Sensitivity Comparison Between GC-MS with Cold EI and Standard EI

Alex Yakovchuk, School of Chemistry, Tel-Aviv University, Tel-Aviv, Israel (Yakovchuk@mail.tau.ac.il)
Alexander Gordin, School of Chemistry, Tel-Aviv University, Tel-aviv, Israel
Aviv Amirav, School of Chemistry, Tel-Aviv University, Tel-aviv, Israel

Sensitivity is one of the most important parameters used to describe GC-MS performance. It is correlated to an instrument’s signal-to-noise ratio (S/N), limit of detection (LOD) and the limit of quantification (LOQ). Improving the sensitivity is therefore of major importance and interest.

Sensitivity in GC-MS is often misrepresented as being solely dependent on the instrument, while in reality, it is also highly dependent on the analyzed compound. All major vendors use octafluoronaphthalene (OFN) for their sensitivity and performance specifications. Since OFN is very easy to analyze, these OFN-based specifications are misleading when used to evaluate GC-MS performance with hard-to-analyze compounds.

GC-MS with Cold EI is based on interfacing the GC and MS with supersonic molecular beams (SMB) along with electron ionization of vibrationally cold sample compounds in the SMB in a fly-through ion source (hence the name Cold EI). Cold EI significantly improves all aspects of GC-MS performance, including sensitivity, and the harder the compound to analyze, the greater is the gain of Cold EI in S/N and LOD.

We demonstrate the superior sensitivity, detectability, and S/N of Cold EI in comparison with standard EI using a range of compounds varying in mass, polarity, and family type. In our comparison we explored the simple OFN as well as n-C₁₆H₃₄, n-C₃₂H₆₆, methyl stearate, cholesterol, pentachlorophenol, benzidine, 6 ring PAH's, phthalate esters, lambda cyhalothrin, decabromodiphenyl ether (PBDE-209) and reserpine. Our comparison shows that Cold EI consistently provides greater sensitivity via enhanced molecular ions, elimination of ion-source related peak tailing, and significantly reduced MS background noise. This further leads to improved library identification, LOD, LOQ, response linearity and measurement dynamic range.

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Short Biography of Presenting Author

M.Sc. student at Prof. Aviv Amirav's lab in Tel Aviv University, currently focusing on instrument development, testing and implementation in the field of analytical chemistry.