Optical fibre sensing element based on xerogel-supported [Au2Ag2(C6F5)4(C14H10)]n for the detection of methanol and ethanol in the vapour phase

An optical fibre sensing element for detecting methanol and ethanol in the vapour phase was constructed based on an organometallic compound with the empirical formula [Au2Ag2(C6F5)4(C10H14)]n. This compound was fixed to a microporous xerogel support, which was synthesized using the sol–gel technique. The optical fibre device was designed to operate via signal reflection. The sensing element responded quantitatively and reversibly to the presence of methanol and ethanol, and the signal was exponentially dependent on the vapour concentration up to 6 mM methanol and 3 mM ethanol. The signal stabilized between 2 and 4 min after methanol injection and between 6 and 10 min after ethanol injection. The limit of detection for methanol was 1.65 mM and for ethanol 0.83 mM. The response was enhanced when ethanol was used as the solvent for fixing the organometallic compound onto the xerogel matrix. Chemical treatment of the optical fibre with either NaOH or HF prior to coating the fibre pigtail did not improve the analytical signal when compared to sensing with non-treated fibres. The absorption spectrum was flat in the region of 400–850 nm. The sensing element response mechanism to methanol and ethanol vapours can be attributed to changes in the refractive index upon analyte binding. Changes in refractive index alter the optical power of the reflected signal, which is enhanced by the organometallic compound.