Facile Determination of Aluminum Content in Industrial Brine by Investigating the Effects of Buffer Systems

The aluminum content of concentrated (27 wt%) sodium chloride solutions could be crucial for large-scale chlor-alkali-based industries applying membrane cell electrolysis. Thus, a facile method which enables a fast and reliable protocol to determine the Al content of these solutions on ppb scale in industrial environments is fundamentally important. It was demonstrated that the increased sensitivity of colorful Al-ECR (eriochrome cyanine R) complex by the use of a cationic surfactant and specific biological buffers could effectively indicate the Al content in an extended pH interval of a concentrated saline medium under industrial conditions. The dependence of the analytical protocol on pH, temperature, time, wavelength, and the salinity of the medium was investigated. It was shown that the absorbance-based measurements of the solution should be performed at least 2-4 h after its preparation. By applying the selected two Good's buffers (HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, MOPS: 3-(N-morpholino)-propanesulfonic acid) and Tris (tris(hydroxymethyl)aminomethane), 32.8-38.1 % increase in the sensitivity was achieved for saturated NaCl solutions. Moreover, the limits of detection and quantification (LOD, LOQ) were also lowered by 19.0-29.8 %, and the salinity dependence of the calibration was also reduced.