Chapter 25 liquid chromotography Flashcards
Why does mobile phase increase as solvent becomes less polar in reversed phase and increase as it becomes more polar in normal phase?
In reversed phase chromatography solutes are nonpolar thus more soluble in nonpolar mobile phase. In normal phase chromatography the solutes are polar thus more soluble in polar mobile phase.
Why are relative eluent strenghts of solvents in adsobrtion fiarly indepenedant of solute?
Solvent is competing for adsoption sites. The strenght of the solventadsorbent interaction is independent of solute
Why is high pressure needed in HPLc?
Small particles gives increased resistance to flow high pressure is required to obtan a usable flor rate
For a given column lenght why does smaller particles give a higher plate number?
Effficancy increases because solute equilibirates between phases more rapidly if the distance that is has to diffuse ir smaller. The effect decreases C term in van Deemter equation. Also flow paths between smaller particles are more uniform, decreaseing the mutliple path (A) term
What is bonded phase in liquid crhomatography?
A bonded stationary phase is vocantly attatched to the support
Why are HPLC particles pourous?
It greatly increases the surface area of the particles which increases the mass of sample that may be loaded into the column without causing overload
