Determination of quercetin in pharmaceutical formulations via its reaction with potassium-titanyloxalate: Determination of the stability constants of the quercetin-titanyloxalato complex

• Published in: Journal of the Serbian Chemical Society 2005, Vol.70 (5), p.753-763
• Main Authors: Kuntic, Vesna, Pejic, Natasa, Micic, Svetlana, Vukojevic, Vladana, Vujic, Zorica, Malesev, Dusan
• Format: Article
• Language: English
• Subjects: dosage form; potassium titanyloxalate; quercetin; spectrophotometric determination; stability constants
• ISSN: 0352-5139; 1820-7421
• DOI: 10.2298/JSC0505753K

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 ?g mL-1 - 16.9 ?g 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 ?g cm-2 and the detection limit is d = 0.67 ?g 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 ?g mL-1. The proposed method was verified for the determination of quercetin in pharmaceutical dosage forms. . Predlozen je brz, jednostavan i tacan metod za odredjivanje kvercetina u farmaceutskim sirovinama i doziranim oblicima.Metod je baziran na spektrofotometrijskom odredjivanju kompleksa formiranog izmedju kvercetina i kalijum-titaniloksalata u 50 % etanolu. Odredjene su konstante stabilnosti kvercetin titaniloksalatnog kompleksa potenciometrijski i spektrofotometrijski na razlicitim temperaturama (T = 26.0oC, 34oC and 39.0oC) i jonskim jacinama (I = 5.0x10-4 mol dm-3, 3.0x10-2 mol dm-3 and 6.0x10-2 mol dm-3) i izracunati su termodinamicki parametri. Kako se kvercetin uobicajeno nalazi zajedno sa vitaminom C u doziranim oblicima, predlozene su dve procedure za odredjivanje kvercetina: bez i u prisustvu askorbinske kiseline.U obe predlozene procedure, Beer-ov zakon vazi u oblasti 00.85 ?g mL-1 - 16.9 ?g 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