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Dushyant Patel Extractive Spectrophotometric Method

S.K.P.C.P.E.R., Kherva 68 M .Pharm. Thesis

CHAPTER: 5 DEVELOPMENT AND VALIDATION OF EXTRACTIVE

SPECTROPHOTOMETRIC METHODS FOR ESTIMATION OF

GABAPENTIN IN PHARMACEUTICAL DOSAGE FORMS

5.1 INTRODUCTION TO EXTRACTIVE SPECTROSCOPY

¾ The addition of an amine in its ionized form to an ionized acidic dye, e.g. methyl orange

or bromocresol purple, yields a salt (ion-pair) that may be extracted into an organic

solvent such as chloroform or dichloromethane. The indicator dye is added in excess and

the pH of the aqueous solution is adjusted if necessary to a value where both the amine

and dye are in the ionized forms. The ion pair is separated from the excess indicator by

extraction into the organic solvent, and the absorbance is measured at the λmax of the

indicator in the solvent.

¾ Usually, the most intensely absorbing form of the indicator is measured, with the

addition of acidified or basified ethanol. Alternatively, the absorbance of the indicator

may be measured in aqueous solution after back extraction from the organic solvent.

Because of higher molar absorptivity (ion-pairs) obtained by acid-dye method, this

method is very sensitive.

¾ The correct choice of pH may permit the selective assay of the mixture of an amine and a

quaternary ammonium salt.

5.2 EXPERIMENTAL WORK:

5.2.1 APPARATUS:

¾ A double beam UV-Visible Spectrophotometer (Shimadzu model UV-1700, Japan),

attached to a computer software UV probe 2.10, with a spectral width of 2 nm,

wavelength accuracy of 0.5 nm and pair of 1 cm matched quartz cells.

¾ Analytical balance (CP224S, Sartorius, Gottingen, Germany).

¾ Ultrasonic cleaner (Frontline FS 4, Mumbai, India).

¾ Corning volumetric flasks, pipettes of borosilicate glass were used in the study.

5.2.2 REAGENTS AND MATERIALS:

¾ GBP bulk powder was kindly gifted by Torrent research centre, Gujarat (India).

¾ The commercial fixed dose products containing 300 mg GBP were procured from the

local pharmacy.

¾ AR grade chloroform (S.D. Fine Chemical Ltd., Mumbai, India).

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