light source that exits narrow bands of energy at well-defined places
in the spectrum (UV and visible)
mercury vapor lamp
Consists of a gas-tight chamber containing anode, a cylindrical cathode, and inert gas such as helium and argon.
hallow cathode lamp
Minimizes unwanted or stray light and prevents the entrance of scattered light into the monochromator system
entrance slit
refers to any wavelength outside the band transmitted by the monochromator, it causes absorbance error
- limits the maximum absorbance that a spectrophotometer can achieve.
- is the most common cause of loss linearity at high-analyte concentration.
stray light
Isolate specific wavelength of light.
monochromator
light radiation of a single wavelength
monochromator light
• Wedge-shaped pieces of glass, quarts, NaCI, or some other material that allows transmission of light
• Disperse white light into a continuous spectrum of colors based on variation of refractive index for different wavelength
• Can be rotated, allowing only the desired wavelength to pass through an exit slit
prism
• Has small grooves cut at such an angle that each groove behaved like a very small prism
• Separates white light into various color component
• Based on the principle that wavelengths are bent as they pass a sharp corner
gratings
• Are simple, least expensive not precise but useful.
• They are made by placing a semi-transparent silver films on both sides of a dielectric such as magnesium fluoride.
filters
2 types of filters:
colored filters
interferece filters
• Made of glass that absorb some portion of the electromagnetic spectrum and transmit others
• Light energy is absorbed by dye compounds on the glass and is dissipated as heat
• Band pass in 35 to 50 nm or more
colored filters
• Utilizes the wave character of light to enhance the intensity of the desired wavelength by constructive interference and reflection
• Band pass is 10 to 20 nm
interferece filters
• Produces linear spectrum and therefore maintaining a constant band pass which is simple.
• Can be used in the regions of spectrum where light energy is absorbed by glass prism
interferece filters
• It controls the width of light beam (bandpass) - allows only a narrow fraction of the spectrum to reach the sample cuvette.
• Spectral purity of the spectrophotometer is reflected by the bandpass - the narrower the bandpass, the greater the resolution.
exit slit
the range of wavelengths between the points at which transmittance is one half peak transmittance
band pass
• Used to hold the solution in the instrument whose concentration is to be measured.
• It is made of glass, quartz or plastic.
analytical cell or cuvette
types of cuvettes: (3)
borosilicate glass cuvette
quartz or plastic
alumina silica glass
type of cuvette: for solution that do not etch glass
borosilicate glass cuvette
does not absorb UV radiation at wavelength below 320 nm
quartz or plastic
- good for 340 nm and above (visible)
- Most commonly used among the cuvettes
alumina silica glass
Electron tube amplifying a current that can convert transmitted energy into an
equivalent amount of electrical or
photoelectric energy.
photodetectors
kinds of detectors: (4)
barrier layer cell (photocell)
phototube (photoemissive tube)
photomultiplier (PM) tube
photodiode
• Simplest detector, least expensive;
temperature sensitive
• Composed of selenium on a plate of iron covered with transparent layer of silver
• It requires an external voltage source but utilized internal electron transfer for current production - low internal resistance
• It is used in filter photometers with a wide bandpass
barrier layer cell
• It contains cathode and anode enclosed in a glass case.
• It has a photosensitive material that gives off electron when light energy strikes it.
• It requires external voltage for operation.
phototube
