sentence: Tryptic digests of mouse HDL ( 1 μ g protein ) were injected onto a C18 trap column ( Paradigm Platinum Peptide Nanotrap , 0.15 × 50 mm ; Michrom Bioresources Inc ., Auburn , CA ) , desalted ( 50 μ l / min ) for 5 min with 1 % acetonitrile / 0.1 % formic acid , eluted onto an analytical reverse-phase column ( 0.15 × 150 mm , Magic C18AQ , 5 μ m , 200 A ; Michrom Bioresources Inc. ) , and separated on a Paradigm M4B HPLC ( Michrom Bioresources Inc. ) at a flow rate of 1 μ l / min over 180 min , using a linear gradient of 5 – 35 % buffer B ( 90 % acetonitrile , 0.1 % formic acid ) in buffer A ( 5 % acetonitrile , 0.1 % formic acid ) .