24 Questions
What is the primary function of the sintered glass disk in a chromatographic column?
To provide a smooth and even surface
What is the main principle of separation in column chromatography?
Differential affinity towards the stationary and mobile phases
What is the purpose of the tap at the bottom of a chromatographic column?
To allow for the elution of the sample
What is the term for the property of how well a component of the mixture sticks to the stationary phase?
Adsorption
What is the result of higher adsorption of a component to the stationary phase?
Slower movement through the column
What is the term for the property of how well a component of the mixture dissolves in the mobile phase?
Solubility
What is the benefit of using a sintered glass disk in a chromatographic column?
To prevent the adsorbent from passing out of the column
How many methods are there for packing a chromatographic column?
Two
What is the purpose of adding a small amount of pure sand above the stationary phase?
To prevent the disruption of the stationary phase
What is the advantage of using a separatory funnel containing the eluent in the column?
It ensures continuous flow of the eluent
What is the type of elution where a mixture of two solvents is used?
Gradual Elution
What is the purpose of preparing the slurry of adsorbent with the eluent?
To prepare the adsorbent for separation
What is the disadvantage of the dry packing method?
Any defect that is formed cannot be corrected
What is the ratio of adsorbent to eluent used in preparing the slurry?
1-3 or 1-4
What is the purpose of allowing the mobile phase to pass through the lower end of the column?
To remove the air bubbles in the column
What is the type of elution where a solvent or a mixture of solvents is used from the beginning to the end of the procedure?
Simple Elution
What is the recommended ratio of sample to adsorbent for achieving good separation?
1:50
What is the primary purpose of vaporization in gas chromatography?
To convert the sample into a gas phase
What is the role of the carrier gas in gas chromatography?
To carry the sample components through the column
What factor affects the flow rate of the eluent in chromatography?
Packing of the column and flow of the tap
What is the advantage of using a finer particle size of adsorbent in chromatography?
It increases the surface area of the adsorbent
What is the purpose of the chromatographic column in gas chromatography?
To separate the sample components
What is the result of using a ratio of 1:20 of sample to adsorbent in chromatography?
Good separation for a sample with 3 components
What is the advantage of using ethyl acetate with 5% ethanol as a mobile phase in chromatography?
It increases the polarity of the mobile phase
Study Notes
Column Chromatography
- A separation technique where the stationary bed is placed within a tube
- Stationary phase consists of very small particles or particles coated with a liquid
- Columns are glass cylinders with a tap at one end and a disk of sintered glass above it
- Benefits of sintered glass disk: smooth, even, and horizontal surface, prevents adsorbent from passing out of the column
Types of Column Chromatography
- Ordinary adsorption chromatography
- Gel filtration
- Ion exchange chromatography
Principles of Separation
- Differential affinities of components towards stationary and mobile phase
- Affinity is dictated by adsorption and solubility properties of molecules
- Higher adsorption to stationary phase = slower movement through column
- Higher solubility in mobile phase = faster movement through column
Methods of Packing the Column
- Dry packing method: introducing dry powder adsorbent with vibration or special piston
- Wet packing method: preparing slurry of adsorbent with eluent, then pouring into column
Wet Packing Method Steps
- Place small amount of mobile phase in column to remove air bubbles
- Prepare slurry of adsorbent with eluent (ratio 1:3 or 1:4)
- Pour slurry into column and allow it to settle
- Remove excess mobile phase
- Add small quantity of pure sand above stationary phase
- Introduce sample dissolved in minimum amount of eluent
- Open lower end to start separation
- Ensure continuous flow of eluent without drying the column
Types of Elution
- Simple Elution: using one solvent or a mixture from start to end
- Fractional or Step-wise Elution: changing mobile phase during procedure
- Gradual Elution: using a mixture of two solvents with gradual change
Factors Affecting Separation
- Size of sample to amount of adsorbent used (ratio 1:50 yields best separation)
- Size of column (length to diameter)
- Flow rate (1ml/min yields good separation)
- Choice of eluent
- Nature of sample and adsorbent
- Choice of adsorbent (activity and particle size)
Gas Chromatography (GC)
- Analytical technique for separating and analyzing volatile compounds
- Widely used in various fields (chemistry, pharmaceuticals, environmental science, food and beverage analysis, forensics)
Gas Chromatography Steps
- Sample Introduction: introducing sample containing mixture of compounds to be analyzed
- Vaporization: vaporizing sample before entering chromatographic system
- Separation: injecting vaporized sample into chromatographic column
- Mobile Phase (Carrier Gas): flowing carrier gas through the column, carrying sample components through the column
This quiz covers the methods of preparing chromatography columns, including dry packing and wet packing techniques, and their respective advantages and disadvantages.
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