Small molecules as substrates for adsorption/desorption in (252)CF plasma desorption mass spectrometry

Department of Chemistry, Texas A & M University, College Station, Texas, USA We present a new approach to substrate selection for californium-252 plasma desorption mass spectrometry ((252)Cf_PDMS) in which small volatile molecules that are water insoluble are used as matrices in place of the polymeric substrates used in previous studies. The desirable features of analyte adsorption are combined with the concept of using a volatile matrix to reduce the level of internal excitation of a desorbed analyte and to assist in ionization during the desorption process. Derivatives of anthracene were found to meet these requirements and to perform satisfactorily as substrates in (252)Cf-PDMS. Spectra were obtained for bovine insulin (m I z 5734) adsorbed onto 9-anthroic acid and 2-aminoanthracene and compared with spectra using a nitrocellulose substrate. Sharper peaks and lower backgrounds are observed when the 9-anthroic acid matrix is used, indicating reduced levels of internal excitation and initial kinetic energy for the desorbed molecular ion of insulin. A comparison of the performance of 9-anthroic acid and 2-aminoanthracene shows the influence of substrate functional groups on desorbed protein yields. Finally, the versatility of the small-molecule matrix concept is discussed with respect to selection of a range of functionality, solubility, and hydrophilicity.