quickly select library items not in any collection

Hi
I've got quite an extensive library and Zotero started being sluggish. So I thought I'd get rid of some junk records that are not in any collection. To my knowledge there is not a quick way of selecting such records. I can do it only by selecting a record and pressing CTRL to see whether it is in a collection - a slow way. I would be very grateful for a tool to address this issue,
Many thanks

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