Analysis for Trace Amounts of Analytes by Electrospray Mass Spectrometry

Electrospray mass spectrometry (ESI-MS) is the based analytical technique, used in proteomics research for biomarkers determination. However, some compounds do not undergo effective ionization process and, therefore, their trace amounts can be analysed only after proper derivatization. Properly designed ionization enhancers may reduce detection limit and allow for the analysis of minimal quantities of analytes by ESI-MS. The quantitative analysis is carried out using the isotope dilution. Recently, we developed synthetic methods of peptides derivatization by quaternary ammonium salts (QAS) and worked out their analysis at the attomole level. Unfortunately, such derivatives undergo the Hoffman elimination during peptide sequencing in tandem mass spectrometry (MS/MS). To overcome this neutral loss, we developed the synthetic methods of peptides derivatized by cyclic quaternary ammonium salts. In this work, we present synthesis of the azoniaspiro conjugate and its isotopologue deuterated on the alpha-carbon of the 5-azoniaspiro[4.4]nonyl group (ASN) and its analysis by ESI-FT-ICR-MS.