Determinations of water, hydrates and pH in fluid inclusions by micro-Raman spectrometry
Determinations of water, hydrates and pH in fluid inclusions by micro-Raman spectrometry (in Proceedings of the Eleventh European symposium on Fluid inclusions research (ECROFI XI), Benedetto De Vivo (editor) and Pierfranco Lattanzi (editor))
European Journal of Mineralogy (October 1992) 4 (5): 885-894
Four new possibilities in the analysis of fluid inclusions by micro-Raman spectroscopy are demonstrated: 1) very low water contents (approx 1 mol %) can be detected in fluid inclusions with no visible water coating the wall of the cavity using a molecular symmetric stretching vibration at 3636 cm (super -1) . With increasing water content the Raman spectrum broadens and shifts towards lower wave numbers, indicating H (sub 2) O-H (sub 2) O interactions which prevent any quantification if X(H (sub 2) O) > 0.1; 2) the Raman spectrum of H (sub 2) S clathrate hydrate shows two bands at 2595 and 2605 cm (super -1) which are assigned to the stretching vibrations of the H (sub 2) S molecule; it is compared with the spectrum of vapour, liquid and aqueous H (sub 2) S; 3) the Raman spectrum of the LiCl.5H (sub 2) O hydrate exhbits a stretching vibration band centred around 3400 cm (super -1) , with an unusual large half-peak width (300 cm (super -1) ) compared to other stoichiometric salt hydrates at -160 degrees C. The sequence of phase melting > -160 degrees C in a natural fluid inclusion was based on the Raman spectrum of salt hydrate including LiCl.5H (sub 2) O; and 4) very acidic solutions (pH of 1 to -0.5) were documented from the identification of HSO (super -) (sub 4) and SO (super 2-) (sub 4) by Raman spectroscopy and the calibration of their intensity as a function of pH.