Download spectroscopy UV/VIS

UV/VIS
SPECTROSCOPY
APPLICATION OF ULTRAVIOLET/VISIBLE

For IDENTIFICATION AND ESTIMATION of
inorganic, organic and biomedical species

Is employed primarily for QUANTITATIVE
ANALYSIS

The function of this instrument is relatively
straightforward.
TYPE OF MEASUREMENT
The ultraviolet (UV) region scanned is normally
from 200 to 400nm, and the visible portion is
from 400 to 800nm.
 Uses a light source emitting in the visible
spectrum
 Two types :single beam and double beam
 Single beam : requires prior calibration using a
standard control
 Double beam : simultaneously measures the
sample and the standard control

The most commonly used solvents are water,
ethanol, hexane and cyclohexane.
 Absorbance may be presented as
TRANSMITTANCE (T=I/I0) or ABSORBANCE
(A= log I0/I)
 The wavelength of maximum absorbance is a
characteristic value, designated as λmax



The intensity of the reference beam, which should have suffered little
or no light absorption, is defined as, I0
The intensity of the sample beam is defined as I
SINGLE BEAM
All the light passes through the sample
 Measure intensity of the incident light
 Less expensive
 Less complicated

DOUBLE BEAM
Light source split into two separate beams
 Passes through the sample
 Used for reference

SINGLE BEAM
DOUBLE BEAM
OPERATING PRINCIPLE
Measures a material light reflection, transmission
or absorbtion properties.
 Measure the spectrum of a compound.
 Operates by passing a beam of light through a
sample.
 Measuring the intensity of light reaching a
detector.
 Spectrum is a graph of intensity of absorbed or
emitted radiation by sample verses frequency or
wavelength

TEST RELATED
Used in analytical chemistry for the quantitative
determination of different analytes, such as
transition metal ions, highly conjugated organic
compounds, and biological macromolecules.
 Spectroscopic analysis is commonly carried out
in solutions but solids and gases may also be
studied.

TEST RELATED
Variables must be controlled :
 The nature of the solvent
 The pH of the solution
 Temperature
 High electrolyte concentrations
 The presence of interfering substances can
influence the absorption spectrum

TEST RELATED
DMF (dimethylformamide)
 THF (tetrahydrofuran)
 ACETONE
 H20
 ETHANOL

TEST RELATED
used in the semiconductor industry to measure
the thickness and optical properties of thin films
on a wafer.
 UV-Vis spectrometers are used to measure the
reflectance of light
 Can be analyzed via the Forouhi-Bloomer
dispersion equations to determine the Index of
Refraction (n) and the Extinction Coefficient (k) of
a given film across the measured spectral range.

FILM ON WATER
SAMPLE OF TEST
The sample compartment provides a light-tight
environment that limits the addition of stray
radiation.
 Samples are normally in the liquid or solution
state, and are placed in cells constructed with
UV/Vis transparent materials, such as quartz,
glass, and plastic.

SAMPLE OF TEST
From left to right (with path lengths in parentheses): rectangular
plastic cuvette (10.0 mm), rectangular quartz cuvette (5.000 mm),
rectangular quartz cuvette (1.000 mm), cylindrical quartz cuvette
(10.00 mm), cylindrical quartz cuvette (100.0 mm).
SAMPLE OF TEST
If we need to monitor an analyte’s
concentration over time, it may not be possible
to physically remove samples for analysis.
 Examples :
 Monitoring industrial production lines or waste
lines
 Monitoring a patient’s blood
 Monitoring environmental systems

SAMPLE OF TEST
Fibre optic probe
ADVANTAGES
rapid means of analysis
 can provide very high precision and accuracy.
 It is useful for a wide variety of chemicals, and
it is non-destructive.
 It can be used both quantitatively and
qualitatively on pure substances.

DISADVANTAGES
limited use in analysing mixtures, due to the
addition of absorbance.
 It requires special equipment (a UV light
source and UV-transparent sample holders, for
example)
 it is not selective for compounds if they absorb
at the same wavelength.

ADVANTAGES
DISADVANTAGES
System lies in the
simplistic design of
the instrument. The
shutter is the only
moving component
of a UV-VIS
spectrometer.
LIGHT SOURCE
No single lamp
emits all the light
wavelengths
necessary for
analysis. Changing
the lamp is a timeconsuming process.
very quick process
compared to other
methods of sample
detection, such as
HPLC. This rapid
analysis is achieved
only through proper
calibration.
CALIBRATION
require frequent
calibrations to
retain the accuracy
and precision of the
instrument.
requires the
knowledge of the
type of sample
being analysed.
technique is nondestructive to the
sample and has a
high sensitivity for
detecting organic
compounds.
SENSITIVITY
user trying to detect
the sample using
too wide of a
wavelength range
or by poor
instrument design,
cause stray light to
occur.