KL low-pH compatible C18 phases are designed for use at extremely low pH. Two very bulky hydrophobic protective groups prevent siloxane bond from hydrolysis at low pH condition and at high temperature, making it the most stable C18 for low pH application in the market. Because KL phase is not endcapped and has more surface silanols, it retains early-eluting polar compounds better. KL-C18 is the most polar C18 phases offer by Chromenta providing alternate selectivity. It is mostly used in polar molecule, metabolite, and small-peptide analyses.