Flow Injection Determination of the Alkaline Compositions in Boiler Water Based on the Response Curve Modeling

Abstract

An analytical method based on modeling the flow injection curves was proposed for the rapid determination of alkaline compositions in boiler water. The sample was injected into a carrier stream of a standard acid solution, and the alkaline constituents in the sample were partially neutralized by the acid on their way to the detector. A flat pH electrode was used to sense the output voltage of the mixture, and the signals were recorded as a typical flow injection peak. The peak widths were found to be proportional to the logarithm of total basicity of the sample. The compositions of the mixed base can be identified by the pH and peak area. A 3D model was constructed by using standard solutions of mixed bases, and the concentration of each constituent was obtained in the simulated 3D model. Calibration curves with good linearity were obtained in the total basicity ranges of 9.25 × 10−4−0.052 mol L−1 for mixed base of Na2CO3 and NaOH and 9.96 × 10−4−0.061 mol L−1 for Na2CO3 and NaHCO3. The method has a low sample and reagent consumption, high sampling rate of 45 samples h−1 and an excellent precision with the relative standard deviation less than 0.3 %. The method was validated by the quantification of mixed base components in boiler water samples.