Solid State Nuclear Magnetic Resonance 30 (2006) 81–88 CP MAS 13 C spectral editing and relative quantitation of a soil sample Claudia Forte a,Ã , Alhena Piazzi a , Silvia Pizzanelli a , Giacomo Certini b a Istituto per i Processi Chimico-Fisici, Consiglio Nazionale delle Ricerche, Area della Ricerca di Pisa, via G. Moruzzi 1, 56124 Pisa, Italy b Dipartimento di Scienza del Suolo e Nutrizione della Pianta, Universita` degli Studi di Firenze, Piazzale delle Cascine 18, 50144 Firenze, Italy Received 26 September 2005; received in revised form 22 February 2006 Available online 6 May 2006 Abstract A hydrofluoric acid (HF)-treated soil sample was studied by 13 C NMR spectroscopy. Cross polarization (CP) Magic Angle Spinning (MAS) 13 C spectral editing and relative CP peak quantitation, obtained through variable-contact-time experiments, were used to aid the interpretation of the spectrum. The combination of these two types of experiment allowed to obtain a higher degree of detail on the composition of the sample with respect to a standard CP MAS experiment. r 2006 Elsevier Inc. All rights reserved. Keywords: CP MAS 13 C; Spectral editing; Relative quantitation; Soil organic matter (SOM) 1. Introduction 13 C Magic Angle Spinning (MAS) NMR has revealed to be one of the most powerful techniques for characterizing soil organic matter (SOM). The main observable used in making structural identifications is the 13 C chemical shift, which is characterized by a range of more than 200 ppm. However, due to the great variety of organic structures present in SOM, 13 C spectra usually contain overlapping resonances, thus making it essential to develop additional strategies in order to identify the different components. Chemical extraction and fractionation have been com- monly employed in order to overcome this problem, but the recovery of SOM components is incomplete and uncontrolled artifacts can be created [1]. 13 C cross polarization (CP) MAS spectral editing techniques, such as dipolar dephasing, have been used to distinguish CH and CH 2 from CH 3 groups and quaternary carbons (C quat ) in systems such as lignins [2], decomposed wood and coalified xylem tissue [3], coals [4], kerogens [5] and humic acids [6,7]. More recently, a more sophisticated spectral editing method [8] that allows the subspectra relative to CH, CH 2 and CH 3 +C quat groups to be produced was profitably applied on a humic material [9] and a similar study has been reported on dried pine needles [10]. This method, proposed by Wu, Burns and Zilm (WBZ), consists in combining four separate CP MAS experiments with carefully chosen periods of CP, depolarization and polarization inversion [9] to produce the mentioned subspectra. Furthermore, a technique based principally on the different dipolar dephasing properties of CH and CH 2 multiple-quantum coherences was recently described for the specific selection of CH groups and applied to some humic acids [11,12]. Very recently, analysis of 13 C CP MAS spectra based on model components, combined with carbon and nitrogen elemental analysis, was used for estimating the molecular composition of natural organic materials including SOM [13]. Moreover, given the importance of accurately determining the degree of aromaticity in soils, often related to the degree of humification, and the errors intrinsically present in the standard approach used for evaluating it, i.e. from the relative spectral area of the region between 110 and 165 ppm, which however may contain contributions from non-aromatic carbons as well as lose aromatic signals resonating upfield, a method based on 13 C chemical shift anisotropy filter has been proposed and applied to humic acids [4]. Besides signal overlap, another important issue in the study of SOM by means of 13 C NMR is quantitation. In fact it is well known that in diamagnetic solids the signal ARTICLE IN PRESS www.elsevier.com/locate/ssnmr 0926-2040/$ - see front matter r 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ssnmr.2006.03.001 Ã Corresponding author. Fax: +390503152442. E-mail address: c.forte@ipcf.cnr.it (C. Forte).