UV(Ultraviolet) visible spectroscopy (Analytical Technique)

CONTENTS
•SPECTROSCOPY
•UV-VISIBLE SPECTROSCOPY
•PRINCIPLE
•THEORY
•LAWS
•ABSORPTION & INTENSITY
SHIFTS
•WOODWARD-FIESCER RULE
WITH EXAMPLES
•INSTRUMENTATION
(DETAILED)
•CHOICE OF SOLVENT
•SOLVENT EFFECT
•EFFECT OF CONCENTRATION,
TEMPERATURE & 𝑝𝐻
•ADVANTAGES &
DISADVANTAGES
•APPLICATIONS
•REFERENCE
24-12-2019V.K. VIKRAM VARMA 2

SPECTROSCOPY
•SPECTROSCOPY IS DEFINED AS THE INTERACTION
BETWEEN MATTER & ELECTROMAGNETIC
RADIATION(EMR) OR LIGHT.

CONTD.
•SPECTROMETRY IS THE APPLICATION OF
SPECTROSCOPY SO THAT THERE ARE QUANTIFIABLE
RESULTS THAT CAN THAN BE ASSESSED.
•SPECTROPHOTOMETER OR SPECTROMETER: THE
INSTRUMENT THAT IS USED TO MEASURE THE
AMOUNT OF ELECTRO MAGNETIC RADIATION
ABSORBED BY AN ORGANIC MOLECULE.

UV-VISIBLE SPECTROCOPY
•IT INVOLVES THE STUDY OF INTERACTION OF UV-VISIBLE
RADIATION WITH MOLECULES & THE ELECTRONIC
SPECTRA OF COMPOUNDS ARE ASSCIATED WITH
MEASUREMENTS OF ENERGY ABSORBED WHEN
ELECTRON IS PROMOTED TO HIGHER ENERGY LEVELS
(LOW ENERGY TO HIGH ENERGY), IN RANGE OF 200-800𝑛𝑚
(UV=200-400 𝑛𝑚 & VISIBLE=400-800 𝑛𝑚).

UV VISIBLE
SPECTROPHOTOMETER

PRINCIPLE
•ANY MOLECULES HAS EITHER 𝑛, 𝜋 𝑜𝑟 𝜎 𝑜𝑟 A CMBINATION OF THESE
ELECTRONS. THESE BONDING(𝜎&𝜋) & NON BONDING (𝑛) ELECTRONS
ABSORB THE CHARACTERISTIC RADIATION & UNDERGOES
TRANSITION FROM GROUND STATE TO EXCITED STATE.
•BY THE CHARACTERISTIC ABSORPTION PEAKS, THE NATURE OF
THE ELECTRONS PRESENT & HENCE THE MOLECULAR STRUCTURE
CAN BE ELUCIDATED.

THEORY
•WHEN THE MOLECULE ABSORBS ULTRAVIOLET OR
VISIBLE LIGHT, ITS ELECTRONS GET PROMOTED FROM
THE GROUND STATE TO THE HIGHER ENERGY STATE.
•IN THE GROUND STATE, THE SPINS OF THE ELECTRONS IN
EACH MOLECULAR ORBITAL ARE ESSENTIALLY PAIRED.
•IN THE HIGHER ENERGY STATE, IF THE SPINS OF THE
ELECTRONS ARE PAIRED, THEN IT IS CALLED AN EXCITED
SINGLET STATE.

CONTD.
•UV-VISIBLE RADIATION INTERACTS WITH MATTER WHICH CAUSES
ELECTRONIC TRANSITIONS.
•HOW EXCITATION OF ELECTRONS OCCURS:
MOLECULE → ABSORBS LIGHT → ELECTRONS ARE PROMOTED
FROM GROUND TO HIGHER STATE.
IN GROUND STATE → SPINS OF ELECTRONS ARE PAIRED → UV
RADIATION → ELECTRON CHARGE CLOUD IS DISTRIBUTED →
DISTORTION OF CHARGE CLOUD PRODUCES DIPOLE.

CONTD.
•HIGHER ENERGY ORBITALS ARE ANTIBONDING MOLECULAR
ORBITALS.
•TRANSITION OF ELECTRON OCCURS FROM HOMO(HIGHEST
OCCUPIED MOLECULAR ORBITAL) TO LUMO(LOWEST UNOCCUPIED
MOLECULAR ORBITAL).
•POSSIBLE ELECTRONIC TRANSITION:
 𝝈 𝒕𝒐 𝝈∗ TRANSITION
 𝒏 𝒕𝒐 𝝈∗ TRANSITION
 𝝅 𝒕𝒐 𝝅∗ TRANSITION
 𝒏 𝒕𝒐 𝝅∗ TRANSITION

ENERGY LEVEL TRANSITIONS

 𝝈 𝒕𝒐 𝝈∗
TRANSITION
•ENERGY REQUIRED 150𝑛𝑚.
•VACCUM UV REGION(BELOW 200𝑛𝑚) – PATH LENGTH
SHOULD BE FREE FROM AIR.
•SATURATED HYDROCARBONS (METHANE, PROPANE).

•ENERGY REQUIRED 175𝑛𝑚(APPROX.).
•WHEN HETEROATOM IS PRESENT IN SATURATED
COMPOUND. E.G.: ALCOHOLS, ALDEHYDES, KETONE,
AMINE, WATER ETC.
 𝒏 𝒕𝒐 𝝈∗
TRANSITION

•ENERGY REQUIRED MORE THAN 200𝑛𝑚 (DEPENDS
ON CONJUGATION) LESS THAN 𝑛 𝑡𝑜 𝜎∗.
•WHEN ANY DOUBLE, TRIPLE BONDED
HYDROCARBONS, AROMATIC COMPOUNDS ARE
PRESENT.
 𝝅 𝒕𝒐 𝝅∗
TRANSITION

•MORE THAN 200𝑛𝑚 (DEPENDS ON CONJUGATION OF
COMPOUNDS).
•WHEN CARBONYL COMPOUNDS ARE PRESENT.
 𝒏 𝒕𝒐 𝝅∗
TRANSITION
ENERGY REQUIRED FOR VARIOUS TRANSITIONS
OBEY THE FOLLOWING ORDER:
𝝈 → 𝝈∗
> 𝒏 → 𝝈∗
> 𝝅 → 𝝅∗
> 𝒏 → 𝝅∗

LAWS
•WHEN A BEAM OF LIGHT FALLS ON A SOLUTION OR HOMOGENEOUS
MEDIA, A PORTION OF LIGHT IS ABSORBED WITHIN THE MEDIUM
WHILE THE REMAINING IS TRANSMITTED THROUGH THE MEDIUM.
•THUS IF 𝐼0 IS THE INTENSITY OF RADIATION FALLING ON THE
MEDIA, 𝐼 𝑎 IS THE AMOUNT OF RADIATION ABSORBED & 𝐼𝑡 AS THE
AMOUNT OF RADIATION TRANSMITTED THEN,
𝑰 𝟎 = 𝑰 𝒂 + 𝑰 𝒕

CONTD.
• WHERE,
 𝑰= INTENSITY OF INCIDENT LIGHT
 𝒄=MOLAR CONCENTRATION OF SAMPLE
 𝒃 =LENGTH OR THICKNESS OF THE
SAMPLE CELL
 𝑰 𝒂= INTENSITY OF ABSORBED LIGHT
 𝑰 𝒕 =INTENSITY OF TRANSMITTED LIGHT

 LAMBERT’S LAW
• WHEN A BEAM OF MONOCHROMATIC LIGHT IS PASSED THROUGH ABSORBING
MEDIUM, THEN THE DECREASE IN INTENSITY OF RADIATION WILL BE DIRECTLY
PROPORTIONAL TO THE THICKNESS(PATH LENGTH) OF THE SOLUTION.
𝑨 = 𝐥𝐨𝐠 𝟏𝟎
𝑰 𝑶
𝑰
𝜶 𝒍
𝑨𝜶 𝒍
𝑨 = 𝜺𝒍
Where,
𝜀- molar absorptivity
𝑙- path length
(units 𝐿
𝑚𝑜𝑙−𝑐𝑚 )

 BEER’S LAW
•WHEN A BEAM OF MONOCHROMATIC LIGHT IS PASSED THROUGH
ABSORBING MEDIUM, THEN THE DECREASE IN INTENSITY OF
RADIATION WILL BE DIRECTLY PROPORTIONAL TO THE
CONCENTRATION OF THE SOLUTION.
𝑰 𝑶
𝑰
𝜶 𝒄
𝑨𝜶 𝒄
𝑨 = 𝜺𝒄
Where,
𝑐-concentration of the solution

 LAMBERT-BEER LAW
•WHEN A BEAM OF MONOCHROMATIC LIGHT IS PASSED THROUGH
ABSORBING MEDIUM, THEN THE DECREASE IN INTENSITY OF
RADIATION WILL BE DIRECTLY PROPORTIONAL TO THE
THICKNESS(PATH LENGTH) AS WELL AS CONCENTRATION OF THE
SOLUTION.
𝑰 𝑶
𝑰
𝜶 𝒍 × 𝒄
𝑨 𝜶 𝒍 × 𝒄
𝑨 = 𝜺 × 𝒍 × 𝒄
Where,
𝑐-concentration of the solution
𝑙- path length

TERMS USED IN UV-VISIBLE
SPECTROSCOPY
•CHROMOPHORES
CHROMOPHORES ARE COVALENTLY BONDED MOIETIES
WITH ANY COMPOUND & RESPONSIBLE FOR ABSORPTION OF
UV-VISIBLE RADIATIONS. E.G. ALDEHYDE, ETHYLENE,
CARBONYL ETC.
TYPES
a.CHROMOPHORE WITH 𝝅 − 𝝅∗. E.G.𝑪 = 𝑪, 𝑪 ≡ 𝑪.
b.CHROMOPHORE WITH 𝒏 − 𝝅∗. E.G.𝑪𝑶𝑶𝑯, 𝑵 = 𝑵.

CONTD.
• AUXOCHROMES
THESE ARE COORDINATELY SATURATED OR UN-SATURATED GROUPS
WHICH THEMSELVES DO NOT ABSORB RADIATIONS, BUT WHEN
PRESENT ALONG WITH A CHROMOPHORE ENHANCES THE ABSORBING
PROPERTIES OF CHROMOPHORE.
ALSO KNOWN AS COLOR ENHANCING GROUP.
EFFECT OF AUXOCHROME IS DUE TO ITS ABILITY TO EXTEND THE
CONJUGATION OF A CHROMOPHORE BY SHARING OF ITS NON-
BONDING ELECTRONS.
E.G. −𝑶𝑯, −𝑵𝑯 𝟐, −𝑶𝑹, −𝑺𝑯 ETC.

ABSORPTION & INTENSITY
SHIFTS

•SHIFT TOWARD LONGER
WAVELENGTH.
•REASONS FOR RED SHIFT:
ADDITION OF CHROMOPHORES
OR AUXOCHROMES.
SOLVENT EFFECT
INCREASING CONJUGATION.
•EXAMPLE: IN ALAKLINE MEDIUM,
𝑝 − 𝑛𝑖𝑡𝑟𝑜𝑝ℎ𝑒𝑛𝑜𝑙 SHOWS RED SHIFT.
 BATHOCHROMIC SHIFT(RED
SHIFT)

 HYPSOCHROMIC SHIFT (BLUE
SHIFT)
• SHIFT TOWARDS SHORTER WAVE
LENGTH.
• REASONS FOR BLUE SHIFT:
REMOVAL OF CHROMOPHORE
OR AUXOCHROME.
SOLVENT EFFECT.
REMOVAL OF CONJUGATION.
• ANILINE SHOWS BLUE SHIFT IN
ACIDIC MEDIUM, IT LOSES
CONJUGATION.

 HYPERCHROMIC SHIFT
•SHIFTING OF ABSORPTION
INTENSITY (𝜀) TOWARDS
HIGHER VALUES.
•IF AUXOCHROMES
INTRODUCED TO THE
COMPOUND, THE INTENSITY
OF ABSORPTION INCREASES.

 HYPOCHROMIC SHIFT
•SHIFTING OF ABSORPTION INTENSITY (𝜀) TOWARDS
HIGHER VALUES.

WOODWARD-FEISER RULE
•WOODWARD (1941): GAVE CERTAIN RULES FOR CORRELATING 𝜆 𝑚𝑎𝑥
WITH MOLECULAR STRUCTURE.
•SCOTT-FEISER (1959): MODIFIED THE RULE WITH MORE
EXPERIMENTAL DATA, THE MODIFIED RULE IS KNOWN AS
WOODWARD-FEISER RULE,
USED TO CALCULATE THE POSITION OF 𝝀 𝒎𝒂𝒙 FOR A GIVEN
STRUCTURE BY RELATING THE POSITION & DEGREE OF
SUBSTITUTION OF CHROMOPHORE.

CONTD.
•HOMOANNULAR DIENE: CYCLIC
DIENE HAVING CONJUGATED
DOUBLE BONDS IN THE SAME RING.
•HETEROANNULAR DIENE: CYCLIC
DIENE HAVING CONJUGATED
DOUBLE BONDS IN DIFFERENT RING.

CONTD.
•ENDOCYCLIC DOUBLE BOND: DOUBLE BOND
PRESENT IN RING
•EXOCYCLIC DOUBLE BOND: DOUBLE BOND
IN WHICH ONE OF THE DOUBLY BONDED
ATOMS IS A PART OF A RING SYSTEM.
RING A HAS ONE EXOCYCLIC &
ENDOCYCLIC DOUBLE BOND.
RING B HAS ONLY ONE ENDOCYCLIC
DOUBLE BOND

WOODWARD-FEISER RULE FOR CONJUGATED
DIENES, TRIENES, POLYENES
•EACH TYPE OF DIENEOR TRIENE SYSTEM IS HAVING A
CERAIN FIXED AT WHICH ABSORPTION TAKES PLACE;THIS
CONSTITUENTS THE BASIC VALUE OR PARENT VALUE.
•THE CONTRIBUTION MADE BY VARIIOUS ALKYL
SUBSTITUENTS OF RING RESIDUE, DOUBLEBONDS
EXTENDING CONJUGATION & POLAR GROUPS SUCH AS
− 𝐶𝑙, −𝐵𝑟 ARE ADDED TO THE BASIC VALUE TO OBTAIN 𝜆 𝑚𝑎𝑥
FOR PARTICULAR COMPOUND.

PARENT VALUES & INCREMENTS FOR DIFFERENT
GROUPS

E
X
A
M
P
L
E
S
CALCULATE 𝜆 𝑚𝑎𝑥

E
X
A
M
P
L
E
S

WOODWARD-FEISER RULE FOR
𝛼, 𝛽 −UNSATURATED COMPOUNDS

E
X
A
M
P
L
E
S

INSTRUMENTATION
COMPONENTS OF SPCETROPHOTOMETER
•LIGHT/ RADIATING SOURCE
•WAVELENGTH SELECTORS/ DISPERSIVE DEVICES
•SAMPLE COMPARTMENT
•DETECTOR
•RECORDER

SCHEMATIC DIAGRAM

 LIGHT/ RADIATING SOURCE
REQUIREMENTS:
•IT SHOLD BE STABLE.
•IT SHOULD PROVIDE CONTINUOUS RADIATION.
•IT MUST BE OF THE SUFFICIENT INTENSTIY FOR THE
TRANSMITTED ENERGY TO BE DETECTED AT THE END OF
THE OPTICAL PATH.

CONTD.
UV RADIATION SOURCES:
•HYDROGEN LAMP
•DEUTERIUM LAMP
•TUNGSTEN HALOGEN
LAMP
•XENON DISCHARGE LAMP
•MERCURY LAMP
VISIBLE RADIATION
SOURCES:
•TUNGSTEN HALOGN LAMP
•MERCURY VAPOUR LAMP
•CARBONONE LAMP

† HYDROGEN & DEUTERIUM
LAMP
•A CONTINUUM SPECTRUM IN THE UV REGION IS PRODUCED BY
ELECTRICAL EXCITATION OF HYDROGEN OR DEUTERIUM.
•INTIALLY THE DEUTERIUM MOLECULE ABSORB ELECTRICAL
ENERGY. WHICH RESULTS I THE FORMATION OF AN EXCITED
SPECIES FOLLOWED BY THE DISSOCIATION OF EXCITED
MOLECULE IN TO TWO ATOMIC SPECIES PLUS A UV PHOTON
•THUS A CONTINUUM SPECTRUM IS OBTAINED FROM 160-375𝑛𝑚.

CONTD.
•THE ENERGY OF PHOTON CAN VARY CONTINUOUSLY. ONLY
QUARTZ CUVETTES AR USED, BECAUSE GLASS ABSORB RADIATION
OF WAVE LENGTH LESS THAN 350𝑛𝑚.
•ADVANTAGES:
INTENSITY OF RADIATION IS EMITTED 3-5 TIMES THE
INTENSITY OF HYDROGEN LAMP.
RADIATION IS STABLE
•DISADVANTAGES:
EXPENSIVE

CONTD.
HYDROGEN LAMP DEUTERIUM LAMP

† TUNGSTEN LAMP
•SIMILAR IN ITS FUNCTIONING TO AN ELECTRIC BULB
•IT PROVIDES A SUPPLY OF RADIATION I THE WVELENGTH
RANGE OF 320-2500𝑛𝑚.
•CONTINUOUS SOURCE OF LIGHT
•WHEN TUNGSTEN FILAMENT IS HEATED TO
INCANDESCENCE BY AN ELECTRIC CURRENT, THE LIGHT
IS PRODUCED.

CONTD.
•THE GLASS BULB ENCLOSING THE FILAMENT CONTAINS
A LOW PRESSURE OF INERT GAS, USUALLY ARGON.
•SMALL AMOUNTS OF HALOGEN LIKE IODINE IS ADDED TO
IMPROVE THE INTENSITY (TUNGSTEN-IODINE LAMP).
•ADVANATGES:
HAVE LONG HALF LIFE
STABLE, CHEAP, EASY TO USE

CONTD.
•DISADVANTAGES:
INTENSITY AT LOWER WAVELENGTH REGION IN VERY
FEEBLE
NEED VOLTAGE CONTROL FOR STABLE RADIATION

† XENON DISCHARGE LAMP
• XENON GAS IS STORED IN LAMPS AT 10-30 ATMOSPHERIC
PRESSURE.
•IT CONTAIN 2 TUNGSTEN ELECTRODES THAT ARE
SEPARATED BY A DISTANCE OF ABOUT 8𝑚𝑚.
•WHEN CURRENT PASSES THROUGH XENON CAUSE
THERMAL EXCITATION.

CONTD.
•IT PRODUCES GREATER UV RADIATION THAN THE
HYDROGEN LAMP.
•CONTINUOUS SOURCE
•ADVANTAGES:
THE INTENSITY OF UV RADIATION PRODUCED ARE
GREATER THAN THAT OF HYDROGEN LAMP.
EMIT BOTH UV & VISIBLE WAVE LENGTH. XENON
DISCHARGE LAMP

CONTD.
•DISADVANTAGES:
THE LAMP SINCE OPERATES AT HIGH VOLTAGE BECOMES VERY
HOT DURING OPERATION & HENCE NEEDS THERMAL
INSULATION.

† MERCURY VAPOUR LAMP
•MERCURY VAPOUR IS STORED
UNDER HIGH PRESSURE &
EXCITATION OF MERCURY ATOMS
IS DONE BY ELECTRIC DISCHARGE.
•NOT SUITABLE FOR CONTINUOUS
SPECTRAL STUDIES, BECAUSE OF
THE PRESENCE OF SHARP LINES
OR BANDS.

 WAVE LENGTH SELECTORS
•MOST OF THE SPECTROSCOPIC ANALYSIS RADIATION THAT
CONSIST OF A LIMITED NARROW CONTINUOUS GROUP OF WAVE
LENGTH IS CALLED AS BAND.
•IDEALLY THE OUTPUT FROM A WAVELENGTH SELECTOR WOULD BE
A RADIATION OF SINGLE WAVELENGTH / FREQUENCY.
•A NARROW BAND WIDTH REPRESENTS BETTER PERFORMANCE.
•A FILTER OR MONOCHROMATORS IS USED WHICH CONVERTS
POLYCHROMATIC LIGHT TO MONOCHROMATIC LIGHT.

† MONOCHROMATOR
•ALL MONOCHROMATORS CONTAIN THE FOLLOWING COMPONENT
PARTS,
AN ENTRANCE SLIT
A COLLIMATING LENS
A DISPERSING DEVICE (A PRISM OR A GRATING)
A FOCUSING LENS
AN EXIT SLIT
•POLYCHROMATIC RADIATION (RADIATION OF MORE THAN ONE
WAVE LENGTH) ENTERS THE MONOCHROMATOR THROUGH THE
ENTRANCE SLIT.

CONTD.
•THE BEAM IS COLLIMATED, & THEN STRIKES THE
DISPERSING ELEMENT AT THE ANGLE.
•THE BEAM IS SPLIT IN TO IT COMPONENT WAVELENGTHS
BY THE GRATING OR PRISM.
•BY MOVING THE DISPERSING ELEMENT OR THE EXIT SLIT,
THE RADIATION OF ONLY A PARTICULAR WAVELENGTH
LEAVES THE MONOCHROMATOR THROUGH THE EXIT SLIT.

CONTD.
•IN SPECTROPHOTOMETER 2
TYPES OF WAVELENGTH
SELECTORS ARE USED,
•MONOCHROMATORS
•FILTERS
•TYPES OF
MONOCHROMATORS
•PRISM TYPE
•DISPERSIVE TYPE
•LITTROW TYPE
•GRATING TYPE
•DIFFRACTION
GRATING
•TRANSMISSION
GRATING

۞ PRISMS
•THE PRISMS DISPERSE THE LIGHT RADIATION
INTO INDIVIDUAL COLORS OR WAVELENGTHS.
•THESE ARE FOUND IN INEXPENSIVE
INSTRUMENTS.
•THE BAND PASS IS LOWER THAN THAT OF
FILTERS & HENCE IT HAS BETTER
RESOLUTION.
•THE RESOLUTION DEPENDS UPON THE SIZE &
REFRACTIVE INDEX OF THE PRISM.
•THE MATERIAL OF PRISM IS NORMALLY GLASS

CONTD.
REFRACTIVE TYPE (DISPERSIVE TYPE)
•THE SOURCE OF LIGHT THROUGH ENTRANCE SLIT FALLS
ON A COLLIMATOR.
•THE PARALLEL RADIATION FROM COLLIMATOR ARE
DISPERSED INTO DIFFERENT COLORS OR WAVELENGTHS
& BY USING ANOTHER COLLIMATOR, THE IMAGES OF
ENTRANCE SLIT ARE REFORMED.

CONTD.
•THE REFORMED ONES WILL BE EITHER VIOLET,
INDIGO, BLUE, GREEN, YELLOW, ORANGE OR RED.
•THE REQUIRED RADIATION ON EXIT SLIT ARE BE
SELECTED BY ROTATING THE PRISM OR BY
KEEPING THE PRISM STATIONARY & MOVING THE
EXIT SLIT.

CONTD.

CONTD.
REFLECTIVE TYPE ( LITTROW TYPE):
•THE PRINCIPLE OF WORKING IS SIMILAR TO THE
REFRACTIVE TYPE EXCEPT THAT, A REFLECTIVE
SURFACE IS PRESENT ON ONE SIDE OF THE PRISM.
•HENCE THE DISPERSED RADIATIONS GETS REFLECTED &
CAN BE COLLECTED ON THE SOURCE OF LIGHT.

CONTD.

GRATINGS
•GRATING ARE THE MOST EFFICIENT ONES IN
CONVERTING A POLYCHROMATIC TO MONOCHROMATIC
LIGHT.
•AS A RESOLUTION OF ± 0.1𝑛𝑚 COULD BE ACHIEVED BY
USING GRATINGS, THEY ARE COMMONLY USED IN
SPECTROPHOTOMETER.
•GRATING ARE OF TWO TYPES:
•DIFFRACTION GRATING
•TRANSMISSION GRATING

CONTD.
DIFFRACTION GRATING
•MORE REFINED DISPERSION OF LIGHT IS OBTAINED BY MEANS OF
DIFFRACTION GRATINGS.
•THESE ARE THE RULINGS MASE ON SAMPLE MATERIAL LIKE GLASS,
QUARTS, OR ALKYL HALIDES, DEPENDING UPON THE INSTRUMENT.
•THESE CONSISTS OF LARGE NUMBER OF PARALLEL LINES
(GROOVES) ABOUT 15000-30000/INCH IS RULED ON HIGHLY
POLISHED SURFACE OF ALUMINUM.

CONTD.

CONTD.
•TO MAKE THE SURFACE REFLECTIVE, A DEPOSIT OF
ALUMINUM IS MADE ON THE SURFACE. IN ORDER TO
MINIMIZE TO GREATER AMOUNTS OF SCATTERED
RADIATION & APPEARANCE OF UNWANTED RADIATION
OF OTHER SPECTRAL ORDERS, THE GRATINGS ARE
BLAZED TO CONCENTRATE THE RADIATION INTO A
SINGLE ORDER.

CONTD.
TRANSMISSION GRATING
•IT IS SIMILAR TO DIFFRACTION GRATING, BUT
REFRACTION TAKES PLACE INSTEAD OF REFLECTION,
REFRACTION, PRODUCES REINFORCEMENT.
•WHEN RADIATION TRANSMITTED THROUGH GRATING
REINFORCES WITH THE PARTIALLY REFRACTED
RADIATION

CONTD.

FILTERS
•A DEVICE THAT ALLOWS LIGHT OF THE REQUIRED
WAVELENGTH TO PASS BUT ABSORBS LIGHT OF OTHER
WAVELENGTH WHOLLY OR PARTIALLY
•SUITABLE FILTER CAN SELECT A DESIRED WAVELENGTH
BAND
•A PARTICULAR FILTER MAY BE USED FOR A SPECIFIC
ANALYSIS,
ABSORPTION FILTERS
INTERFERENCE FILTERS

CONTD.
ABSORPTION FILTERS
• THESE FILTERS HAVE A BANDWIDTH THAT RANGES FROM 30-250𝑚𝑚
• THE ABSORPTION FILTERS CONSISTS OF COLORED GLASS OR A DYE SUSPENDED
IN GELATIN & SANDWICHED BETWEEN THE TWO GLASS PLATES
• THE COLORED GLASS FILTER HAS THE ADVANTAGE OF GREATER THERMAL
STABILITY.
• EACH INSTRUMENT IS PROVIDED WITH A SET OF 12 FILTERS TO COVER THE
RANGE FROM 390-700𝑚𝑚
• A NARROW SPECTRAL BAND CAN BE OBTAINED BY COUPLING CUT OFF FILTERS
WITH OTHER FILTERS BUT THIS COMBINATION DECREASES THE INTENSITY OF
LIGHT.

CONTD.
ADVANTAGES
•SIMPLE IN CONSTRUCTION
•CHEAPER, SELECTION OF FILTER
IS EASY
DISADVANTAGES
•LESS ACCURATE, INTENSITY OF
RADIATION BECOME LESS DUE TO
ABSORPTION BY FILTERS.

CONTD.INTERFERENCE FILTERS
•BASED ON INTERFERENCE PHENOMENON AT DESIRED
WAVELENGTH THUS PERMITTING REJECTION OF UNWANTED
RADIATION BY SELECTIVE REFLECTION & PRODUCING
NARROW BAND.
•IT CONSISTS OF A DIELECTRIC LAYER(EG:CAF2) BETWEEN 2
PARALLEL SILVER FILMS WHICH IS SANDWICHED BY GLASS
PLATE.
•IT HAS A BAND PASS OF 100-150Å & A PEAK TRANSMITTANCE OF
40-60%.

CONTD.
ADVANATGES
• INEXPENSIVE
• LOWER BAND PASS WHEN COMPARED TO
ABSORPTION FILTERS & HENCE MORE
ACCURATE
DISADVANTAGES
• PEAK TRANSMISSION IS LOW &
BECOMES 50 WHEN ADDITIONAL
FILTERS ARE USED TO CUTS OFF
UNDESIRED WAVE LENGTH.
• THE BAND PASS IS ONLY 10-15𝑐𝑚

 SAMPLE
CONTAINER/CELLS•THE CELLS OR CUVETTES ARE
USED FOR HANDLING LIQUID
SAMPLES.
•THE CELL MAY EITHER BE
RECTANGULAR OR CYLINDRICAL
IN NATURE.
UV REGION- QUARTZ OR FUSED
SILICA
VISIBLE REGION- GLASS

 DETECTORS
•DEVICE WHICH CONVERTS LIGHT ENERGY INTO ELECTRICAL
SIGNALS.
•THE TRANSMITTED RADIATION FALLS ON THE DETECTOR
WHICH DETERMINES THE INTENSITY OF RADIATION
ABSORBED BY SAMPLE.
3 TYPES:
•BARRIER LAYER CELL/PHOTOVOLTAIC CELL
•PHOTOTUBES/ PHOTO EMISSIVE TUBE
•PHOTOMULTIPLIER TUBE

CONTD.
REQUIREMENTS OF IDEAL DETECTORS:
•IT SHOULD GIVE QUANTITATIVE RESPONSE.
•IT SHOULD HAVE HIGH SENSITIVITY & LOW NOISE LEVEL
•IT SHOULD HAVE A SHORT RESPONSE TIME
•IT SHOULD PROVIDE SIGNAL OR RESPONSE
QUANTITATIVE TO WIDE SPECTRUM OF RADIATION
RECEIVED.

† BARRIER LAYER/PHOTOVOLTAIC
CELL
•THE DETECTOR HAS A THIN FILM METALLIC LAYER
COATED WITH SILVER OR GOLD & ACT AS ANOTHER
ELECTRODE.
•IT ALSO HAS A METAL BASE PLATE WHICH ACT AS
ANOTHER ELECTRODE.
•THESE 2 LAYERS ARE SEPARATED BY A SEMICONDUCTOR
LAYER OF SELENIUM.

CONTD.
•THIS CREATES A POTENTIAL
DIFFERENCE BETWEEN 2
ELECTRODES & CAUSES THE FLOW
OF CURRENT.
•WHEN IT IS CONNECTED TO
GALVANOMETER, A FLOW OF
CURRENT OBSERVED WHICH IS
PROPORTIONAL TO THE INTENSITY
& WAVE LENGTH OF LIGHT
FALLING ON IT.

CONTD.
• WHEN LIGHT RADIATION FALLS ON SELENIUM LAYER, ELECTRONS
BECOME MOBILE & ARE TAKEN UP BY TRANSPARENT METAL LAYER.
ADVANTAGES
• SIMPLE IN DESIGN DO NOT NEED EXTERNAL POWER SUPPLY.
• CHEAPEST & INEXPENSIVE.
DISADVANTAGES
• AMPLIFICATION OF DETECTOR IS NOT POSSIBLE
• LESSER RESPONSE OF DETECTOR WITH LIGHT OTHER THAN BLUE OR
RED LIGHT.

† PHOTOTUBES/ PHOTO EMISSIVE
TUBE
•CONSISTS OF A EVACUATED GLASS TUBE WITH A PHOTOCATHODE &
COLLECTOR ANODE.
•THE SURFACE OF PHOTOCATHODE IS COATED WITH A LAYER OF
ELEMENTS LIKE CESIUM, SILVER OXIDE OR MIXTURE OF THEM.
•WHEN RADIANT ENERGY FALLS ON PHOTOSENSITIVE CATHODE,
ELECTRONS ARE ATTRACTED TO ANODE CAUSING CURRENT TO
FLOW.
•MORE SENSITIVE COMPARED TO BARRIER LAYER CELL &
THEREFORE WIDELY USED

CONTD.

† PHOTOMULTIPLIER TUBES
•THE PRINCIPLE EMPLOYED IN THIS DETECTOR IS THAT,
MULTIPLICATION OF PHOTOELECTRONS BY SECONDARY
EMISSION OF ELECTRONS.
•IN A VACCUM TUBE A PRIMARY PHOTO-CATHODE IS FIXED
WHICH RECEIVES RADIATION FROM THE SAMPLE.
•SOME EIGHT TO 10 DYNODES ARE FIXED EACH WITH
INCREASING POTENTIAL OF 75-100V HIGHER THAN
PRECEDING ONE

CONTD.

CONTD.
• PHOTOMULTIPLIER IS EXTREMELY SENSITIVE TO LIGHT & IS BEST SUITED
WHERE WEAKER OR LOW RADIATION IS RECEIVED
• NEAR THE LAST DYNODE IS FIXED AN ANODE OR ELECTRON COLLECTOR
ELECTRODE
ADVANTAGES
• IDEAL FOR MEASURING WEAK LIGHT INTENSITIES
• FAST IN RESPONSE
DISADVANTAGES
• VERY INTENSE LIGHT CAUSE IRREVERSIBLE DAMAGE OF PHOTO EMISSIVE
SURFACE .HENCE SHOULD BE PROTECTED FROM DAY LIGHT OTHER STRINGER
RADIATIONS

† TYPES OF
SPECTROPHOTOMETER•A SPECTROPHOTOMETER CAN BE EITHER SINGLE BEAM
OR DOUBLE BEAM.
•IN A SINGLE BEAM INSTRUMENT (SUCH AS THE
SPECTRONIC 20), ALL OF THE LIGHT PASSES THROUGH
THE SAMPLE CELL.
• 𝐼 𝑂 MUST BE MEASURED BY REMOVING THE SAMPLE
•THIS WAS THE EARLIEST DESIGN & IS STILL IN COMMON
USE IN BOTH TEACHING & INDUSTRIAL LABS.

۞ SINGLE
BEAM
ADVANTAGES
•THIS TYPE IS CHEAPER.
•THE SYSTEM IS LESS
COMPLICATED
•LOW COST
•HIGH SENSITIVITY
CONTD.

۞ SINGLE BEAM INSTRUMENT

۞ DOUBLE BEAM INSTRUMENT
CONTD.

CONTD.
• IN A DOUBLE-BEAM INSTRUMENT, THE LIGHT IS SPLIT
INTO TWO BEAMS BEFORE IT REACHES THE SAMPLE.
•ONE BEAM IS USED AS THE REFERENCE, & THE SECOND
BEAM PASSES THROUGH THE SAMPLE.
•THE REFERENCE BEAM INTENSITY IS TAKEN AS 100%
TRANSMISSION (OR 0 ABSORBANCE), & THE
MEASUREMENT DISPLAYED IS THE RATIO OF THE TWO
BEAM INTENSITIES.

CONTD.
•MEASUREMENTS FROM DOUBLE BEAM INSTRUMENTS ARE
EASIER & MORE STABLE.
ADVANTAGES
•HIGH STABILITY BECAUSE REFERENCE & SAMPLE ARE
MEASURED VIRTUALLY AT THE SAME MOMENT IN TIME.
DISADVANTAGES
•HIGH COST, LOWER SENSITIVITY

۞ DOUBLE BEAM INSTRUMENT

CHOICE OF SOLVENT
•PROPERTIES OF IDEAL SOLVENT:
 IT SHOULD NOT ITSELF ABSORB RADIATIONS IN THE
REGION UNDER INVESTIGATIONS.
IT SHOULD BE LESS POLAR SO THAT IT HAS MINIMUM
INTERACTION WITH THE SOLUTE MOLECULE.
MOST COMMONLY: 95%ETHANOL
CHEAP, GOOD DISSOLVING POWER, DOES NOT ABSORB
RADIATION ABOVE 210𝑛𝑚.

CONTD.
SOLVENT WAVELENGTH (nm)
WATER 205
METHANOL 210
ETHANOL 210
ETHER 210
CHLOROFORM 245
CHLOROFLOUROCARBON 265
E
X
A
M
P
L
E
S

SOLVENT EFFECT
•POSITION & INTENSITY OF AN ABSORPTION BAND MAY
SHIFT WHEN THE SPECTRUM IS RECORDED IN
DIFFERENT SOLVENTS.
•DILUTE SAMPLE SOLUTION IS PREFERED FOR ANALYSIS.
•MOST COMMONLY USED SOLVENT: 95%ETHANOL
(BEACAUSE IT IS CHEAP & TRANSPARENT).

CONTD.
• 𝛼, 𝛽 −UNSATURATED CARBONYL COMPOUNDS SHOW 2
DIFFERENT SHIFTS.
•ABSORPTION BAND MOVES TO SHORTER WAVE
LENGTH(BLUE SHIFT) BY INCREASING THE POLARITY OF
THE SOLVENT.
•GROUND STATE IS MORE POLAR AS COMPARED TO THE
EXICTED STATE.

EFFECT OF CONECNTRATION, 𝑝𝐻 &
TEMPERATURE
• CONCENTRATION:
NORMALLY EFFECTS THE INTENSITY OF BAND
AT HIGH CONCENTRATION MOLECULAR INTERACTION MAY CAUSE
CHANGE IN POSITION OF ABSORPTION BAND
• 𝒑𝑯: EFFECT OF 𝑝𝐻 ON SPECTRA IS QUITE SIGNIFICANT & RESULT
PRIMARILY FROM SHIFTING OF EQUILIBRIUM BETWEEN 2 DIFFERENT
FORMS.
• TEMPERATURE: IT MAY EFFECT EQUILIBRIUM, WHICH CAN EITHER
CHEMICAL OR PHYSICAL.

ADVANTAGES & DISADVANTAGES
ADVANTAGES
•HIGH ACCURACY
•EASY TO HANDLE
•SMALL SAMPLE VOLUME IS
REQUIRED
DISADVANTAGES
•DOES NOT WORK WITH
COMPOUNDS THAT DO
NOT ABSORB LIGHT AT
THIS WAVE LENGTH

APPLICATIONS
• QUALITATIVE & QUANTITATIVE ANALYSIS:
USED FOR CHARACTERISING AROMATIC COMPOUNDS & CONJUGATED
OLEFINS.
TO FIND OUT THE MOLAR CONCENTRATION OF THE SOLUTE UNDER STUDY.
• DETECTION OF ISOMERS ARE POSSIBLE
• DETECTION OF IMPURITIES:
IMPORTANT METHOD TO DETECT IMPURITIES IN ORGANIC SOLVENTS
• CHLORIDE & FLUORIDE QUANTIFICATION
• DETERMINATION OF LEAD & COPPER IN WATER
• DETERMINATION OF SULPHUR DIOXIDE

REFERENCE
• INTRODUCTION TO SPECTROSCOPY BY
PAVIA.
• A TEXTBOOK OF ORGANIC CHEMISTRY
BY BAHL ARUN & BAHL B.S.
• HTTP://WWW.CHEM.UCALGARY.CA/COUR
SES/350/CAREY5TH/CH13/CH13-0.HTML
• WWW.YOUTUBE.COM
• WWW.SLIDESHARE.COM
• WWW.GOOGLE.COM
• HTTPS://WWW.SCIENCEDIRECT.COM/TOP
ICS/EARTH-&-PLANETARY-
SCIENCES/SPECTROSCOPY
• HTTPS://WWW2.CHEMISTRY.MSU.EDU/FA
CULTY/REUSCH/VIRTTXTJML/SPECTRPY
/UV-VIS/UVSPEC.HTM
• HTTPS://WWW.SCIENCEDIRECT.COM/TOP
ICS/CHEMISTRY/UV-VIS-SPECTROSCOPY
• HTTPS://WWW.RESEARCHGATE.NET/PUB
LICATION/46671265_ULTRAVIOLET-
VISIBLE_SPECTROSCOPY
• WWW.WIKIPEDIA.COM

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