E Ca 2 Flashcards
(33 cards)
What is the difference between Gas Chromatography (GC) and Liquid Chromatography (LC)?
GC uses small mobile phase molecules for smooth passage through the column, while LC uses larger molecules, resulting in longer retention times.
How does High-Performance Liquid Chromatography (HPLC) reduce retention times?
By applying pressure to the column, increasing the flow rate of the mobile phase.
What are the main uses of HPLC and What phases does HPLC employ?
It is used for both quantitative and qualitative determinations
A liquid mobile phase and a stationary phase
How does HPLC compare to Gas Chromatography (GC)?
HPLC can analyze thermolabile, very polar, or high molecular weight compounds that GC cannot, although GC has better column efficiency.
What are the main components of an HPLC system?
Injector, mobile phase, high-pressure pump, column, detector, and chromatogram.
What are the three types of elution in HPLC?
Isocratic mode: Single solvent with fixed composition.
Gradient mode: Composition changes over time.
Flow mode: Flow rate changes during the process
What are the benefits of gradient elution?
Shorter separation time, sharper peaks, improved sensitivity
What is the difference between binary and quaternary pumps in HPLC?
Binary pump: Two solvents mixed after separate pumping.
Quaternary pump: One pump with a proportioning valve to mix up to four solvents
Why are smaller particle sizes (e.g., 3 µm vs. 5 µm) beneficial in HPLC?
They provide better separation efficiency
What are reverse-phase HPLC columns commonly packed with?
Octyl bonded to a silica gel
How does normal-phase chromatography differ from reverse-phase?
Normal-phase: Polar stationary phase, nonpolar mobile phase (e.g., hexane).
Reverse-phase: Nonpolar stationary phase, polar mobile phase (e.g., water/methanol).
What is the difference between selective property detectors and universal detectors?
Selective property detectors look at the solute property.
Universal detectors look at bulk solution properties.
What must occur for a molecule to absorb UV/Vis light?
Electrons in the molecule must be excited
Which types of compounds absorb in the UV/Vis region?
Organic compounds with double/triple bonds or benzene rings
Inorganic ions and transition metal complexes
What is a diode array detector (DAD)
A detector that measures multiple wavelengths simultaneously
How does a DAD differ from a VWD?
VWD: Measures one wavelength at a time.
DAD: Measures all wavelengths simultaneously, providing a full spectrum.
How does an RI (Refractive index) detector work?
Measures the change in refractive index between the mobile phase (reference cell) and the sample.
How does HPLC compare to TLC and GC?
TLC – Best for screening.
GC – Good for volatile compounds.
HPLC – Best for quantifying polar, thermally unstable, or non-volatile compounds.
What is the principle behind Ion Exchange Chromatography (IEC)?
IEC is based on an ion-exchange process between the mobile phase and ion-exchange groups bonded to a support material
What is Ion Exclusion Chromatography (ICE) used for?
To separate weak inorganic and organic acids, amino acids, alcohols
Why are organic polymers used instead of silica-based materials in IEC?
Organic polymers are more stable at extreme pH values
What are the four types of ion-exchange resins?
Strong acid cation exchangers (SCX)
Weak acid cation exchangers (WCX)
Strong base anion exchangers (SAX)
Weak base anion exchangers (WAX)
How does charge affect selectivity in IEC?
Higher charged ions bind more strongly than lower charged ions.
How can acid/base solutes be eluted in IEC?
Acid: By reducing the pH
Base: By increasing the pH.
