Preliminary Identification and Quantification of Quercetin Concentration and Its Comparison in Psidium Guajava L. (Guava) Fruit Ethanol Extract 50% and 70%, Dwiwina, Resti Gradia,, Dhianawaty Dyah, Defi Irma Ruslina, and Atik Nur , Pharmacognosy Journal, April 2023, Volume 15, Issue 2, p.399-405, (2023)