HPLC | Notion

In general:

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Depending on the polarity:

normal - stationary phase is polar and the solvents used are non-polar.
reverse-phase - stationary phase is nonpolar and the solvent is polar (most popular)

Different retention times due to: polarity, hydrophobicity, ionization (changes in adsorption)

HPLC vs GC (Gas Chromatography )

Mobile phase - liquid(polar or non-polar) vs inert gas
HPLC for samples liable to decompose at higher temps; GC for volatile compounds(easily evaporates) at high temperatures, such as ethanol or acetone.

HPLC in general more versatile.

Parameters to consider: