Download instrumental-analysis-2

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ANALYTICAL STRATEGY FOR ANALYSIS
Following are the main steps involved in an analysis.
Sampling
Sample preparation
Analytical method
Data handling
Calculation & Reporting of results
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CATAGORIES OF INSTRUMENTAL ANALYSIS
Spectroscopy:
Chromatography:
Electro Analytical
Involved in using some
Involves more complex
light and measure the
samples in which analyte
Involves measurement
is separated from
of voltage or current
interfering substances
resulting from
using specific instruments.
electrodes immersed
Components are
into solution.
analyte under certain
electronically detected
e.g.
conditions.
with the electrical signal
pH Meter.
e.g. Atomic Absorption
generated by detection
Spectrophotometery,
devices.
UV/Visible
e.g. Gas Chromatograph.
amount of either
absorbed or emitted
light by solutions of
spectroscopy, etc .
Chemistry:
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COMPONENTS OF INSTRUMENTS
Sensor:
It is a type of translator that converts some property (T, P, Light or pH) of analyte into
weak electrical signal.
Signal Processor:
It amplifies or scales the signal and converts it to a useable form.
Readout Device:
It displays the signal for analyst to see components.
Power Supply;
It provides the power to run these components.
Standard & Sample
Solutions
Sensor
Signal
Processor
Power Supply
Readout
Devices
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VARIOUS ANALYSES CARRIED OUT IN
FFBL LABORATORY

Water Analysis

Product Analysis

Raw Material Analysis

Metal Analysis

Gas Analysis, etc
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INSTRUMENTS USED IN FFBL LABORATORY

Atomic Absorption Spectrophotometer

Gas Chromatograph

UV - Visible Spectrophotometer

Karl Fisher Titrator

pH Meter

Conductivity Meter, etc.
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AA Spectrophotometer
Atomic Absorption Spectroscopy
Atomic absorption spectrophotometer being used in FFBL laboratory
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BASIC PRINCIPLE:
ATOMIC ABSORPTION SPECTROSCOPY (AAS) is an analytical technique that
measures the concentrations of atoms. It makes use of the absorption of light
by these atoms in order to measure their concentration.
- Atomic-absorption spectroscopy quantifies absorption of ground state atoms in the
gaseous state.
The Atomic Absorption:
Atomic absorption spectrometers have 4 principal components:
1 - An atom cell ( atomizer )
2 - A light source ( usually a hollow cathode lamp )
3 - A monochromator
4 - A detector , and read out device.
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Schematic Diagram of an
Atomic Absorption Spectrometer
Light source
atomizer
hollow cathode Lamp
monochromator
Detector and
readout device
1 – Atomizer:
Elements to be analyzed needs to be in atomic sate.
Atomization is separation of particles into
individual molecules and breaking molecules into atoms .This is done by
exposing the analyte to high temperatures in a flame or graphite furnace .
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Flame
Flame AA can only analyze solutions , where,
it uses a slot type burner to increase the path length, and therefore to increase the
total absorbance .
Sample solutions are usually introduced into a nebulizer being sucked up by
a capillary tube. In the nebulizer the sample is dispersed into tiny droplets,
which can be readily broken down in the flame.
Excited State Atoms
Light Emission
Source
Excitation + De-excitation
(Resonance)
Light Source
Free Ground State Atoms
Absorption
Measured
Atomization
Ionic Formula Units
Solvent Evaporation
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2- Light Source
The light source is usually a hollow cathode lamp of the element that is being
measured. It contains a tungsten anode and a hollow cylindrical cathode made
of the element to be determined.
Hollow Cathode Lamp:
e-
+
-
+
-
Ar
+
Ar
+
-
Ar +
+
-
M+
M
M
Ar +
M+
M
Light
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3- Monochromator:
Entrance Slit
Dispersing
Element
Source
Spray of
Rainbow Colors
Violet
Exit Slit
Red
Monochromatic
Green Light
To Source
4- Detector and Read out Device:
The light selected by the monochromator is directed on to a detector that is
typically a photomultiplier tube , whose function is to convert the light signal
into an electrical signal convert proportional to the light intensity.
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Analysis of Iron (Fe)
1.00 mL pipette
1 mL
2 mL 3 mL
4 mL
Fe:
0.05
mg mL-1
50.00 mL volumetric flasks
5 mL
Determination of Fe
Calibration curve for absorbance of Fe
Absorbance
Absorbance
1.5
1
y = 0.2093x + 0.001
0.5
0
0
1
2
3
4
Fe concentration / ppm
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Gas Chromatograph (GC)
The separation of a mixture by distribution of its components
between a mobile and stationary phase over time.
Gas Chromatograph being used in FFBL Laboratory
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Purpose of Chromatography:
Analytical - determine chemical composition of a sample.
Preparative - purify and collect one or more components of a sample.
Classification
Gas Chromatography
Gas - solid
Gas - liquid
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GAS SOLID CHROMATOGRAPHY:
This method is based upon adsorption of gaseous substances on solid
surfaces.
Distribution coefficients are generally much larger than those for gas-liquid
chromatography
Used primarily for the separation of species that are not retained by gasliquid columns such as the components of air, hydrogen sulfide, carbon
disulfide, NOx, CO, CO2, and the rare gases.
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Gas Chromatography
H
RESET
Gas Carrier
Hydrogen
Air
Gas inlet system
Column
Detector
Data system
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Schematic Diagram of Gas Chromatography
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Detectors for GC
Flame ionization (FID)
Destruction of combustible sample in flame produces measurable current.
Thermal conductivity (TCD)
Change in resistance of heated wire.
Flame Ionization Detector:
High temperature of hydrogen flame (H2 +O2 + N2) ionizes compounds
eluted from column into flame. The ions collected on collector or electrode
and recorded on recorder due to electric current.
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Flame Ionization Detector
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Thermal Conductivity Detector
Measures the changes of thermal conductivity due to the sample (mg).
Sample can be recovered without destruction.
Principal:
Thermal balance of a heated filament
When the carrier gas is contaminated
by sample
, the cooling effect of
the gas changes. The difference in
cooling is used to generate the
detector signal.
Flow
Flow
The TCD is a nondestructive,
concentration sensing detector.
A heated filament is cooled by
the flow of carrier gas.
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UV Spectrophotometer
Spectral Distribution of Radiant Energy
Wave Number (cycles/cm)
X-Ray
UV
200nm
Visible
400nm
IR
Microwave
800nm
WAVELENGTH(nm)
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Principle of UV/VIS Spectrophotometer:
• Light Intensity Change : By Absorbance or Transmittance
• Quantity : Using Absorbance
The human eye sees the complementary color to that which is absorbed
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Lambert-Beer’s Law:
Light
I0
A = abC
I
Cell filled with
solution
a = Absorbance Constant
b = Sample path length
Standard Curve, Calibration curve:
• Standard Samples
• Proportional Constant
Absorbance
C = Sample Concentration
• Absorbance Measurement of Samples
Concentration
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Limitation of Lambert-Beer’s Law:
• At high concentrations (>0.01M) due to electrostatic interactions between
molecules in close proximity.
• Scattering of light
due to particulates in the sample
• Fluorescence or Phosphorescence of the sample
• Changes in refractive index at high analysis concentration
• Shifts in chemical equilibria as a function of concentration
• Stray light
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LIGHT SOURCES
UV Spectrophotometer
Deuterium Lamp
Wavelength Range: 190 ~ 420nm
Visible Spectrophotometer
Tungsten Lamp
Wavelength Range: Part of UV and Whole of
Visible Range
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Absorption Cells
UV Spectrophotometer
Quartz (crystalline silica)
Visible Spectrophotometer
Glass
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Conventional UV / Visible Spectrophotometer:
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Karl Fisher Titration
The fundamental principle behind it is based on the Bunsen Reaction between iodine
and sulfur dioxide in an aqueous medium.
Karl Fisher Titrator being used in FFBL Laboratory
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Karl Fischer Reaction:
ROH + SO2 + R’N [R’NH]SO3R + H2O + I2 + 2R’N 2[R’NH]I + [R’NH]SO4R
[alcohol] [base] [alkylsulfite salt] [water] [iodine] [hydroiodic acid salt] [alkylsulfate salt]
WORKING:
Water and iodine are consumed in a 1:1 ratio in the above reaction. Once all of the water
present is consumed, the presence of excess iodine is detected
Types of Karl Fischer Titration
•Volumetric KFT
•Coulometric KFT
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pH Meter
pH simply stands for the negative logarithm of the hydronium ion
concentration.
Tools for measuring pH:
Potentiometry is a measurement of voltage.
The tools used for this are:
pH Meter:
To accurately measure and transform the voltage caused by hydronium ion
into a pH value.
pH electrode:
To sense all the hydronium ions and to produce a potential.
Reference Electrode:
To give a constant potential no matter what the concentration of our hydronium
ion is.
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The pH meter:
Basically, a pH meter measures the potential between pH electrode (which is sensitive
to the hydronium ions) and the reference electrode (which doesn't care what's in the
solution).
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Conductivity Meter
Conductometry:
Conductometry means measuring the conductivity –a conductometer measures the
electrical conductivity of ionic solutions. This is done by applying an electric field
between two electrodes.
Principle:
When two electrodes are immersed in a solution and a potential is applied across them,
a current is produced in the external circuit that connects the two electrodes.
V=IR
Conductivity Meter being used in FFBL Laboratory
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Solution Conductance:
The reciprocal of solution resistance is called conductance.
•The quantity κ, above, is called conductivity
•The conductivity, κ, is an intrinsic property of a solution.
APPLICATION:
Conductance used to determine relative ionic strengths of solutions.
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