Spectrometry Flashcards
Qualitative analysis
- Identity or properties of the drug or substance
- Separation, isolation or purification required in most cases, but not all
Quantitative analysis
How much substance is present
Frequency
- How quickly light gets to you
- hertz (Hz) (1 cycle/sec)
- kilohertz (1000 cycle/sec)
Wavelength
distance in meters between peak and trough
Electromagnetic energy properties
waves, frequency, and wavelength
1 micron = X meters
10^-6 meters
1 nanometer = X meters
10^-9 meters (1 m)
1 Angstrom = X meters
10^-10 meters
Wavelengths of the visible part of the spectrum in nanometers
390 - 750 nm
Wavelengths of the visible part of the spectrum in angstroms
4300 A (violet) - 7000 A (red)
The shorter the wavelength, the _____ the frequency and the ____ higher the energy
The shorter the wavelength, the greater the frequency and the higher the energy.
Short wavelength = high energy = blue/violet light
As molecules are exposed to light (or other energy) they can absorb energy by:
- electromagnetic excitation
- molecular vibrations
electromagenetic excitation
electrons in the molecule goes from a low energy state to a higher energy state)
molecular vibrations
each compound has natural vibration frequency
Simplest molecule of 2 atoms bound together, we can excite the electrons and they can vibrate, stretch, and bend
After a molecule is excited it can release the energy in various forms
- heat (most common!)
- rupture of the molecule (washing a red shirt fades to pink when hung in the sun to dry)
- re-emission of energy as altered electromagnetic energy (fluorescence)
The useful parts of the spectrum are:
- UV
- visible
- infrared radiation
UV and visible absorption
electronic absorption (electrons in molecules are excited to a higher energy state)
Infrared absorption
due to vibrational energies of a molecule: bending, stretching, and rotation (cannot see infrared)
chromophores
Most molecules have chromophores that absorb light. Chromophores may be certain molecular groups, such as phenyl groups or double bonds.
chromosphere
Parts of the molecule that allow it to absorb light/radiation.
Ie: phenyl group on a drug can be analyzed by UV radiation
Basic Instrument Components of a Heme Oximeter
1) Energy source to produce, radiation (a deuterium [uv] or tungsten lamp [visible])
2) A system to select limited part of the spectrum (prism or grating)
3) Sample chamber
4) Detector
prisms
Prisms slow down wavelengths of different waves of white light and reflect the colors of the rainbow
Detector or Photomultiplier Tube
converts light energy to electrical energy
For any compound, absorbance is proportional to:
- thickness of the cuvette (or light path)
- the concentration of the compound
absorption
- Absorption is dependent on the probability of radiation causing an electron being excited in the substance.
- If coefficient is small, substance poorly absorbs light
Light intensity across a cell
is an exponential decay
Light intensity calculation
I=Ioe-kL
I = emergent light Io = incident light k = a constant L = length of light path
absorbance
log of the ratio of incident to emergent light
Io/I
absorbance is referred to as
absorbance, extinction, or optical density
