Pharma Analysis

                           Instrumentation

The main parts of IR spectrometer are as follows:

1. Detection of Impurities
UV absorption spectroscopy is one of the best methods for determination of impurities in organic molecules. Additional peaks can be observed due to impurities in the sample and it can be compared with that of standard raw material. By also measuring the absorbance at specific wavelength, the impurities can be detected.
Benzene appears as a common impurity in cyclohexane. Its presence can be easily detected by its absorption at 255 nm.

When a light passes through absorbing medium at right angle to the plane of surface or the medium or the solution, the rate of decrease in the intensity of the transmitted light decreases exponentially as the thickness of the medium increases arithmetically.

Accordingly, Lambert’s law can be stated as follows:

The entire range over which the electromagnetic radiation exists is known as electromagnetic spectrum. This electromagnetic spectrum ranges from very short wavelengths (including gamma and x-rays) to very long wavelengths (including microwaves and broadcast radio waves). The following chart displays many of the important regions of this spectrum.

Solvent Effect
Solvents play an important role in UV spectra. Compound peak could be obscured by the solvent peak. So a most suitable solvent is one that does not itself get absorbed in the region under investigation. A solvent should be transparent in a particular region. A dilute solution of sample is always prepared for analysis. Most commonly used solvents are as follows.

It was earlier stated that σ, π, and n electrons are present in molecule and can be excited from the ground state to excited state by the absorption of UV radiation. The various transitions are n→∏*, ∏→∏*, n→σ*, & σ →σ*