Analysis of total- and water-soluble chloride in concrete using an optical sensor

An optical chloride-sensitive film was prepared and utilized to measure the chloride content in powdered concrete samples. The sensor is composed of N,N'-dimethyl-9,9'-biacridiniumnitrat (Lucigenin), a phosphorescent ruthenium complex in dense silica microparticles and a custom-made poly(acrylonitrile-co-acrylamide) matrix, allowing utilization of the dual lifetime referencing (DLR) technique. No dependency on pH value was observed at pH values from 1.0 to 7.0. Among the relevant anions, the sensor did not show any cross-talk to sulphate, but the response towards chloride was reduced in presence of nitrate and acetate ions. The sensor remains stable in water and 50 % acetic acid, which enables measurements of water-soluble chloride and total chloride. The sensor was challenged with concrete samples of various origins and with strong differences in chloride contamination (0.02-0.38 %w/w). The results of the optical measurements are in excellent agreement with results obtained from potentiometric titrations. The divergent binder chemistry of the selected concrete samples and the reliability of the measured results suggest wide applicability of the sensor. The sensor also shows potential to be suitable for field measurements.