Differentiation of dihydroxyarene isomers using metal complexation and electrospray ionization mass spectrometry

BUTLER M.; ARROYO MAÑEZ P.; CABRERA G. M.

Denver, Colorado

Conferencia; 59th ASMS Conference on Mass Spectrometry and Allied Topics; 2011

American Society for Mass Spectrometry

Novel Aspect: An efficient and convenient method for the rapid analysis and detection focusing on the differentiation of isomeric compounds was developed. Introduction  Complexation with metal ions in solution, followed by efficient transport of charged complexes to the gas phase by electrospray ionization (ESI), represents a promising method for ionization of a variety of analytes, including those that are not directly amenable to ESI. Moreover, transition and alkaline earth metal ions have been used to differentiate isomeric compounds by mass spectrometry. [1] Dihydroxyarenes are common structural features of agrochemicals, pharmaceutical drugs and their metabolites, as well as environmental pollutants. Furthermore, their derivatives are of widespread occurrence among natural products, such as coumarins and flavonoids. Differentiation by mass spectrometry of dihydroxyarene isomers and their derivatives is relevant in the development of methods for their simultaneous analysis. Methods  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. The analyte solutions of catechol, resorcinol, 2,3-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, 6,7-dihydroxycoumarin, 7,8-dihydroxy-4-methylcoumarin and 5,7-dihydroxy-4-methylcoumarin, each at a concentration of 10 mM, were prepared using methanol. The metal ion stock solutions, each at a concentration of 10 mM, were prepared from the metal salts of Al (III), Ca (II), Mn (II), Fe (III), Co (II), Cu (II) and Ga (III) in the form of chlorides or sulphates. The metal solutions were used in excess relative to the sample solutions. Preliminary Data  Protonated molecules of the isomeric dihydroxyarenes as well as the singly/doubly charged adducts formed from neutral or deprotonated ligands and a doubly/triply charged metal ion were produced in the gas phase using ESI. Mass spectra with different metal ions were recorded for each isomer. Besides, benzenediols injected alone were not detected in the positive ion mode mass spectra. Mass spectra obtained with the different metal cations exhibited several characteristic species for each isomer thus allowing the differentiation. It is interesting to note the preponderance of the species with two ligands for the ortho benzene- and naphthalene- diols respect to their isomeric counterparts. Nevertheless, the differences observed are difficult to generalize and explain just considering the homology in the core of dihydroxybenzene shared by the compounds studied. For instance, the presence of the carbonyl in the structure of the coumarins probably accounts for the predominance of the protonated molecule ion over the metal cation adducts. The practical application of metal complexation in LC/ESI-MS, as a detection method for distinguishing the dihydroxyarene isomers was tested. The metal solution was added postcolumn at the interface between the LC column and the source providing an easy way to obtain similar spectra to the previously recorded. Thus, with a simple LC/ESI-MS experiment, significant structural information might be derived from the spectra observed according to the metal utilized. [1] M. Butler, P. Arroyo Mañez, G. M. Cabrera. Differentiation of Isomeric Hydroxypyridine N-Oxides Using Metal Complexation and Electrospray Ionization Mass Spectrometry. J Am Soc Mass Spectrom 2011, in press.