INSTRUMENTATION PROPER part 2

– electrical energy from a detector is displayed

– the output of the detector is used to drive a sensitive meter directly without further amplification

the output of the detector is balanced against the output of a reference circuit

– numerical display of absorbance or converted values of concentrations

• All components are duplicated except the light source • The beams of light pass through different components but at the same time

Uses a light beam chopper (a rotating wheel) – with alternate silvered sections and cut out sections, inserted after the exit slit.

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.

It is used primarily to determine concentration of sodium, potassium or lithium since these alkali metals are easy to excite.

mixture of hydrogen and oxygen gas

– draws sample into the flame

creates a fine spray of sample solution to be fed into the flame of the burner

provides heat energy for excitation

– aspirate sample directly into the flame, the gases are passed at high velocity over the end of the capillary suspended in the solution

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

transmit yellow light (589 nm)

transmit violet light (767 nm)

transmit red light (761 nm)

The Internal Standard in Flame Photometry:

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.

Measures the amount of light absorbed by ground state atom

What light source does AAS use? CLUE: which produces a wavelength of light specific for the kind of metal in the cathode

modulates light beam coming from the hollow cathode lamp

uses flame to dissociate the chemical bonds and form free, unexcited atoms

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.