Ionization sources and systems and methods using them

A chemical ionization source comprising:

• an ionization block comprising first, second, third and fourth supporting structures coupled to each other to form an ionization chamber, the first supporting structure comprising an entrance aperture configured to receive an analyte, wherein the third supporting structure comprises an exit aperture configured to permit ionized analyte to exit the ionization block, wherein the ionization block is configured to receive an ionization gas through an inlet in the first supporting structure of the ionization block;
• an electron source fluidically coupled to a first aperture in the second supporting structure of the ionization block;
• an electron collector positioned substantially coaxially with the electron source and within the ionization chamber and adjacent to the fourth supporting structure, wherein the electron collector is configured to receive electrons from the electron source that enter into the ionization chamber through the first aperture in the second supporting structure;
• an ion repeller positioned adjacent to the entrance aperture of the first supporting structure of the ionization block and positioned substantially orthogonal to the electron source;
• and
• at least one electrode configured to provide an electric field within the ionization chamber when a voltage is provided to the at least one electrode to control a fragmentation pattern of the analyte received in the ionization chamber.