Automated molecular weight assignment of electrospray ionization mass spectra.

Process improvements in the synthesis of therapeutic agents and their intermediates are often facilitated by identification of reaction by-products. Analysis by liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization is a powerful approach for obtaining molecular weight information for these compounds. Such analyses are well suited for 'open-access' mass spectrometry using generic chromatographic conditions, provided spectral interpretation for unknown compounds is facile. We have developed a software application (MassAssign) that facilitates automated data processing and molecular weight assignment for chromatographic peaks detected by any standard ultraviolet-visible wavelength detector. The program assigns [M + H](+) ions (and thus molecular weight) in the mass spectra using predetermined criteria. This evaluation process differentiates [M + H](+) ions from other signals in a complex mass spectrum such as those resulting from chromatographic coelution or the presence of multiple species (i.e., fragment ions, singly charged ions, doubly charged ions, adduct ions, proton-bound dimers, etc.). Once the program has evaluated all ions in a mass spectrum that exceed a preset abundance threshold, MassAssign reports either a numeric value-indicating the chromatographic peak consists of a single component having the displayed molecular weight, 'MC'-indicating the peak consisted of multiple components, or 'ND'-that a molecular weight could not be determined unequivocally. The performance of the program was evaluated by comparing mass assignments made by MassAssign against manual interpretation for 55 samples analyzed by positive electrospray ionization using a generic HPLC method. Correct molecular weight assignments were obtained in 90% of the cases.

Identification of a pharmaceutical packaging off-odor using solid phase microextraction gas chromatography/mass spectrometry.

The use of a solid phase microextraction (SPME) sampling technique, in conjunction with gas chromatography/mass spectrometry (GC/MS) analysis, to identify an off-odor in a heat-stressed pharmaceutical packaging material is described. The ability of the commercially available polydimethylsiloxane (PDMS) coated microfiber to concentrate a trace volatile compound of interest enabled identification of the odor compound of interest. Despite being present at levels that defied detection using conventional headspace sampling techniques, ethyl-2-mercaptoacetate was determined to be the compound responsible for the offending odor. Formation of the thioester resulted from an unanticipated reaction (either esterification or transesterification) between a common residual solvent (ethanol), present in a commonly used pharmaceutical tablet dispersant, and low-level amounts of reactants or synthetic intermediates of an FDA-approved polyvinyl chloride (PVC)-resin thermal stabilizing agent.

Mass spectral fragmentation reactions of a therapeutic 4-azasteroid and related compounds.

Mass spectra were acquired for a therapeutic 4-azasteroid (dutasteride), and some related compounds, using various ionization conditions (EI, CI, APCI and ESI) in both positive and negative ion modes. The ionization and fragmentation behavior of the compound dutasteride, its precursors and several analogs is reported. Positive atmospheric pressure chemical ionization (APCI+) and positive electrospray ionization (ESI+) produced distinctive collision-induced dissociation (CID) spectra for the respective [MH]+ ions of dutasteride. The spectral differences are attributed to ion populations having either different structures or different internal energy distributions (as a consequence of the method of ionization). Irrespective of their origin, the protonated molecules undergo interesting fragmentation reactions when collisionally activated. The identity of the major fragmentation products was confirmed by accurate mass measurement. The negative APCI mass spectrum of dutasteride displays extensive dehydrohalogenation, apparently due to the thermal component of the APCI process. Some of the resulting radical anions display remarkable stability toward collisional decomposition. Details of the fragmentation behavior for the negative ion species and their relationship to the positive ion results are discussed.