Spectrometry Flashcards
Qualitative Analysis
- What is the 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
Major identification technique involves the interaction of the molecules of interest with ____________________
Electromagnetic Energy
Electromagnetic energy has properties of ________ and has ____________ and wavelengths
- Properties of waves
2. Has frequency
Frequency
- Hertz (hz) (1 cycle/second), kilohertz (1,000 cycles/sec)
2. Think of it as how quickly it gets to you
Wavelengths
- Meters
- Think of a typical wave going up and down
Example: standing on beach- every time waves hits you that’s the frequency. Distance between the peaks and trophy is the wavelength
1 micron (u)
10-6 meters
1 nanometer (nm)
10-9 meters (1 mu)
Most frequently seen in chemistry
1 angstrom (A)
10-10 meters
The Electromagnetic Spectrum: Radio, tv, radar VS x rays and gamma rays?
- Radio, tv, radar: lower frequency, long wavelengths
2. X rays and gamma rays: high frequency, short wavelengths
Wavelengths of the visible part of the spectrum in nanometers and in angstroms:
- 390 nm-750 nm
2. 4300 A (violet)- 7000 (red)
The shorter the wavelength, the ____________ the frequency and the ___________ the energy
- The greater the frequency
2. Higher the energy
Angstrom length (m)
10 (-10)
Nanometer Length
10 (-9)
Micrometer
10 (-6)
Millimeter length
10 (-3)
Centimeter length
10 (-2)
Meter length
1
As molecules are exposed to light (or other energy) they can absorb energy by:
- Electromagnetic excitation: electrons in the molecule goes from low energy state to a higher energy state
- Molecular vibrations: each compound has a natural vibration frequency
After a molecule is excited it can release the energy in various forms: (3)
- Heat ** most common result
- Rupture of molecule
- Re-emission of energy as altered electromagnetic energy (fluorescence)
The useful parts of the spectrum are UV, visible, and ________ radiation?
- Infrared radiation
UV and visible absorption:
- Electronic absorption (electrons in molecules are excited to a higher energy state). Then they relax and emit energy
Infrared absorption is due to:
- Vibrational energies of a molecule: bending, stretching, and rotation. (lower energy radiation)
Most molecules have chromophores that do what?
- Absorb light.
2. Chromophores may be certain molecular groups, such as phenyl groups or double bonds
Basic instrument components: (4)
- Energy source to produce radiation, usually UV or visible light by deuterium (UV) or tungsten lamp (visible)
- A system to select limited part of spectrum (prism or grating)
- Sample chamber
- Detector (photomultiplier tube-converts light energy to electrical energy)
For any compound, absorbency is proportional to: (2)
- The thickness of the cuvette (or light path)— thicker=more absorption
- Concentration of the compound
Absorption is dependent on the probability of radiation causing an electron being ___________ in the substance?
- Electron being excited.
2. If coefficient is small, substance poorly absorbs light
Light intensity across a cell is exponential decay equation?
Log 10= IO/I = K X L / 2.303
I= emergent light IO= incident light K= constant for any pure compound L= length of light path
Therefore, absorbance is proportional to the thickness of the cell (L)
Absorbance, extinction and optical density?
- All mean the same thing, that light is being absorbed
Beer- Lambert Law
A= E X L X C
If c is measured in moles x L (-1), and length (L) is in cm, then E has the units of L x moles (-1) x cm (-1). This is referred to as the molar absorption coefficient
Note: beer-lambert law assumes one wavelength
Using multiple wavelengths different compounds in a single solution can what?
- Both can be measured
- Example: Nad+ and NADH
- Wavelength that gives the best absorbance is usually chosen for compound measurement, however, when measuring NADH for example it is best to use the wavelength of maximum difference
