In dilute sulphuric acid medium, trace naphthol can catalyze potassium bromate to oxidize alizarin red, resulting in the decreas of absorbance, and the concentration of naphthol is proportional to the absorbance (△4). Based on this principle, a spectrophotometric method was established for the determination of trace naphthol in human urine. The factors affecting absorbance were investigated, and the reaction conditions were optimized. The maximum absorption peak was at 422.0 nm. The △A exhibited good linear relationship with the concentrati...