Chapter 1
Pharmaceutical Analysis
Definition and Scope of Pharmaceutical Analysis
- Pharmaceutical analysis is a branch of chemistry which involves the application of analytical procedures to ensure the purity, quality and safety of pharmaceutical products. It involves qualitative and quantitative analysis that consists of series of procedures for the identification, determination, quantitation and purification. The major application of pharmaceutical analysis includes identification of chemical category of compounds, determination of compounds in mixture, separation of the components from the mixture, isolation, purification and structural identification of compounds.
- When a chemical is free from impurities or contaminants, it is said to be chemically pure. It is extremely difficult to achieve 100 % of chemical purity during manufacturing processes, however with special care in production processes, achieving the optimum purity is possible.
Chemical Methods
Volumetric Methods:
- In volumetric methods, measurement of volume of solution is taken as a parameter for assay. The volume of known strength of a solution that is required to react completely with the substance to be analyzed is measured. The quantity of analyte is determined from the volume of solution by calculation.
- Volumetric methods are classified into different types depending upon the type of reactions involved in the reaction which are as follows:
- In Gravimetric analysis, quantitation is done on the basic of weight of compound. This process involves isolation.
- In this method, the measurement of the volume of gases forms the basics of analysis. When a chemical reaction is carried out under the specific process, the volume of gas evolved or absorbed in the reaction is measured.
- Example, for gases that are measured by gasometrical methods are cyclopropane, carbon dioxide, nitrous oxide, oxygen, octal nitrate, nitrogen, amyl nitrate, ethylene and helium.
Instrumental Methods
- These methods involve the usage of instruments to measure the physical or physiochemical property of the compound to be analyzed thus lead to quantitation of the compound. Depending on the physical property of the compound various instruments have been used for the measurement.
Microbiological Methods
- Microbiological methods are employed for compounds especially for antibiotics, for which the chemical methods are not useful. This method involves the determination of inhibition of growth of bacteria by the substances to be analyzed in comparison with the standard compound. On the basis of the result, the therapeutic efficacy of the antibiotics is decided.
Biological Methods
- Biological assays are carried out to observe the biological effect of the drug on some type of living matter. They are also called as bioassays. These are recommended when the chemical or physical methods are not capable to estimate the potency of a drug. These methods are carried out by comparing the biological effect of the sample to be tested with the biological effect produced by a standard compound in identical test conditions.
There are different methods of expressing concentrations in pharmaceutical analysis. These methods are discussed as follows
Solution Concentration
Solutions used in quantitative analysis require some basis for the expression of solution concentration. Generally, the expression of solution concentration involves similar basis in all systems with respect to weight relationships of solute and solvent.
Volumetric Analysis
- Volumetric analysis is also called as titrimetric analysis. It involves determination of volume of solution as a basic parameter. In this reaction or titration, the substance in solution is analyzed by reaction with a solution of accurately known concentration.
- Neutralization
- aqueous titrations
- Precipitation titrations
- Complexometric titrations
- Redox titrations
Primary and Secondary Standards
- Standard solutions are the solutions which are prepared with known strength. The accurate weight of very pure reagents of high stability is taken, dissolved and diluted to exact known volume and concentration is calculated on theoretical basis.
- Those substances which can easily be obtained in highly pure and crystalline form and used in preparation of standard solution are known as Primary Standard Substances.
- Accurately weighed quantities of these primary standards are used in the standardization of solutions of unknown strength. e.g., Oxalic acid, sodium carbonate etc.
- Acid-base titrations
- Redox titrations
- Precipitations titrations
- Complexometric titration
- These are the substances used for the standardization and whose concentration has been determined by comparison with the primary standard. As the number of primary standard substances is limited, a substance with less but known purity is used in standardization process.
Preparation and Standardization of Various Molar and Normal Solutions
- For preparation of standard solutions, a known quantity of standard substances depending upon the requirement is dissolved in a known amount of water and desired volume is made.
- Since, these substances have a constant weight, high purity, non - hygroscopic property, the solution obtained is of known and definite concentration.
Purity:
There are various techniques of pharmaceutical analysis which can be divided into two major categories.
1. Qualitative analysis
2. Quantitative analysis
1. Neutralization titrations
2. non-aqueous titrations
3. Precipitation titrations
4. Oxidation - reduction titrations.
5. Complex metric titrations
Gravimetric Methods:
Volumetric Methods of Analysis:
There are two types of standard substances:
1. Primary standards
2. Secondary standards.
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Pharmaceutical Analysis
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