Solid-state 13C NMR, X-ray photoelectron and electron spin resonance spectroscopies: a suggested approach to carbon analyses in aquatic solid phases

Abstract

Detailed solid-state 13C NMR and X-ray photoelectron (XPS) studies on particles from waters collected from the River Seinece (Northern France) are reported. These techniques have made possible the direct measurement of the percentages of inorganic and organic carbon in untreated suspended matter. CP/MAS 13 C NMR spectroscopy has allowed us to identify the various types of organic carbon and the percent aromaticity in the untreated particles. Valuable information on the content of organic carbon bonded to 0, 1 and 2 oxygen atoms in the particles has been assessed by XPS (with particulate silicon used as an internal standard). The NMR and XPS results have been compared and discussed. Furthermore, electron spin resonance (ESR) spectroscopy has been used to determine the concentration of free radicals of the semiquinone type in the particles to which was added DPPH (diphenylpicryl hydrazyl) as an internal standard. The results indicate that free radicals are stable and persist over long periods of time, but their content remains very low in all the particulate samples studied.