PHASES OF LAB TESTING (Spectrophotometer) Flashcards
Parts of the spectrophotometer
- Light source
- Entrance slip
- Monochromator
- Exit slip
- Cuvette
- Photodetector
- Read-out device
visible spectrum range
400 - 700 nm
invisible spectrum range
below 400 nm (ultraviolet)
above 700 ( infrared)
explain beer’s law
the concentration of a substance is directly proportional to the amount of light absorbed while inversely proportional to the logarithm of transmitted light
2 types of spectrophotometer
single or double beam
provides the incident light for the system
light source
most common source of light in the visible and IR regions
tungsten iodide lamp or incandescent
best light source for uv spectrum
deuterium lamps
mercury lamps
best light source for IR spectrum
silicon carbide
isolates light of a specific wavelength from the light source
monochromator
most commonly used monochromator and consist of manny parallel groves etched on the polished surface
difraction grating
kind of monochromator that refracts a narrow beam to the denser glass
quartz prism or glass prism
holds the solution to measured
cuvette (sample cell)
converts the transmitted radiant energy into a qualitative amount of eletrical energy
photodetectors
least expensive but still durable kind of photodetector
photocell (barrier-layer cell)
it is composed of a fil of light sensitive material, frequently selenium, on a plate of iron
photocell (barrier-layer cell)
type of detector mainly used in filter photometers
photocell (barrier-layer cell)
they are temperature sensitive and non linear in very high and low levels of illumination
photocell (barrier-layer cell)
contains a cathode and an anode in a glass case
phototube
like a photocell, it contains photosensitive material that gives of electrins when light energy strikes it (outside voltage is required)
phototube
detects and amplifies radiant energy
photomultiplier (PM) tube
in photomultiplier (PM) tube, when does electrons be transmitted?
when an incident light strikes the coated cathode
in photomultiplier (PM) tube, what are the series of anodes that give off many secondary electrons when hit by single electrons (emitted electrons are attracted to this)
Dynodes
the photomultiplier (PM) tube is how many times more sensitive than the phototube?
200x
photodetector used in instruments design to to be extremely sensitive to very low light levels and light flashes of very short duration
photomultiplier (PM) tube
photodetector where the absorption of radiant energy by a reversed-bias positive-negative (PN) junction diode prodices a photocurrent that is proportional to the incident radiant power
Photodiodes
photodetector useful in application where light levels are adequate because if their excellent linerity an speed
Photodiodes
