Brown R S, Gilfrich N L
Department of Chemistry, Colorado State University, Fort Collins 80523.
Rapid Commun Mass Spectrom. 1992 Nov;6(11):690-6. doi: 10.1002/rcm.1290061112.
The ion detection process in a discrete-dynode electron multiplier can result in significant mass resolution losses in time-of-flight mass spectrometry (TOF-MS) for higher mass-to-charge (m/z) ion species. This resolution loss is attributed to propagation time delays and signal broadening in the ion detector. This is presumed to be due to the generation of a distribution of secondary ion species produced initially upon impact of a primary ion with the first dynode surface of the ion detector. Comparisons are made between the signals produced by a standard discrete dynode ion detector (which amplifies the negatively charged species produced by impact of a primary ion) and a detector modified to respond to only the positively charged secondary ion species produced by a primary ion impact. Ion signals for higher m/z ions with the standard detector geometry are seen to be due to a narrow signal component, most likely due to the generation of secondary electrons and/or very low mass secondary ions (H-), and a broad signal component, apparently due to secondary ions which take significant amounts of time to traverse the low potential fields between the first and second detector dynode. This results in ion signal tailing for higher m/z ion species. Numerical subtraction of the ion signal obtained with the standard and modified detector geometries (singly protonated molecular ion species of equine myoglobin) results in an improvement in mass resolution, such that a new adduct ion species (from trifluoroacetic acid) can be resolved.
在离散打拿极电子倍增器中的离子检测过程，对于较高质荷比（m/z）的离子种类，可能会导致飞行时间质谱（TOF-MS）中出现显著的质量分辨率损失。这种分辨率损失归因于离子探测器中的传播时间延迟和信号展宽。据推测，这是由于初级离子撞击离子探测器的第一打拿极表面时最初产生的二次离子种类分布所致。对标准离散打拿极离子探测器（其放大初级离子撞击产生的带负电种类）和经过改进以仅响应初级离子撞击产生的带正电二次离子种类的探测器所产生的信号进行了比较。对于具有标准探测器几何形状的较高m/z离子，离子信号被认为是由一个窄信号分量（很可能是由于二次电子和/或极低质量二次离子（H-）的产生）和一个宽信号分量（显然是由于二次离子需要大量时间穿过第一和第二探测器打拿极之间的低电位场）组成。这导致较高m/z离子种类的离子信号拖尾。对使用标准和改进探测器几何形状（马肌红蛋白的单质子化分子离子种类）获得的离子信号进行数值相减，可提高质量分辨率，从而能够分辨出新的加合物离子种类（来自三氟乙酸）。
