I learnt from some grammar sites (BBC and Grammar-Monster) that "quantity" is followed by inanimate count nouns: e.g. a large quantity of drugs. Sometimes singular nouns are used but this usage is considered outdated by modern grammarians: e.g. a large quantity of money (we have "monies" in dictionaries). However, i checked more examples from reputable dictionaries like Cambridge and discovered a contradictory example: a large quantity of equipment. We all know that "equipment" is totally a mass noun.