What is Chromatography?
Applications of Chromatography
Types of Chromatography
1- Column Chromatography
2- Planar chromatography
Paper Chromatography
Gas Chromatography
Detectors
ION EXCHANGE CHROMATOGRAPHY
ByM.Vharshini
B.Sc. Bio Medical Science
Sri Ramachandra University
ION EXCHANGE CHROMATOGRAPHY
Ion-exchange chromatography is a process that allows the separation of ions and polar molecules based on their affinity to the ion exchanger.
It can be used for almost any kind of charged molecule including large proteins, small nucleotides and amino acids.
Cations or Anions can be separated using this method.
PRINCIPLE
It is based on the reversible electrostatic interaction of ions with the separation matrix (i.e.)
The separation occurs by reversible exchange of ions between the ions present in the solution and those present in the ion exchange resin.
CLASSIFICATION OF RESINS
According to the chemical nature they classified as-
1. Strong cation exchange resin
2. Weak cation exchange resin
3. Strong anion exchange resin
4. Weak anion exchange resin
According to the Source they can -
Natural resins : Cation - Zeolytes, Clay
Anion - Dolomite
Synthetic resins: Inorganic & Organic resins
◘Organic resins are polymeric resin matrix.
The resin composed of –
Polystyrene (sites for exchangeable functional groups)
Divinyl benzene(Cross linking agent)-offers stability.
Ion exchange resin should have following requirements
»It must be chemically stable.
»It should be insoluble in common solvents.
» It should have a sufficient degree of cross linking.
»The swollen resin must be denser than water.
»It must contain sufficient no. of ion exchange groups.
Physical properties of ion exchange resins
Cross linking:
It affects swelling & strength & solubility
Swelling:
When resin swells, polymer chain spreads apart
Polar solvents → swelling
Non-polar solvents → contraction
Swelling also affected electrolyte concentration.
Particle size and porosity
Increase in surface area & decrease in particle size will increase the rate of ion exchange.
Regeneration
Cation exchange resin are regenerated by treatment with acid, then washing with water.
Anion exchange resin are regenerated by treatment with NaOH, then washing with water until neutral.
EXPERIMENTAL SETUP OF ION EXCHANGE CHROMATOGRAPHY
Metrohm 850 Ion chromatography system
Instrumentation of ion exchange chromatography
PRACTICAL REQUIREMENTS
1.Column
» glass, stainless steel or polymers
2.Packing the column
» Wet packing method:
A slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column. Care must be taken to avoid air bubbles.
3.Application of the sample
After packing, sample is added to the top of the stationary phase, use syringe or pipette.
This layer is usually topped with a small layer of sand or with cotton or glass wool to protect the shape of the organic layer from the velocity of newly added eluent.
4.Mobile phase
Acids, alkalis, buffers…
6.Stationary phase
The ionic
ION EXCHANGE CHROMATOGRAPHY
ByM.Vharshini
B.Sc. Bio Medical Science
Sri Ramachandra University
ION EXCHANGE CHROMATOGRAPHY
Ion-exchange chromatography is a process that allows the separation of ions and polar molecules based on their affinity to the ion exchanger.
It can be used for almost any kind of charged molecule including large proteins, small nucleotides and amino acids.
Cations or Anions can be separated using this method.
PRINCIPLE
It is based on the reversible electrostatic interaction of ions with the separation matrix (i.e.)
The separation occurs by reversible exchange of ions between the ions present in the solution and those present in the ion exchange resin.
CLASSIFICATION OF RESINS
According to the chemical nature they classified as-
1. Strong cation exchange resin
2. Weak cation exchange resin
3. Strong anion exchange resin
4. Weak anion exchange resin
According to the Source they can -
Natural resins : Cation - Zeolytes, Clay
Anion - Dolomite
Synthetic resins: Inorganic & Organic resins
◘Organic resins are polymeric resin matrix.
The resin composed of –
Polystyrene (sites for exchangeable functional groups)
Divinyl benzene(Cross linking agent)-offers stability.
Ion exchange resin should have following requirements
»It must be chemically stable.
»It should be insoluble in common solvents.
» It should have a sufficient degree of cross linking.
»The swollen resin must be denser than water.
»It must contain sufficient no. of ion exchange groups.
Physical properties of ion exchange resins
Cross linking:
It affects swelling & strength & solubility
Swelling:
When resin swells, polymer chain spreads apart
Polar solvents → swelling
Non-polar solvents → contraction
Swelling also affected electrolyte concentration.
Particle size and porosity
Increase in surface area & decrease in particle size will increase the rate of ion exchange.
Regeneration
Cation exchange resin are regenerated by treatment with acid, then washing with water.
Anion exchange resin are regenerated by treatment with NaOH, then washing with water until neutral.
EXPERIMENTAL SETUP OF ION EXCHANGE CHROMATOGRAPHY
Metrohm 850 Ion chromatography system
Instrumentation of ion exchange chromatography
PRACTICAL REQUIREMENTS
1.Column
» glass, stainless steel or polymers
2.Packing the column
» Wet packing method:
A slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column. Care must be taken to avoid air bubbles.
3.Application of the sample
After packing, sample is added to the top of the stationary phase, use syringe or pipette.
This layer is usually topped with a small layer of sand or with cotton or glass wool to protect the shape of the organic layer from the velocity of newly added eluent.
4.Mobile phase
Acids, alkalis, buffers…
6.Stationary phase
The ionic
Paper chromatography is an analytical method used to separate colored chemicals or substances. It is primarily used as a teaching tool, having been replaced by other chromatography methods, such as thin-layer chromatography.
HPLC Principle,Instrumentation and ApplicationAlakesh Pradhan
HPLC Chromatography and its principle
Liquid chromatography
High Performance Liquid Chromatography ( HPLC )
The components of the high performance liquid chromatograph (HPLC).
The separation process.
The chromatogram
High performance liquid chromatography is a powerful tool in analysis, it yields high performance and high speed compared to traditional columns chromatography because of the forcibly pumped mobile phase.
HPLC is a chromatographic technique that can separate a mixture of compounds.
The principle involved in HPLC can be either adsorption or partition.
Introduction to chromatography, Definition of Chromatography, Types of column chromatography, Theory of chromatography, Practical considerations in column chromatography , Factors affecting efficiency of a column, Applications.
Paper chromatography is an analytical method used to separate colored chemicals or substances. It is primarily used as a teaching tool, having been replaced by other chromatography methods, such as thin-layer chromatography.
HPLC Principle,Instrumentation and ApplicationAlakesh Pradhan
HPLC Chromatography and its principle
Liquid chromatography
High Performance Liquid Chromatography ( HPLC )
The components of the high performance liquid chromatograph (HPLC).
The separation process.
The chromatogram
High performance liquid chromatography is a powerful tool in analysis, it yields high performance and high speed compared to traditional columns chromatography because of the forcibly pumped mobile phase.
HPLC is a chromatographic technique that can separate a mixture of compounds.
The principle involved in HPLC can be either adsorption or partition.
Introduction to chromatography, Definition of Chromatography, Types of column chromatography, Theory of chromatography, Practical considerations in column chromatography , Factors affecting efficiency of a column, Applications.
The paper-chromatography explains that separating mixtures into their components in order to analyze, identify, purify, and/or quantify the mixture or components.
Chromatography is a bioanalytical technique used for separation of analytes into pure components. Biomolecules such as amino acids, proteins and carbohydrates can be purified by different chromatographic methods.
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Chromatography
1. Prepared By : Yahia Mohamed Reda
Benha university – faculty of science
Chemistry department
2. What is Chromatography?
Derived from the Greek word Chroma meaning colour,
chromatography provides a way to identify unknown compounds
and separate mixtures
3. What is Chromatography?
Chromatography is a technique for
separating mixtures into their components
in order to analyze, identify, purify,
and/or quantify the mixture or
components.
• Analyze
Separate • Identify
• Purify
Mixture Components
• Quantify
6. •What Are The Branches of
Chromatography
According To Distribution
Between The Mobil & Stationary
Phases ??
7. 1- Adsorption Chromatography
It Depends On The Ability Of Different Solutes
To be Adsorbed On The Surface Of The
Stationary Phase At Different Strengths
It Can Be Found In GLC & LSC
8. 2-Partition Chromatography
It Depends On The Difference in Solubility Of
Different Solutes In The Stationary Liquid Phase
The Rate Of Separation Depends On The
Equilibrium Of The Solute Between The Mobil
Phase “Liquid “ & Stationary Phase ”liquid”
9. 3 - Ion Exchange Chromatography
In this type of chromatography, the use of a resin
(the stationary solid phase) is used to covalently
attach anions or cations onto it. Solute ions of the
opposite charge in the mobile liquid phase are
attracted to the resin by electrostatic forces.
10. 4 - Molecular Exclusion
Chromatography
Also known as gel permeation or gel filtration,
this type of chromatography lacks an attractive
interaction between the stationary phase and solute. The
liquid or gaseous phase passes through a porous gel which
separates the molecules according to its size. The pores are
normally small and exclude the larger solute molecules,
but allows smaller molecules to enter the gel, causing them
to flow through a larger volume. This causes the larger
molecules to pass through the column at a faster rate than
the smaller ones.
11.
12. 5 - Affinity Chromatography
This is the most selective type of chromatography
employed. It utilizes the specific interaction between one
kind of solute molecule and a second molecule that is
immobilized on a stationary phase. For example, the
immobilized molecule may be an antibody to some specific
protein. When solute containing a mixture of proteins are
passed by this molecule, only the specific protein is reacted
to this antibody, binding it to the stationary phase. This
protein is later extracted by changing the ionic strength or
pH.
13.
14. •What Is The Main Types Of
Chromatography According To
The Kind Of Mobil & Stationary
Phases?
16. •What Are The Techniques
according To Chromatography
Red Shapes?
17. 1- Column Chromatography
Column chromatography is a separation technique
in which the stationary bed is within a tube. The
particles of the solid stationary phase or the
support coated with a liquid stationary phase may
fill the whole inside volume of the tube (packed
column) or be concentrated on or along the inside
tube wall leaving an open, unrestricted path for the
mobile phase in the middle part of the tube (open
tubular column). Differences in rates of movement
through the medium are calculated to different
retention times of the sample
18.
19. 2- Planar chromatography
Planar chromatography is a separation technique in which the
stationary phase is present as or on a plane. The plane can be a
paper, serving as such or impregnated by a substance as the
stationary bed (paper chromatography) or a layer of solid particles
spread on a support such as a glass plate (
thin layer chromatography). Different compounds in the sample
mixture travel different distances according to how strongly they
interact with the stationary phase as compared to the mobile
phase. The specific Retention factor (Rf) of each chemical can be
used to aid in the identification of an unknown substance.
21. 1 – Paper Chromatography
•separates dried liquid samples with a liquid
solvent (mobile phase) and a paper strip (stationary
phase)
22. Principles of Paper Chromatography
Capillary Action – the movement of liquid within the spaces of a porous
material due to the forces of adhesion, cohesion, and surface tension. The
liquid is able to move up the filter paper because its attraction to itself is
stronger than the force of gravity.
Solubility – the degree to which a material (solute) dissolves into a
solvent. Solutes dissolve into solvents that have similar properties. (Like
dissolves like) This allows different solutes to be separated by different
combinations of solvents.
Separation of components depends on both their solubility in the mobile
phase and their differential affinity to the mobile phase and the stationary
phase.
23. Illustration of Chromatography
Stationary Phase
Separation
Mobile Phase
Mixture Components
Components Affinity to Stationary Phase Affinity to Mobile Phase
Blue ---------------- Insoluble in Mobile Phase
Black
Red
Yellow
26. Overview of the Experiment
Purpose:
To introduce students to the principles and
terminology of chromatography and demonstrate
separation of the dyes in Sharpie Pens with paper
chromatography.
Time Required:
Prep. time: 10 minutes
Experiment time: 45 minutes
Costs:
Less than $10
27. Materials List
6 beakers or jars
6 covers or lids
Distilled H2O
Isopropanol
Graduated cylinder
6 strips of filter paper
Different colors of Sharpie
pens
Pencil
Ruler
Scissors
Tape
28. Preparing the Isopropanol Solutions
• Prepare 15 ml of the following isopropanol solutions
in
appropriately labeled beakers:
- 0%, 5%, 10%, 20%, 50%, and 100%
29. Preparing the Chromatography
Strips
Cut 6 strips of filter paper
Draw a line 1 cm above the
bottom edge of the strip with
the pencil
Label each strip with its
corresponding solution
Place a spot from each pen on
your starting line
30. Developing the Chromatograms
Place the strips in the beakers
Make sure the solution does not
come above your start line
Keep the beakers covered
Let strips develop until the
ascending solution front is
about 2 cm from the top of the
strip
Remove the strips and let them
dry
35. Black Dye
1. Dyes separated – purple and black
2. Not soluble in low concentrations of
isopropanol
3. Partially soluble in concentrations of
isopropanol >20%
0% 20% 50% 70% 100%
Concentration of Isopropanol
36. Blue Dye
1. Dye separated – blue
2. Not very soluble in low
concentrations of isopropanol
3. Completely soluble in high
concentrations of isopropanol
0% 20% 50% 70% 100%
Concentration of Isopropanol
37. Green Dye
1. Dye separated – blue and yellow
2. Blue – Soluble in concentrations
of isopropanol >20%
3. Yellow – Soluble in concentrations
of isopropanol >0%
0% 20% 50% 70% 100%
Concentration of Isopropanol
38. Red Dye
1. Dyes separated – red and yellow
2. Yellow –soluble in low concentrations of isopropanol and
less soluble in high concentrations of isopropanol
3. Red – slightly
soluble in low
concentrations
of isopropanol,
and more
soluble in
concentrations
of isopropanol
>20%
0% 20% 50% 70% 100%
Concentration of Isopropanol
39. Alternative Experiments
Test different samples:
Other markers, pens, highlighters
Flower pigments
Food Colors
Test different solvents:
Other alcohols: methanol, ethanol, propanol,
butanol
Test different papers:
Coffee filters
Paper towels
Cardstock
Typing paper
43. 2 - Thin Layer Chromatography
Sample – marker
Standard – food dyes
Stationary phase – chromatography paper
Mobile phase - water
44. Structures of E numbers…..
E122 pink
E110 yellow
E124 red E133 blue
45. So what will happen?
Each dye will travel up the paper at different
speeds
The speed depends on the solubility of the dye
in water and its interaction with the paper
The dyes are all different molecules with
different characteristics
47. Analysis
Calculation of results
You must now calculate an Rf value for each spot.
Rf = Distance from the start to the middle of a spot
Distance from start to finish point of the water
48. Conclusions – writing up
One of the key elements of all scientific
experiments is to write up your results
At the end of this experiment we would like
each person to conclude from the Rf values as
to which E numbers are contained in the
markers
51. THE CHROMATOGRAPHIC PROCESS - PARTITIONING
(gas or liquid)
MOBILE PHASE
Sample
Sample
out
in
STATIONARY PHASE
(solid or heavy liquid coated onto a solid or support system)
64. Properties of Selected Gas Chromatography
Detectors
Approximate Limit Approximate
Type Comments
of Detection (gs-1) Linear Range
Thermal conductivity Universal detector -measures
10-5-10-6 103-104
(TCD) changes in heat conduction
Universal detector -measures ion
Flame ionization (FID) 10-12 106-107
currents from pyrolysis
Selective detector for compounds
Electron capture (EC or
10 -14
10 -10
2 -3
containing atoms with high
ECD) electron affinities
Flame photometric Selective detector for compounds
10-13 102
(FPD) containing S,P
Selective for N,P containing
Nitrogen-phosphorus 10-8-10-14 105-107
compounds
Universal (some selectivity due to
Photoionisation (PID) 10-8-10-12 105
identity of gas in lamp)
Specific detector for compounds
Hall Detector 10-11 105
which contain halogen, S, or N
variable,
Mass spectrometer (MS) 10-12
depends on MS
Universal
Fourier-transform
10-10 102 Polar molecules
infrared (FTIR)
65. 1- Mass Spectrometry
Molecular weight can be obtained from a
very small sample.
It does not involve the absorption or
emission of light.
A beam of high-energy electrons breaks the
molecule apart.
The masses of the fragments and their
relative abundance reveal information about
the structure of the molecule.
66. Electron Impact Ionization
A high-energy electron can dislodge an electron
from a bond, creating a radical cation (a positive
ion with an unpaired e-).
H H
H C C H
H H
H H H H
e- + H C C H H C C+ H
H H H H
H H
H C+ C H
H H
67. Separation of Ions
Only the cations are deflected by the magnetic
field.
Amount of deflection depends on m/z.
The detector signal is proportional to the
number of ions hitting it.
By varying the magnetic field, ions of all masses
are collected and counted.
70. The GC-MS
A mixture of compounds is separated by gas
chromatography, then identified by mass
spectrometry.
71. High Resolution MS
Masses measured to 1 part in 20,000.
A molecule with mass of 44 could be C3H8,
C2H4O, CO2, or CN2H4.
If a more exact mass is 44.029, pick the correct
structure from the table:
C3H8 C2H4O CO2 CN2H4
44.06260 44.02620 43.98983 44.03740
72. Molecules with Heteroatoms
Isotopes: present in their usual abundance.
Hydrocarbons contain 1.1% C-13, so there will
be a small M+1 peak.
If Br is present, M+2 is equal to M+.
If Cl is present, M+2 is one-third of M+.
If iodine is present, peak at 127, large gap.
If N is present, M+ will be an odd number.
If S is present, M+2 will be 4% of M+.
77. Mass Spectra of Alkanes
More stable carbocations will be more abundant.
78. Mass Spectra of Alkenes
Resonance-stabilized cations favored.
79. Mass Spectra of Alcohols
Alcohols usually lose a water molecule.
M+ may not be visible.
=>
80. 2- Flame Ionisation Detector (FID)
Destruction of combustible sample in flame produces measurable current
•Elute is burnt in a mixture of H2 and air
•Electrical conductivity of a gas is
directly proportional to the
concentration of charged particles
within the gas
•It responds to most hydrocarbons
Compounds that give no response
include:
air, water, inert gases, CO, CO2,
CS2, NO, SO2 and H2S
• Very sensitive detector with a
wide linear range
• Excellent detector for
quantitative trace analysis
81. Thermal Conductivity cell (TCD)
(most common in the past)
•Thermal conductivity measures the ability of a substance to transport heat
from a hot region to a cold region
•Differences in the thermal conductivity of gasses are based on the mobility
•The smaller the molecule the higher the mobility and thermal conductivity
•Helium is the carrier gas commonly used
•Simple and universal
•Respond to all analytes
•104 linear response range
•Not sensitive to detect minute quantities
•Mostly used with tubular columns with
>0.053 mm in diameter or packed
columns
•Sensitivity increases with:
Increasing filament current
Decreasing flow rate
Lower detector block temperature
82. Other detectors
Nitrogen-phosphorus detector
Modified Flame Ionization detector. Especially sensitive to N and P, 10 4-
106 greater response than to carbon. Important for the analysis of drugs,
herbicides and pesticides
Sulfur chemiluminescence detector
Sulfur is oxidized to SO during ionization and converted to blue light
emitting SO2 by reaction with ozone. Intensity of emission is proportional to
the mass of S eluted. The response to Sulfur is 107 greater than to carbon
A nitrogen chemiluminescence detector works in analogous
manner, combustion of eluent converts to NO which reacts with O 3 to form
a chemiluminescent product. Response to N is 107 greater than to carbon
Atomic emission detector
Detector can be set to observe almost any element in each analyte as
it emerges through the column.
84. Desirable characteristics of detectors
•High sensitivity
•Negligible baseline noise
•Large linear response range (analyte concentration range over
which detector response is proportional to concentration)
•Insensitive to temperature changes and solvent composition
•Universality or predictable specificity
•Low dead volume
•No sample destruction
•Stability over time
•Reliable
•Inexpensive to produce and continuous operation
•Capable of providing information on solute identity
85. Characteristics of Selected Liquid
Chromatography Detectors
Approximate Limit Approximate
Type Comments
of Detection Linear Range
Ultraviolet and visible Specific for light-absorbing
10-11 g 104
absorption compounds
Universal detector -measures
Differential Refractive
10 -10
-9 -10
g 103
changes in refractive index.
Index Cannot be used with gradients
Electrochemical Specific detector. Compound
10-10-10-11 g 105
Amperometric must be electroactive
Electrochemical
10-8 g/mL 105 Specific detector, but for all ions
Conductometric
Specific detector. Compound
Fluorescence 10-14 g 105
must be fluorescent
Universal detector. Also can be
Mass Spectrometry 10 -10-7 -9
105
used to identify analytes with
great certainty
Used to determine MW’s of
Solution Light polymers as they elute.
10-6 g/mL 105
Scattering Concentration usually far above
limits of detection
Evaporative Light Universal except for volatile
10-9 g 106
Scattering analytes. Not a linear response
86. HPLC Detectors respond to:
Solute property not Bulk property that Direct
exhibited by MP changes with solute
eluted solute detection
UV/VIS (0.1-1 ng)
•Fixed Refractive Mass
•Variable (VWD) Index Spectrometry
•Photodiode array (DAD) (100-1000 ng) (1-1000 pg)
FTIR (1mg) Conductivity ELSD
(500-1000 ng) (100-1000 pg)
Electrochemical (10-1000 pg)
•Amperometric
•Coulobmetric
Fluorescence (1-10 pg)
Requires fluorophore
87. UV-vis Light Absorption Detectors
•Most common HPLC detector
•Many solutes absorb ultraviolet (UV) light
•Most employ the most intense 254 nm
(emission of a mercury lamp)
Light
•Modern HPLC instruments have the source Detector
capability to choose the appropriate wave
length for a given analyte
•Use of photodiode arrays which can record
the entire UV region at once in a fraction of a
second (spectrum of each solute as it is
eluted)
•Full scale absorbance range 0.0005-3 absorbance units
•Linear range 5 orders of magnitude of solute concentration
•Good for gradient elution
88. Refractive Index (RI) Detector
• Light passes through the cell
and is directed to the photocell
by the deflection plate. When
solute with a different RI enters
the cell, the beam is deflected
and the photocell output
changes.
• Respond almost to every solute but sensitivity is lowered by a factor
of 1000 compared to a UV detector
• Sensitive to changes in pressure and temperature
• Unsuitable for gradient elution due to problem of matching sample
and reference while the composition is changing
• Its primary appeal is due to a nearly universal response to all solute
including those with little UV absorption
89. Electrochemical Detector
•Respond to analytes that can be
oxidized or reduced
•Potential is maintained at a
selected value with respect to
Ag/AgCl reference electrode and
current is measured between the
working and counter electrodes.
• Current is proportional to the concentration of
solute over 6 orders of magnitude
• Oxygen free aqueous or polar solvent containing
dissolved electrolyte are required.
•Very sensitive to fluctuations of temperature and the flow rate
90. Electrochemical Detector
Pulsed electrochemical detection of alcohols in an ion exchange column with
0.05M HClO4
Peaks: 1, glycerol; 2,ethylene glycol; 3, propylene glycol 4, methanol; 5,
ethanol; 6, 2-propanol; 7, 1-propanol; 8, 2-butanol; 9, 2-methyl-1-butane; 10,
1-butanol; 11, 3-methyl-1-butanol; 12, 1-pentanol; 13, cyclohexanol; 14,
diethyleneglycol.
91. Evaporative Light-Scattering
Detector (ELSD)
•Responds to any solute which is less volatile than the MP
•Response is related to mass of material (large peak = more
material in contrast to UV detectors peak intensity
is related to how well the solute absorbs UV)
•Response is non linear, so polynomials are used to
construct calibration curve
•Compatible with gradient elution. No peaks associated
with the solvent front, so less interference from
early eluting peaks
97. ELSD vs UV
• Obtain a more accurate
representation of
sample mass than UV
• See what may be missing
from the UV
chromatogram
• Detects compounds without
chromophores
98. Conclusion: Is ELSD the Ideal Detector?
Advantages Disadvantages
•Universal: Detect any • Destructive
compound less volatile than the
MP • Compatible with isocratic
and gradient elution but NOT
•Very Sensitive: Typical buffers/salts.
detection limits 0.1-1 ng.
•The response is proportional
to the analyte concentration,
and not affected by solvent
properties
•Reliable and easy to use
100. Important Definitions
K partition coefficient :- defined as the molar concentration of
analyte in the stationary phase divided by the molar concentration
of the analyte in the mobile phase.
retention time (tR ) : The time between sample injection and
an analyte peak reaching a detector at the end of the column
101. Retention factor, k' : is often used to describe the migration
rate of an analyte on a column. You may also find it called
the capacity factor. The retention factor for analyte A is defined as;
k'A = (t R - tM) / tM
Selectivity factor, a :
which describes the separation of two species (A and B) on the column;
a = k 'B / k 'A
When calculating the selectivity factor, species A elutes faster
than species B. The selectivity factor is always greater
than one.
102. Contact me
Dr.yahia1@yahoo.com
www.facebook.com/yahia.reda
Editor's Notes
Chromatography is widely used by forensic teams to analyse blood and urine samples for drugs, for paint analysis and testing for the presence of explosives. Most chromatography uses modern instrumentation and involves placing the sample to be analysed on a support (paper or silica) and transporting it along a mobile phase. The mobile phase can be a liquid (liquid chromatography) or a gas (gas chromatography). ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ Real-life examples of uses for chromatography: Pharmaceutical Company – determine amount of each chemical found in new product Hospital – detect blood or alcohol levels in a patient’s blood stream Law Enforcement – to compare a sample found at a crime scene to samples from suspects Environmental Agency – determine the level of pollutants in the water supply Manufacturing Plant – to purify a chemical needed to make a product
Most chromatography uses modern instrumentation and involves placing the sample to be analysed on a support (paper or silica) and transporting it along a mobile phase. The mobile phase can be a liquid (liquid chromatography) or a gas (gas chromatography).
separates dried liquid samples with a liquid solvent (mobile phase) and a glass plate covered with a thin layer of alumina or silica gel (stationary phase) _________________________________________ The principle is that the inks are water soluble and travel up the paper. Each marker is composed of more than one dye so each dye will separate as it moves up the paper with the water. The inks used in the dye are soluble in water and so will travel up the paper. The sample refers to what you want to test which in this case are colour markers. The standard refers to the reference material you will compare the sample to. In this case it is Goodalls food dye. Each food dye contains E numbers. The stationery phase is the support you apply your sample to – in this case chromatography paper. You spot each sample on the paper and allow it to dry. The mobile phase is water and the paper is placed in the water. Since each E number is a different chemical with its own characteristics and properties it will behave differently when you run it on the chromatography paper.
First you spot the food dye. Check on the bottle and confirm which E numbers are contained in the food dye. Make a note of it in your workbook. Then you spot your marker. Make sure you note down which spot is which because once they move along the paper you won’t be able to recognise them. The key point is that you don’t just visually compare the two. You must calculate a value for each spot and compare them so you can conclusively say whether the E numbers in the food dye are the same as the ones in the marker.
The Rf value is a measure of how far each spot has moved relative to the solvent front. Each dye will have its own Rf value so you can compare Rf values and confirm whether food dyes were used in making these markers.
Direct Inj - 8141, 625, 551.1, 604 P & T - 502.2
Isothermal - Keep oven at one temp thru run. Not very useful. Possibly useful for series of very similar compounds differing by boiling points such as alcohols ( MeOH, EtOH, n-PrOH, i-PrOH, BuOH, i-BuOH). BP 64.6 78.3 97.2 82.4 117.6 99.5 Gradient - temp profile: 40 deg hold for 10 min then 10deg/min to 240 deg and hold there for 20 min. Advantages: 1- resolution and 2- analysis time.
Packed - As suggested by the term, it is filled with a coated inert solid support such as fire brick, alumina, and graphite with a specific mesh size. The coatings are called phases and for best results are chemically bonded to the support. Chemical bonding provides for longer column life and less bleeding (major source of background noise) contributing to lower sensitivity. Column dimensions 1/8” - 1/4” ID x up to about 6’ using glass or stainless steel. Advantages - higher capacity (higher conc). Disadvantages: low resolution and low S/N. Capillary - Here the phase (film) is coated on the inside diameter of the capillary wall with film thickness range of 0.1 to 5μ where the ticker film provides for better resolution but also allows for more bleed. Typical dimensions .25mm - .53mm ID x up to 60m made of fused silica coated with polyamide. Advantages: high resolution and better S/N. Disadvantages: low capacity and cost.
Non - Polar : Equal distribution of electrons over the entire molecule. Look at the structure of fluorene. Polar: Non-equal distribution of electrons in a molecule causing one size of the molecule to be more positive or negative thus creating poles of charges. Look at 2,4,5-T (2,4,5-trichlorophenoxyacetic acid).
Here are some of the commonly used phases. They range in polarity from non-polar such as low polarity DMS to the higher polarity of mixtures with DPS with any combination available. There are specialty phases with very high polarity such as cyanopropylphenyl siloxane or trifluoropropyl methyl siloxane for fluorinated compounds. Some of these columns are used for separation confirmation such as the cyanopropylphenyl siloxane column for method 551.1.
MS - Mass Spectral - EI Electron impact - used for absolute confirmation. Molecules are ionized and their mass to charge ratio is plotted against its abundance. The resulting spectrum is unique to each molecule and can be looked up in a standard library and the % fit is noted. CI- chemical ionization is used for research and for structure elucidation. FID - Air/Hyd. Flame combusts the compound and the conductivity due to the ionization of the resulting carbon is determined and is presented as a signal. Very large range. NPD - Similar to FID except the combusted compound is passed over a heated bead of rubidium which provides for specificity in determining N and P where P is 500x more sensitive than N. NPD-P limited range, NPD-N broader range. FPD - Similar to FID but detector is light-tight where a PMT/filter assembly collects signal from emission for P at 393nm and S at 529nm. Haal/ELCD - furnace at about 900°C produces ionized acidic gases such as HCl or HF which is dissolved into a deionized solvent to produce conductivity proportional to the mass of the halogen in the org. compound.
TCD -Not normally used. Low sensitivity but good range. Change in resistance due to cooling effect of effluent over the resistance wire. ECD - limited range but very sensitive mainly to Cl org samples. The sample passes thru a Ni-63 foil where the Ni-63 gives off a constant amount of β particles and the Cl captures these electrons and the resulting loss produces a signal. PID - sample passes thru chamber it is constantly bombarded with high energy, 10.2 eV, where resulting ionization is produced and the ion current collected.
Note peaks 15, 16 17 & 18 on the DB-5 column and note the same peaks on the DB-1701 column. This shows the need for confirmatory columns (columns with different phases) so that separation of the compounds can be verified.
Note peaks 1 and 2 using the different columns. The separation is achievable because the compounds are different. Also note peaks 4 and 5 and 11 and 12. Even using different columns, positional isomers, o-, m- and p- cresol are difficult to separate.