Intrument (on Final) Flashcards
What is the name of the instrument (including detector) used today to provide positive identification of ion chemicals detected in environmental sampling
Ion chromatograph with conductance cell
What is the name of the instrument (including detector) used today to provide positive identification of metal chemicals detected in environmental sampling?
Atomic absorption spectrophotometer with photomultiplier tube
What is the name of the instrument (including detector) used today to provide positive identification of organic chemicals detected in environmental samples
Gas chromatograph with flame ionization detector
Explain chromatography
The separation of a mixture of compounds in its separate components. This makes it easier to identify (qualitative) and measure (quantitative) of sample components
What % of compounds can be analyzed with GC?
10-20%
What does a compound need to be to be analyzed by GC?
- sufficiently volatile
- all or some compounds of a compounds molecules are in vapour phase at 400-450c or below
- and that they don’t decompose at these temps
What are the components of of a GC?
- carrier gas
- sample injection system
- analytical column
- detectors
- temperature programming
What does the carrier gas in GC do?
- carries sample components through column detector
- flushes out sample components from GC(specifically column)
- cools and supports detector
What does the sample injection system do ?
- provides a means of introducing the sample into GC (carrier flow stream)
- provides a means of selecting the sample volume
What does the analytical column do in GC?
- heart of GC
- where separation occurs
- separates because the columns stationary/active phase has a different affinity/attraction for each of the components in the mixture
- carrier gas pushes sample through column, stationary active phase holds sample in column this results in components of the sample mixture eluting at different times
Explain how detectors work in GC?
As solutes elute from column, they interact with the detector.
- Interaction turned into electronic signal that is sent to data system
- mag of signal(y) vs time since injection = chromatogram
Explain how thermal conductivity detector (TCD) work in GC
tCD consists of an electrically heated wire or thermistor.
-temp sensing element dependant on thermal conductance of gas
-changes to thermal conductance such as when an organic molecule displaced some of the carrier gas will cause temp
Rise in element which is sensed as resistance
What are the advantages to TCD
1) nom specific and non destructive
2) moderate sensitivity and most rugged (idk what rugged means)
3) low cost low maintenance
4) broad response
Explain how flame ionization detection (FID)works
Consists of a hydrogen/air flame (very small and non luminous) and a collector plate.
- effluent from GC column passes through the flame, this breaks down organic molecules and produces ions (CHO+)
- ions collected on a biased electrode and produce an electrical signal
Advantages of an FID
1) extremely sensitive (specific to hydrocarbons)
2) large dynamic range
3) moderate cost and maintenance
4) high repeatability
Explain temperature programming for GC
A GC technique in which the temperature of the column is raised during the separation of the mixture.
-temp or pressure programming reduces elution (retention) times of strongly retained components and sharpen peaks
Explain liquid chromatography (LC)
Chromatographic methods in which analyte is distributed between liquid and mobile phase.
What is ion exchange chromatography (IEC)
An example of liquid chromatography that uses coulombic attraction between the charged sample and oppositely charged site on the stationary phase as the retention mechanism.
-generally buffers are used as the mobile phase since ion formation is favoured in aqueous solution and because they prevent unwanted pH changes
