Primary & Secondary Standard
Miss Preeti Verma
Assistant Professor
Faculty of Pharmaceutical Sciences,
Rama University,
Kanpur, U.P.
Standards
In Pharmaceutical Analysis, the word standard means a material
containing a substance of our interest with a known
concentration. We can express this with definite numbers with
proper units.
Functions
To provide a reference using which we can determine unknown
concentration of solution
To standardization of volumetric solutions
Preparation of secondary standard
To calibrate an instrument
Primary and Secondary Standards
Primary
Standards
Standards
Secondary
Standards
Primary Standards
Primary standard is a reagent which is very pure,
generally representative of the number of moles the
substance contains and easily weighed.
A Primary standard is a reagent that’s stable, it’s not a
hydrate /has no water of hydration, and has a high
molecular weight.
Primary standards are typically used in titration to determine
an unknown concentration and in other analytical techniques.
High level of purity, low reactivity (high stability), high
equivalent weight (to reduce error from mass measurements)
Not hygroscopic (to reduce changes in mass in humid versus dry
environments), non-toxic, inexpensive and readily available
It should have a high relative molecular weight so that weighing
errors may be negligible.
The substance should be readily soluble under the conditions in
which it is employed.
The substance commonly employed as primary standards are
mention below…
Acid- base reactions: sodium carbonate Na2CO3, sodium
tetraborate Na2B4O7, potassium hydrogenphthalate KH(C8H4O4),
potassium hydrogeniodate KH(IO3)2.
Complex formation reactions: pure metals ( zinc, copper,
magnesium and manganese) and salts, depending upon the
reaction used.
Precipitation reactions: silver, silver nitrate, sodium chloride,
potassium chloride and potassium bromide.
Oxidation- reduction reaction: potassium dichromate
(K2Cr2O7), potassium bromate (KBr), potassium iodate ( KIO3),
sodium oxalate Na2C2O4 and pure iron.
Secondary standard
Secondary standard is a chemical that has been
standardized against a primary standard for use in a
specific analysis. Secondary standards are commonly used
to calibrate analytical methods.
A secondary standard is a substance which may be used
for standardization
A secondary standard is a standard that is prepared in
the laboratory for a specific analysis. It is usually
standardized against a primary standard.
It follows that a secondary standard solution is a solution in
which the concentration of dissolved solute has not been
determined from the weight of the compound dissolved but by
reaction (titration) of a volume of the solution against a
measured volume of a primary standard solution.
A secondary standard is a chemical or reagent which has
certain properties such as….
• It has less purity than primary standard
• Less stable and more reactive than primary standard But
its solution remains stable for a long time
• Titrated against primary standard
References
• A.H. Beckett & J.B. Stenlake's, Practical Pharmaceutical Chemistry Vol I,
Stahlone Press of University of London
• A.I. Vogel, Text Book of Quantitative Inorganic Analysis
• Bentley and Driver's Textbook of Pharmaceutical Chemistry
• John H. Kennedy, Analytical Chemistry Principles
• Indian Pharmacopoeia & Merck Index
Thank You…!!!
