various uv spectrophotometric
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Various UV spectrophotometric Simultaneous
estimation methods
The quantitative estimation is the method to determine how much of each constituent is in the
sample1-2. Estimation of a given drug or medicine in the dosage forms needs the quantitative analysis of
that drug or medicinal in it. The first quantitative analyses were gravimetric, made possible by the
invention of a precise balance. It was soon found that carefully calibrated glassware made considerable
saving of time through the volumetric measurement of gravimetrically standardized solutions.
In contrast to above two techniques namely gravimetric and volumetric analysis, methods of drug
analysis today utilize rather sophisticated instruments involving simple physico-chemical properties.
In instrumental analysis, a physical property of a drug is utilized to determine its chemical composition.
A study of the physical properties of drug molecules is a prerequisite for product formulation and often
leads to a better understanding of the inter-relationship between molecular structure and drug action.
These properties may be thought of as either additive or constitutive such as mass is an additive
property. Many physical properties are constitutive and yet have some measure of additivity such as
specific gravity, surface tension and viscosity. Molar refraction of a compound is the sum of the
refraction of the atoms and groups making up the compound. The arrangements of atoms in each group
are different however and so the refractive index of two molecules will be different; that is the
individual groups in two different molecules contribute different amounts to the overall refraction of the
molecules. In the instrumental analysis some physical properties of molecules such as absorption of
radiation, scattering of radiation, Raman Effect, emission of radiation, rotation of the plane of the
polarized light and diffraction phenomenon are involving interaction with the radiant energy. Physicalproperties encompass specific relations between the molecules and well defined forms of energy e.g.
Half-cell potential, current voltage, electric conductivity, dielectric constant, heat of reaction, thermal
conductivity or other yardsticks of measurements. By carefully associating specific physical properties
with the chemical nature of closely related molecules. Conclusions can be drawn that (1) Describe the
spatial arrangement of drug molecules (2) Provide evidence for the relative chemical or physical
behavior of a molecule and (3) Suggest methods for quantitative and qualitative analysis of a particular
pharmaceutical agents3,4.
Analytical methods, in a broad sense, can be classified into chemical methods and instrumental
methods. Chemical methods are defined as those that depend on chemical operations in combination
with the manipulation of simple instruments. In general, the measurement of mass, i.e. gravimetric and
of volume, i.e., volumetric analysis falls in this class. An instrumental method encompasses the use of
more complicated instrumentation based on analytical methods:
Although in recent years, spectrophotometric methods are extensively used, but it would be wrong to
conclude that instrumental methods have totally replaced chemical methods. In fact, chemical steps are
often an integral part of an instrumental method. The sampling, dissolution, change in oxidation state,
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removal of excess reagent, pH adjustment, addition of complexing agent, precipitation, concentration
and the removal of interferences are the various chemical steps which are part of an instrumental
method. In recent years HPLC5 (High Performance Liquid Chromatography) is extensively used, because
HPLC is not limited by sample volatility or thermal stability. HPLC is able to separate macromolecules
and ionic species, labile natural products, polymeric material and a wide variety of other high molecular
weight poly-functional group because of the relatively high pressure necessary to perform this type of
chromatography; a more elaborate experimental setup is required.
Because of the high cost of the instrument and costly analytical process, small-scale industries cannot
afford to procure and use HPLC. So, in spite of other advantages of HPLC, we often select the
spectrophotometric method of analysis. The variation of the color of a system with change in
concentration of some component forms the basis of what the chemists commonly term as colorimetric
analysis. The color is usually due to the formation of a colored compound by the addition of an
appropriate reagent, or it may be inherent in the constituent itself. Colorimetry is concerned with the
determination of the concentration of a substance by measurement of the relative absorption of light
with respect to a known concentration of the substance. Colorimetric determinations are usually madewith a simple instrument termed a colorimeter.
In spectrophotometric analysis a source of radiation is used that extend into the ultraviolet region of the
spectrum. From this, definite wavelengths of radiation are chosen possessing a bandwidth of less than 1
nm. This process necessitates the use of a more complicated and consequently more expensive
instrument. All atoms and molecules are capable of absorbing energy in accordance with certain
restrictions; these limitations depend upon the structure of the substance. Energy may be furnished in
the form of electromagnetic radiation (light). The kind and amount of radiation absorbed by a molecule
depend upon the structure of the molecule, the amount of radiation absorbed also depend upon the
number of molecules interacting with the radiation. The study of these dependencies is calledabsorption spectroscopy.