For improving sensitivity, dynamic range, and specificity of GC-MS analysis there are disclosed embodiments of novel apparatuses based on improved characteristics of semi-open source with electron impact ionization, providing much higher brightness compared to known open EI sources. In an implementation, the source becomes compatible with multi-reflecting TOF analyzers for higher resolution analysis for improving detection limit. With improved schemes of spatial and temporal refocusing there are proposed various tandem TOF-TOF spectrometers with PSD, CID, and SID fragmentation and using either singly reflecting TOF or MR-TOF analyzers.