Absorbance (A)
Substance to absorb radiation; log of 1/T
Absorptivity
measure of absorption at a given wavelength
absorbtivity equals
absorbance divided by the product of concentration and path length
Beer's law
equation that states absorbance (A) is proportional to absorbtivity (a), path length(b) and concentration(c)
Blank
a solution without analyte
Infrared (IR) radiation
770-12,000 nm region on the spectrum
Molar absorptivity
1 molar solution @ 1 cm path length under prescribed conditions
Monochromatic
one wavelength
Photodetector
device to measure presence of light
Refraction
deflection from straight path
Ultraviolet (UV) radiation
180-390 nm region of the spectrum
Visible light
390-780 nm region of the spectrum
Wavelength
distance between 2 wave crests
Spectrophotometry
measurement of light intensity @ a selected wavelength
Transmittance
Amount of light allowed through a solution
Calculate reference transmittance
IR/I0
Calculate sample transmittance
IS/IR
Beer's law says concentration is proportional to
light absorption
Beer's law says that concentration is inversely proportional to
log of T
a" is constant under what conditions?
Temperature, pH, solvent, incubation time, same wavelength
Concentration is always reported to what decimal place?
Same decimal place as the standard concentration
What are the units for A?
None
Composition of reagent blanks should be
identical to the calibration of the unknown solution
Basic components of a spectrophotometer
light source, means to isolate wavelength, fiber optics, cuvettes, photodetector, readout device, computer
Most common light source is
tungsten light bulb
most common systems to isolating radiant energy
filter, prism, diffraction gratings
simplest type of filter
thin layer of colored glass
photo-detectors convert light into
electric signal
most commonly used photo-detector
photomultiplier tube (PMT)
Readout devices are a visual numerical display of
absorbence or concentration
Computers for spectrophotometry must do what 3 things?
digitally store calibration; automatically subtract blanks from calibrator; automatically calculate concentration