Gas chromatography-mass spectrometry (GC-MS) is a powerful analytical technique for identifying, confirming and quantifying organic compounds in complex matrices.1,2 The gas chromatograph separates the analytes of interest from matrix interference and the mass spectrometer is used for idenfying the compounds based on the unique fragmentation pattern of the molecule. Extensive libraries, for example NIST/EPA/NIH Mass Spectral Library, are available to compare the generated mass spectra in order to ascertain the identity of the compounds. For a unit mass resolution instrument like a single quadrupole mass spectrometer, the library matching score along with the compound’s retention time are used to confirm the identity.
When analysing compounds in complex matrices, one common occurrence is co-elution of compounds of interest or co-elution of analytes with matrix interferences. Figure 1 shows an example where there are two pesticides co-eluting to form a single chromatographic peak.
A NIST library search done at the apex of the peak identifies the compound as Simetryn, but on closer examination of the actual and reference spectrum, one can observe that some of the mass spectral fragments (like m/z 184 and 129) are prominently missing from the library spectrum. By extracting the ion chromatogram (EIC) for masses 184 and 213 in comparison with the total ion chromatogram (TIC), as shown in Figure 2, it is evident there are two different retention times, 13.72 and 13.74 minutes, for two peaks indicating the presence of two different compounds.
By performing a library search on the spectrum at 13.74 minutes while subtracting the mass spectrum at 13.72 minutes, the compound can be idenfied as Fuberidazole. This manual process of deconvoluting a peak is tedious and requires extreme care and attention, and in a case where the analyte concentration is so low that it is hidden in the noise, the peak cannot be identified.
SpectralWorks’ AnalyzerPro is designed to automatically deconvolve coeluted chromatographic peaks into multiple components, library search the found components and create a user-defined library of target components.
Figure 3 shows the automated deconvolution of the Simetryn and Fuberidazole peaks by AnalyzerPro as well as the NIST Library search results for the two components.
The component spectra can be automatically included in a Target Component Library. The Target Component Library searching, and matching is the basis for further data processing in AnalyzerPro such as MatrixAnalyzer and PCA analysis for product authencation and comparison analyses.
1. Sparkman, O. D.; Penton, Z. E.; Kitson, F. G. Gas Chromatography and Mass Spectrometry – A Practical Guide; Academic Press, 2011.
2. Hübschmann, H.-J. Handbook of GC-MS; Wiley-VCH, 2015.
ThermoFisher Scientific for the provision of the data from their ISQ 7000 GC-MS system.