英语翻译
The molecular weight were determined through LC/MS analysis used in the negative ion mode,where a signal located at m/z:619 a.m.u.and corresponding to [M–H]- was observed for the four derivatives and probably consisted of two catechin units linked through a CH–CHO group as shown in Fig.3.
主要不知道where a signal located at m/z:619 a.m.u.这句应该如何翻译.