Complex sentence: He has appraised and authenticated thousands of items, both within his collection and outside of his collection, and since the late 1980s has made collecting in general, and improvement and exhibition of this collection in particular, his sole aim.
Split into simpler sentences: He has appraised and authenticated thousands of items, both within his collection and outside of his collection. Since the late 1980s he has made collecting in general, and improvement and exhibition of this collection in particular, his sole aim.