INSTRUMENTATION PROPER part 2 Flashcards
(43 cards)
– electrical energy from a detector is displayed
READ-OUT DEVICES
– the output of the detector is used to drive a sensitive meter directly
without further amplification
Direct reading system
the output of the detector is balanced against the output of a reference
circuit
Null Point System
– numerical display of absorbance or converted values of concentrations
Digital Read-out
- All components are duplicated except the light source
- The beams of light pass through different components but at the same time
Double Beam-In-Space
Uses a light beam chopper (a rotating wheel) – with alternate silvered sections and cut out
sections, inserted after the exit slit.
Double Beam-In-Time
FLAME PHOTOMETRY / FLAME EMISSION SPECTROPHOTOMETRY / FILTER PHOTOMETRY:
PRINCIPLE:
It involves the measurement of emitted light when electrons in an atom become ______ by ________
produced by the flame. When these electrons return to their ______ they emit ______ characteristic
of the ions present.
excited
heat energy
ground state
light
It is used primarily to determine concentration of sodium, potassium or lithium since these alkali metals
are easy to excite.
FLAME PHOTOMETRY / FLAME EMISSION SPECTROPHOTOMETRY / FILTER
PHOTOMETRY
mixture of hydrogen and oxygen gas
GASES
– draws sample into the flame
Aspirator
creates a fine spray of sample solution to be fed into the flame of the
burner
Atomizer (Nebulizer)
provides heat energy for excitation
Flame
– aspirate sample directly into the flame, the gases are passed at
high velocity over the end of the capillary suspended in the solution
Total Consumption Burner
involves the gravitational feeding of solution through a restricting capillary into an area of high velocity gas flow where small droplets are produced and passed into the flame
Premix Burner
transmit yellow light (589 nm)
Na filter
transmit violet light (767 nm)
K filter
transmit red light (761 nm)
Lithium
The Internal Standard in Flame Photometry:
Uses Lithium or Cesium
ATOMIC ABSORPTION SPECTROPHOTOMETRY (AAS)
PRINCIPLE:
the element is __________ in the flame but merely ____ from its chemical bond and placed in an __________. The atom, at a lower energy level, _________. The light source emits radiant energy to be absorbed by the element.
not excited
dissociated
unexcited state
absorbs light
Measures the amount of light absorbed by ground state atom
ATOMIC ABSORPTION SPECTROPHOTOMETRY (AAS)
What light source does AAS use?
CLUE:
which produces a wavelength of light specific for the kind of metal in the cathode
hollow cathode lamp
modulates light beam coming from the hollow cathode lamp
MECHANICAL ROTATING CHOPPER
uses flame to dissociate the chemical bonds and form free, unexcited atoms
BURNER
gases are mixed and the sample is atomized before entering the flame and the large droplets go to waste and not in the flame. It has less noisy signals with longer pathlength and greater absorption and sensitivity.
Pre-mix burner
