Keep reading to find out how the Aviv Analytical 5975-SMB GC-MS with Cold EI uniquely enables the effective analysis of synthetic organo-iodine compounds and provides unambiguous identification of all the synthetic organo-iodine reaction mixture compounds and as a result helps optimizing the synthesis reaction conditions and yields.
In Figure 2 we show the Cold EI mass spectrum (upper MS trace) and standard EI mass spectrum (bottom trace) of the first to elute peak in the doublet TIC peaks (2.32 min elution time in Cold EI and 5.22 min in standard EI). This peak belongs to the target organo-iodine synthetic compound. As demonstrated in Figure 2, Cold EI provides highly informative mass spectrum with abundant molecular ion of m/z=248 while standard EI does not exhibit any molecular ion. Evan worse, while no ions at all with m/z=248 are exhibited, a few small ions with other masses are observed and serve only to mislead about the possible identity of the target compound. Furthermore, the low mass spectral range of the standard EI mass spectrum reveals clear indication of intra ion source decomposition of the target compound in the form of m/z=91 and 92 ions of toluene decomposition product (plus other intra ion degradation products) while the Cold EI mass spectrum is free from such adverse effects.
In short, while standard EI provided useless and even misleading information, Cold EI provided accurate and valuable identification information in which the molecular ion is highly abundant and m/z=M-127 is the most abundant fragment ion that clearly indicates the presence of iodine. The synthesis target compound C8H9OI cannot be identified from an EI mass spectrum (Cold or Standard) with the NIST library since this compound is not included in the library. However, the Cold EI MS provides accurate isotope abundances of the molecular ion group of isotopomers. Thus, we used the Tal-Aviv Molecule Identifier (TAMI) software for the elucidation of the sample compound elemental formula. Further information on the usefulness of the TAMI software can be found in our blog post on identification.
In Figure 3 the TAMI software search screen is shown, reporting that among 340,200 possible elemental formula with nominal molecular weight of 249 amu, 1,158 are chemically possible and among them only the correct compound with elemental formula C8H9OI passed the required minimum matching factor of 850 with a very high matching factor of 998 and thus its elemental formula is certain. Accordingly, the 5975-SMB GC-MS with Cold EI outperforms high resolution GC-MS (with TOF or QTOF) since its capability of elemental formula provision is similar or better than that of 5 ppm TOF-MS while its ability to elute intact labile compounds and measure their molecular ions is far superior to any GC-MS with standard EI.
In Figure 4 we show the Cold EI mass spectrum of the main TIC peak which is absent in standard EI. Again, informative mass spectrum is shown with a molecular ion of m/z=478. This compound was fully identified by the NIST MS library as Bis(2-iodo-1-phenylethyl)ether and Figure 5 shows the NIST identification which is with a high 90.6% identification probability. Note that while the NIST library mass spectrum is very similar to the experimental Cold EI mass spectrum, Cold EI uniquely provides molecular ion mass spectral peak of m/z=478 which is missing in the library standard EI mass spectrum. However, since the identified compound molecular weight is 478 amu the Cold EI provision of molecular ion further confirms the NIST library identification and the TAMI software further fully supports the NIST library identification with the correct elemental formula of C16H16I2O which is an organo-iodine compound with two iodine atoms. However, unlike with high resolution LC-MS that provides elemental formula, the use of NIST library identification automatically provides also the compound name and structure as shown in the bottom trace of Figure 4. Using this structure it became immediately clear to the synthetic organic chemists that this compound emerged from a reaction of two synthetic target compounds that polymerized while eliminating one water molecule.
Finally, a very important unique capability of GC-MS with Cold EI is the provision of chemical reaction yields as described in Measurement and Optimization of Organic Chemical Reaction Yields by GC-MS with Cold EI. Cold EI is uniquely characterized by uniform compound independent response. Thus, one can use as shown in Figure 6 the Chemstation percent area report for the Cold EI TIC trace of Figure 4. According to the % area report that is shown in Figure 6, the most abundant compound #5 that is identified and described in Figures 4 and 5 above represents ~72% reaction yield while the reaction target compound which is #2 (Identified in Figures 2 and 3 above) resulted in reaction yield of only 10.5%. The other two compounds in the TIC were also identified but are not important for this note.