of this detector is nonlinear unless
the applied potential across the detector is pulsed.

46. Schematic
diagram of
ECD:

47. Electron capture detectors:
Advantages
• The advantages of ECDs are
the high selectivity and
sensitivity towards certain
organic species with
electronegative functional
groups
Disadvantages
• However, the detector has a
limited signal range and is
potentially dangerous owing
to its radioactivity. In addition,
the signal-to-noise ratio is
limited by radioactive decay
and the presence of O2 within
the detector.

48. Atomic
Emission
Detectors:
• Atomic emission detectors (AED), one of the newest addition
to the gas chromatographer's arsenal, are element-selective
detectors that utilize plasma, which is a partially ionized gas,
to atomize all of the elements of a sample and excite their
characteristic atomic emission spectra.
• AED is an extremely powerful alternative that has a wider
applicability due to its based on the detection of atomic
emissions.
• There are three ways of generating plasma: microwave-
induced plasma (MIP), inductively coupled plasma (ICP) or
direct current plasma (DCP). MIP is the most commonly
employed form and is used with a positionable diode array to
simultaneously monitor the atomic emission spectra of
several elements.

49. Instrumentation:
• The components of the Atomic emission
detectors include:
• 1) an interface for the incoming capillary GC
column to induce plasma chamber.
• 2) a microwave chamber.
• 3) a cooling system.
• 4) a diffraction grating that associated optics.
• 5) a position adjustable photodiode array
interfaced to a computer.

50. Schematic Diagram of Atomic Emission
Detectors:

51. Photoionization
Detectors:
• Another different kind of detector for GC is the
photoionization detector which utilizes the properties of
chemiluminescence spectroscopy.
• Photoionization detector (PID) is a portable vapor and gas
detector that has selective determination of aromatic
hydrocarbons, organo-heteroatom, inorganic species and
other organic compounds.
• PID comprise of an ultraviolet lamp to emit photons that are
absorbed by the compounds in an ionization chamber exiting
from a GC column.
• Small fraction of the analyte molecules are actually ionized,
nondestructive, allowing confirmation analytical results
through other detectors. In addition, PIDs are available in
portable hand-held models and in a number of lamp
configurations. Results are almost immediate.

52. Instrumentation:
• In a photoionization detector high-energy photons, typically in the vacuum
ultraviolet (VUV) range, break molecules into positively charged ions.
• As compounds enter the detector they are bombarded by high-energy UV
photons and are ionized when they absorb the UV light, resulting in ejection of
electrons and the formation of positively charged ions.
• The ions produce an electric current, which is the signal output of the detector.
The greater the concentration of the component, the more ions are produced,
and the greater the current.
• The current is amplified and displayed on an ammeter or digital concentration
display. The ions can undergo numerous reactions including reaction with oxygen
or water vapor, rearrangement, and fragmentation. A few of them may recapture
an electron within the detector to reform their original molecules; however only a
small portion of the airborne analytes are ionized to begin with so the practical
impact of this (if it occurs) is usually negligible
• . Thus, PIDs are non-destructive and can be used before other sensors in
multiple-detector configurations.

53. Schematic
Diagram of
photoionization
detector:

54. Photoionization Detectors:
Advantages
• PID is used commonly to detect
VOCs in soil, sediment, air and
water, which is often used to
detect contaminants in ambient
air and soil.
Disadvantages
• The disadvantage of PID is
unable to detect certain
hydrocarbon that has low
molecular weight, such as
methane and ethane.

55. Application
of GC:
Gas chromatography is a physical separation method in
where volatile mixtures are separated. It can be used in
many different fields such as pharmaceuticals,
cosmetics and even environmental toxins.
The samples have to be volatile, human breathe, blood,
saliva and other secretions containing large amounts of
organic volatiles can be easily analyzed using GC.
Knowing the amount of which compound is in a given
sample gives a huge advantage in studying the effects
of human health and of the environment as well.

56. Applications
of GC:
Air samples can be analyzed using GC. Most of the time,
air quality control units use GC coupled with FID in order
to determine the components of a given air sample.
GC/MS is also another useful method which can
determine the components of a given mixture using the
retention times and the abundance of the samples.
This method be applied to many pharmaceutical
applications such as identifying the amount of chemicals
in drugs.
Moreover, cosmetic manufacturers also use this method
to effectively measure how much of each chemical is used
for their products.

57. References:
• Skoog, D. A.; Holler, F. J.; Crouch, S. R. Principles of Instrumental Analysis. Sixth Edition, Thomson Brooks/Cole, USA,
2007.
• Krugers, J. Instrumentation in Gas Chromatography. Centrex Publishing Company-Eindhoven, Netherlands, 1968.
• Hubschmann, H. Handbook of GC/MS: Fundamentals and Applications. Wiley-VCH Verlag, Germany, 2001.
• Scott, R. P. W. Chromatographic Detectors: Design, Function, and Operation. Marcel Dekker, Inc., USA, 1996.
• J.N. Driscoll. REview of Photoionization Detection in Gas Chromatography: The first Decade. Journal of
CHromatographic Science , Vol 23. November 1985. 488-492.
• Boer, H. , "Vapour phase Chromatography", ed. Desty, D. H., 169 (Butterworths Sci. Pub., London, 1957).
• Dimbat, M. , Porter, P. E. , and Stross, F. H. , Anal. Chem., 28, 290 (1956). | Article | ISI | ChemPort .

58. THANKS