Abstract:

In order to overcome the disadvantages of the existing content determination methods of ethoxyl in ethyl cellulose,a new method based on the headspace gas chromatography ( HS-GC) is proposed. In this method,first,ethyl cellulose is conversed into ethyl iodide by reacting with hydriodic acid. Next,sodium hydroxide is added in headspace sample vials to neutralize excessive hydroiodic acid before the HS-GC performance,thus avoiding the damage to the sample injection system and the column. Then,toluene is used as the internal standard to perform a HS-GC process. Finally,the content of ethoxyl in ethyl cellulose is determined according to the ethyl iodide content obtained by the internal standard method. The authors investigate the effects of hydrolysis temperature,hydrolysis time,equilibration temperature,equilibration time and matrix additive on the determination and find that,when the hydrolysis temperature ranges from 140 to 150℃,the determination results vary slightly and the reaction ends within 1. 0 h,that a vapor-liquid equilibrium is reached at 80℃ after a vial equilibration for 30min,that the addition of cellulose helps to eliminate the matrix effect and to obtain good linearity between ethyl iodide content and peak area. The authors also indicate that the proposed method is of good repeatability and average recovery because the RSD ( Relative Standard Deviation) of determination results is very low ( 2. 83%) and the recovery rate is very high ( 99. 6%) ,and that results obtained by the proposed method accord well with those obtained by chemical titration.

Key words: content determination, headspace gas chromatography, ethyl cellulose, ethoxyl