INTRODUCTION:

In 1664 by Sir Robert Boyle first time reported the use of natural dyes as acid-base indicator in his collection of essays Experimental History of Colors^[1].Indicators are may be dyes or pigments; we can isolate them from a variety of sources, like plants, algae and fungi. Any flower, like, red, pink, yellow, blue or purple in color contains a organic pigment called anthocyanin that change color with change in pH^[2]. Boyle give important contribution in classification of substances according to acid-base theory using acid base indicator but this idea is practiced by earlier medieval painters, to make water colorants they use the dye treated with vinegar and lime water^[3].

We see many examples of colour change around us like change in colour of ice tea after addition of lemon juice. In acid base chemistry nature of solution confirmed by change in colour of litmus for acidic blue paper turns in to red, for basic it change red to blue, while in neutral state paper show no colour change. The plant products like tea, red cabbage, grape or turmeric at molecular level react with acid and bases and causes change in colour at different pH levels^[4][5]. the principle of change in colour of solution is depend up on donating or accepting the protons between titrate and titrend (according to protonic theory acids are proton donors and vice versa). After reaction solution reach up to certain ph at that time indicator play important role by change in colour. Numbers of indicators gives only two colours after treating with acid or base, but some shows wide range of colours^[6]. Acid base titration having many applications like to determine the unknown concentration of acid or base by exactly neutralizing the known concentration of acid and base, in qualitative analysis, for quantitative analysis etc^[7]. Change in colour during acid base titration is used to signal the end of acid base titration. Natural indicators prepared from various plant parts like flowers, leaves or fruits are advantageous than synthetic one, because synthetic indicators are costlier than natural also they can causes chemical pollution during manufacturing process^[8][9]. We can use some common flower pigments in acid base titration as an indicator for example, Red rose, Hibiscus Rosa sinensis^[10], Copper leaf, Clitoria ternetea^[11].

Figure 1: Bauhinia racemosa Flower

Bauhinia racemosa Lam (The Sonpatta Tree) is a small, crooked, bushy, deciduous tree with drooping branches, which can grow in poor and very harsh climatic conditions. The deciduous tree is propagated easily from seed. Bauhinia is a genus of more than 200 species of flowering plants of subfamily, Caesalpiniaceae. Many species are widely planted in the tropics as orchid trees, particularly in northern India, Vietnam and southeastern China. This particular species racemosa is widely distributed throughout India, ascending to an altitude of 1,650 m from sea level in the western Himalayas, and in Ceylon, China and Timor. It is a useful species for filling blanks in forest plantings and helps in preventing soil erosion. In the United States of America, the trees grow in Hawaii, coastal California, Texas, Louisiana, and Florida^[12]. The plant is popularly known as Sittacha (Tamil), Banraj ( Bengali), Ashta, Jhinjeri, Katmauli, Kachnal (Hindi), Aapta, Aralukadumandara, Vana samtige (Kannada), Apto (Konkani), Omboroda (Odia), Kosundra (Punjabi), Arampaali, Kutabuli, Malayaththi (Malayalam), Asundro (Gujrati), Apta, Sona (Marathi), Yamalapatrakah, Yugmapatra, Ashmantaka, Kanchini (Sanskrit), Atti, Tataki, Kokku mandarai, (Tamil), Arechettu (Telugu), Kachnaar (Unani). Other common names include Mountain Ebony and Kachnar (India and Pakistan).

Botanical Description:

B. racemosa is a small crooked tree with dark scabrous bark, containing numerous drooping branches. The trees typically reach a height of 6–12 m and their branches spread 3–6 m outwards. The other important associated species under this genus Bauhinia include B. tomentosa Linn, B. retusa Roxb. B. vahlii Wight, B. purpurea Linn, B. variegate Linn, B. malabarica Roxb, B. macrostachya Wall. The bark of B. racemosa is bluish black, rough, pinkish red inside, which turns brown on exposure. The leaves are broader than long, having size 2-5 cm by 2.5- 6.3 cm, divided a little less than half way down into two rounded lobes. The upper surface of leaf being green and glabrous, rigidly coriaceous, slightly cordate, clothed more or less densely beneath with grey pubescence and base is usually cordate. The five-petaled flowers are 7.5– 12.5 cm diameter, generally in shades of red, pink, purple, orange, or yellow, and are often fragrant. The tree begins flowering in late winter and often continues to flower into early summer. The flowers are in shortpeduncle, lax, terminal and leaf-opposed racemes. The calyx being pubescent, contain very short tube, limbs are of 6-8 mm long and the petals are narrowly oblanceolate, acute, 10-15 mm long. The flowers contain 10 fertile stamens with densely hairy filaments at the base and ovary is pubescent with sessile stigma. The pods are stalked, 15-25 in number having size of 1.3-2.2 cm, blunt at the apex and tapering to the base, somewhat falcate, glabrous, turgid, scarcely veined. Each pod contains 12-20 dark reddish brown, oblong, compressed, rounded at the apex, seeds. The bark of B. racemosa is bluish black, rough, pinkish red inside, which turns brown on exposure^[13,14,15].

MATERIAL AND METHOD:

Collection and authentification of flowers:

The flowering plant of Bauhinia racemosa flower collected from the sangli district region, Maharashtra. And authenticated from Kusumtai Rajarambapu Patil College, Islampur.

Extraction of flowers:

Collected flowers of Bauhinia racemosa flower washed with distilled water and cut in to small pieces by using Sharpe blade. Then pigments are extracted by the maceration process using ethanol as solvent, pieces of petals are soaked into the ethanol for overnight. Then solution of pigment is filtered to remove the remaining flower matter (petals) from solution and used as natural indicator.

Chemicals:

Conc. HCl, Sodium hydroxide, ammonia, acetic acid, Methyl red. All reagents of analytical grade were available by Rajarambapu College of Pharmacy, Kasegaon.

Glassware’s:

pH meter, conical flask (100 ml), burettes (50 ml), pipettes (10 ml), test tube etc.

Method:

Method for screening of Bauhinia racemosa flower:

Screening of Bauhinia racemosa flower was done by carry out various titrations between strong acid-strong base (HCl Vs NaOH), strong acid–weak base (HCl Vs NH₃), and weak acid-strong base (CH₃COOH Vs NaOH) and weak acid-weak base (CH₃COOH Vs NH₃) each having strength 1M, and using both flower extract and Methyl red as indicator. At the end of titration change in color with respect to change in pH is determined.

Method for experimental screening of Bauhinia racemosa flower:

Experimental screening of Bauhinia racemosa flower was done by carry out various titrations between strong acid-strong base (HCl Vs NaOH), strong acid–weak base (HCl Vs NH₃), and weak acid-strong base (CH₃COOH Vs NaOH) and weak acid-weak base (CH₃COOH Vs NH₃) each having strength 0.1N, 0.5 N, 1N and 1.5N. In each titration 10ml of acid is diluted with 20ml of distilled water in volumetric flask and 2-3 drops of flower extract and Methyl red is taken as indicator in respective titration then volume required for color change (i.e. end point) was taken.

Table 1: Screening of Bauhinia racemosa flower

Titrant	Titrand	Indicator colour change (pH range)
Titrant	Titrand	Standard	Flower extract
HCl	NaOH	Red to Yellow (4.5-6.2)	Red to colorless (3.9-6.9)
HCl	NH₃	Red to Yellow (7.3-8.5)	Red to colorless (4.9-8.3)
CH₃COOH	NaOH	Red to Yellow (4.5-7.2)	Red to colorless (6.7-8.5)
CH₃COOH	NH₃	Red to Yellow (3.2-5.8)	Red to colorless (5.5-6.7)

Table-2: Experimental screening of Bauhinia racemosa flower

Titration	Strength	Indicator	Bauhinia Racemosa
Titration	Strength	Indicator	Mean ±SD(n=5)
HCl Vs NaOH	0.1	Methyl red	8.14±0.15
	0.1	Flower extract	7.5±0.10
	0.5	Methyl red	5.70±0.28
	0.5	Flower extract	5.5±0.72
	1.0	Methyl red	7.8±0.12
	1.0	Flower extract	6.3±0.34
	1.5	Methyl red	7.96±0.21
	1.5	Flower extract	7.9±0.33
HCl Vs NH₃	0.1	Methyl red	21.98±0.21
	0.1	Flower extract	21.4±0.16
	0.5	Methyl red	24.83±0.20
	0.5	Flower extract	23.3±0.40
	1.0	Methyl red	26.21±0.24
	1.0	Flower extract	25.01±0.30
	1.5	Methyl red	24.21±0.10
	1.5	Flower extract	23.20±0.30
CH₃COOH Vs NaOH	0.1	Methyl red	9.60±0.31
	0.1	Flower extract	8.50±0.20
	0.5	Methyl red	7.91±0.30
	0.5	Flower extract	7.80±0.20
	1.0	Methyl red	7.80±0.14
	1.0	Flower extract	6.60±0.21
	1.5	Methyl red	8.80±0.01
	1.5	Flower extract	7.60±0.34
CH₃COOH Vs NH₃	0.1	Methyl red	26.12±0.20
	0.1	Flower extract	25.40±0.90
	0.5	Methyl red	25.41±0.20
	0.5	Flower extract	24.30±0.21
	1.0	Methyl red	24.40±0.20
	1.0	Flower extract	23.30±0.20
	1.5	Methyl red	24.30±0.20
	1.5	Flower extract	23.10±0.12

RESULT AND DISCUSSION:

The screening of Bauhinia racemosa flower extract is done for use as natural indicator in acid base titration and these obtained result from screening was compared with result obtained from standard indicator such as Methyl red for strong acid-strong base (HCl and NaOH), strong acid–weak base (HCl and NH₃), and weak acid-strong base (CH₃COOH and NaOH) and weak acid-weak base (CH₃COOH and NH₃) titrations. The results obtained from titration of natural indicator (i.e. Bauhinia racemosa flower extract) are near to the result obtained from titration of standard indicator (i.e. Methyl red).

CONCLUSION:

The natural indicator (i.e. extract of Bauhinia racemosa flower) is also beneficial because this natural indicator gives end point upon slight change in pH as same as standard indicator (i.e. Methyl red), we can use these natural indicator alone in such acid-base titration. Hence this natural indicator economical and very useful as compare to synthetic one.

ACKNOWLEDGEMENT:

Authors are highly Acknowledge the help of laboratory staff of Rajarambapu College of Pharmacy, Kasegaon. For providing necessary equipment required for research work. also we are highly Acknowledge the help and guidance of Principal and vice principal of RCP, Kasegaon.

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Received on 24.04.2019 Accepted on 05.05.2019

Asian J. Pharm. Ana. 2019; 9(2):89-92.

DOI: 10.5958/2231-5675.2019.00017.6