November 29, 2021, 02:58:03 AM
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Topic: Calculating % analytes in HPLC  (Read 183 times)

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Offline Spleens

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Calculating % analytes in HPLC
« on: November 12, 2021, 06:10:30 PM »
When calculating the % of an analyte in a product, say Benzoyl Peroxide in a lotion, the raw material was found to be 79% pure, and the standard used to analyze was 75% pure.  Do you take into account both purities when determining the actual % BZP?   Just the purity of the standard?  Just the purity of the raw material?  Don't include purity in the calculation?

Offline Orcio_Dojek

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Re: Calculating % analytes in HPLC
« Reply #1 on: November 13, 2021, 04:15:56 AM »
Standard was 75 % pure, so its surface should cover 75 % of all peaks surface. Raw material was found to be 79 % pure, because its peak covers 79 % of all peaks surface ?

Of course - if the raw material is that what you have put in the chromatograph....

Offline Orcio_Dojek

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Re: Calculating % analytes in HPLC
« Reply #2 on: November 14, 2021, 03:57:41 AM »
To be correct - standard was 75 % pure, because its peak surface was 75 % in comparison to pure (100 %) benzoyl peroxide.

And raw material was found to be 79 % pure because its peak covers 79 / 75 = 105 % of standard's peak surface.

I mean - sum of the all peaks does not need to represent 100 % of the what is it in the sample (may be 50, 70 or 90 %), because we don't know what kind of detector you were using.

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