Chapter 1: The first chapter of this thesis is dedicated to the principles and the applications of peptides and proteins quantification by mass spectrometry. The problematic of monoclonal antibodies analysis is also presented in this chapter. Chapter 2: The second chapter focuses on the development of an analytical method for the absolute quantification of the des-acyl ghrelin and ghrelin peptides. Chapter 3: The third chapter describes the application of differential ion mobility spectrometry. Chapter 4: The fourth chapter is dedicated to the development of an immunoaffinitybased extraction procedure for the MS analysis of monoclonal antibodies glycoforms in plasma samples. Chapter 5: The fifth chapter presents preliminary study focused on the quantification of peptides in plasma using the high resolution mass spectrometry (HRSIM/MS).