Extractive Spectrophotometric Methods for Determination of Tamsulosin HCl in Pharmaceutical Formulations Using Acidic Triphenyl Methane Dyes

 

Susmitha K.2, Radha K.2 and Venkateshwarlu G.1*

1Department of Chemistry, Nizam College, Hyderabad -500001, A.P. India

2Department of Chemistry, St. Anns College for Women, Hyderabad -500028, A.P. India

*Corresponding Author E-mail: venkateshwarlugoud@yahoo.com

 

ABSTRACT:

Four simple and sensitive extractive spectrophotometric methods have been described for the assay of Tamsulosin hydrochloride either in pure form or in pharmaceutical formulations. The developed methods involve formation of colored chloroform extractable ion-pair complexes of the drug with bromothymol blue (BTB), bromophenol blue (BPB), bromocresol purple (BCP) and bromocresol green (BCG) in acidic medium. The extracted complexes showed absorbance maxima at 415 nm for all four methods. Beer’s law is obeyed in the concentration ranges 2.5-25, 2.5-25, 2.0 - 25 and 2.5 - 25. µg/ml with BTB, BPB, BCP and BCG, respectively. The effect of concentration of dye, pH, and interference of excipients have been studied and optimized. The limits of detection and quantification have been determined for four methods. All the four methods have been validated as per the guidelines of ICH. The methods have been applied to the determination of drug in commercial tablets and results of analysis were validated statistically through recovery studies.

 

KEYWORDS: Tamsulosin hydrochloride; Bromothymol blue; Bromophenol blue; Bromocresol green; Bromocresol purple, Spectrophotometry.

 

 


 

INTRODUCTION:

Tamsulosin HCL is an selective alpha blocker used in the symptomatic treatment of benign prostatic hyperplasia (BPH)1-3 .Chemically, Tamsulosin is R-5-(2-(2-(2-ethoxyphenoxy) ethylamino) propyl) - 2-methoxybenzene sulfonamide and is official in USP volume 3 pharmacopoeia. Review of the literature revealed that there are five simultaneous spectrophotometric methods for the estimation of Tamsulosin with different combinations4-8

 

LC-MS-MS, HPTLC, Tandem mass and LC-ESI-MS/MS methods with high sensitivity and selectivity for the estimation of Tamsulosin in pharmaceutical dosage forms and human plasma have been reported9-12.

 

Literature survey on Spectrophotometric determination of drugs also revealed that certain acidic dyes viz  BCP, BTB, BCG and BPB act as complexing agents and form ion pair complexes with cation salts13-16 and form a basis for quantitative determination of drugs.

 

The methods based on ion pair complexes extractable into a suitable organic solvent have been shown to be simple, sensitive, accurate and economical.

 

In this paper we report four simple and sensitive extractive spectrophotometric methods for the assay of Tamsulosin hydrochloride. The methods are based on ion-pair complexation of drug with dyestuffs viz bromothymol blue (BTB), bromophenol blue (BPB), bromocresol purple (BCP), bromocresol green (BCG) and subsequent extraction into chloroform and measure the absorbance of color complex.

 

MATERIALS AND METHODS:

Materials:

Tamsulosin hydrochloride is procured from Aurobindo Labs Limited, Hyderabad as a gift sample. The dyestuffs viz., BTB, BPB BCP and BCG (AR grade) supplied by SD Fine Chemicals Ltd. Mumbai, are used without any further purification. The dyestuffs were used as 0.025% solutions in doubly distilled water. Sodium acetate-hydrochloric acid buffers17 of pH 2.5, 2.8 and 3.5 were prepared by mixing 50ml of 1.0M sodium acetate solution with 50.50, 49.50 or 46.25 ml, respectively, of 1.0 M HCl solution and diluted to 250 ml with double distilled water. The pH of each solution was adjusted to an appropriate value with the aid of a pH meter. Chloroform (HPLC grade) supplied by SD Fine Chemicals Ltd. Mumbai is used throughout the work. Stock solutions were prepared for all the dyes and drug (25mg/100ml).

 

The spectra (Fig.1) of ion-pair complexes have been recorded on SHIMADZU 140 double beam spectrophotometer, Thermo Nicolet 1000 and also on ELICO 159 UV-Visible single beam spectrophotometer using quartz cells of 10 mm path length. An Elico model Li-120 pH meter was used for pH measurement.

 

Fig 1 – Absorption spectra of  Tamsulosin hydrochloride – dyes complexes

(a) drug = BPB (b) drug = BTB (c) drug = BCG (d) drug = BCP

 

Methods

Different aliquots of drug solution were transferred into 125 ml separating funnel. To this 5 ml of buffer (pH 2.5, 2.8 and 3.5), 5 ml of dye were added and total volume was made up to 20 ml with water. 10 ml of chloroform was added and the contents were shaken for 5 min. The two layers were allowed to separate for 5 min.

 

The organic layer was separated and absorbance of yellow colored solution which is stable at least for 3 hrs is measured at 415nm against blank similarly prepared. The same procedure of analysis is followed either for assay of pure drug or for dosage form. The calibration graphs (Fig. 2) are linear over the concentration ranges are within the permissible range. The optical characteristics and statistical data for the regression equation of the proposed methods are presented in (Table -1).

 

Fig 2 – Calibration graphs of Drug – Dyes ion pair complex

Procedure for the assay of pure drug:

Four different solutions of pure drug in the range of calibration curve were selected and the recovery experiments were performed. The recoveries and their relative standard deviations are tabulated (Table -2) for six replicates.

 

Procedure for the assay of dosage forms:

Five tablets of Veltam 0.4 mg are powdered and dissolved in doubly distilled water and stirred thoroughly, filtered through a Whatman No. 42 filter paper. This solution was transferred into 100 ml standard volumetric flask and diluted with doubly distilled water as required. Different solutions of drug in the range of calibration curve were chosen and the assay was estimated using the calibration curve in six replicates.

 

RESULTS AND DISCUSSION:

Tamsulosin hydrochloride forms ion-pair complexes in acidic buffer with dyestuffs viz; bromothymol blue (BTB), bromophenol blue (BPB) bromocresol purple (BCP) and bromocresol green (BCG) and these complexes are quantitatively extracted into chloroform. Ion-pair complexes of drug with BTB, BPB, BCP and BCG absorbed maximally at 415nm. The reagent blank under similar conditions showed no absorption.

 

In order to establish molar ratio between Tamsulosin hydrochloride and dyestuffs used, the Job’s method of continuous variation18 has been applied. In this method, solutions of drug and dyestuff with identical molar concentrations [8 x 10-5M] were mixed in varying volume ratios in such a way that the total volume of each mixture was the same.

 

The absorbance of each solution was measured and plotted against the mole fraction of the drug, [drug]/ [drug] + [dyestuff] (Fig. 3). This measurement showed that 1:1 complex was formed with each dyestuff. The formation constants19,20, were also estimated and found to be  1.96 x 104, 2.35 x 104 , 2.82x 104  and 3.53 x 104 M-1 for complexes with BTB, BPB, BCP and BCG  respectively.

 

Fig .3 - Continuous – variation study of drug – dye system.

[Drug] = [Dye] = 8 x 10-5


Table No.1: Optical  Characteristics and Statistical for the regression equation of  the  proposed  methods

Parameters

 

Extraction methods with

BPB

BCG

BTB

BCP

λmax (nm)

Beer’s law limit (μg ml-1)

Molar absorptivity (L mol-1 cm-1)

Formation constant, K, M-

Sandell sensitivity (μg cm-2)

Slope (specific absorptivity),  b

Intercept (a)

Correlation coefficient (r)

Standard deviation of intercepts (% n=6)

Limit of detection, μgml-1

Limit of quantification, μgml-1

Regression equation

415

3.0 - 25

2.12 x 104

1.96 x104

0.0162

0.06140

-0.02

0.9995

0.02

1.0

3.0

Y=0.0614xC-0.02

415

2.5 - 25

2.30 x 104

2.35 x104

0.0150

0.0666

-0.05

0.9991

0.018

0.8

2.4

Y=0.0666xC-0.05

415

2.5 – 25

2.45 x 104

2.82 x 104

0.0140

0.07102

-0.06

0.9998

0.015

0.69

1.8

Y= 0.0710xC-0.06

415

2.0 - 22.5

2.87 x 104

3.53 x 104

0.0120

0.08313

0.0054

0.9999

0.012

0.4

1.2

Y=0.08313xC+0.0054

aWith respect to Y=bc+a, where C is the concentration (μg ml-1) and Y is absorbance

bSix replicate samples.

 

Table No. 2: Appplication  of  Proposed Methods for  the Analysis of Tamsulosin  Hydrochloride in  pure form

Taken

(μg ml-1)

Found

(μg ml-1)

 

 

 

Proposed

method

 

 

 

Reference

method

 

BPB

BCG

BTB

BCP

BPB

BCG

BTB

BCP

Recovery (%)

2.5

5.0

7.5

10.0

2.4

4.9

7.45

10.05

2.52

4.95

7.52

9.98

2.46

5.02

7.42

9.95

2.49

4.92

7.51

9.94

96

98

99.3

100.5

100.8

99

100.2

99.8

98.4

100.4

98.9

99.5

99.6

98.4

100.1

99.4

99.0

100.1

100.5

98.0

100.9

RSD (%)

 

 

 

 

1.956

0.75

0.866

0.717

1.18

Mean±SD

 

 

 

 

98.45±1.92

99.95± 0.75

99.3± 0.860

99.37± 0.713

99.7 ±1.18

t-test

 

 

 

 

1.23

0.398

0.610

0.533

 

F-test

 

 

 

 

0.37

2.4

1.8

2.7

 

 



 


Scheme – 1


 

Table No. 3: Appplication  of  Proposed Methods for  the Analysis of Tamsulosin  Hydrochloride in Pharmaceutical form

Taken

(μg ml-1)

 

 

Proposed methods

Reference method

Found (μg ml-1)

Recovery (%)

Recovery (%)

BCP

BCG

BTB

BPB

BCP

BCG

BTB

BPB

Veltam 0.4  mg/Tablet

10

8

6

4

2

RSD (%)

 

 

9.96

8.05

5.99

4.03

1.97

 

 

10.05

7.98

5.91

4.03

2.02

 

 

 

10.01

7.95

6.02

4.00

1.96

 

 

 

10.56

8.03

5.98

4.06

2.01

 

 

99.60

100.62

99.83

100.75

98.5

0.841

 

 

100.5

99.75

98.50

100.7

101.0

0.999

 

 

100.10

99.38

100.33

100.00

98.00

0.944

 

 

100.56

100.34

99.677

101.4

100.65

0.615

 

 

99.00

100.10

100.50

98.00

100.90

1.18

Mean±SD

t-test

F-test

 

 

 

 

99.87±0.84

0.261

1.94

100.1±1.00

0.576

1.39

99.56 ±0.94

0.207

1.57

100.65±0.62

1.588

3.62

99.7 ±1.18

 


Tamsulosin hydrochloride contains secondary amino and sulphonamide groups. Hence we propose the protonation of secondary nitrogen in acidic medium, while sulphonic acid group is present in BTB, BPB BCP and BCG, that is the only group undergoing dissociation in the pH range 1-5. The color of such dyes is due to the opening of lactoid ring and subsequent formation of quinoid group. It is supposed that the two tautomers are present in equilibrium but due to strong acidic nature of the sulphonic acid group, the quinoid body must predominate. Finally the protonated Tamsulosin hydrochloride forms ion-pairs with the dyestuffs which are quantitatively extracted into chloroform. The possible reaction mechanisms are proposed and given in (Scheme 1).

 

Fig.4 - Effect of pH

[Drug] = 12.5μg/ml, [Dye] = 5ml of 0.025%

 

The influence of pH on the ion-pair formation of Tamsulosin hydrochloride with various dyestuffs has been studied using sodium acetate-hydrochloric acid buffer. The results are shown in (Fig.4).

 

It is evident that absorbance of complexes with BTB, BPB, BCP and BCG was found to be constant within the pH ranges 2.2-3.3, 2.0-3.0 and 2.8-3.8 respectively. Thus, all the absorbance measurements were made at pH 2.8 (BTB), 2.5 (BPB, BCP) and 3.5 (BCG) respectively.

The effect of dyestuff concentrations was also studied by adding different volumes of dyestuff to a constant amount of Tamsulosin hydrochloride (12.5 µg ml-1). It is apparent from (Fig. 5) that the maximum absorbance, in each case, was found with 2.0 ml of dyestuff, beyond which absorbance was constant. Thus, 5 ml of each dyestuff was used for ion-pair formation throughout the experiment.

 

Fig.5 - Influence of volume of 0.025%Dye   [Drug] = 12.5μg/ml

 

Table No. 4:

Foreign species

Tolerence limit (μg/ml)

Methacrylic acid copolymer disper  NF,

30

Microcrystalline cellulose, NF

40

Triacetin, USP,

20

Calcium Stearate NF

30

Gelatin

10

Talc

30

 

A systematic study of the effect of foreign species present along with Tamsulosin hydrochloride on the determination of Tamsulosin hydrochloride at 12.5 µg ml-1 levels was undertaken. This study was carried out by following the proposed procedures for a 10 ml sample system, by adding a known amount of foreign species to Tamsulosin hydrochloride solution of 12.5 µg ml-1. (Table- 4) summarizes the results obtained. However, the drug content from the powdered tablets was extracted into chloroform, which completely removes any interference by the common excipients found in formulations.

 

CONCLUSIONS:

Tamsulosin hydrochloride forms extractable ion pair complexes with triphenyl methane acidic dyes. Complexes are of 1:1 composition and have stability of 104. Calibration curves for quantification of the drug have been constructed and method is validated.

 

ACKNOWLEDGEMENTS:

The authors are grateful to Head, Department of Chemistry and Principal Nizam College for providing facilities. The support rendered by Principal St. Ann’s college is duly acknowledged.

 

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Received on 19.05.2011        Modified on 25.05.2011

Accepted on 30.05.2011        © AJRC All right reserved

Asian J. Research Chem. 4(7): July, 2011; Page 1114-1118