determiner , pronoun ~ of (~ of them)
USAGE NOTE: The use of the preposition of is necessary when a pronoun follows. When a noun follows, two constructions are possible -- we saw ~ student; we saw ~ of the students.
EACH
Meaning of EACH in English
The Bbi combinatory dictionary of English, a guide to word combinations. Комбинаторный словарь английского языка Bbi. Руководство по словосочетаниям. 2012