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ELUENT - solvent that enter the column

ELUATE - solvent that leave the column at the end

RETENTION TIME , Rt
 time taken for the species to travel from the input of the column to the detector

High Performance Liquid Chromatography (HPLC)
→ slight change

stationary phase -  made up of much2 smaller particles 
                           - with greatest surface area
(smaller particles have more total surface area compare to one large particle)
mcm gula melaka dgn gula halus  Gula halus have much more total surface area

→ it takes a very long time for the species to move through the column
because there is so much absorption going on

➤Therefore , HPLC need to be conduct at higher pressure in order to pump the mobile phase through a very high pressure.

→ Normal phase & Reversed phase 

Normal phase 
Mobile phase is non polar 
Stationary phase is polar hydrophilic ❤H2O
Column is filled with silica SiO2 particles (which act as the stationary phase)
Silica is polar. Polar molecule will absorb to it . Therefore, non polar molecule such as hexane will pass more quickly through the stationary phase

Reversed phase *most commonly used form of HPLC
Mobile phase is polar
Stationary phase is non polar hydrophobic 💔H2O
The silica in the column is modified to make it non polar. The non polar molecule will absorb to it and polar molecule such as water & acetonitrile will pass more quickly through the stationary phase

Notes on how to choose solvent system