Software mass spectra interpretation

An alternative to quantitative analysis by ICP-MS is semiquantitative analysis, which is generally considered as a rapid multielement survey tool with accuracies in the range 30-50%. Semiquantitative analysis is based on the use of a predefined response table for all the elements and a computer program that can interpret the mass spectrum and correct spectral Interferences. This approach has been successfully applied to different types of samples. The software developed to perform semiquantitative analysis has evolved in parallel with the instrumentation and, today, accuracy values better than 10% have been reported by several authors, even competing with typical ones obtained by quantitative analysis. The development of a semiquantitative procedure for multielemental analysis with ICP-MS requires the evaluation of the molar response curve in the ICP-MS system (variation of sensitivity as a function of the mass of the measured isotope) [17]. Additionally, in the development of a reliable semiquantitative method, some mathematical approaches should be employed in order to estimate the ionisation conditions in the plasma, its use to correct for ionisation degrees and the correction of mass-dependent matrix interferences. 

For unknown mass spectra the Mass Frontier software is a unique tool for spectrum interpretation. Structure proposals and fragmentation pathways are provided for mass spectra allowing a deeper sample and unknown elucidation. 

Mass spectra of chemical compounds have a high information content. This article describes computer-assisted methods for extracting information about chemical structures from low-resolution mass spectra. Comparison of the measured spectrum with the spectra of a database (library search) is the most used approach for the identification of unknowns. Different similarity criteria of mass spectra as well as strategies for the evaluation of hitlists are discussed. Mass spectra interpretation based on characteristic peaks (key ions) is critically reported. The method of mass spectra classification (recognition of substructures) has interesting capabilities for a systematic structure elucidation. This article is restricted to electron impact mass spectra of organic compounds and focuses on methods rather than on currently available software products or databases. 

Since the data obtained by low resolution instruments, like QqQ, are enough simple to interpret if compared with the huge amount of data obtained by a HR instrument, interpretation of a product ion spectrum generated by the QqQ is often not straightforward, because of the complex dissociation mechanisms for formation of fragment ions. However, a structure elucidation software, such as ACD/MS Fragmenter or Mass Frontier, developed to predict the fragment ions formed by Cff), has been used to assist the spectral interpretation of unknown structures. 

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