Identification of metabolites of ampicillin using liquid chromatography/thermospray mass spectrometry and fast atom bombardment tandem mass spectrometry.

Mass spectrometry is combined with liquid chromatography (LC/MS) and mass spectrometry (MS/MS) to identify ampicillin and two known metabolites--ampicillin penicilloic acid and ampicillin piperazine-2,5-dione--in human urine samples. Identifications were based on the fact that the metabolites or degradation products contain a substructure of ampicillin. In addition, two previously unidentified components in human urine samples were detected, corresponding to newly discovered metabolites or degradation products of ampicillin. Different chromatographic retention times in the LC mass spectra indicated two different compounds. However, the tandem mass spectra of these two components were similar, suggesting that they are stereoisomers. The use of LC/MS and MS/MS confirmed that the unknown components are the (3S,5R) and (3S,5S) epimers of ampicillin penilloic acid. Further study showed that only one of the components was eliminated from the body; the other arises from interconversion to the epimer in a urine sample. It is speculated that the component produced in vivo is the (3S,5R) epimer of ampicillin penilloic acid.

Enhanced analysis of poly(ethylene glycols) and peptides using thermospray mass spectrometry.

The effects of a needle-tip repeller electrode on thermospray mass spectra of poly(ethylene glycols) and peptide samples have been studied. A significant increase in ion current was observed for increased repeller potentials in the low-mass region (m/z 300 to m/z 1100) and the high-mass region (m/z 1100 to m/z 1900). The change in ion current is due to a change in ion extraction efficiency because of increased ion diffusion rates. The amount of peptide sample needed for direct injection studies was decreased 1 to 2 orders of magnitude by using an ion source with both a needle-tip repeller electrode and a restricted vaporizer probe tip.

Enhanced analysis of sulfonated azo dyes using liquid chromatography/thermospray mass spectrometry.

Modifications to a thermospray vaporizer probe and ion source have been made that enhance ion evaporation resulting in increased sample ion current. These modifications include restricting the thermospray vaporizer exit orifice and the addition of a needle-tip repeller electrode to the thermospray ion source. The interaction and effect of probe-tip size, repeller voltage, and flow rate on sulfonated azo dye detection are reported. An increase in signal response for sulfonated azo dyes was observed. An efficient chromatographic separation procedure for sulfonated azo dyes, which is compatible with thermospray mass spectrometric detection, is also presented. Five disulfonated azo dyes were separated and detected by using selected ion monitoring. Mass spectra of disulfonated dyes show a number of molecular ions and adduct ions that provide unequivocal molecular weight information.

Tandem mass spectrometric studies of the fragmentation of penicillins and their metabolites.

The fragmentation of two penicillins, ampicillin and amoxicillin, and their principal metabolites has been studied by a combination of liquid chromatography/thermospray mass spectrometry and tandem mass spectrometry. A high-resolution tandem mass spectrometer was used to obtain chemical ionization, fast-atom bombardment, and collision-induced dissociation mass spectra. Structural information and fragmentation mechanisms have been deduced from ions in the mass and collision spectra. This knowledge is useful in the analysis and identification of metabolites of ampicillin and related drugs in human body fluids.