FIELD: analytical chemistry, more particularly monitoring of industrial and purified sewage at enterprises which make pharmaceuticals. SUBSTANCE: acids are concentrated with isobutyl alcohol from aqueous sample in the presence of 10-20 wt % of lithium sulfate with respect to sample. Acids are identified directly in extract by photometric titration method with respect to complexing reaction with Fe3+. Titrant is FeU3•6H2O solution in dioxane. EFFECT: lower identification limit up to 0.01 mg/cubic dm and greater accuracy of assay, error does not exceed 9%. 1 dwg, 10 ex, 2 tbl
