Corolla of Roselle (Hibiscus sabdariffa L.) as acid-base indicator

Abstract

KEYWORDSAcid-base titration requires indicators to show color change at each pH interval. Synthetic indicators applied recently have some negatives, such as chemical pollution, availability and expensive production cost. Effort to obtain natural product-based-indicator from corolla of Roselle (Hibiscus sabdariffa L.) has been conducted. Firstly, anthocyanin contained in the Roselle's corolla was identified. Then, the indicator was obtained by extracting the corolla consecutively with n-hexane, ethyl acetate and methanol-HCl 0.5%. Then the filtrate was evaporated at 65 o C. The obtained indicator was applied in weak base-strong acid and weak acid-strong base titrations. The comparison indicators used in this research were methyl orange and phenolphthalein. The results showed that the Roselle's corolla indicator gave red color in acidic solution, while green in basic solution. Additionally, its performance is similar to that of methyl orange.

Extraction of Green Acid-Base Indicators From Acanthus Pubescens Flower for Use in the School Laboratory

“…The UV-Vis absorption spectra for the dye solution extracted using the ethanolic and acidified ethanol are shown in Figures 5 below. As shown in the figures, the extracted solutions have shown absorption peaks at 224 nm, 267 nm, 331 nm and 524 nm in ethanolic extract. These absorption peaks of the extracted dye are closely related to flavonoids and anthocyanin as reported by other investigators (Obaseki et al, 2017;Nuryanti et al, 2013;Wuletaw et al, 2016). The UV-Vis absorption spectra of flavonoids consist of two distinctive bands in a broad range of 240 -550 nm.…”

“…All the extracted solutions show a UV-Vis absorption peak in the UV-Vis region of the spectrum at 224 nm, 267 nm, 331 and 524 nm for ethanol extracts of Acanthus pubescens flower; and 224 nm, 275 nm, 331 nm and 526 nm for acidified ethanol extracts of Acanthus pubescens flower. As shown in Figures 5A and 5B below, these absorption regions are also the main characteristics of flavonoid and anthocyanin pigments (Obaseki et al, 2017;Nuryanti et al, 2013;Khoddami et al, 2013).…”

“…Anthocyanins generally have two absorption maxima, one in the UV-region of spectrum 260 -280 nm (band II) and the second in the visible region of spectrum 490 -550nm (band I) (Ahmed et al, 2013). Almost all flavonoid classes give the same absorption at the region of band II, thus, anthocyanins can be distinguished from other classes by observing the absorption region wavelength of band I (Nuryanti et al, 2013).…”

Rosella (Hibiscus sabdariffa) Flowers as Alternative Indicators of Blue and Red Litmus

“…The use of synthetic indicators such as methyl orange, phenolphthalein and litmus become obstacles in the implementation of practicum in high school. The price is expensive because the materials and processes used are synthetic materials 1 . Therefore, there is a need to replace indicators of natural materials that are easy to obtain, cultivated, harmless, low cost and environmentally friendly.…”

New chemometric strategies in the spectrophotometric determination of pKa

“…[1,2]. In other words, the predominance of one of the two forms will condition their distribution in the environment, their biological activity or chemical reactivity, among others.…”