Spectrophotometric determination of 1, 3-dipropyl urea and 1, 3-dibutyl urea

Dialkyl urea, 1, 3-dipropyl urea (DPU) or 1, 3-dibutyl urea (DBU) were determined by spectrophotometric method. The procedure is as follows: The amount equivalent to about 750 μg of DPU or DBU was measured accurately. Sodium hydroxide was added to make the solution alkaline. After the solution was extracted 3 times with about 20 ml of chloroform, the extracts were combined and concentrated by an evaporator. The residue was dissolved in 5.0 ml of dimethylformamide and used as a sample solution. Just 2 ml of the sample solution was transferred into a brown test tube with a ground stopper, mixed well with 5.0 ml of a mixture of diacetyl monoxime-thiosemicarbazide-phosphoric acid, and then, heated in a boiling water bath for 20 min. After cooling in running water, the absorption was measured at 538 nm using a blank solution prepared in the same procedure with water instead of the sample, and the content was calculated by the previously prepared calibration curve. Calibration curve of DPU and DBU followed Beer's law up to 200 μg/ml. This method of determination was applied to determination of DPU, which is a decomposed product of tolbutamide and that of DBU. Chlorpropamide, tolbutamide and their decomposed products did not interfere with the determination. When chlorpropamide solution (5% pH 9.5) and tolbutamide solution (5% pH 9.7) were heated at 120°C for 1 hour, a change of composition was observed, and they were as follows: Chlorpropamide; decrease of chlorpropamide by 13.2%, increase of p-chlorbenzenesulfonamide by 8.4%, increase of n-propylamine by 0.8%, and increase of DPU by 2.2%, and tolbutamide solution; decrease of tolbutamide by 14.9%, increase of p-toluenesulfonamide by 10.1%, increase of n-butylamine by 1.1%, and increase of DBU by 3.2%.