According to the United States Pharmacopeia (USP), L1 column packing is defined as
ìoctadecyl silane chemically bonded to porous silica or ceramic micro-particles, 3 to 10 µm
in diameter.î Some USP methods specifying an L1 column use intermediate pH, and many
of these methods were done on a 10 µm, 3.9 x 300 mm column. Until recently there was no
modern alternative to the older 10 µm C18 column for intermediate pH-range applications.