A critical comparison of different solid supports to develop room-temperature phosphorescence sensing phases of air moisture

Abstract

The metal chelates of 8-hydroxy-7-iodo-5-quinolinesulfonic acid (ferron) with Al(III) exhibit strong room-temperature phosphorescence (RTP) when adsorbed on different solid supports. Moisture is a strong quencher of the solid-surface RTP emitted due to weakening of the bonds between the metal chelates and the solid support by water molecules. This effect can be exploited for moisture sensing. Different materials including anion-exchange resins and membranes or xerogel are described here to immobilize the Al-ferron chelate. The resulting active phases are compared in terms of the intensity of the corresponding RTP emissions and their phosphorescent lifetimes, and the effect of moisture is studied over a wide range of humidities. Both argon and air gaseous media have been investigated for relative humidity (RH) sensing by RTP-quenching measurements. Results demonstrate that the nature of the solid support plays a critical role in the efficiency of the humidity quenching and so in the RTP sensing response. Air humidity sensing is described in more detail. Anion-exchange resins and membranes require lifetime measurements for reliable sensing instead of RTP intensity measurements. Linear dynamic ranges, however, are wider using anion-exchange resins or membranes as solid supports of the RTP metal chelates. The sensing phases prepared using sol-gel techniques show better potential for the RTP analytical quantification of humidity in gaseous media in both continuous and flow-injection systems. Detection limits observed are around 0.09% RH in air, while the precision is ± 3.2% at 8% RH levels using the sol-gel active phase in a flow-cell system.