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  • Sunday 24 September 2017

    [How to] Calculate the Assay of product in Liquid

    Good Evening all......!!!

    Back after many days with a post, this may confuse all the readers, but don't get desperate after reading it.

    Being a guy from Tech transfer / Process Engineering department, some time we might be a part of project execution and in that case this may help you 0.00001%,

     While a new project execution many a time during analysis, it will be a nail biting situation waiting for result, especially this will help you while you are desperately waiting for a Assay content in a liquid product layer.

    But before that, i should deliver some basic things to ensure that it will be in reach of every one.

    What is Assay ?

    Assay is nothing but just the actual content of something desirable in a sample which we need to determine.

    What are the ways to determine the Assay ?

    In a Pharma industry, Usually Assay will be determined based on a standard, i.e., there should be a 100% pure active content material which is used to compare the sample with the standard.

    For ex. Lets suppose there is product layer sample, i mean our product is dissolved in some solvent, and the sample is injected in a HPLC column against the 100% standard sample solution,

    and it has returned some peaks, 
    Let the peak area of the sample is At, 
    Peak area of standard be As,
    Wt is the weight of sample injected,
    Ws is the standard weight injected,
    P is potency(concentration) of standard [ usually it will be 100%].

    Assay =  Read this.

    The above mentioned thing a Quality Control related strategy for Assay determination, but we process engineers should be somewhat smart than those guys, to get a rough view about the result.

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    Forget to mention that, if you reading the post to determine standard's assay content, this is useless.

    This post will help you to know the product content in the final organic/aqueous layer that to only if the final solvent is having a single solvent, for binary solvent mixture this might not be helpful.

    Anyway, now i'll start my show,

    I'll give you a Case study, during a product manufacturing in the final weight declaration, we need to concentrate a product layer sample in a lab distillation setup and based on the final concentrated residue, we need to calculate and declare the weight.

    Lets our product is in Acetonitrile solvent, total product layer qty is 2000 L.
    Sample Qty. 500 ml, Weight of sample is 410 gm.

    Lets calculate the product content,

    500 ml of acetonitrile should weigh around 500*0.786 = 393 gm.

    but out sample is weighing around 410 gm,

    So now the difference is 410-393 = 17 gms.

    Assay(includes impurities) = ( 17 / 410 ) x 500 = 20.73 %

    So total weight of dissolved product in 2000 L of acetonitrile will be 

    ( 20.73 / 100 ) x 2000 = 414 Kg. 

    That's it.....!!! Hope you understood.......!!!

    Any queries feel free to comment / message me....!!!

    Comments are appreciated....!!!!

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    About The Author

    Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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    1. Sir in our plant I have seen a quality report of a recovered solvent acetone is written as GC 98% moisture 6% and other organic impurity 2%,Is it possible as total sum of the percentage of the component exceeds 100% or GC and moisture is totally different there is no relation between their percentage composition?? Please response sir

    2. Replies
      1. Dear Prathim,

        Actually with a single TIR sheet, the QC as performed 2 tests, one is GC and other is MC,

        Both procedures are different,
        GC is used for mapping the standard peaks, and if integrated we can know about other unknown peaks also,
        MC shall be performed with karl fisher reagent.

        So, both are different,

        AJAY K


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    Hi! I am Ajay Kumar Kalva, owner of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.

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