NIST Library Identification Probabilities Are the Highest with Cold EI Mass Spectra.

Abstract

Cold EI improves all of the central GC-MS performance aspects, but even though it is known for providing enhanced molecular ions, it is important to realize that Cold EI mass spectra also include all of the standard EI fragment ions. Thus, Cold EI mass spectra are fully compatible with mass spectral libraries, such as NIST for sample identification. As a result, Cold EI mass spectra (unlike any other soft ionization method) provide highly effective identifications that are often better than those obtained with standard EI for a few reasons:1).Cold EI mass spectra with enhanced molecular ions typically provide higher identification probabilities than standard EI, even though scoring lower matching factors (false alternatives scores are lowered much more).2).The visually observed molecular ions further serve to confirm or reject the NIST library identifications.3).Molecular ions provide isotope abundances that serve with our TAMI software for automatic confirmation or rejection of the NIST library identification and provide an elemental formula in case the compound is not in the library.4).The Cold EI identification probability can be even higher than that of a mass spectrum with a perfect match of 999 that can be obtained by NIST library searching its own mass spectrum.5).The clear Cold EI molecular ion enables the use of the NIST library option of constraints search with the molecular ion that further significantly increases the identification probability. Our findings are demonstrated with mass spectra of hexadecane (n-C₁₆H₃₄), n-C₄₀H₈₂, pyrene, nitrobenzene, chlorpromazine, di-n-octyl phthalate, and deltamethrin.