Department of Chemistry, Hannam University, Daejeon 305-811, South Korea.
J Chromatogr A. 2010 Jul 2;1217(27):4623-8. doi: 10.1016/j.chroma.2010.04.082. Epub 2010 May 6.
Asymmetrical flow field-flow fractionation (AsFlFFF) was coupled online with multiangle light scattering (MALS) to study the changes in the molecular weight and the size distribution of the corn starch during carboxymethylation. A corn starch was derivatized with sodium chloroacetate in alcoholic medium under alkaline condition to produce carboxymethyl starches (CMS) having various degrees of substitution (DS). The change in thermal characteristics and granule structure of the native corn starch and CMS were compared using Thermogravimetric analysis and scanning electron microscope. The ionic strength of the carrier liquid (water with 0.02% NaN(3)) was optimized by adding 50mM NaNO(3) to minimize the interactions among the starch molecules and between the starch molecules and the AsFlFFF membrane. A field-programmed AsFlFFF allowed determination of the molecular weight distribution (MWD) of starches within about 25min. It was found that carboxymethylation of starch results in reduction in the molecular weight due to molecular degradation by the alkaline treatment. The weight-average molecular weight (M(w)) was reduced down to about 4.4x10(5) from about 7.2x10(6) when DS was 0.14. It seems AsFlFFF coupled with MALS (AsFlFFF/MALS) is a useful tool for monitoring the changes taking place in the molecular weight and the size of starch during derivatization.
不对称流场流分离（AsFlFFF）与多角度光散射（MALS）在线耦合，研究了羧甲基化过程中玉米淀粉分子量和粒径分布的变化。在碱性条件下，用氯乙酸钠在醇介质中将玉米淀粉衍生化，制得取代度（DS）不同的羧甲基淀粉（CMS）。采用热重分析和扫描电子显微镜比较了天然玉米淀粉和 CMS 的热特性和颗粒结构的变化。通过添加 50mM NaNO3 优化载液（含 0.02%NaN3 的水）的离子强度，以最小化淀粉分子之间以及淀粉分子与 AsFlFFF 膜之间的相互作用。场程控 AsFlFFF 允许在约 25 分钟内确定淀粉的分子量分布（MWD）。结果发现，由于碱性处理导致分子降解，淀粉的羧甲基化导致分子量降低。当 DS 为 0.14 时，重均分子量（M（w））从约 7.2x10（6）降低至约 4.4x10（5）。AsFlFFF 与 MALS （AsFlFFF/MALS）的耦合似乎是监测衍生化过程中淀粉分子量和大小变化的有用工具。
