Overcoming oxygen quenching in fluorescence spectrometry with a highly efficient in-line degassing device interfaced with a flow cell Original Research Article

To overcome the quenching effect of oxygen in fluorescence spectrometry, an in-line flow degassing device (FDD) was successfully applied to the removal of oxygen from sample solutions. The FDD consisted of a 3 m long coil of capillary silicone rubber tubing, installed in a glass flask maintained under reduced pressure of N2 (2.400 Pa). To avoid recontamination of the emerging flow with O2, the connection of the silicone tube with the fluorimetric cell is made with flexible silica capillary tube. Solutions can be injected with a syringe or feed with a pump. Aqueous solution of ruthenium(II) tris-bipyridil chloride, subject to quenching by oxygen, served as a luminescent probe. The performance was checked against independent amperometric measurements of O2 with a Clark cell, that correlated well with the O2 obtained from the fluorescence data using the Stern–Volmer relationship. At a flow rate of 1.0 ml min−1, the concentration of O2 (measured amperometrically) dropped from 8.24 mg l−1 to 15 μg l−1 for a residence time of 34 s in the FDD, rendering the oxygen quenching effect on [Ru(bipy)3]2+ undetectable. The FDD compares favorably with direct inert gas purging of the solution in efficiency and speed. Moreover, it is compatible with flow injection analysis. A frequency of 35 determinations per hour was attained at 1 ml min−1, with good repeatability of the peaks (R.S.D.=0.8%, n=25 injections of 200 μl of 1×10−4 M [Ru(bipy)3]2+).