Pharmaceutical Analysis

Pharmaceutical Analysis

INTRODUCTION

Pharmaceutical analysis is a branch of practical chemistry that involves a series of process for identification, determination, quantification and purification of a substance, separation of the components of a solution or mixture, or determination of structure of chemical compounds.

The substance may be a single compound or a mixture of compounds and it may be in any of the dosage form. The substance used as pharmaceuticals are animals, plants, micro organisms, minerals and various synthetic products.

The sample to be analysed is called as analyse and on the basis of size of sample, they can be classified as macro(0.1 g or more), semi micro (0.01 g to 0.1 g), micro(0.001 g to 0.01 g), sub micro (0.0001 g to 0.001 g), ultramicro (below 10-4 g), trace analysis(100 to 10000 ppm). Among all, the semi micro analysis is widely used

TYPES

There are main two types of chemical analysis.

1. Qualitative (identification)

2. Quantitative (estimation)

1. Qualitative Analysis is the determination of non-numerical information about a chemical species, a reaction, etc. Examples would be observing that a reaction is creating gas that is bubbling out of solution or observing that a reaction results in a color change. Qualitative analysis is not as reliable as quantitative analysis but is often far easier, faster and cheaper to perform. This chapter discusses how to perform a systematic analysis on inorganic material to ascertain its composition.

These tests are performed to indicate whether the substance or compound is present in the sample or not. 

Qualitative tests : detection of evolved gas, formation of precipitates, limit tests, colour change reactions, melting point and boiling point test etc.

2. Quantitative analytical techniques are mainly used to quantify any compound or substance in the sample. These techniques are based in (a) the quantitative performance of suitable chemical reaction and either measuring the amount of reagent added to complete the reaction or measuring the amount of reaction product obtained, (b) the charatristic movement of a substance through a defined medium under controlled conditions, (c) electrical measurement, (d) measurement of some spectroscopic properties of the compound.

Various types of Qualitative analysis:

1.Chemical methods

a) volumetric or titrimetric methods

b) gravimetric methods

c) gasometric analysis

2.Electrical methods

3.Instrumental methods

4.Biological and microbiological

1.Chemical methods 

a)Titrimetric or volumetric method

It involves reaction of substance to be determined with an appropriate reagent as a standard solution, and volume of solution required to complete the reaction is determined. Volumetric methods require simple and less apparatus and they are susceptible of high accuracy.

The analyte is prepared by dissolving the substance being studied into a solution. The solution is usually placed in a flask for titration. A small amount of indicator is then added into the flask along with the analyte. The reagent is usually placed in a burette and slowly added to the analyte and indicator mixture. The amount of reagent used is recorded when the indicator causes a change in the color of the solution.

Various types of titrimetric methods are:

i)Acid-base titrations (neutralization reactions)

Acid-Base titrations are usually used to find the amount of a known acidic or basic substance through acid base reactions. The analyte is the solution with an unknown molarity. The reagent (titrant) is the solution with a known molarity that will react with the analyte.

ii)Complexometric titrations

iii)Precipitation titrations

iv)Oxidation reduction titrations

v)Non aqueous titrations

b)Gravimetric methods

In gravimetric analysis, a substance to be determined is converted into an insoluble precipitate in the purest form, which is then collected and weighed. It is the time consuming process.

In electrogravimetry, electrolysis of the sample is carried out on the electrodes is weighed after drying.

Thermogravimetry (TG) records the change in weight, differential thermal analysis (DTA) records the difference in temperature between test substance and an inert reference material, differential scanning calorimetry (DSC) records the energy needed to establish a zero temperature difference between a test substance and reference material.

c)Gasometric analysis

Gasometry involves measurement of the volume of gas evolved or absorbed in a chemical reaction.

Some of the gases which are analysed by Gasometry are CO2 , N2O,cyclopropane, amyl nitrate, ethylene, N2, helium etc.

2.Electrical methods

Electrical methods of analysis involve the measurement of electric current, voltage or resistance in relation to the concentration of some species in the solution.

Electrical methods of analysis include:

(a)Potentiometry

(b)Conductometry

(c)Polarography

(d)Voltametry

(e)Amperometry

Potentiometry measures electrical potential of an electrode in equilibrium with an ion to be determined. Conductometry measures electrical conductivity of an electrode with a reference electrode while Polarography, Voltametry and Amperometry measures electrical current at a micro-electrode.

3.Instrumental methods of analysis

Instrumental method involves measurement of some physical properties of the compound or a substance. These methods are employed for determination of minor or trace concentration of element in the sample.

Instrumental methods are preferred due to their selectivity, high speed, accuracy and simplicity of analysis. Any change in the properties of the system are detected by measurement of absorbance, specific rotation, refractive index, migration difference, charge to mass ratio etc.

Spectroscopic methods of analysis depend upon measurement of the amount of radiant energy of a particular wavelength emitted by the sample.

Methods which include absorption of radiation are ultra violet, visible, infra red, atomic absorption, nuclear magnetic resonance spectroscopy etc.

Emission methods involve heating or electrical treatment of the sample so that the atoms are raised to the excited state to emit the energy and the intensity of this energy is measured. Emission methods include emission spectroscopy, flame photometry, flourimetry etc.

Chromatographic techniques and electrophoretic methods are separation methods for the mixure of compounds, but also applied for identification of compounds of mixures. Various chromatographic techniques are GC, HPLC, TLC, HPTLC, PC etc.

Mass spectrometry involves vaporization of material using a high vaccum and the vapour is bombarded by a high energy electron beam. Vapour molecules undergo fragmentation to produce ions of varying size. These ions are differentiated by accelerating them in electrical field and then deflecting them in a magnetic field. Each kind of ion gives a peak in the mass spectrum.

4.Biological and microbiological methods

Biological methods are used when potency of a drug or its derivative can not be properly determined by any physical or chemical methods. They are called bio-assays.

Microbiological methods are used to observe potency of antibiotic or anti- microbial agents. In antimicrobial assay, inhibition of growth of bacteria of the sample is compared with that of the standard antibiotic. These methods include cup plate method and turbidimetric analysis.