# Assay Calculation by Titration

The formula for assay calculation by titration is based on the principle of chemical equivalence, which states that the number of moles of reactant in a reaction is equal to the number of moles of another reactant.

This technique used to work out the concentration of an unknown solution based on its chemical reaction with a solution of known concentration.

The titration process usually involves adding the known quantity of a solution (the titrant) to a unknown solution (the analyte) until the reaction is complete. To calculate the concentration of the analyte, you measure the volume of titrant used.

Assay by Titrations = [Titrate value of (sample - blank) x M x F x 100 x 100] / [Ws x (100- LOD)]

Where,

• M  = Molarity of Volumetric Solution,
• Ws = Weight of solution,
• F  = Factor for drug substance,
• LOD = Loss on Drying.

#### Assay Calculation Formula by Titration Method

Or

Where,

• VSfactor = factor of VS (volumetric solution),
• W = weight (mg),
• LC = label claim,
• f = factor of the titrant
• Eq. wt = equivalent weight (molecular weight/ Valency).

Equivalent weight is the mass of the substance in grams that reacts with one mole of the titrant.

% Assay (on anhydrous basis) = (Assay × 100) ÷ (100-LOD/WC)

Where,

• LOD = Loss on drying
• WC = Water content

For a back-titration with a blank, use the following formula:

• VBlank:  Volume of the equivalence point from the blank determination in mL
• VEP:  Volume at the equivalence point in mL
• cTitrant:  Nominal titrant concentration in mol/L
• fTitrant:  Titer factor of the titrant (unitless)
• r:  Stoichiometric ratio (unitless)
• MA:  Molecular weight of analyte A in g/mol
• mSample:  Weight of sample in mg
• 100:  Conversion factor, to obtain the result in %