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Clinical Instrumentation - Photometry
Clinical Instrumentation Photometry
20
Medical
Undergraduate 2
03/24/2012

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Cards

Term
-Photometry
Definition

-used most frequently in clincal chemistry

-consists of absorbance or reflectance technology

-uses color and color variation to determine concentration

Term
-Fundamentals of Color
Definition

-light is a type of radiant energy

-travels in waves

-distance between waves is the wavelength of light

Term
-Visible Energy
Definition

-human eye response to wavelengths between 380-750 nm

-technology can measure shorter (UV) and longer (IR)

-wavelength determines the color

Term
-Visible Spectrum
Definition

-red

-orange

-yellow

-green

-blue

-violet

Term
-Wavelengths
Definition

-infrared 900

-red 650

-orange 610

-yellow 600

-green 540

-blue 475

-violet 425

-ultra violet 350

Term
-Beer's law
Definition
-the concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the logarithm of the transmitted light
Term
-%T
Definition

-the amount of light that passes through a colored substance (transmittance)

-will not plot a straight line on a graph

Term
-Spectrophotometers 
Definition
-used to measure the light transmitted by a solution to determine the light absorbing substance in the solution
Term
-Spectro Setup
Definition
light source -> entrance slit -> grating/monochromator -> exit slit -> cuvette -> photodetector
Term
-Spectro Light Source
Definition
-most common is incadescent tungsten or tungsten-iodide lamp
Term
-Monochromator
Definition

-isolated individual wavelengths

-uses the width of entrance and exit slits

Term
-Spectral Bandpass
Definition

-the range of wavelengths

-the smaller the better, based on slit width

Term
-Types of Monochomators
Definition

-interference filter

-prism

-diffraction gratings

Term
-Interference Filter
Definition
-two pieces of glass, mirrored on one side that are separated by transparent spacer
Term
-Prism
Definition

-narrow bean of light is focused on prism and refracted as it enters the more dense glass

 

Term
-Diffraction Gratings
Definition

-most commonly used monochromator

-many parallel grooves etched onto a polished surface (15,000 - 30,000/inch)

Term
-Photodetector Types
Definition

-Barrier-layer Cell or Photocell

-Phototube

-Photomultiplier Tube

Term
-Barrier-Layer Cell
Definition

-lease expensive

-durable, but temp sensitive

-light passes through selenium layer and excites electrons into the silver layer, which flow towards the iron forming barrier

Term
-Phototube
Definition

-contain a negative charged cathode and a positive charged anode in a glass case

-cathode is made of rubidium or lithium, emits electrons when exposted to light

-electrons jump to the positive anode, collected and returned through a measurable circuit

Term
-Photomultiplier Tube
Definition

-light hits a coated cathode emitting electrons

-electrons attracted to a series of anodes known as dynoes

-each then has a successively higher voltage

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