Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Development of specthrophotometric methods of analysis for flavonoids in plant extracts and textile dyes

Natural dyes used in dyeing fibers are made from natural living sources such as plants and animals. These dyes include mainly carotenoids, hydroxyketones, anthraquinones, naphthoquinones, flavonoids, indigoids and related compounds. These compounds can be found either directly in crude extracts or gain colour from extracted colourless precursors as a result of such reactions as hydrolysis, oxidation, condensation, etc. Flavonoid dyes on textile products can be detected by non-invasive techniques such as FTIR microscopy and SEM/EDS, or estimated by extractive techniques such as HPLC with diode-array detection, RP-HPLC/MS or pyrolysis-GC/MS after derivatization with hexamethyldisilazane. Naturally these high-cost sophisticated techniques are not available to many conventional laboratories, and visible spectroscopy has been widely applied to such analyses. Unfortunately, these sophisticated and costly techniques are not available to many routine laboratories. Thus it is necessary to develop simple, low-cost, rapid, and sensitive methods for the assay of flavonoid content of natural dyes. In this regard, the aim of this thesis work is to determine the total flavonoid contents of plant extracts and textile dyes with the devised methods and to establish the compliance of the obtained results with those found by the reference method.

In this study, the determination of antioxidant flavonoids was based on the use of the cupric ion reducing antioxidant capacity assay (known in the literature as CUPRAC method) originally developed in our laboratories for the measurement of total antioxidant capacity (TAC). The CUPRAC method was rendered to measure the flavonoid capacity of natural dyestuffs. The flavonoid capacity measurement was based on the oxidation of these compounds to the corresponding quinones by the chromogenic copper(II)-neocuproine (Cu(II)-Nc) reagent, which was itself reduced to the cuprous neocuproine chelate showing maximum absorbance at 450 nm wavelength.

As the reference method of comparison, the widely used AlCl3/potassium acetate spectrophotometric method was applied to total flavonoid assay of these dyes. This method is based on the chelate formation of Al(III) with the C-4 keto and either one of C-3 or C-5 hydroxyl substituents of the flavonoid molecule (flavones and flavonols). The flavonoid capacity was measured by absorbance measurement of this coloured Al-chelate at the 427 nm-analytical wavelength of Al(III)-quercetin chelate used as reference. The results of the proposed (CUPRAC) and comparison (AlCl3/potassium acetate) methods applied to selected natural dye extracts were correlated with the reference high performance liquid chromatography (HPLC) findings using a C-18 column.

During the first phase of the study, the optimal conditions of measurement with the AlCl3/potassium acetate were determined. In the succeeding phases, the calibration equations for the polyphenolic compounds potentially contained in natural dyes (e.g., flavonoids, anthraquinones, etc.) were established with the use of both spectrophotometric methods, and the quercetin (QR) equivalent flavonoid concentrations (QREFC) of each compound was found. The method of standard additions using quercetin increments was applied to both methods to see if there was any deviation from Beer’s law; the results showed the absence of any chemical deviations. The quercetin capacities with respect to both methods (in the units of QREFC coefficients) of some natural dyes widely used in fibre dyeing were; Rubia tinctorum (common madder), Curcuma longa L. (curcumin), Alkanna tinctoria (dyers' bugloss), Matricaria chamonilla (chamomile), and Coccus ilicis (cochineal); CUPRAC values: 21.49, 38.91, 19.04, 48.60, and 143.49 μmol QR g-1, and AlCl3/potassium acetate values: 24.58, 165.89, 6.53, 15.02, and 33.02 μmol QR g-1, respectively. The differences in the QREFC coefficients of individual phenolics measured with different assays caused variations in the TFC (Total flavonoid capacity) order of the measured dye extracts. Both of spectrophotometric methods were validated against HPLC method.