Page 15 - Pharmaceutical analytical chemistry |

Volumetric Methods of Analysis

Standard solution

(or standard titrant) is a reagent of known concentration that is used
to carry out a volumetric analysis.
A primary standard is a highly purified compound that serves as a
reference material in all volumetric methods. Important requirements for
a primary standard are:

• Highly pure.
• Stable in air.
• Soluble in the titration medium.
• Large formula weight to minimize weighing error.
• Readily available at a reasonable cost.
The substances commonly employed as primary standards are:
a) Acids: potassium hydrogen phthalate, benzoic acid, and oxalic
acid.
b) Bases: sodium carbonate and borax.
c) Oxidizing agents: potassium dichromate, potassium bromate, and
potassium iodate.
d) Reducing agents: sodium oxalate, arsenious oxide, and iron metal.
e) Others: sodium chloride, potassium chloride, potassium bromide,
and silver nitrate.
Standard solutions play a central role in all volumetric methods of
analysis. The ideal standard solution for volumetric method should:
• Be stable so that its concentration is determined only once.
• React rapidly and completely with the analyte so that

satisfactory end points are realized.
• Undergo a selective reaction with the analyte that can be

described by a simple balanced equation.

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