@article{
author = "Kuntić, Vesna and Pejić, Nataša and Mićić, Svetlana and Vukojević, Vladana and Vujić, Zorica and Malešev, Dušan",
year = "2005",
abstract = "Asimple, rapid and accurate procedure for the quantitative determination of quercetin in its pure form and in formulations has been developed. The method is based on the spectrophotometric determination of a complex formed between quercetin and potassium titanyloxalate in 50 % ethanolic solutions. To characterize the quercetin titanyloxalato complex, the stability constants of the complex were determinated potentiometrically and spectrophotometrically at different temperatures (T = 26.0oC, 34oC and 39.0oC), as well as at different ionic strengths (I = 5.0x10-4 mol dm-3, 3.0x10-2 mol dm-3 and 6.0x10-2 mol dm-3) and the thermodynamic parameters were calculated. As quercetin is usually conjugated to vitamin C in pharmaceutical formulations, two procedures for the quantitative determination of quercetin by this complexing reaction were tested - both in the absence and presence of ascorbic acid. In both procedures, the Beer law was obeyed over the same concentration range of quercetin, i.e., 0.85 μg mL-1 - 16.9 μg mL-1. In the first procedure in the absence of ascorbic acid the molar absorptivity coefficient of the quercetin-titanyloxalate complex is a=2.49 x 104 mol-1 dm3 cm-1, Sandells sensitivity of the method is S = 1.35 x 10-2 μg cm-2 and the detection limit is d = 0.67 μg mL-1. Whereas, in the presence of ascorbic acid (second procedure) a = 3.04 x 104 mol-1 dm3 cm-1, S = 1.11 x 10-2 μg mL-1. The proposed method was verified for the determination of quercetin in pharmaceutical dosage forms., Predložen je brz, jednostavan i tačan metod za određivanje kvercetina u farmaceutskim sirovinama i doziranim oblicima.Metod je baziran na spektrofotometrijskom određivanju kompleksa formiranog između kvercetina i kalijum-titaniloksalata u 50 % etanolu. Određene su konstante stabilnosti kvercetin titaniloksalatnog kompleksa potenciometrijski i spektrofotometrijski na različitim temperaturama (T = 26.0oC, 34oC and 39.0oC) i jonskim jačinama (I = 5.0x10-4 mol dm-3, 3.0x10-2 mol dm-3 and 6.0x10-2 mol dm-3) i izračunati su termodinamički parametri. Kako se kvercetin uobičajeno nalazi zajedno sa vitaminom C u doziranim oblicima, predložene su dve procedure za određivanje kvercetina: bez i u prisustvu askorbinske kiseline.U obe predložene procedure, Beer-ov zakon važi u oblasti 00.85 μg mL-1 - 16.9 μg mL-1 kvercetina. Prema prvoj proceduri, molarni apsorpcioni koeficijent kvercetin–titaniloksalatnog kompleksa je a=2.49 x 104 mol-1 dm3 cm-1, Sandelova osetljivost metode je S = 1.35 x 10-2 μg cm-2, a limit detekcije je d = 0.67 μg mL-1. Prema drugoj proceduri, a = 3.04 x 104 mol-1 dm3 cm-1, S = 1.11 x 10-2 μg mL-1. Predloženi metod je primenjen za određivanje kvercetina u doziranim oblicima.",
publisher = "Srpsko hemijsko društvo, Beograd",
journal = "Journal of the Serbian Chemical Society",
title = "Determination of quercetin in pharmaceutical formulations via its reaction with potassium-titanyloxalate: Determination of the stability constants of the quercetin-titanyloxalato complex, Određivanje kvercetina u farmaceutskim preparatima preko reakcije sa kalijum-titaniloksalatom - određivanje konstanti stabilnosti kvercetin-titaniloksalatnog kompleksa",
volume = "70",
number = "5",
pages = "753-763",
doi = "10.2298/JSC0505753K"
}
