Quantitative Determination of Paracetamol in Pharmaceutical Formulations by FTIR Spectroscopy

The a im of t his wo rk was to use a spectrophotometric m ethod for the determination of parace tamol in pha rmaceutical form ulations.The qua ntification of para cetamol through in frared spectr oscopy was developed an d validated f or pharmaceuticals in tablet forms. The method involves the extraction of the active ingredient with chloroform and the measurement of the area of the infrared band corresponding to the carbonyl group ce ntered at 1650cm -1 . The spe cificity, linearity,detection li mits,precision and a ccuracy of the c alibration c urve, paracetamol extraction, infrared analysis and data manipulation were determined in order to validate the method. The stati stical res ults were compared wit h the quantification of paracetamol through UVdetection.The recovery values obtained in the analysis of pharmaceuticals are within the range 98-105%.

cell.The absorbance was measured at 243 nm.

A. Extraction of paracetamol from pharmaceutical formulations in tablet form
The extraction of paracetamol from pharmaceuticals in tablet forms was achieved through the selective dissolution of the active ingredient with chloroform according to the indications of the USP for the identification of paracetamol (US Pharmacopoeia, 2005) [12].Ten tablets of a pharmaceutical (SDI 500 mg ) were weighed, powdered and homogenized.An accurately weighed quantity of the powder was dissolved in 10.00 ml of chloroform, stirring for 10 minutes and centrifuged in order to separate the excipients.The supernatant solution was diluted to 25 ml with chloroform in a volumetric flask.Figure 1 shows the IR spectra of paracetamol as active ingredient (standard) and the active ingredient (solution of paracetamol tablets in chloroform) recovered after the extraction.

B. Linearity
The relationship between the concentration of a substance and its absorbance of radiation is given by the Beer-Lambert law : A = log ( Io / I ) = b c Where A is absorbance, (Io / I ) is the ratio between the intensities of incident and transmitted radiation that goes through a substance with C concentration contained in a cell of width b.The parameter , known molar absorptivity, is a property of the substance [13].The range of linearity of absorbance versus concentration of paracetamol and the molar absorptivity at constant b was determined through a series of solutions of different concentrations of paracetamol in chloroform.Each of them were analyzed through infrared spectroscopy and the area of the signal corresponding to the carbonyl species ( typically in the 1650 cm -1 range was determined.The limits of detection and the parameters of the linear regression are presented in table 1.

C. Precision and Accuracy
The precision and accuracy were determined from the following steps of the analytical method: the preparation of standard solutions of paracetamol, the determination of the IR spectra of the solutions and the extraction of paracetamol from the tablets.The precision and accuracy of the preparation of standard solutions was investigated through the preparation of six solutions containing 0.3 % w/v of standard paracetamol in chloroform that were further analyzed through IR spectroscopy.The IR analysis and data processing involve transferring a solution to the cell, digitalize the infrared spectra and the mathematical manipulation of the data for area calculation.The statistical study of those steps was performed through the preparation of three solutions containing concentrations of paracetamol that correspond to the limits (0.056 % w/v and 0.500 % w/v) and center of the calibration curve (0.300 % w/v) obtained in section B. Each of those solutions was analyzed three times through IR spectroscopy and the area of the infrared signal of the carbonyl species was determined.same commercial pharmaceutical with chloroform as described in section A. Step    PDF created with pdfFactory Pro trial version www.pdffactory.com Finally, the precision and accuracy of paracetamol extraction was determined treating ten tablets of the PDF created with pdfFactory Pro trial version www.pdffactory.com

Figure
Figure (1) Infrared spectra of paracetamol (standard) and active ingredient after extraction with chloroform.

Table 2
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& Tech. Journal,Vol.28, No.15, 2010 Quantitative Determination of Paracetamol in Pharmaceutical Formulations by FTIR Spectroscopy .
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Table ( 2) Precision and accuracy of the different steps of the quantitative analysis of paracetamol in tablets through IR spectroscopy.
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Table ( 4) Comparison of precision, accuracy and recovery of the quantification of paracetamol through IR and other reported methods, [14], [15], [16].
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