全挥发顶空气相色谱法测定乙氧基含量

本文建立了一种全挥发顶空气相色谱法测定乙基纤维素乙氧基含量的方法。按照改进的蔡氏法(Zeisel),在顶空瓶中通过氢碘酸与乙基纤维素反应,使乙氧基转化为碘乙烷,反应结束后加碱液中和过量氢碘酸防止腐蚀进样器和色谱柱,随后抽取μL级样品全挥发顶空进样,进行气相色谱分析。以甲苯为内标物,采用内标法测定碘乙烷含量,从而计算得出乙基纤维素乙氧基含量。考察了平衡温度,平衡时间和样品量等影响因素,结果表明μL级样品(<40μL)在90℃的平衡温度下4min内可达到近乎完全挥发,碘乙烷和甲苯的质量比与它们的峰面积比呈良好的线性关系(r=0.9998,n=7),碘乙烷回收率98.9%(RSD=2.2%,n=6)。该方法操作简便,快速准确,可用于乙基纤维素的质量控制。

Determination of Ethoxyl Content by Full Evaporation Headspace Gas Chromatography

This study demonstrated a full evaporation headspace gas chromatography(HS-GC) method to measure the ethoxyl content of ethyl cellulose with toluene as internal standard.The procedure consisted of reaction of ethyl cellulose with 57wt% hydroiodic acid in headspace sample vials by a modified Zeisel method and neutralizing the remaining hydroiodic acid with sodium hydroxide before the HS-GC performance,which can avoid the damage of the sample injection system and column by residual hydroiodic acid.The data show that a near-complete mass transfer of sample from liquid to the vapor phase(headspace) was achieved within 4min at 90℃ when a very small(<40μL) sample was added to a 20mL headspace sample vial.The results showed that the method has a good linear relationship of standard calibration curve(r=0.9998,n=7) and accuracy(recovery=98.9%).The proposed method is simple,rapid,and precise.It is well suited for the quality control of ethyl cellulose.