The present invention relates to a use of a tertiary amine as buffer in sample preparation, preferably for mass spectrometry and/or UV/vis spectroscopy, wherein the sample comprises proteins, polypeptides and/or peptides, and said sample preparation comprises: (a) protein, polypeptide and peptide denaturation; and (b) chemical isotope labelling and/or chemical cross-linking, wherein said sample preparation does not use primary amine buffers.