Methylisobutyl carbinol (MIBC) and a methoxy polypropylene glycol (Dowfroth 250) were determined by a colorimetric procedure using salicylaldehyde. Linear calibration curves in absorption spectrophotometry were obtained for MIBC between 0.05 and 0.2 mg/sample at similar to520 nm, and for D250 between 0.2 and 0.5 mg/sample at similar to535 nm. When standards and sample are run side by side under identical conditions, errors of approximately 3.5% and 6.0% in the determination of C-MIBC and C-D250 are achieved, respectively. The analysis is unaffected by the presence of sodium isopropyl xanthate, Ca, and Cu at typical plant concentrations in the sample. The colorimetric reactivity is demonstrated for a series of common frothers with alcoholic behavior. The method combines the ease of determination with high sensitivity. (C) 2004 Elsevier Ltd. All rights reserved.