Clays electron paramagnetic resonance

Goodman, B. A., and Hall, P. L. (1994). Electron paramagnetic resonance spectroscopy. In Clay Mineralogy Spectroscopy and Chemical Determinative Methods, Wilson, M. J., ed., Chapman Hall, London, pp. 173-225. 

Direct methods for determining the combinational form of an element or its oxidation state include infrared absorption spectrometry, X-ray diffraction and, more recently, electron paramagnetic resonance - nuclear magnetic resonance -and Mossbauer spectrometry. With such techniques the combinational forms of major elements in soil components such as clay minerals, iron, manganese and aluminium oxyhydroxides and humic materials and the chemical structures of these soil components have been elucidated over the past 50 years. These direct, mainly non-destructive, methods for speciation are dealt with in some detail in Chapter 3 and are not further discussed here. 

Spectroscopic techniques such as electron spin resonance (ESR) offer the possibility to "probe" the chemical environment of the interlayer regions. With the ESR technique, an appropriate paramagnetic ion or molecule is allowed to penetrate the interlayer, and chemical information is deduced from the ESR spectrum. Transition metal ions, such as Cu2+, and nitroxide radical cations, such as TEMPAMINE (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) have been used as probes in this manner (6-14). Since ESR is a sensitive and non-destructive method, investigations of small quantities of cations on layer silicate clays at various stages... 

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