CH 265 - Ch 25 Liquid Chromatography
(Back of book problems)
Why does mobile phase strength increase as solvent becomes less polar in
reverse phase chromatography, whereas mobile phase strength increases as
solvent becomes more polar in normal phase? - correct answer ✔In reverse
phase chromatography, the solutes are nonpolar and more soluble in a
nonpolar mobile phase.
In normal phase, the solutes are polar and become more soluble in a polar
mobile phase.
What kind of gradient is used in supercritical fluid chromatography? - correct
answer ✔A gradient of increasing pressure gives increasing solvent density,
which gives it increasing eluent strength.
Why are the relative eluent strengths of solvents in adsorption
chromatography fairly independent of solute? - correct answer ✔Solvent is
competing with solute for adsorption sites. The strength of the solvent-
adsorbent interaction is independent of solute.
In hydrophilic interaction chromatography, why is eluent strength increased by
increasing the fraction of water in the mobile phase? - correct answer ✔In
HILIC, solute equilibriates btween the mobile phase and an aqueous layer on
the surface of the polar stationary phase. The more water in the eluent, the
better it can compete to dissolve polar solute and elute it from the column.
Why is high pressured needed in HPLC? - correct answer ✔Small particles
are resistant to flow. High pressure is required to obtain a usable flow rate.
For a given column length, why do smaller particles give a higher plate
number? - correct answer ✔Efficiency increases because solute equilibrates
(Back of book problems)
Why does mobile phase strength increase as solvent becomes less polar in
reverse phase chromatography, whereas mobile phase strength increases as
solvent becomes more polar in normal phase? - correct answer ✔In reverse
phase chromatography, the solutes are nonpolar and more soluble in a
nonpolar mobile phase.
In normal phase, the solutes are polar and become more soluble in a polar
mobile phase.
What kind of gradient is used in supercritical fluid chromatography? - correct
answer ✔A gradient of increasing pressure gives increasing solvent density,
which gives it increasing eluent strength.
Why are the relative eluent strengths of solvents in adsorption
chromatography fairly independent of solute? - correct answer ✔Solvent is
competing with solute for adsorption sites. The strength of the solvent-
adsorbent interaction is independent of solute.
In hydrophilic interaction chromatography, why is eluent strength increased by
increasing the fraction of water in the mobile phase? - correct answer ✔In
HILIC, solute equilibriates btween the mobile phase and an aqueous layer on
the surface of the polar stationary phase. The more water in the eluent, the
better it can compete to dissolve polar solute and elute it from the column.
Why is high pressured needed in HPLC? - correct answer ✔Small particles
are resistant to flow. High pressure is required to obtain a usable flow rate.
For a given column length, why do smaller particles give a higher plate
number? - correct answer ✔Efficiency increases because solute equilibrates
