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Hello Damon,

I am working on a spreadsheet in excel that lists 4 compounds, there molecular weights, k-values, Peak Areas, Mole and Mass Fractions. There are 5 samples of these for compounds. The k-values are constant throughout. The Peak Areas are different for each compound and each sample. I have written a VBA code to calculate the Mole and Mass Fraction. Everything is correct in the array boxes.

Sample   MW   k-Values   Peak Areas   Mole Frac.  Mass Frac.
 1    16.04   0.150        3.6          0.156      0.062
      30.07   0.287        2.8          0.233      0.173
      44.09   0.467        2.4          0.324      0.353
      58.12   0.583        1.7          0.287      0.412
 2     --      --          --          --         --
and so on through sample 5.

I have been asked to construct a user form to return the mole and mass fractions as well.  The user will enter the k-values, number of compounds, number of samples, and peak areas. The Moles and Mass Fractions are to be displayed on the worksheet and not the user form. I am not real sure how to write the code for this.

The information for this project is suppose to be values that are collected from a gas chromatograph.

For this example the moles for each compound = k * Peak Area.
The Mole Fraction = moles(i) / total moles in each sample.
The Mass Fraction = Mass(i) / total Mass in each sample.

Can you please help?

Also I am a beginner to VBA and UDF codes.

Thank you for your time!


Stephen Meiring

Hi Stephen,

Firstly I want to apologize for my slow response.  I saw your question last week but didn't have time then to do it, and I forgot that I had a question pending until I got notification from AllExperts that it was overdue.

It would take quite a bit of explanation to give all the steps in setting up such a userform and I think that showing you such a userform and its associated code would be much easier. Here is my email address:  If you email me I will send you back an example userform that does basically what you describe.  Even better, if you could send me your Excel worksheet with the sample 1-5 data sets I could add the userform and code to your workbook and email it back to you.

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Damon Ostrander


I have extensive experience with VBA programming in Excel 5 through Excel 2013. As a former aerospace engineer with a large aerospace corporation and consultant in a small defense technology services company, I have developed a wide range of applications in VBA, including simulations involving mixed-language programming, satellite orbit mechanics, graphics and animation, and real-time applications. I am interested in moderate to hard VBA-related questions only.


I have developed and taught several courses in Excel VBA programming and also VBA programming in Office 97, 2000, and 2007. I have developed a number of large technical applications in Excel VBA for use within the aerospace industry.

B.S. in Electrical Engineering and Computer Science, University of California, Berkeley.

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