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

To overcome the quenching effect of oxygen in fluorescence spectrometry, an in-line flow degassing device (FDD) was successfully applied to the remova l 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 und er reduced pressure of N-2 (2.400 Pa). To avoid recontamination of the emer ging flow with O-2, the connection of the silicone tube with the fluorimetr ic cell is made with flexible silica capillary tube. Solutions can be injec ted with a syringe or feed with a pump. Aqueous solution of ruthenium(II) t ris-bipyridil chloride, subject to quenching by oxygen, served as a lumines cent probe. The performance was checked against independent amperometric me asurements of O-2 with a Clark cell, that correlated well with the O-2 obta ined from the fluorescence data using the Stern-Volmer relationship. At a f low rate of 1.0 ml min(-1), the concentration of O-2 (measured amperometric ally) dropped from 8.24 mg l(-1) to 15 mu g l(-1) for a residence time of 3 4 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 t he solution in efficiency and speed. Moreover, it is compatible with flow i njection analysis. A frequency of 35 determinations per hour was attained a t 1 ml min(-1), with good repeatability of the peaks (R.S.D. = 0.8%, n = 25 injections of 200 mu l of 1x10(-4) M [Ru(bipy)(3)](2+)). (C) 2000 Elsevier Science B.V. All rights reserved.