Calcium complexation applied to the analysis of resorcinol and analogs in mixtures using HPLC-ESI-MS

BUTLER, MATÍAS; ARROYO MAÑEZ PAU; CABRERA, GABRIELA M

Conferencia; 5° BrMASS Conference; 2013

Complexation with metal ions in solution, followed by efficient transport of the charged complexes to the gas phase by electrospray ionization (ESI), represents a promising method for ionization of a variety of analytes, especially for those that are not directly amenable to ESI. The use of metal ions may produce very stable metal coordination complexes, and therefore alkaline earth and transition metal ions have been used in ESI for many types of compounds, allowing the differentiation of isomers by mass spectrometry. Most of the published articles dealing with metal complexation and ESI-MS analysis of compounds with phenolic functionalities are referred almost exclusively to natural products of the polyphenol family. Resorcinol (1,3-dihydroxybenzene) is a common structural feature of agrochemicals, pharmaceutical drugs and their metabolites, as well as an environmental pollutant. Furthermore, their derivatives are of widespread occurrence among natural products, such as resveratrol and alkylresorcinols. Mass spectrometric analyses were performed using a Bruker micrOTOF-Q II mass spectrometer equipped with ESI and Agilent 1200 Series LC was used for HPLC studies. Resorcinol and its isomer, catechol, were not detected in the positive ion mode mass spectra. Adding the metal solution postcolumn at the interface between the LC column and the source provided an easy way to obtain the mass spectra with significant structural information. Thus, singly/doubly charged adducts formed from neutral or deprotonated ligands as well as the protonated molecules, were produced in the gas phase using calcium. Quantum chemical calculations were carried out at the B3LYP/6-311+G(d,p) level, proposing structures for some of the observed species and providing a better understanding of their formation. Mango peel is known to contain 5-alk(en)ylresorcinols, which have been characterized by HPLC-APCI-MS. Calcium complexation was essayed on mango peel extracts, observing peaks related to the protonated molecule of the alk(en)ylresorcinols as well as doubly charged calcium complexes. Therefore, useful structural information could be obtained from the observed ionic species.