A Study of the Factors Influencing the Formation of Singly Charged Oligomers and Multiply Charged Monomers by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry(Ⅱ)—Negative Charged Ions

By the observation of negative MALDl mass spectra obtained with different concentration of sample solution; different matrices and different substrates, the factors iafluencing the formation of singly charged oligomers and multiply charged monomers are investigated. The results demonstrate that singly charged oligomers increased with the increase of sample concentration; more multply charged monomers appeared with the use of nitrocellulose mernbrane as substrate than that with silver plate. The above results are simila to that observed in positive ion MALDI mass spectra. By the comparison of MADLI mass spectra obtained with the use of Q-cyano,4-hydroxycinnandc acid(4HHCA) and sinapinic acid(SA)as matrix, more multiply charged monomers are found with 4HCCA as matrix. That is also the seem as in positive ion spectra. The mechanism of the formation of negative ion spectra mentioned above are discussed.