Volumetric Acid-Base Titration by using of Natural Indicators and Effects of Solvent and Temperature

Research Article

Austin Chromatogr. 2016; 3(1): 1041.

Volumetric Acid-Base Titration by using of Natural Indicators and Effects of Solvent and Temperature

Bahadori A* and Maroufi NG

University of Applied Science and Technology, Iran

*Corresponding author:Ali Bahadori, University of Applied Science and Technology, Iran

Received: December 28, 2015; Accepted: April 07, 2016; Published: April 15, 2016


In this work, many natural sources as acid-base indicators which are extracted from different parts of fruits, flowers and plants were investigated for volumetric acid-base titration at room temperature, 60°C, 92°C and 98°C. Pigments from some fruits and plants were extracted, separated, and purified in carbon tetrachloride, chloroform, ethanol, methanol and toluene as solvents. These indicators in acid-base titrations shown sharp color changes with variation of pH at the equivalence point and we could determine the pH range. For some indicators the color of indicator in different solvents was similar that suggested there was no obvious modification of chemical structure of indicators in different solvents. In addition, the effect of temperature on indicators and their stability were studied. The result proved to be acceptable in introducing natural pigments as suitable acid - base indicators. These natural indicators are found to be a very useful, economical, simple, accurate and nature-friendly.

Keywords: Acid- base indicator; Natural pigment; Solvents; Titration; pH


Several types of synthetic chemical indicators are available for different types of titrimetric analyses. Acid-base indicators are known as pH indicators. Acid–base indicators are substances (dyes) which change color with pH. They are usually weak acids or bases, which when dissolved in water dissociate slightly and form ions. Volumetric analysis is one of the major quantitative techniques. In titrimetry, the equivalent point is usually determined by the end point in the titration. The end of point in traditional titrimetry is usually indicated by some substances added into the analyte solution, which change color immediately after the equivalent point has been attained. These substances are generally referred to as indicators. Several types of indicators are available for different types of titrimetric analyses. Most pH indicators are either weak organic acids or bases dyes which accept or donate electrons [1]. Although there are automated titration apparatus that determine the equivalent point between reacting species, indicators are still needed for teaching and research laboratories for simple titration [2]. Commercial indicators are expensive and some of them have toxic effects on users and can also cause environmental pollution [3]. For these reasons there has been an increasing interest in searching for alternative sources of indicators from natural origins. Historically, plants have been used for the extraction of a majority of natural dyes. As interest in natural dyes grew, information from the old literature was collected and traditional dyeing practices in different regions were documented and compiled by various researchers. The use of natural dyes as acidbase indicator was first reported by Sir Robert Boyle in collection of assays “Experimental History of Colors” in 1664 [4,5]. A large number of dyes are obtainable as natural products. In Nigeria, several workers have extracted a number of dyes from a variety of local plants. According to Akpuaka et al. [6] and Osabohien et al. [7], the local plants - Camwood, Redwood, Henna, Annato, Rothmania, Terminalia, Indiqovine, Kola, Banana, Tumeric, Roselle and Ginger all contain different types of dyes which are used for various purposes. Natural dyes are derived from natural resources and based upon their source of origin; these are broadly classified as plant, animal, mineral, and microbial dyes although plants are the major sources of natural dyes. Recent environmental awareness has again revived interest in natural dyes mainly among environmentally conscious people. Natural dyes are considered eco-friendly as these are renewable and biodegradable. Ekandem et al. [8] and Eze et al. [9] have reported their findings on the use of some natural dye extracts as indicators in acid-basetitrimetry. In recent years, there are numerous natural acidbase indicators that can be obtained from common flowers, fruits and vegetables [3,10].

Among of natural dyes as acid-base indicator, Flavones, Flavonols, Anthocyanidins, Anthocyanins are some types of indicator, which have been studied in order to substitute these compound instead of synthetic indicators [11,12]. For example, the chemical structure forms and colors of an anthocyanin at different pHsare presented in Figure 1.