Following this step, the sample passes into the vacuum chamber of the mass spectrometer.

LC is the separation technique of choice for larger and non-volatile molecules such as proteins and complex peptides. When combined with MS, LC-MS offers broad sample coverage because different column chemistries, such as reversed phase liquid chromatography, can be used.

LC is also an ideal method for separating isomers, which have the same mass and will otherwise not be differentiated (i.e., resolved) by a mass spectrometer. In fact, due to its superior resolving power and broad mass range, LC has largely replaced gel electrophoresis for molecular separation. Finally, LC helps reduce ion suppression, which occurs when molecules interact with one another and impede the process of complete ionization.

HPLC, which is defined as high performance liquid chromatography, has improved upon and largely replaced LC. HPLC was initially defined as high pressure liquid chromatography because it operates at a higher pressure ranging from 50-350 bar. In contrast, LC relies on gravity for the passage of the mobile phase through the column.

In this section, you will: