Effects of experimental parameters on electrospray ionization (ESI) mass spectra of tetracyclines and nucleoside antiviral agents
The effects of mobile phase additives, solution pH, and analyte concentration on the sensitivities and electrospray ionization (ESI) mass spectra of a series of tetracyclines and nucleoside antiviral agents are presented. Parameters that enhance ionization and give the best analyte signal for both positive and negative ion modes are reported. 1% acetic acid gave the greatest sensitivity for (M+H) $\sp+$ ions and 50 mM NH$\sb4$OH gave the greatest sensitivity for (M-H) $\sp-$ ions. The spectra of the more basic tetracyclines and purine antiviral agents showed no (M+NH$\sb4\rbrack\sp+$ adduct ions with ammonium salts, but (M+NH$\sb4\rbrack\sp+$ was the major peak in the spectra of the less basic pyrimidine antiviral agents. Spectra obtained with 5 mM sodium acetate solutions showed greatly reduced sensitivities because of the formation of sodium acetate cluster ions. The sensitivity as (M+H) $\sp+$ did not depend on the pH of the mobile phase. At higher analyte concentrations, the absolute signal reached a plateau due to ESI solution processes. The ammonium adduct ion was formed preferentially when the proton affinity (PA) of the analyte was close to that of NH$\sb3.$ These studies aid in understanding the interaction of mobile phase components with analyte and can be adapted to obtain highly sensitive analyses of other groups of pharmaceuticals.^ The collision-induced dissociation (CID) mass spectra of all protonated purine bases dissociate through two principal pathways: elimination of ammonia and loss of cyanamide. In the negative ion mode, deprotonated guanine appears to dissociate by elimination of NH$\sb3$ and loss of NH$\sb2$CN. Deprotonated adenine, however, proceed by elimination of HCN and NCHNH. The CID mass spectra of protonated pyrimidine bases dissociate through three principal pathways: (1) elimination of NH$\sb3,$ (2) loss of H$\sb2$O, and (3) elimination of NHCO. Trifluridine base, however, dissociates primarily through elimination of HF followed by loss of NHCO. In the negative ion mode, the formation of the NCO$\sp-$ ion is the principal decomposition pathway for all of these substituted pyrimidine nucleosides. The mass spectra of the antiviral agents studied can serve as models for the determination of the structures of other purine and pyrimidine antiviral analogs. ^
Chemistry, Analytical|Chemistry, Biochemistry|Chemistry, Pharmaceutical
Amin M Kamel,
"Effects of experimental parameters on electrospray ionization (ESI) mass spectra of tetracyclines and nucleoside antiviral agents"
Dissertations and Master's Theses (Campus Access).