ABSTRACT

 A simple and sensitive spectrophotometric method for the determination of paracetamol was explored, using zirconium(IV) and vanadium(V) oxides. The method was based on the oxidation of paracetamol by zirconium(IV) and vanadium(V) in  alkaline and acidic media respectively. The stoichiometric studies indicated a mole-ratio of 1:1 for the reactions of paracetamol with both zirconium(IV) and vanadium(V). Effects of other variables like pH, temperature and time were determined and showed that the optimum conditions for the oxidation of paracetamol by zr(IV) were pH of 9.0,  temperature of 50˚C and at 20 min yielding red- brown p-benzoquinone which absorbed at a λ_max of 420 nm. Similarly, optimum conditions for the oxidation of paracetamol by V(V) were pH of 1.0, temperature of 70˚C at 8 min, and V(V) reduced to bluish-violet vanadium(II) ions which absorbed at a λ_max of 600 nm. The Beer-Lambert’s law was obeyed at a concentration range of 5.0-40.0 μg/cm³ for paracetamol with both Zr(IV) and V(V) respectively; and the correlation coefficients for both oxidants were 0.997 and 0.999 respectively. The mean % recovery of paracetamol in dosage form with Zr(IV) was 99.06 %, while V(V) gave 100.17 %. Hence, the recovery studies had proved the method to be accurate, simple and precise.

CHAPTER ONE

1.0    INTRODUCTION

Spectroscopy involves the study of the absorption and emission of light and other radiations as related to wavelength of the radiation. Hence, spectroscopy is the branch of science dealing with the study of interaction between electromagnetic radiation and matter. It is the most powerful tool available for the study of atomic and molecular structures, and is used in the analysis of wide range of samples. Optical spectroscopy includes the region on electromagnetic spectrum between 100 Ǻ and 400 m. Hence, the regions of electromagnetic spectrum are thus – far (or vacuum) ultraviolet (10-200 nm), near ultraviolet (200-400 nm), visible (400 – 750 nm), near infrared (0.75 – 2.2 m), mid infrared (2.5 – 50 m), and far infra red (50 – 100 m) region.^{2, 3}

1.1    Ultraviolet – visible spectrophotometry (UV-visible spectrophotometry).

UV – visible spectrophotometry is one of the most frequently employed techniques in pharmaceutical analysis. It involves measuring the amount of ultraviolet or visible radiations absorbed by a substance in solution.⁴ Instruments which measure the ratio, or function of ratio, of the intensity of two beams of light in the UV-visible region are called ultraviolet-visible spectrophotometers.⁴

A spectrophotometer consists of two instruments, a spectrometer and a photometer, both housed in one cabinet. The spectrometer is used to split or resolve light in bands of wavelength before it is fed to the photometer. To achieve the designed resolution, a spectrometer is specially equipped with a high resolution wavelength selector known as monochromator. This monochromator can isolate an extremely narrow bandwidth almost comparable to a single wavelength.⁵

In qualitative analysis, organic compounds can be identified by the use of spectrophotometer; if any recorded data is available; and quantitative spectrophotometric analysis is used to ascertain the quantity of molecular species absorbing the radiation.⁴

Spectrophotometric technique is simple, rapid, moderately specific and applicable to small quantities of compounds. The fundamental law that governs the quantitative spectophotometric analysis is the Beer-Lambert’s law.

Beer’s Law: it states that the intensity of a beam of parallel monochromatic radiation decreases exponentially with the number of absorbing molecules. In other words, absorbance is proportional to the concentration.

Lambert’s law: It states that the intensity of a beam of parallel monochromatic radiation decreases exponentially as it passes through a medium of homogeneous thickness. A combination of these two laws yields the Beer – Lambert law.⁴

Beer – Lambert’s Law: When a beam of light is passed through a transparent cell containing a solution of an absorbing substance, reduction of the intensity of light may occur. Mathematically, Beer – Lambert’s law is expressed as –