Eco-friendly Indicator from the Leaf Extract of Alternanthera dentata
Shyama Nair* and Sheetal P.
Department of Chemistry, N. S. S. College, Pandalam, Pathanamthitta, Kerala ,India.
*Corresponding Author E-mail: shyamanair2009@gmail.com
ABSTRACT:
Alternanthera dentata belongs to family Amaranthacea. The extract of leaves of Alternanthera dentata can be used as a natural indicator in neutralisation titrations. The aqueous extracts of leaves of the plant are found to be red in colour. The colour of the extract changes from red to greenish yellow when pH changes from acid to alkaline region. The extract is found to have anthocyanins which impart red colour to its solution. Anthocyanins are water soluble and also sensitive to pH changes. So they can be used an efficient pH indicator. The results obtained by using this natural indicator was comparable with that obtained by using conventional acid - base indicator. This natural indicator can be used as an efficient alternative to commercial indicators. More over they are eco friendly, cheap and have more aesthetic values than commercially available indicators.
KEYWORDS: Acid base indicator, Alternanthera dentata, Natural indicators, Neutralisation titrations.
INTRODUCTION:
Alternanthera dentata belongs to family Amaranthaceae genus, and the species dentata. The plant is a perennial shrub, evergreen, which has white or nearly white flowers. Flowers are small and are axillary and clustered. The plant has a purple foliage and leaves are simple and opposite. It is distributed in topical temperature areas. The toxicity of the plant in unknown1.
In the seventeenth century, Chemist Robert Boyle described indicators extracted from roses and other plant materials in his book “The Experimental History of Colors” published in 1664. He also included the ability to turn plants juices red among the properties of acid2. Any flower, fruit, leaf or any other parts of plants that is red, blue, violet or purple has a class of compound called anthocyanins which change colour with the changes in pH3 There are many natural dyes obtained from plants which has different colours at different pH values4. An indicator in a substance which change colour over a range of H+ concentration or pH range5.
The transition range may shift slightly, depending on the concentration of the indicator solution and on the temperature at which the indicator is used. Natural colours giving a sharp, distinct and stable colour change on a change of acid to alkaline medium may be used as acid-alkali indicators in volumetric titrations.
An intense colour is desirable so that a very little indicator is needed, the indicator itself thus will not affect the acidity of the solution.
In this study the extract of leaves of Alternanthera dentata was used as a natural indicator for determining the acidity and alkalinity of the solutions in neutralisations titrations. A comparative study was also carried out using commercial indicators with the measurement of pH. The extract of leaves of Alternanthera dentata is red in colour when extracted. The red colour of the extract is due to the presence of plant pigment anthocyanins which can be easily isolated as they are water soluble6. These anthocyanins helps in pollination by attracting insects and also act as a protective UV screen7. The colouring matters, flavanoids and anthocyanins are pH sensitive8 and hence they can be used as an indicator for different types of acid-base titrations. Due to deleterious environmental effects of the conventional indicators, their availability and the cost factor a need for the application of natural indicators arises. More over natural dyes have more aesthetic quality than synthetic dyes when used as indicator.
MATERIAL AND METHODS:
The leaves of Alternanthera dentata were collected from the plants growing wild in the premises of our institution in Pandalam and was authenticated from the Department of Botany, N.S.S. College, Pandalam, Pathanamthitta. All the indicator solutions were prepared as per recommended procedures9. 1molar solutions of HCl, H2C2O4, NaOH, NH4OH were prepared and standardized according to standard methods9. Different dilutions of acid and alkali solutions were prepared by dilution, from the 1 molar solutions and were also standardised9 All chemicals used were of AR grade and solution were prepared in double distilled water. The experiments were carried out by using same set of glasswares Each estimation was performed using 10ml of the titrant and 10 drops of the extract of the leaves. The conventional indicators were added as recommended in the standard procedures.
The collected leaves of Alteranthera dentata were washed with distilled water cut into small pieces and macerated with ethanol, washed with distilled water and the water soluble portion was used as indicator. The equivalence point was noted at the sharp change in colour of the indicator used during titrations. pH was measured using pH meter (Elico- Model No: L1610) and the absorbance was determined by using UV. Spectrophotometer (Schimadzu Model. No: 8100)
RESULTS AND DISCUSSION:
The extract of leaves was used as indicator for titrations of strong acid with strong base (NaOH and HCl) weak acid with strong base (H2C2O4 and NaOH), weak base with strong acid (NH4OHandHCl), weak base with weak acid (NH4OHandH2C2O4). The results obtained were compared with those obtained by using the standard indicators methyl red, phenolphthalein and mixed indicator (methyl orange : bromocresol green(0.1:0.2)10. The result of the analysis is given in Table.1. The leaf extract of Alternanthera dentata shows two absorption maxima; 1st in the visible region at 521nm and other in the UV region at 284nm. As anthocyanins shows two absorption bands one in visible region 475-560nm and the other in UV region 275-250nm, the extract of leaves should contain anthocyanins. The actual colour depends on the number and position of hydroxyl and methoxyl groups; when these are fixed, the colour depends on pH and the solvent properties. The colour change is found to be from red to greenish yellow as the pH changes from acidic region to the basic one. These anthocyanins and flavanoids, which are mainly the colouring materials, are pH sensitive. The colour changes observed during volumetric estimations is given in Table-2. The colour changes were found to be very sharp. The titrations carried out for different concentrations of acid and alkali with both commercial as well as natural indicator prepared from the extract of leaves were found to be in good agreement with each other.
From the results obtained it can be inferred that extracts of leaves of Alternanthera dentata can be successfully used as an indicator in neutralization titrations. Phenolphthalein cannot be used in weak base strong acid titrations and methyl red cannot be used for weak acid strong base titrations. But the natural indicator can be used in all the different types of neutralisation titrations, even in case of weak acid - weak base neutralisation, where a mixed indicator in conventionally used. The natural indicators work best where freshly prepared.
Table – I Results of the titrations using various indicators
|
Titration (Titrant v/s Titrand |
Strength of solutions (moles) |
Indicator |
Volume used up with standard deviation |
|
1. NaOH v/s HCl |
1 |
Phenolphthalein |
9.5+ 0.13 |
|
|
|
Leaf extract |
9.6+ 0.03 |
|
|
0.1 |
Phenolphthalein |
9.6+0.13 |
|
|
|
Leaf extract |
9.1+0.04 |
|
|
0.01 |
Phenolphthalein |
9.8+0.15 |
|
|
|
Leaf extract |
9.5+0.03 |
|
2. NH4OH v/s HCl |
1 |
Methyl red |
10.3+0.16 |
|
|
|
Leaf extract |
9.8+0.10 |
|
|
0.1 |
Methyl red |
10.2+0.15 |
|
|
|
Leaf extract |
10+0.09 |
|
|
.01 |
Methyl red |
11.4+0.08 |
|
|
|
Leaf extract |
11.2+0.03 |
|
3. NaOH v/s H2C2O4 |
1 |
Phenolphthalein |
9.1+0.05 |
|
|
|
Leaf extract |
9.0+0.02 |
|
|
0.1 |
Phenolphthalein |
8.9+0.13 |
|
|
|
Leaf extract |
9.1+0.03 |
|
|
.01 |
Phenolphthalein |
8.4+0.12 |
|
|
|
Leaf extract |
8.8+0.03 |
|
4. NH4OH v/s H2C2O4 |
1 |
Mixed indicator |
6.3+0.23 |
|
|
|
Leaf extract |
6.5+0.12 |
|
|
0.1 |
Methyl red |
5.9+0.20 |
|
|
|
Leaf extract |
5.7+0.10 |
|
|
01 |
Methyl red |
5.5+0.12 |
|
|
|
Leaf extract |
5.3+0.05 |
HCl- Hydrochloric acid, NaOH – Sodium hydroxide ,NH4OH – Ammonium hydroxide ,H2C2O4 – Oxalic acid
Table – 2 Comparison of colour changes of indictors used with pH range
|
Titrand |
Titrant |
Indicator colour change |
|
|
|
|
Standard (pH range) |
Extract of leaf (pH range) |
|
HCl |
NaOH |
Colourless to pink (8-9.8) |
Red to greenish yellow (8-10) |
|
HCl |
NH4OH |
Red to yellow (3.5-8.5) |
Red to greenish yellow (4-9) |
|
H2C2O4 |
NaOH |
Colourless to pink (8-9.8) |
Red to greenish yellow (9-10) |
|
H2C2O4 |
NH4OH |
Orange to blue green (4-7.5) |
Red to greenish yellow (4-8) |
HCl- Hydrochloric acid, NaOH – Sodium hydroxide ,NH4OH – Ammonium hydroxide, H2C2O4 – Oxalic acid
Thus the natural indicator prepared from the extract of leaves in an efficient alternative to commercial indicator in acid-base titrations. They are eco friendly, cheap, and easily available and less toxic compared to the conventional indicators that are being used.
CONCLUSION:
The conventional indicator like phenolphthalein and methyl red are toxic to the environment. The natural coloured pigments are eco friendly, cheap and easily available. They also give a sharp colour change in neutralisation titrations and can be replace the conventional acid-base indicators.
ACKNOWLEDGMENT:
The authors thank University Grants Commission for financial support.
REFERENCES:
1. Plant files : Detailed information on Ruby leaf, Parrot leaf, Calico Plant, Joy weed ‘Rubiginosa’ (Alternanthera dentata) cited on 30/03/2006.
2. www.google.com
3. Gulrajani MLand Gupta D. Natural dyes and their application to textiles. IIT Delhi. 1992.
4. Indrayan AK. Natural dyes as neutralisation indicators. J.Indian Chemical Soc. 2003: 80: 505-509.
5. Lange’s Handbook of Chemistry. 8th edn. Hand book publishers. Inc. 1952.
6. Madsci network@1997, Washington University medical school web natural indicator solutions (anthocyanins) htm.
7. Sullivan Jack. International carnivorous plant society News Letter, 1998.
8. Chatwal.GR. Organic Chemistry of Natural products 4th edn. Vol II. Himalaya Publishing house. New Delhi. 2007: 2.38-240.
9. Jaffery GH, Besset,J. Denny, R.C. Mendham.J. Vogel’s textbook of Quantitative chemical analysis 5th edn. ELBS Publication. Longnnann Group. England. 1996.
10. http:/enwikipedia.org/wiki/pH indicator.
Received on 25.03.2011 Modified on 03.04.2011
Accepted on 08.04.2011 © RJPT All right reserved
Research J. Pharm. and Tech. 4(7): July 2011; Page 1095-1097