Determination of anthraquinone-2-sulfonate in alkaline pulping liquor by spectrophotometry using a Nafion membrane interface Original Research Article

A flow analysis system with a membrane interface has been developed for the determination of anthraquinone sulfonic salt (AQ-S) in alkaline pulping liquors. The Nafion membrane interface was kept at an elevated temperature of 90 °C to increase the AQ-S transport rate through the membrane. A sample solution was used as a donor, and the AQ-S species in the sample liquor penetrated through the membrane into a carry stream to constitute the acceptor stream. The AQ-S species that penetrated through the membrane can react with hydrosulfite to form AHQ-S that absorbs light in the visible region and can be determined spectroscopically. The effective separation of large lignin molecules from the AQ-S was achieved for accurate measurements of AQ-S in pulping liquors. The present method is simple and quick, and can be used for online monitoring of AQ-S in pulping liquors.