ANALYTICAL METHODS Flashcards
Distance between two successive peaks and expressed in terms of nanometer (nm)
Wavelength
Infrared region
> 700 nm
Visible spectrum
400-700 nm
Ultraviolet region
<400 nm
Wavelength is ________________ to Frequency and Energy
INVERSELY related
Measurement of light intensity in a narrower wavelength
Spectrophotometric measurement
Measurement of light intensity
Photometric measurement
Involves measurement of light transmitted by a solution to determine the concentration of the light-absorbing substances in the solution
Spectrophotometry
Simplest type of absorption spectrometer
Designed to make on measurement at a time at one specified wavelength
Single beam spectrophotometer
Instrument that splits the monochromatic light into two components:
1 beam passes through the sample, 1 beam passes through a reference solution or blank
Double beam spectrophotometer
Function of additional beam
Corrects for variation in light source intensity
Provides polychromatic light and must generate sufficient radiant energy or power to measure the analyte of interest
Light or Radiant Source
Emits radiation that changes in intensity;
Widely used in the labroatory
Type of Light source
Continuum source
Commonly used light source in the visibule and near infrared region
Example of Continuum source
Tungsten light bulb
Routinely used to provide UV radiation
Example of Continuum source
Deuterium lamp
Produces a continous source of radiation, which covers both the UV & Visible range
Example of Continuum source
Xenon discharge lamp
Emits limited radiation and wavelength
Type of Light Source
Line Source
Also used as light sources for spectrophotometry
LASER
Light Amplification by Stimulated Emission of Radiation
Tungsten Light Bulb
Mercury Arc
Visible Region
Deuterium lamp
Mercury lamp
Xenon lamp
Hydrogen lamp
Ultraviolet Region
Merst glower
Globar (Silicone carbide)
Infrared Region
Minimizes unwanted or stray light and prevents the entrance of scattered light into the monochromator system
Entrance Slit
Any wavelengths outside the band transmitted by the monochromator
Does not originate from the polychromatic light source
Causes Absorbance error
Stray light
Most common cause of loss of linearity at high-analyte concentration
Any wavelengths outside the band transmitted by the monochromator
Does not originate from the polychromatic light source
Causes Absorbance error
Stray light
Most common cause of loss of linearity at high-analyte concentration
Any wavelengths outside the band transmitted by the monochromator
Does not originate from the polychromatic light source
Causes Absorbance error
Stray light
Most common cause of loss of linearity at high-analyte concentration
Isolates specific or individual wavelength of light
Monochromator
Most commonly used Monochromator
Made by cutting grooves or slits into an aluminized surface of a flat piece of crown glass
Diffraction gratings
Controls the width of light beam
Allows only a narrow fraction of the spectrum to reach the sample cuvette
Exit Slit
Holds the solution whose concentration is to be measured
Cuvette
Aka Absorption Cell/ Analytical Cell/ Sample Cell
Holds the solution whose concentration is to be measured
Cuvette
Aka Absorption Cell/ Analytical Cell/ Sample Cell
Most commonly used cuvette
Can be used in 350-2000 nm
Alumina silica glass
Used for measurement of solution requiring visible and ultraviolet spectra
Kinds of Cuvets
Quartz/ Plastic
Used for measurement of solution requiring visible and ultraviolet spectra
Kinds of Cuvets
Quartz/ Plastic
Detects and converts transmitted light into photoelectric energy Detects the amount of light that passes through the sample in cuvet
Photodetector
Simplest detector; Least expensive; Temperature sensitive
Used for detecting and measuring radiation in the visible region
Kinds of Detector
Barrier layer cell/ Photocell/ Photovoltaic cell
Contains Cathode and Anode enclosed in a glass case
Kinds of Detector
Phototube
Most commonly used detector
Measures visible & UV regions
Kinds of Detector
Should never be exposed to room light because it will burn out
Photomultiplier Tube
Not as sensitive as PMT but with excellent linearity
Most useful as a simultaneous multichannel detector
Kinds of Detector
Photodiode
Displays output of the detection system
Meter or Read-out device
Mathematically establishes the relationship between concentration and absorbance
Beer’s Law
Concentration is ____ to Absorbed light
DIRECTLY
Concentration is ____ to Transmitted light
INVERSELY
Amount of light absorbed
Proportional to the INVERSE log of transmittance
Absorbance
Formula of Absorbance
A = abc
A = 2-log%T
350 - 430 nm
A: Violet
O: Yellow Blue
A for Absorbed, O for Observed