OTHER TYPES SPECTROPHOTOMETRY Flashcards
OTHER TYPES SPECTROPHOTOMETRY
● Double beam spectrophotometry
● Flame emission spectrophotometry
● Atomic absorption spectrophotometry
● Light is directed forward in two directions by a rotating chopper.
DOUBLE BEAM SPECTROPHOTOMETRY
One light path is directed forward the_____ cuvette, while, simultaneously the other is directed towards the_____ cuvette
DOUBLE BEAM SPECTROPHOTOMETRY
sample
reference
● The intensity of the two light beams is then measured by one or two photodetectors.
● The sample beam is then compared to that of the reference beam
Double beam spectrophotometer
TWO FUNDAMENTAL INSTRUMENT DESIGNS of Double Beam Spectrophotometer
Double Beam in Space
Double Beam in Time
uses two photo detectors (one for the sample and one for the reference beam)
sample and reference are measured simultaneously and the signal from the reference is subtracted from the transmittance of light of the sample
Double Beam in Space
one photo detector and alternately passes the monochromatic radiation through the sample cuvette to the reference cuvette using a chopper
each beam consisting of a pulse of radiation breaks up separated in time by a dark interval
Double Beam in Time
■ device consist of circular disk
■ is a rotating sector of mirror that breaks up or rotates radiation beams
Chopper
Chopper
⅓ of the disk is_____;
⅓ is________ and the remaining
⅓ is______
opaque
transparent
mirrored
Splits the monochromatic beam of light into 2 beams of equal intensities
Chopper
measures Group 1 Metals that contains plus 1 in charge
FLAME EMISSION SPECTROPHOTOMETRY
Principle: “Involves measurement of electromagnetic radiation emitted by the excited atoms in the flame”
measures light emitted by excited atoms
FLAME EMISSION SPECTROPHOTOMETRY
The measurement of emitted light when electrons in an atom become excited by heat energy produced by the flame and returns to ground state.
Flame emission spectrophotometry
are no longer routinely used in clinical chemistry due to the development of iron selective electrodes ( Sodium, Potassium and Lithium)
Flame Photometers
Components of flame emission spectrophotometry
Atomizer
Flame
¡ breaks up the solution into finer droplets so that the atom will absorb heat energy from the flame and get excited
Atomizer
convert the analyte of the liquid sample into vapour state (breaks the chemical bonds to produce atoms)
source of energy that will be absorbed by the atoms to enter the excitation state
Flame
Types of burners
Total consumption burners
Premix burner
§ the sample is aspirated directly into the flame. All the sample that enters the capillary will enter the flame regardless of the droplet size
Total consumption burners
ADVANTAGE:
▪ Design is simple and entire sample is consumed
DISADVANTAGE:
▪ Uniform and homogeneous flame is not obtained
▪ Droplet size vary, leading to fluctuations in the flame intensity
Total consumption burners
§ aspirated sample, fuel and oxidant are thoroughly mixed before reaching the burner opening and then entering the flame
Premix burner
Only a small portion (about 5%) of the sample reaches the flame in the form of small droplets and is easily decompose.
Premix burner
▪________ is non-turbulent, noiseless and stable.
▪ Easy decomposition which leads to high atomization
Premix burner
Flames in flame emission
Potassium K
Violet
Flames in flame emission
Lithium Li
Red
Flames in flame emission
Calcium Ca
Orange
Flames in flame emission
Sodium Na
Yellow
Flames in flame emission
Barium Ba
Lime green
INTERFERENCE FILTER
■ Transmits only yellow light (589 nm)
○ Na filter
INTERFERENCE FILTER
■ Transmits only violet light (367 nm)
K filter
INTERFERENCE FILTER
■ Transmits only red light (767 nm)
Lithium
● Group two metals
● 2 (+) charges
● NOT EASILY EXCITED but can ABSORB light!!!
ATOMIC ABSORPTION SPECTROPHOTOMETRY
Principle ○ Measures concentration of element by detecting absorption of electromagnetic radiation by atoms
It is sensitive and precise and routinely used to measure concentration of Trace metals that are not easily exciting.
ATOMIC ABSORPTION SPECTROPHOTOMETRY
Atomic absorption spectrophotometry
The elements are not excited but they are dissociated from their chemical bonds and placed in the_______, _______
unionized, unexcited ground state
Atomic absorption spectrophotometry
Components (6)
Light source
Mechanical rotating chopper
Burner
Monochromator
Detector
Read-out device
Atomic absorption spectrophotometry
Light Source :
hollow cathode lamp
AAS
modulates light beam coming from the light source
Mechanical Rotating Chopper
AAS
Uses flame to dissociate the chemical bonds and form free unexcited atoms
Burner
AAS
selects the desired wavelength from a spectrum of wavelength
Monochromator
○ It measures the radiation emitted by the excited atoms that is related to concentration
Flame Emission
○ It measures the radiation absorbed by the unexcited atoms that are determined
Atomic Absorption
depends only upon the number of unexcited atoms, the absorption intensity is not directly affected by the temperature of the flame.
Atomic absorption
in contrast being dependent upon the number of excited atoms, is greatly influenced by temperature variations.
flame emission intensity
ATOMIC ABSORPTION SPECTROPHOTOMETRY
● Interferences:
■ _________ - Situation at which the flame could not dissociate the sample into neutral atoms
■ _________ - Situation at which atoms in the flame become excited and emits energy
Chemical
Ionization
