Tuesday, July 5, 2011

Calculations in Analytical Methods(HPLC and GC)

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

5 comments:

  1. This comment has been removed by the author.

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  2. In the calculation the total value must be multiplied by 100 for percentage

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    Replies
    1. For Calculation for Assay substances method (By HPLC)

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    2. Hello,

      Can you please clarify about the potency..


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

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  3. Hello how can i calculate the potency of a peak from a chromatogram. i have an agilent 1100. i have the standards and my sample. Any suggestions?

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