Cody Robert B, Fouquet Thierry
JEOL USA, Inc ., 11 Dearborn Road , Peabody , Massachusetts 01960 United States.
Research Institute for Sustainable Chemistry , National Institute for Advanced Industrial Science and Technology (AIST) , Tsukuba 305-8565 , Japan.
Anal Chem. 2018 Nov 6;90(21):12854-12860. doi: 10.1021/acs.analchem.8b03413. Epub 2018 Oct 18.
A new approach to determining the repeat unit compositions of homopolymers is reported in which a mass defect graph is rotated to zero slope to give a graph identical to a Kendrick mass defect graph. Because the Kendrick mass defect (KMD) is directly related to the elemental composition of the base unit, the process can be reversed. A mass defect graph (fractional m/ z plotted against exact m/ z) of a homopolymer can be rotated until the slope of the data points is zero. This is equivalent to finding a new constant factor by which the measured exact masses would have to be multiplied to create a Kendrick mass defect graph with zero slope. The elemental composition of the repeat unit can be determined by matching the new factor against the calculated factors for candidate compositions. This approach provides some benefits over simply looking for pairs of peaks corresponding to oligomer units. The primary benefit is to assist in visualization of the data. Rotating the data points corresponding to polymer masses to zero slope makes it easier to visualize the polymer data, and it facilitates the graphical isolation of polymer masses from background interferences. The repeat unit composition is determined not from a single pair of peaks but from multiple data points, and systematic errors in mass assignment can be visualized as deviations from linearity. Resolution-enhanced KMD graphs can be constructed for the calculated repeat unit composition by using fractional base units.
本文报道了一种确定均聚物重复单元组成的新方法，即通过将质量缺陷图旋转至零斜率，得到与肯德里克质量缺陷图相同的图形。由于肯德里克质量缺陷（KMD）与基本单元的元素组成直接相关，因此该过程可以逆向进行。均聚物的质量缺陷图（以分数m/z对精确m/z作图）可以旋转，直到数据点的斜率为零。这相当于找到一个新的常数因子，将测量的精确质量乘以该因子，以创建斜率为零的肯德里克质量缺陷图。通过将新因子与候选组成的计算因子进行匹配，可以确定重复单元的元素组成。与简单地寻找对应于低聚物单元的峰对相比，这种方法具有一些优势。主要优势在于有助于数据的可视化。将对应于聚合物质量的数据点旋转至零斜率，使得聚合物数据更容易可视化，并且有助于从背景干扰中以图形方式分离聚合物质量。重复单元组成不是由一对峰而是由多个数据点确定的，质量分配中的系统误差可以表现为与线性的偏差。通过使用分数基本单元，可以为计算出的重复单元组成构建分辨率增强的KMD图。
