In this study, the stability constants of the copper(II) and aluminium(III) complexes of quercetin were determined potentiometrically by using Calvin-Bjerrum and Irwing Rossotti methods. The protonation constants of quercetin were found:

The objective of this work was to compare the extraction of phenolic compounds from Tilia argentea flowers and bracts by using conventional (solvent extraction) and novel (ultrasound assisted) extraction methods. Ethanol (70 %) extracts were analyzed for their antioxidant activities. Total phenolic content was determined using Folin-Ciocalteu method and the antioxidant potential was determined by DPPH radical scavenging and Ferric Reducing Antioxidant Power (FRAP) assays. To determine the effect of ultrasound treatment on the extraction, same extraction parameters were applied in both methods. The results showed that extracts obtained by ultrasound assisted extraction have higher total phenolic content and antioxidant activity.

Objective of this study was to determine the total polyphenol content, antioxidant activity properties of the methanolic, ethanolic and aqueous extracts of Cydonia oblonga Miller leaves. Quince leaves have been used as folk medicine in Turkey. Total polyphenol content was determined by Folin-Ciocalteu assay. The antioxidant capacity was determined by ferric ion reducing antioxidant power method (FRAP) and DPPH (2, 2-diphenyl-1 picryl hydrazyl) free radical scavenging method by spectrophotometry. The methanol extract had the highest total phenolic content and the highest antioxidant activity. The results demonstrated that the correlation between total polyphenol content and antioxidant activity which was measured by DPPH and FRAP assays was positive and quince leaves are cheap and natural sources of antioxidants.

Nateglinide is an insulin secretagogue which has been used for the treatment of Type 2 Diabetes mellitus. A simple analytical methodology for determination of nateglinide in tablet formulation is described. An isocratic reversed phase high performance liquid chromatographic (HPLC) method was developed using Kinetex pentafluorophenyl (PFP) (5µm particle size and 4.6 x 150 mm id) core-shell column as stationary phase and 0.05 M Na2HPO4 (pH=2.0) / methanol (30:70 v/v) mixture as mobile phase with the flow rate of 1.0 mL min -1 and diode-array detector at 215 nm. Column was termostated at 22°C. Under these conditions nateglinide was eluted with a symmetrical peak shape and the retention time was 4.779 minutes. The system suitability parameters such as tailing factor, capacity factor and theoretical plate were evaluted. The method was validated as per International Council on Harmonisation (ICH) guidelines. Linearity was obtained in the 2.54 -40.70 µg mL -1 concentration range with equation y= 10.818x + 4.7048 (R 2 = 0.998). Limit of detection and limit of quantification were 1.07 and 2.54 µg mL -1 . Accuracy of the method was tested by recovery studies which were in the range of 98.78 -100.76 %. The intra-day and inter-day precision studies were carried out and the relative standard deviation values of peak areas were within ICH limits. The proposed method was successfully applied to the determination of nateglinide in tablet dosage form.