3.16 - Chromatography Flashcards
If the Stationary Phase is a Liquid, Separation occurs by ____ ?
Relative Solubility
Uses of GC (Gas Chromatography)?
Separate Components - particularly volatile ones
low boiling points
Stationary Phase: GC (Gas Chromatography)?
Solid or Solid coated with Liquid packed into a capillary tube
Limitations of GC (Gas Chromatography)?
|> Many similar compounds have the same Retention time
|> Peaks of higher concentrations can hide peaks of lower concentrations
|> Unknown compounds have no Reference values
Stationary Phase: CC (Column Chromatography)?
Solid packed in a glass column
Properties that affect Strength of Adsorption & Relative Solubility?
Charge
Polarity
Chirality
Size
Mobile Phase: CC (Column Chromatography)?
Liquid solvent (eluent) moves down the column
Uses of TLC (Thin Layer Chromatography)?
Check Purity of Compounds
Stages of GC-MS
|> GC is first used to separate components in the mixture
|> Each separated component is directed to the mass spectrometer in turn
|> Each mass spectrum can be analysed or compared with a spectral database
|> Each component can be identified
|> Quantity of each component can be determined
Stages of GC (Gas Chromatography)?
|> Mixture is injected into Gas chromatograph where it vapourises
|> Carrier gas flushes mixture through the column
|> Components slow down as they interact with the stationary phase
|> Each component leaves the column at a different time & is detected
Stages of CC (Column Chromatography)?
|> Fill a Glass tube w/ stationary phase, held by a filter or mineral wool plug
|> Cover all powder in solvent
|> Dissolve the mixture to be sampled in minimum amount of solvent
|> Place mixture on top of solid phase
|> Run mixture through column by opening tap & adding solvent
|> Time taken for each component to reach end of column is recorded = retention time
Stages of TLC (Thin Layer Chromatography)?
|> Dissolve small sample of mixture in solvent
|> Draw pencil line @ bottom of TLC plate
|> Place small spot of sample on pencil line, allow to dry
|> Place TLC plate in a beaker containing small amount of solvent - below pencil line
|> Cover with a lid
|> Allow solvent to rise
|> Once solvent has risen almost to top of plate, remove & mark solvent front
|> Use a locating agent to make compounds visible
Mass Spectrometry is used to ____ the separated components by ____ ?
Identify
Comparing Mass spectra to a Database
Examples of Locating Agents?
|> Ninhydrin
|> UV Light
|> I₂
|> KMnO₄
Why is a Locating Agent useful for TLC (Thin Layer Chromatography)?
Make Compounds Visible)
Advantages of CC (Column Chromatography)?
Fairly large amounts can be separated
Advantages of TLC (Thin Layer Chromatography) compared to Paper Chromatography?
|> Better Resolution
|> Faster
|> Smaller amounts of Samples needed
Mobile Phase: GC (Gas Chromatography)?
Unreactive Gas passes through column @ high pressure & high temp
If the Stationary Phase is a Solid, Separation occurs by ____ ?
Adsorption
The Stronger the Adsorption to the Stationary ____ phase the ____ the component moves through the ____ phase?
Solid
Slower
Mobile
What is a Mass Spectrum?
Plot of Relative Abundance against Mass to Charge Ratio (m/z)
In a Mass Spectrum, Peak with Highest m/z is due to the ____ ?
Molecular ion
M⁺ Peak
Gives Mr
Limitations of TLC (Thin Layer Chromatography)?
|> Unknown compounds have no Rf values for reference
|> Similar compounds have similar Rf values
|> Can be difficult to find a solvent that gives good separation
Define: Rf
Rf = Distance moved by spot/Distance moved by solvent
Uses of CC (Column Chromatography)?
Separate & Collect larger quantities of compounds of a mixture
Why must the Solvent be Below the Pencil line in TLC (Thin Layer Chromatography)?
Prevent samples Dissolving into Solvent
The Greater the Solubility in the Stationary ____ phase, the ____ the component moves through the ____ phase?
Liquid
Slower
Mobile
Define: Adsorption
Process by which a solid holds molecules to its surface
Define: Retention time
Time taken for each component to reach the end of the column from injection to detection
What can Chromatography be used for?
Separating & Identifying components in a mixture
Two Phases of Chromatography?
Moving Phase
Stationary Phase
Define: Phase
A state,
such as a Solid, Liquid or Gas
Stationary Phase: TLC (Thin Layer Chromatography)
Solid on a Glass Support
Mobile Phase: TLC (Thin Layer Chromatography?
Liquid Solvent which moves vertically up the plate
What does separation depend on?
Balance between Solubility in Moving Phase
&
Retention in the Stationary Phase
Uses of GC-MS?
|> Forensic & Drug Analysis
|> Environmental Sampling
|> Airport Security - Drugs & Explosives
|> Space Probes
What does the No. of Peaks of a Gas Chromatograph represent?
Number of Components in the mixture
The Rate of Movement of a Component is recorded as ____ ?
an Rf value
or
a Retention time
What can Rf values or Retention times be used for?
Identifying a Compound
Why does TLC (Thin Layer Chromatography) require a Lid?
Avoid Evaporation of Solvents
What is the Area under each Peak of a Gas Chromatograph proportional to?
The amount of a component in the mixture
Gas Chromatography can be combined with ____ to improve identification?
Mass Spectrometry
Gas Chromatography is used to ____ components but is not good @ ____ ?
Separate
Identifying
What is the Solvent Front?
Distance travelled up Plate by Solvent
Why must a Pencil be used on TLC (Thin Layer Chromatography) plates?
Pen would dissolve into solvent & affect result
