Podcast
Questions and Answers
What is the primary purpose of choosing an appropriate polarity index for a solvent?
What is the primary purpose of choosing an appropriate polarity index for a solvent?
How is the polarity of a solvent mixture typically characterized in relation to its application?
How is the polarity of a solvent mixture typically characterized in relation to its application?
What does a change of 2 units in the polarity index indicate in terms of a solute's capacity factor?
What does a change of 2 units in the polarity index indicate in terms of a solute's capacity factor?
What is usually true about optimizing a solvent's composition in practice?
What is usually true about optimizing a solvent's composition in practice?
Signup and view all the answers
What is the starting point in choosing a polarity index for chromatographic analysis?
What is the starting point in choosing a polarity index for chromatographic analysis?
Signup and view all the answers
What is used as the stationary phase in reverse phase chromatography?
What is used as the stationary phase in reverse phase chromatography?
Signup and view all the answers
How does the polarity of the mobile phase affect its strength in chromatography?
How does the polarity of the mobile phase affect its strength in chromatography?
Signup and view all the answers
Which solvents are typically used as the mobile phase in reverse phase chromatography?
Which solvents are typically used as the mobile phase in reverse phase chromatography?
Signup and view all the answers
What happens to the retention time as the non-polarity of the mobile phase increases?
What happens to the retention time as the non-polarity of the mobile phase increases?
Signup and view all the answers
Which of the following is NOT a characteristic of mobile phase in reverse phase chromatography?
Which of the following is NOT a characteristic of mobile phase in reverse phase chromatography?
Signup and view all the answers
Which substance has the highest polarity based on the given information?
Which substance has the highest polarity based on the given information?
Signup and view all the answers
What is the primary characteristic of the stationary phase in partition chromatography?
What is the primary characteristic of the stationary phase in partition chromatography?
Signup and view all the answers
In the context of polarity, which of the following is arranged correctly from highest to lowest polarity?
In the context of polarity, which of the following is arranged correctly from highest to lowest polarity?
Signup and view all the answers
What is the mobile phase in partition chromatography?
What is the mobile phase in partition chromatography?
Signup and view all the answers
What is the most common type of chromatography mentioned?
What is the most common type of chromatography mentioned?
Signup and view all the answers
What factor does not influence separation in the context of ionic drugs?
What factor does not influence separation in the context of ionic drugs?
Signup and view all the answers
Which of the following conditions would likely enhance the separation of ionic drugs?
Which of the following conditions would likely enhance the separation of ionic drugs?
Signup and view all the answers
Which parameter is crucial for the separation of both acidic and basic drugs?
Which parameter is crucial for the separation of both acidic and basic drugs?
Signup and view all the answers
What can be considered a viable strategy to enhance separation if a mixture contains ionic drugs?
What can be considered a viable strategy to enhance separation if a mixture contains ionic drugs?
Signup and view all the answers
Which of the following describes an element affecting drug separation that is not commonly acknowledged?
Which of the following describes an element affecting drug separation that is not commonly acknowledged?
Signup and view all the answers
What is the purpose of a sample splitter in the given context?
What is the purpose of a sample splitter in the given context?
Signup and view all the answers
What fractions can a sample splitter deliver according to the information provided?
What fractions can a sample splitter deliver according to the information provided?
Signup and view all the answers
What happens to the remainder of the sample after it has been split by the sample splitter?
What happens to the remainder of the sample after it has been split by the sample splitter?
Signup and view all the answers
In what scenario is a sample splitter most likely necessary?
In what scenario is a sample splitter most likely necessary?
Signup and view all the answers
What is a common characteristic of the fractions provided by a sample splitter?
What is a common characteristic of the fractions provided by a sample splitter?
Signup and view all the answers
What role does viscosity play in fluid dynamics?
What role does viscosity play in fluid dynamics?
Signup and view all the answers
Why are carrier gases required to be sufficiently inert?
Why are carrier gases required to be sufficiently inert?
Signup and view all the answers
Which of the following effects does viscosity NOT have?
Which of the following effects does viscosity NOT have?
Signup and view all the answers
What can happen if a carrier gas is reactive?
What can happen if a carrier gas is reactive?
Signup and view all the answers
Which statement accurately describes the relationship between viscosity and fluid flow?
Which statement accurately describes the relationship between viscosity and fluid flow?
Signup and view all the answers
Study Notes
Thin-Layer Chromatography (TLC)
- Planar chromatographic methods include thin-layer chromatography (TLC), paper chromatography (PC), and electrochromatography.
- Each method uses a thin layer of material, either self-supporting or coated on a glass, plastic, or metal surface.
- TLC is faster, has better resolution, and is more sensitive than paper chromatography.
TLC Principles
- Thin-layer chromatography is carried out on silica gel or alumina dispersed on an inert support (flat glass plates).
- The mobile phase is drawn over the surface by capillary action.
- TLC and liquid chromatography are similar in theory and stationary/mobile phases.
- TLC is faster and less expensive than HPLC.
TLC Technique Steps
- Preparation of the plate: A slurry of the active material is uniformly spread over the plate using a spreader. Air-dry overnight or oven-dry at 80-90°C for 30 minutes. Commercial plates can be conventional or high-performance.
- Sample application: This is a critical step. Manual application uses a capillary tube or syringe. Mechanical dispensers are commercially available.
- Chromatogram development: The plate is placed in a closed chamber (tank) lined with filter paper to avoid direct contact between the sample and the solvent system. The developing solvent travels up the plate, dissolving the sample and carrying it up.
- Locating the spots: Colored compounds are located visually. For colorless compounds, iodine or sulfuric acid are used. Ninhydrin is used for amino acids and 2,4-dinitrophenylhydrazine is used for aldehydes and ketones.
TLC Applications
- Identification of unknown compounds
- Analysis of reaction mixtures
- Monitoring chemical reactions
- Determination of the purity of a compound
- Quantitative determination of an unknown concentration (external standard method)
- Quantitative determination of an unknown concentration (internal standard method).
High-Performance Liquid Chromatography (HPLC)
- HPLC is a fast technique using liquid as the mobile phase.
- HPLC uses pressure for fast flow.
- HPLC is used for organic and inorganic analysis.
HPLC Advantages
- Speed
- High resolution
- High accuracy
- High sensitivity
- Automation is possible
HPLC Disadvantages
- Expensive instrumentation
- Requires skill
- Not universally applicable
HPLC Instrumentation
- Solvent mixing valve
- Pump
- Sample injection valve
- Column
- Detector
- Recorder
Mobile Phase Reservoir
- Often contains a filtration system for filtering dust and particulate matter.
- Equipped with a degasser to remove dissolved gases (usually oxygen and nitrogen).
HPLC Pump
- Generates a flow of the mobile phase through the HPLC injector, column, and detector
- Requirements include: generation of pressures up to 6000 lbs/in2
- Pulse-free output
- Flow rate ranging from 0.1 to 10 ml/min
- Made of corrosion-resistant materials
Types of HPLC Pumps
- Constant pressure pumps: simple, inexpensive, easy to operate, free from pulsations, resulting in smooth baselines. However, flow rate must be constantly monitored.
- Constant flow pumps: the ability to repeat elution volume and peak area (regardless of viscosity changes and column blockage), up to the pressure limit of the pump. This type is the most widely used in all common HPLC applications.
Mobile Phase
- Must solvate the analyte molecules and the solvent they are in.
- Be suitable for the analyte to transfer between the sample and solvent during separation.
- Be readily available
- Compatible with the instrument (pumps, seals, fittings, detector, etc)
- Compatible with the stationary phase
- Adequate purity
- Not too compressible (causes pump/flow problems)
- Filtered. Free of gases
Stationary Phases
- HPLC stationary phases are packed columns made from stainless steel.
- Columns have lengths of 3-50 cm and diameters of 3-10 mm.
- Packed with stationary phase: 1 to 20 µm diameter
- Particles: silica gel, alumina.
- Microbore/capillary columns (open tubular column)
Isocratic versus Gradient Elution
- Isocratic elution: constant mobile phase composition.
- Gradient elution : varying mobile phase composition. Using multiple pumps.
- Gradient elution is commonly used for complex mixtures
HPLC Detectors
-
Bulk property detectors: Respond to some physical property of the mobile phase (e.g. refractive index, dielectric constant, density).
- Advantages: universal application
- Disadvantages: low sensitivity and limited range
-
Solute property detectors: Respond to some physical or chemical property of solutes (e.g., UV absorbance, fluorescence).
- Advantages: High sensitivity and wide range.
- Disadvantages: More selective; may require multiple detectors;
Standard Absorbance Detector
- Single beam UV-VIS instrument with a flow-through cell
- Uses Hg vapor lamps and 254 nm
- Can use any UV-VIS with a special flow cell.
- For non-destructive analysis.
Diode Array Detector (DAD)
- Versatile research-grade HPLC instrument
- Scans a range of wavelengths every few seconds.
Refractive Index Detector
- Universal HPLC detector; non-destructive.
- Responds to changes in refractive index.
- Temperature sensitive (needs regulated temperature).
Evaporative Light Scattering Detector (ELSD)
- Universal detector; destructive.
- Useful for large molecules.
- Analytes desolvated in the detector.
Other GC Detectors
- Mass Spec
- Electrochemical
- Conductivity
- Fluorescence
HPLC Recorder
- Recorder that plots the separation of individual components over time.
Common HPLC Techniques
- Partition chromatography
- Normal phase chromatography
- Reverse phase chromatography
- Adsorption chromatography
- Ion chromatography
- Size exclusion chromatography
- Ion-pair chromatography
- HILIC chromatography
- Affinity chromatography
- Chiral chromatography
Types of Chromatography
- Adsorption chromatography
- Partition chromatography
Partition Chromatography
- Normal phase chromatography: polar stationary phase, nonpolar mobile phase.
- Reverse phase chromatography: nonpolar stationary phase, polar mobile phase.
Partition Chromatography
- Mostly bonded-phase packings are prepared by reaction of an organochlorosilane with the -OH groups on the silica particles.
- In reversed phase chromatography, the organic group R is typically a straight-chain octyl- (C8) or octyldecyl- (C18) group.
GC Theory
- Separation based on the partition of solutes between a stationary phase and an inert mobile phase (gas).
- Vaporization of the sample before injection into the column.
- Components separate based on their interaction with the stationary phase.
- Elution in order of increasing boiling points (and polarities).
GC Column
- Various lengths and diameters; often coiled.
- Temperature control is crucial.
- Types: packed columns (inert support material); capillary columns (liquid film coated inside).
GC Stationary Phases
- Low volatility
- Thermal stability of column at operating temperature
- Chemical inertness
- Characteristc solvents for the separation.
GC Detectors
- General function: monitors the carrier gas as it emerges from the column
- Types: thermal conductivity detector (TCD), flame ionization detector (FID), electron capture detector (ECD).
Sample Injection
- Methods: On-column and split-splitless injectors, injection volume, injection techniques.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers essential concepts related to polarity indices of solvents in chromatographic analysis. It examines the role of solvent mixtures, mobile and stationary phases, and their impact on solute behavior during chromatography. Test your understanding of these critical topics!
