- most of the small compounds that are amenable for GC-MS analysis can be fully identified by the available extensive EI libraries.
- large compounds on the GC-MS scale are often incompatible with GC-MS analysis and/or do not exhibit molecular ions in their EI mass spectra.
- While the compound of interest may exchange its labile hydrogen atoms with deuterium, reversed exchange may occur at the GC liner, long column and particularly at the ion source metal surfaces that quickly react with ever-present water in the mass spectrometer vacuum chamber.
In order to further explore the effectiveness and value of deuterium exchange we tested it also with 17β-estradiol (C18H24O2) as shown in Figure 3. In Figure 3 the upper trace shows the generated total ion mass chromatogram with only one major peak of 17β-estradiol at 5.2 min. The middle trace shows the Cold EI mass spectrum of 17β-estradiol obtained when it was dissolved in deuterated methanol (CD3OD) while the bottom trace zoom on this Cold EI mass spectrum near the m/z range values 269-279 of its molecular ions. As demonstrated, deuterium exchange is effective with 17β-estradiol and the most abundant molecular ion is at m/z=274 instead of 272. While the process of deuterium exchange is incomplete it is sufficiently effective to clearly indicate that 17β-estradiol as its name implies (diol) has two OH groups that can exchange their labile hydrogen atoms into deuterium atoms while all other hydrogen atoms are passive and do not participate in the deuterium exchange process.
- The range of compounds amenable with GC-MS with Cold EI for analysis is significantly increased.
- All compounds practically exhibit abundant molecular ions in Cold EI.
- Reversed hydrogen exchange at the GC liner and column is minimized with the use of shorter columns and particularly with the use of high column flow rates and it is fully eliminated at the Cold EI fly-through ion source.
Enhancing the Identification Capabilities of EI GC-MS - How Quadrupole GC-MS can compete with High Resolution TOF
The Effects of Enhanced Molecular Ions on NIST's Identification Probability
TAMI - Molecule Identification Software