Evaluation of nano-liquid chromatography–tandem mass spectrometry in a column switching setup for the absolute quantification of peptides in the picomolar range

A standard nanospray-liquid chromatography–tandem mass spectrometry system in a column switching setup for the absolute quantification of leucine-enkephalin was evaluated. Analytes were loaded on a C18 trapping column and back-flushed in the 75 μm analytical column. Quantification was performed with a triple quadrupole instrument. Validation results show that it is feasible, with a conventional nano-LC system in the column switching setup, to quantify peptides as low as 500 amol on column (50 pmol/L). Weighted linear regression analysis proves a good linearity in a dynamic range of almost three orders of magnitude. Nevertheless, robustness remains a key issue in nano-LC–MS/MS.