Cerimetric Estimation of Terazosin hydrochloride in Bulk Drugs and in Pharmaceutical Formulations

Terazosin hydrochloride dehydrate RS-1-(4-amino-6, 7- dimethoxy-2-quinazolinyl)-4-[(tetra-hydro-2-furanyl) carbonyl]- piperazine monohydrochloride [Fig.1] is a?1adrenoceptor blocker with a long lasting action. Various methods reported in literature for the determination of terazosin hydrochloride in pharmaceutical dosage forms which includes spectrophotometric method1-3, Fluorimetric Method4-6,  Spectrophotometric and Spectrofluorimetric Method7, Potentiometric and Fluorimetric Method8 HPLC Determination9, and,  RP-HPLC Method10

       
           
       
    Fig.1: Terazosin hydrochloride

The methods is based on the oxidation of the drug by a known excess amount of cerium(IV) sulphate in acid medium, and the determination of the unreacted oxidant by spectrophotometry after treatment with iron(II) sulphate and complexing the iron(III) sulphate produced with thiocyanate. . The present investigation was undertaken with the aim of developing new, simple, rapid and accurate for the analysis of terazosin hydrochloride in bulk drug form and in various formulations. The reaction scheme is presented in Figure 3.The developed colour was stable for more than 30 min.

MATERIALS AND METHODS

Instrumentation

Spectronic 1000 plus UV Visible Spectrophotometer with 1 cm matched quartz cells was used for all spectral and absorbance measurements.

Reagents

All the chemicals and reagents used were of analytical grade and solutions were prepared in double distilled water. AR grade hydrochloride acid  was used in the present study.

Cerric ammoniune sulphate(0.05M):

2.9826 g of AR cerric Ammonium Sulphate is dissolved in double distilled water and the resulting solution is made up to the mark in the 100 ml standard flask with double distilled water.

Ammonium ferrous sulphate Solution (0.02M):

0.7842 g of AR Ammonium Ferrous Sulphate is dissolved in distilled water and the solution is made up to the mark in the 100 ml standard flask with distilled water.

Ammonium Thio-Cyanate (1M):

7 g of AR Ammonium thio-cyanate is dissolved in double distilled water and the resulting solution is made up to the mark in the 100 ml standard flask with double distilled water.

Preparation of standard terazosin hydrochloride solution:

50 mg of pure terazosin hydrochlorideis dissolved in methanol and the volume is adjusted to 50 ml with methanol. The stock solution is further diluted to get working concentration of 100

µg/mL.

DETECTION WAVELENGTH FOR LOPINAVIR AND TERAZOSIN HYDROCHLORIDE

The detection wavelength was determined by scanning the blood red solution in the range 380-620 nm using reagent blank. The overlain spectra (fig.2) were scanned and the wavelength was detected as 490 nm by using the following procedure. 1.0 ml of terazosin hydrochloride solution (100 µg/mL) is transferred into a standard flak and followed by the addition of 1 ml of 5 N hydrochloric acid and 1 ml cerium(IV) sulphate, and the overall volume are adjusted to 5 ml by adding a requisite volume of water. The flasks are let stand for 15 min with occasional shaking. Subsequently, 1ml of ammonium ferrous sulphate are added to each flask and the contents are mixed well. After 1 min, 3 ml of 1 M ammonium thiocyanate are added and the volume was made up to the mark, and the resultant solution gives blood red colour. The absorbance of the blood red colour solution is measured in the wavelength range of 380 to 620 nm, against the reagent blank.

 Assay procedure:

In each of a series of 10 ml standard flasks were placed 0.5-2.5 ml of terazosin hydrochloride followed by the addition of 1 ml of 5 M hydrochloric acid and 1 ml cerium(IV) sulphate, and the overall volume are adjusted to 5 ml by adding a requisite volume of water. The flasks are let stand for 15 min with occasional shaking. Subsequently, 1 ml of ammonium ferrous sulphate was added to each flask and the contents are mixed well. After 1 min, 3 ml of 1 M ammonium thiocyanate are added and the volume was made up to the mark, and the absorbance is recorded at 490 nm against water blank. The concentration of the drug in an unknown solution is read from the calibration graph in the fig.3.

 A linear relation is found between absorbance and concentration in the ranges given in Table 1.In method B, Beer’s lawis obeyed in the inverse manner. The calibration graphs were described by the equation Y= a+bX where Y=absorbance, a=intercept, b=slope and X=concentration in µg ml-1 obtained by the method of least squares. Correlation coefficients, intercepts and slopes for the calibration data are also presented in Table 1

Pharmaceutical Formulations:

Twenty tablets are weighed and ground into a fine powder. A portion of the powder equivalent to 100 mg of terazosin hydrochloride is accurately weighed into a 100 ml calibrated flask, 60 ml of water is added and the contents are shaken thoroughly for about 20 min to extract the drug. The contents are diluted to the mark, mixed well and filtered using a quantitative filter paper to remove insoluble residue. An appropriate aliquot is subjected to analysis by spectrophotometry using the procedure described above. The results are given in Table.2.

*Y = a+bX, where Y is the absorbance and X concentration in ?g/ml

Table.2 Assay of terazosin hydrochloride