Instrumentation Flashcards
(19 cards)
What is chromatography?
Separation of a mixture of compounds into its separate components making it easier to ID and measure
To be considered for GC a sample must be?
- Sufficiently volatile
- have thermal stability
- be in a vapour state between 400-450*c
- and the compound doesn’t decompose at this temp
Components of a GC
- carrier gas
- sample injection system
- analytical column
- detectors
- temp programming
Purpose of a Carrier gas
- carries the sample components through the column to the detector
- cleans the column by flushing out sample components
- cools and supports the detector
Purpose of sample injection system
- provides means of introducing the sample
- selects sample volume
Purpose of analytical column
- heart if gc, where separation occurs
- separates components in the sample mixture b/c the columns stationary/active phase has a different affinity/attraction for each component
- carrier gas carries the sample through the column while the stationary active phase holds it in place
- combination of forces results in various components eluting at different times
Purpose of detector and 2 types
Detector coverts interaction with sample into an electronic signal that is sent to the data system. Signal plotted versus time of injection
Thermal conductivity detector-electrically heated wire
Flame ionization detector-effluent passes through flame, ions collected on biased electrodes producing a signal
Advantages of TCD
1-non specific or destructive
2-moderate sensitivity but most rugged
3-low cost and low maintenance
4-broad response
Advantages of FID
1-extremely sensitive (for hydrocarbons)
2-large dynamic range
3-moderate cost and maintenance
4-high repeatability
Purpose of temp programming
Temp increase reduces elution time and sharpens peaks
What is liquid chromatography
Chromatographic methods in which the analyze is distributed between a liquid mobile phase and either a solid or a liquid stationary phase
What is ion exchange IEC
A type of LC that uses coulombic attraction b/t the charged sample and the oppositely charged site on the stationary phase as the retention mechanism
What is ion exchange capacity
The number of exchange groups per unit of mass
Components of an IC
- Eluent
- pump
- injector
- guard column
- analytical column
- suppressor
- detector
- waste
What is atomic absorption spectrophotometry
Sees how an atom will absorb or emit a photon
- electrons move from ground state to excited state with addition of energy
- can move back to ground state through emission of a photon
Components of AA
- a line light source (hollow cathode lamps)
- chopper (alternates signal from hcl to sample bean)
- flame atomizer, nebulizer
- wavelength selector
- detector
- amplifier and read out device
Applications for atomic absorption
Metal analysis
Applications for GC
Almost any volatile sample
Organic liquids
Applications of IC
Used for separation of inorganic ions
