I want to write this topic for giving an idea about how to calculate the Assay, related substances and Residual solvents.

**Calculations for Assay Method (Tirtimetry)**

Titire value(Sample - Blank) x M x Factor x 100 x 100

--------------------------------------------------------

Ws x (100-LOD)

M= Molarity of the volumetric solution

Ws= Weight of the sample

Factor = Factor for Drug substance

LOD is Loss on drying or MC is water content

**Calculations for Assay Substances Method (HPLC)**

**At x Ws x P x (100-WC of std)**

Assay % = ----------------------------------

As x Wt x (100-WC of sample)

At = Area due to sample Preparation

As= Area due to working standard solution

Wt= Weight of the sample in mg

Ws= Weight of the working standard

P=Potency or Assay of the standard

WC=% water content of the sample or standard

Note: WC may be replaced by LOD based on the drug substance

**Calculations for Related Substances Method (HPLC)**

ri

% of Known Impurity = ---x 100 X RF

rs

ri

% of unknown Impurity = ---x 100

rs

Total Impurities = Sum of all known and unknown impurities

ri =Area of each impurity Peak in the chromatogram of the sample solution preparation

rs=Sum of areas of Main drug and all impurity Peaks in the chromatogram of the sample solution preparation

RF= Response factor

**Calculations for Residual solvents Method (GC)**

**At Volume of solvent taken x density 0.1 ml dilution of sample(ml)**

= ------x -------------------------------------------x ---------x-------------------------------x 10 ^ 6

As 10 ml 10 ml Weight of the sample

At= Area of the solvent in the sample - Blank

As= Area of the solvents in the standard -blank

Note: Volume of the solvents taken should be mentioned in microliters

As we are multiplying with 10 power 6 we can get the results in PPM

Note: Refer Merck index for solvent densities

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ReplyDeleteIn the calculation the total value must be multiplied by 100 for percentage

ReplyDeleteFor Calculation for Assay substances method (By HPLC)

DeleteHello,

DeleteCan you please clarify about the potency..

is the Potency is on 'as-is' basis or 'Anhydrous' basis in the Calculation for Assay...