Fractal dimension in mass spectra from herbal extracts: Hypothesis for a new method of phytocomplex characterization

In order to optimize the quality control of phytochemical products, we propose a non-conventional method of analysis of complex systems, called fractal analysis, applied to ESI (Electrospray Ionisation) mass spectra. The ESI spectra obtained with phytochemical commercial products (Mattoli et al., J. Mass Spectrom. 41: 1534, 2006; Mattoli et al., Metabolomics 7:437, 2011) were submitted to fractal analysis using the “box counting” method. Subsequent cluster analysis permitted to determine a distinctive fractal dimension (DB) for single plant extracts, as well as for mixtures of plant extracts contained in commercial herbal products. On several replicates obtained with different batches, DB tended to display a normal distribution around a mean value, which might be suggested as a typical reference tag for that product. The fractal approach permitted to characterize the repeatability of the instrumental measure too. Changes in DB following thermal treatment of samples, to simulate ageing, indicated the ability of the method also to identify appropriate conditions of storage and to suggest stability control interventions. In conclusion, evaluation of mass spectra DB might be proposed as a new promising technique to be used as a summary measurement of the complexity of the overall composition of a phytochemical product.