Automated determination of silicate and carbonates in detergents

Abstract The analysis of silicate and carbonate builders in detergents is time consuming by standard gravimetric procedures (1,2). By modifying established Technicon AutoAnalyzer methods, rapid and simple methods of analyzing these detergent builders have been achieved. Standard AutoAnalyzer modules, arranged for colorimetric analysis, are used, and 10–15 samples per hour can be handled. In the silicate analysis, an aqueous solution of the sample is reacted with ammonium molybdate in an acid medium to form silicomolybdic acid. This acid is partially reduced by ascrobic acid forming the pentavalent molybdenum blue complex. The carbonate method is based upon the evolution of carbon dioxide gas, which is reacted with a buffered phenolpthalein solution. The color intensity of the system is inversely proportional to the carbon dioxide concentration. When a blend of carbonate and bicarbonate is present in the sample, analysis before and after heating is required.