Development & Validation of Analytical Methods for Doxophylline

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Need for Drug analysis: 1

The number of drugs introduced into the market is increasing every year. These drugs may be either new entities or partial structural modification of the existing one. Very often there is a time lag from the date of introduction of a drug into the market to the date of its inclusion in pharmacopoeias. This happens because of the possible uncertainties in the continuous and wider usage of these drugs, reports of new toxicities (resulting in their withdrawal from the market), development of patient resistance and introduction of better drugs by competitors. Under these conditions, standards and analytical procedures for these drugs may not be available in the pharmacopoeias. It becomes necessary, therefore to develop newer analytical methods for such drugs.

In brief, the reasons for the development of newer methods of drug analysis are:

The drug or drug combination may not be official in any pharmacopoeias, A proper analytical procedure for the drug may not be available in the literature due to patent regulations, Analytical methods may not be available for the drug in the form of a formulation due to the interference caused by the formulation excipients, Analytical methods for the quantitation of the drug in biological fluids may not be available, Analytical methods for a drug in combination with other drugs may not be available, The existing analytical procedures may require expensive reagents and solvents. It may also involve cumbersome extraction and separation procedures and these may not be reliable.

Analytical techniques that are generally used for drug analysis are biological and microbiological methods, radioactive methods, physical methods and miscellaneous techniques like conventional titrimetric, gravimetric and polarimetric methods.


The spectrophotometric assay of drugs rarely involves the measurement of absorbance of samples containing only one absorbing component. The pharmaceutical analyst frequently encounters the situation where the concentration of one or more substances is required in samples known to contain other absorbing substances, which potentially interfere in the assay. If the formula of the samples is known, the identity and concentration of the interferents are known and the extent of interference in the assay may be determined.

There are various spectrophotometric methods are available which can be used for the analysis of a combination samples. Following methods can be used: Simultaneous equation method
Derivative spectrophotometric method
Absorbance ratio method ( Q-Absorbance method)
Difference spectrophotometry
Solvent extraction method

But for single drug molecule, we can use simple U.V. method which involves use of Double Beam Spectrophotometer.

Double Beam Ultraviolet Spectrophotometer
Description as follows: 3, 4

1)The radiation from the source is allowed to pass via a mirror system to the monochromator unit. The function of the monochromator is to allow a narrow range of wavelengths to pass through an exit slit. 2)The radiation coming out of the monochromator through the exit slit is received by the rotating sector which divides the beam into two beams, one passing through the reference & the other through the sample cell. 3)After passing through the sample & reference cells, the light beams are focused onto the detector. 4)The output of the detector is connected to a phase sensitive amplifier which responds to any change in transmission through sample & reference. 5)The phase sensitive amplifier transmits the signals to the recorder which is followed by the movement of the pen on chart. The chart device is coupled to the rotation of the prism & thus the absorbance or transmittance of the sample is...
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